quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

source rock evaluation of middle jurassic coals northeast greenland by artificial maturation aspects of petroleum generation from coal paralic liptinite enriched coals and carbonaceous mudstones in northeast greenland constitute potential highly oil prone source rocks whereas the humic coals may be marginal source rocks the liptinite rich coals are dominated by resinite or fluorescing amorphous organic matter and alginite resulting in hydrogen index hi values generally above 300 and reaching up to 728 during artificial maturation up to 330 degreesc 72 hr the coals follow the maturation paths of kerogen types i and ii on an hi vs tmax diagram and calculations show that upon passage through the oil window roughly 85 of their generation potential is realized activation energy ea distributions with prominent principal ea values centered around 60 62 kcal mole and frequency factors from 5 855 x 1015 s 1 to 3 249 x 1016 s 1 strongly influence the generation characteristics from 300 to 330 degreesc 72 hr artificial maturation important changes include marked loss of liptinite fluorescence and increase in resinite reflectance small change in tmax significant decrease in hi pronounced increase in extract yields increased generation of saturates and generation of labile bitumen with low ea values these observations indicate significant bitumen petroleum formation from the coals during a relatively narrow temperature range which together with the petrographic composition may facilitate expulsion of a waxy crude oil the coals demonstrate that under certain depositional conditions highly prolific coal source rocks can form with the capacity not only to generate but also to expel liquid petroleum begin page 234

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

mineralogy and petrography of the two lower eocene lacustrine coals sorgun and suluova turkey abstract coal reserves of lower eocene age are limited in turkey and the most important are situated in the sorgun and suluova basins a thick and laterally extensive coal seam occurs at the base of the celtek formation in the two basins the celtek formation was developed in a fluvial lacustrine facies and was unconformably overlain by transgressive units of middle upper eocene age the coal samples were studied mineralogically and petrographically and to define fluorescence emission spectra of sporinite and cutinite a total of 75 coal samples collected from the two basins are characterized on an air dried basis by relatively low moisture contents 0 69 9 31 wt av 3 90 wt a broad range of ash yields 2 4 67 8 wt av 19 9 wt total sulphur contents 0 55 7 60 wt av 2 15 wt and calorific values 1689 7480 kcal kg av 5458 kcal kg minerals of the coals from the two basins determined on an air dried basis by x ray diffraction method are mainly kaolinite quartz and pyrite kaolinite and pyrite contents of the sorgun coals are higher and quartz contents are lower than those of the suluova coals in addition a few samples in the sorgun coals contain epigenetic calcite whereas some samples in the suluova coals contain syngenetic siderite calcite and dolomite the coals in general are characterized by high contents of macerals of the huminite group av 69 0 vol and contain liptinite av 4 9 vol inertinite av 0 8 vol and mineral matter av 25 3 vol on the tpi and gi diagram the coals plot in the limno telmatic and telmatic areas in which the sorgun and suluova peats accumulated between the high and low water tables fluorescence emission spectra of sporinite and cutinite macerals are in general similar in the coals of both basins but the spectral maxima of sporinites and cutinites are between 594 658 nm and 592 671 nm respectively the values for the sporinites indicate a relatively broad range of coal rank however the range of values of the mean random ulminite mainly eu ulminite a reflectances 0 46 0 60 rr av 0 53 rr the proximate and ultimate analyses imply that the rank is a subbituminous a coal transitional to high volatile c bituminous coal according to the astm classification

palaeoclimatic evolution and vegetational changes during the late oligocene miocene period in western and central anatolia turkey abstract neogene basins are widespread in turkey and contain important lignite deposits in this study we reconstruct quantitatively the late oligocene miocene climate evolution in western and central anatolia by applying the coexistence approach to the palynofloras obtained from the published literatures and ongoing studies the coexistence approach results show that sedimentation occurred mainly under warm subtropical climatic conditions during the chattian and aquitanian period in western anatolia 16 5 21 3 c mean annual temperature mat and 5 5 13 3 c mean temperature of coldest month cmt rare occurrences of dinoflagellate cysts in the chattian and aquitanian indicates a marine influence after the regression of the sea during the burdigalian period climate becomes cooler due to a decrease of the palaeotropical arctotertiary ratio during the latest burdigalian langhian vegetation developed under terrestrial conditions which had started in the burdigalian time in western and central anatolia and continued to the early middle serravallian period the climate was subtropical in western and central anatolia during the early late serravalian 17 2 to 20 8 c for mat and 9 6 to 13 1 c for cmt besides increase of the cmt and mat values in western and central anatolia supports the latest chattian earliest aquitanian warming and middle miocene climatic optimum being also globally observed warm temperate climatic conditions are observed in the late miocene during the early middle tortonian the values are 15 6 to 20 8 c for the mat 5 5 to 13 3 c for the cmt and 823 and 1520 mm for the mean annual precipitation map they had experienced dry seasons due to lower boundary of map lying at 823 mm during the middle late tortonian the palaeotopography of central anatolia was higher compared to that of western anatolia during the middle late miocene as indicated by a rich species diversification in mountain forests this study provides the first quantitative model for late oligocene miocene palaeoclimatic evolution in western and central anatolia

u pb age trace element and hf isotope compositions of zircon in a quartz vein from eclogite in the western dabie mountains constraints on fluid flow during early exhumation of ultrahigh pressure rocks quartz veins in high pressure hp to ultrahigh pressure uhp rocks are the products of fluid rock interaction and thus provide insight into fluid processes in subduction zones in this paper we report an integrated study of mineral inclusion trace element u pb age and lu hf isotope compositions of hydrothermal zircon grains from a quartz vein within an uhp eclogite outcrop from the hong an area western dabie mountains these data are used to decipher the age conditions of formation and source of fluid for zircon formation during the exhumation of uhp rocks zircon grains from the vein have perfect euhedral shape and show sector zoning or weak zoning indicating that they precipitated from the aqueous fluid responsible for the vein formation raman spectroscopy analysis reveals that the zircon grains contain inclusions of garnet omphacite rutile quartz and h2o implying that they crystallized from aqueous fluid under hp eclogite facies conditions the zircon grains show low th u and lu hf ratios nearly flat hree patterns absent eu anomalies and low lree contents these characteristics are consistent with their precipitation in the presence of garnet and epidote and absence of feldspar and thus suggest that trace element concentrations in hydrothermal zircon are controlled by co precipitation of mineral assemblages crystallization temperatures of 670 to 712 c which were calculated using the ti content of zircon are consistent with their formation under eclogite facies conditions and may correspond to the temperature of the infiltrating fluid the weighted mean 206pb 238u age of 224 7 1 3 ma is taken as the best estimate for the age of quartz vein formation and records aqueous fluid flow during the early exhumation stage of uhp rocks the zircon grains in the quartz vein have hf compositions similar to those in the host eclogite which demonstrates isotopic equilibrium between fluid and rocks and that the fluid rock ratio was likely low

two stage exhumation of ultrahigh pressure metamorphic rocks from the western dabie orogen central china abstract zircon trace element u pb age and lu hf isotope composition were determined for two eclogite samples from the xinxian ultrahigh pressure uhp unit in the western dabie orogen to constrain its exhumation processes cathodoluminescence imaging reveals that most zircons are metamorphic while some have inherited magmatic cores in one sample the magmatic cores have high th u and lu hf ratios high trace element contents and a clear negative eu anomaly consistent with their igneous genesis they yield an upper intercept age of ma and a positive ehf t value of 8 0 arguing for reworking of early mesoproterozoic crust during the middle neoproterozoic in the western dabie orogen the metamorphic zircons contain mineral inclusions of garnet omphacite rutile and quartz they are characterized by low nb ta y and heavy rare earth elements hree contents a nearly flat hree pattern and an insignificant negative eu anomaly these indicate that the metamorphic zircons formed under high pressure

shrimp u pb dating of coesite bearing zircon from the ultrahigh pressure metamorphic rocks sulu terrane east china this paper provides further evidence for the ongoing discussion as to whether the dabie uhpm belt formed in triassic or palaeozoic time and whether the sulu uhpm belt formed in triassic or neoproterozoic time combined use of laser raman spectrometer lr cathodoluminescence imaging cl and ion probe u pb in situ dating shrimp provided accurate ages of uhpm from rocks collected from weihai ne sulu uhpm belt lr was used to identify coesite and other uhp minerals as inclusions in zircon separates from an amphibolized peridotite and an eclogite cl was used to examine the zoning structure of these zircon and shrimp dating was performed on specific spots on zircon to obtain ages of different geological events an age of 221 12 ma was obtained for coesite bearing zircon from the amphibolized peridotite an age of 228 29 ma for eclogite was obtained from the lower intercept of a concordia plot these ages are interpreted as the time of uhpm in the weihai region ultramafic rocks to the east of weihai yield a magmatic age at 581 44 ma the zircon in the ultramafic rocks possibly also records a thermal event at c 400 ma but no independent geological evidence for this event has been found the eclogite protolith formed in the middle proterozoic 1821 19 ma which is similar to the age of country rock gneisses of 1847 1744 ma the new geochronological data confirm that uhpm occurred in the triassic in the sulu area when subduction took the ultramafic body and the eclogite protolith together with the adjacent supracrustal rocks to mantle depths

fluid flow during exhumation of deeply subducted continental crust zircon u pb age and o isotope studies of a quartz vein within ultrahigh pressure eclogite quartz veins in high pressure to ultrahigh pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis this flow can occur in the direction of changing temperature pressure during subduction or exhumation shrimp u pb dating of zircon from a kyanite quartz vein within ultrahigh pressure eclogite in the dabie continental collision orogen yields two age groups at 212 7 and 181 13 ma which are similar to two groups of la icpms age at 210 4 and 180 5 ma for the same sample these ages are significantly younger than zircon u pb ages of 224 2 ma from the host eclogite thus the two age groups from the vein date two episodes of fluid flow involving zircon growth the first due to decompression dehydration during exhumation and the second due to heating dehydration in response to a cryptic thermal event after continental collision laser fluorination o isotope analyses gave similar 18o values for minerals from both vein and eclogite indicating that the vein forming fluid was internally derived synchronous cooling between the vein and eclogite is suggested by almost the same quartz mineral fractionation values with regularly decreasing temperatures that are in concordance with rates of o diffusion in the minerals while the quartz veining was caused by decompression dehydration at 700 650 c in a transition from ultrahigh pressure to high pressure eclogite facies retrogression the postcollisional fluid flow was retriggered by heating dehydration at 500 c without corresponding metamorphism in either case the kyanite quartz vein formed later than the peak ultrahigh pressure metamorphic event at the middle triassic pointing to focused fluid flow during exhumation rather than subduction the growth of metamorphic zircon in the eclogite appears to have depended on fluid availability so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles

the mountains of north east greenland are not remnants of the caledonian topography a comment on pedersen et al 2012 tectonophysics vol 530 531 p 318 330 abstract pedersen et al 2012 suggest that the present day mountains in north east greenland represent remnants of the original caledonian topography modified during early rifting and that the area has undergone slow steady exhumation since 250 ma they base this hypothesis on inverse modelling calibrated by new apatite fission track data from samples of exposed caledonian basement however apatite fission track data on their own register only cooling and must be integrated with geological evidence to reveal episodes of reheating reflecting re burial the well documented geological record of north east greenland shows that the caledonian mountains were obliterated as topographic features during the late palaeozoic and provides clear evidence of a history involving episodic post caledonian exhumation and re burial the high grade metamorphic basement was at great depth during the devonian and was exhumed to the surface before being reburied by up to 2 km of upper carboniferous and younger sediments these sediments were then partially removed during renewed early middle jurassic exhumation that led to the formation of a low lying landscape which eventually subsided and was buried below a km thick cover of middle jurassic and younger sediments this cover was then partially removed during later phases of uplift and exhumation that eventually led to the formation of the present day relief in post jurassic times the geological record in east greenland is incompatible with the idea of slow steady exhumation since the caledonian orogeny

constraints on timing of peak and retrograde metamorphism in the dabie shan ultrahigh pressure metamorphic belt east central china using u th pb dating of zircon and monazite abstract the dabie shan ultrahigh pressure metamorphic uhpm belt occupies the suture between the yangtze and sino korean blocks in east central china the timing of uhpm in the dabie belt is controversial and most recent data come from dating of zircons monazite has recently been recognized as useful for dating of multiple tectonic events due to its preservation of multiple growth zones and monazite growth has been documented to occur during prograde peak and retrograde metamorphism zircons and monazites from uhp mafic rocks from maowu and a uhp jadeite quartzite from shuanghe were imaged in thin sections and in mineral separates and dated using a high resolution ion microprobe maowu mafic rocks are unique in that they contain high light rare earth element concentrations and therefore contain abundant monazite maowu eclogites and garnet pyroxenites contain zircons with mean 206 pb 238 u age of 230 4 ma and monazites from a clinopyroxenite have 208 pb 232 th ages of 209 4 ma multiple lines of evidence suggest that the measured ages represent the timing of new growth and recrystallization and are not cooling ages i e they do not correspond to the cessation of diffusional pb loss as rocks cooled below the closure temperature during exhumation shuanghe jadeite quartzites contain zircons with cores that define a discordia with an upper intercept age 1921 22 ma and lower intercept age of 236 32 ma interpreted to represent the ages of the source rocks and of peak metamorphism respectively zircon rims contain jadeite inclusions that restrict growth to pressures greater than 1 5 gpa their pooled age of 238 3 ma agrees well with the lower intercept defined by cores suggesting that pb loss from cores and growth of new rims occurred during uhpm at 235 240 ma monazite records multiple events during retrograde metamorphism maowu clinopyroxenite and shuanghe jadeite quartzite experienced monazite growth at 209 ma interpreted to reflect regional amphibolite facies overprinting resulting from pervasive retrograde fluid infiltration only the jadeite quartzite records growth at 223 1 ma estimated exhumation rates for maowu are 7 8 km ma

geomorphology and topography of relict surfaces the influence of inherited crustal structure in the northern scandinavian mountains low relief surfaces in northern norway are mapped and analysed to explore 1 whether surfaces were once continuous and possibly correlative recording an ancient relict landscape 2 whether the distribution of now disrupted surfaces reveals a tectonic history related to rifting of the north atlantic and 3 how topography changes across the transition between the north atlantic and barents sea margins elevation contours on surfaces a smoothed fit to mean elevations and histograms of elevation show three distinct coast parallel zones onshore northern norway and a different pattern in coastal lofoten vesteralen a sharp transition from continuous surfaces to lower discretely stepped discontinuous surfaces is located where the crust thins rapidly to the nw from 39 to 100 km north of the senja fracture zone and then decrease gradually further ne the spatial pattern suggests that a continuous low relief relatively low elevation surface formed in late mesozoic time and was preserved despite modification by cenozoic faulting uplift and slow erosion scandinavia9s present day topographic envelope reflects a crustal strength profile set up during earlier hyperextension and maintained by slow neogene erosion rather than resulting from opening of the north atlantic or caused by glacial erosion supplementary material a map of polygons of all surface heights within the study area and data on the location of median centres of polygons assigned attributes and selected zonal statistics are available at https doi org 10 6084 m9 figshare c 3312960

thermobaric structure of a traverse across western dabieshan implications for collision tectonics between the sino korean and yangtze cratons as the best preserved high and ultrahigh pressure hp and uhp metamorphic terrane in the qinling dabieshan sulu orogen western dabieshan is divided into six lithotectonic units along a traverse across the orogen i e from north to south the nanwan balifan huwan xinxian hong an and mulanshan units in this terrane five eclogite bearing zones i v are developed the garnet and clinopyroxene in eclogites from these zones exhibit chemical zoning suggesting that the rims record general peak temperature and pressure thermobarometric study indicates that the peak p t conditions of eclogite are 550 570 c and 21 kbar for zone i 470 500 c and 14 17 kbar for zone ii 620 670 c and 26 29 kbar for zone iii 530 560 c and 20 22 kbar for zone iv and 490 510 c and 19 20 kbar for zone v the symmetrical thermobaric pattern in conjunction with structural and geochronological data demonstrates that the huwan and hong an units belong to the same hp slice overlying the uhp slice this pattern together with the mulanshan lt hp blueschist greenschist belt in the south roughly constitutes a normal metamorphic zonation however clear metamorphic gaps occur between different slices it is inferred that the lt hp hp and uhp slices were broken up from the downgoing slab during subduction and reached different depths along different geothermal gradients the successive subduction of underlying slices leads to a nearly concomitant uplift of overlying slices whereas exhumation of the deepest uhp slice was effected by underthrusting of the lower crust of the yangtze craton

mineral matter major and trace element content of the afsin elbistan coals kahramanmaras turkey abstract the afsin elbistan coal basin is one of the most important coal deposits of turkey the mineral matter major and trace element concentrations of the afsin elbistan coals and their modes of occurrence are discussed in this study the coal seam is located within the upper miocene pliocene aged ahmetcik formation which is represented by fluvial lacustrine facies thickness of the coal zone is 80 m but it reaches 105 m in the kislakoy sector a total of 86 samples were taken from the kislakoy open pit mine and from the 14 boreholes drilled by the general directorate of mineral research and exploration mta for coal exploration the proximate xrd sem eds major and trace element analyses were conducted on the samples the studied coals are characterized by relatively high moisture ash total sulfur volatile matter contents and low gross calorific values the mineral matters of the afsin elbistan coal are represented by calcite quartz pyrite feldspar aragonite opal ct gypsum jarosite and clay minerals strontium rb sm zr hf nb mo u zn pb as mn co cr and ni concentrations detected by edp xrf are higher than the world brown coal values many of the trace elements showing positive correlations with ash content imply inorganic affinity the element concentrations of the coals are mainly related to the carbonate silicate sulfide phosphate ore minerals and fossil shells however some elements have also organic affinities

40ar 39ar thermochronology from the northwestern dabie shan constraints on the evolution of qinling dabie orogenic belt east central china abstract seven structural units with distinct kinematics have been recognized in the northwestern dabie shan 114 e 115 e and 31 n 32 n east central china they are from north to south 1 the north verging mafan fold belt mfb involving early paleozoic metamorphic rocks 2 the liangting melange belt lmb which is separated from the mfb by a south dipping thrust and consists of gneissic and marble blocks surrounded by highly sheared greenschist 3 the north verging laoshan ductile fold belt lfb which was thrust northward over the liangting melange belt and involves proterozoic schists 4 the suhe thrust sheet sts which consists of phyllite and slate above a folded thrust fault dipping both to the north and south 5 the 5 8 km wide huwan shear belt hsb in the footwall of the folded thrust consisting of mylonitic gneisses and sheared ecologite 6 the kafang eclogite bearing gneiss dome kgd which is defined by broadly warped foliations and 7 the 10 km wide pendian ductile shear belt psb characterized by dextral strike slip deformation nine phengite and muscovite samples in eclogites mylonitic shear zones and metamorphic gneisses from four of the seven structural units have been dated by the 40ar 39ar step heating method phengites from deformed eclogites in the hsb yield complex age spectra that we interpret as most likely indicating closure with respect to ar loss between 350 and 430 ma the rock samples collected from the eclogite bearing gneiss display a significant static recrystallization of quartz which suggests temperatures in excess of ca 350 400 c the ages of 350 430 ma from samples 9669b and 9669c are therefore interpreted as retrograde metamorphic ages for the eclogites six additional phengites sampled from mylonitic rocks yield two groups of ages 263 249 and 236 214 ma the older group samples 96 5 9667 and 9692 were collected from mylonitic rocks with top to north shear sense in the lmb hsb and kgd respectively 9667 and 9692 exhibit a strong static recrystallization which means that ductile deformation took place at a temperature in excess of 350 400 c we therefore adopt the age of 263 249 ma as the cooling ages of white micas considering sample 96 5 shows microfabrics formed at lower temperature around or slight below the closure temperature of white mica there is a strong possibility that the age of 254 1 ma represents a crystallization age rather than a cooling age because these samples are taken from the top to north shear zones we also interpret the 263 249 ma event as a result of thrusting induced denudation the younger group samples 96106 96124 and 96113 collected from dextral shear belts in the hsb and psb exhibit a strong static recrystallization at a temperature in excess of 350 400 c their ages 236 214 ma are therefore interpreted as the cooling ages related to later dextral strike slip faulting sample 96101 collected from weakly foliated rock without penetrative deformation on the north limb of the kgd shows poorly recovered quartz microfabrics at the temperature around or slightly below the closure temperature of white mica its age of 187 1 ma is therefore interpreted as crystallization age during the downdip detachment event related to doming the 40ar 39ar data from the northwestern dabie shan suggest four distinctive cooling events on the basis of the local structural framework and regional tectonic relationships we suggest that the 410 350 ma cooling event was related to either subduction of an oceanic plate beneath the sino korean plate or collision between the sino korean plate and a microcontinental block in the middle paleozoic the three younger episodes of cooling between the late permian and the late triassic may all have been related to the collision between the sino korean and yangtze plates specifically the 263 249 ma event could have been a result of thrusting induced denudation whereas the 236 214 ma cooling event is likely related to strike slip faulting the younger ages of 195 187 ma obtained from the gneiss dome are interpreted to be a result of regional denudation related to doming during the late stage of collision between the sino korean and yangtze plates

yo yo subduction recorded by accessory minerals in the italian western alps high pressure metamorphic rocks form during subduction of earth s crust to mantle depths at convergent plate margins their exposure at the surface of earth today provides a record of the subduction zone process in general such metamorphic rocks record only a single cycle of subduction and exhumation yet tectonic models suggest that individual rock units should undergo multiple subduction exhumation cycles here we investigate the microstructure and chemical composition of metamorphic minerals in high pressure rocks exposed in the sesia zone in the italian western alps we find that the minerals white mica garnet allanite and zircon each exhibit multiple generations of mineral overgrowths in particular two generations of white mica with high silicon content indicative of formation at high pressure are separated by an overgrowth with low silicon content that formed during exhumation at low pressures furthermore the trace element signatures of distinct zones within zircon and allanite also reveal two episodes of high pressure metamorphism separated by a period of rapid exhumation we use uranium lead dating of zircon and allanite overgrowths to constrain the timing of this subduction exhumation subduction cycle to 79 65 myr ago we conclude that slices of the sesia zone crust experienced two cycles of burial to mantle depths in less than 20 million years the yo yo subduction occurred during oblique convergence between the african and european plates which involved a continental margin

age and nature of eclogites in the huwan shear zone and the multi stage evolution of the qinling dabie sulu orogen central china abstract in situ la icpms u pb trace element and hf isotope data in zircon demonstrate a carboniferous age for eclogite facies metamorphism in siluro devonian protoliths in the huwan shear zone dabie mountains central china this age contrasts with the more prevailing triassic age for high to ultrahigh pressure hp to uhp metamorphism in the qinling dabie sulu orogen metamorphic zircon in two eclogite samples from sujiahe is characterized by low th u ratios small negative eu anomalies flat hree patterns and low 176 lu 177 hf ratios these geochemical signatures suggest that the zircon crystallized in the presence of garnet and in the absence of plagioclase feldspar furthermore temperatures of 655 and 638 c calculated using the ti content of zircon are consistent with their formation during eclogite facies metamorphism the weighted mean 206 pb 238 u age of 309 4 ma 2 for this zircon improves previous age estimates for eclogite facies metamorphism in the huwan shear zone ranging from 420 to 220 ma metamorphic zircon from one eclogite sample from hujiawan most likely formed during prograde metamorphism yields an equivalent age estimate of 312 11 ma magmatic zircon cores in the three samples yield ages for the magmatic protoliths of the eclogites ranging from 420 7 to 406 5 ma and post dating the middle paleozoic collision of the north china and the qinling terrain the zircon crystals in the three eclogite samples display a large variation of e hf t values of 4 9 to 21 3 the metamorphic zircon overgrowths show the same range of e hf t values as those of the inherited magmatic crystal interiors this suggests that the metamorphic zircon overgrowths may have formed by dissolution reprecipitation of pre existing magmatic zircon thereby preserving their original hf isotopic composition the high e hf t values suggest that the protoliths were derived from depleted mantle sources most likely paleotethyan oceanic crust while the low e hf t values are attributed to crustal contamination some eclogites in the huwan shear zone have a distinctive signature of continental crust most probably derived from the yangtze craton the coexistence of paleozoic oceanic crust and neoproterozoic continental crust with similar metamorphic ages in the huwan shear zone implies that paleozoic paleotethyan oceanic crust was produced within a marginal basin of the northern yangtze craton the opening of the paleo tethyan ocean was slightly younger than the collision of the north china craton and the qinling terrain during the late paleozoic in the qinling dabie sulu orogen subduction of the paleo tethyan oceanic crust and associated continental basement resulted in the 309 2 ma 2 eclogite facies metamorphism in the huwan shear zone the subsequent triassic continent continent collision led to the final coalescence of the yangtze and sino korean cratons amalgamation of the yangtze and north china cratons was therefore a multistage process extending over at least 200 ma

thermochronologic constraints on deformation and cooling history of high and ultrahigh pressure rocks in the qinling dabie orogen eastern china the hong an block is the best place to study the exhumation of high pressure hp and ultrahigh pressure uhp metamorphic rocks in the qinling dabie orogen of eastern china because it lacks the extensive cretaceous tectonic and thermal overprint observed in the dabie shan we measured timing of deformation and rate of cooling of the hp uhp rocks by 40ar 39ar analyses of synkinematic minerals from tectonites of key structural zones in the hong an and tongbai shan normal sense shear along the north dipping huwan detachment at the northern edge of the hong an block occurred between 237 and 231 ma this detachment facilitated the bulk of the exhumation of the hp uhp rocks our new 40ar 39ar ages combined with u pb zircon and sm nd ages of 245 240 ma suggest that exhumation of uhp rocks from mantle depths occurred at rates of 5 25 mm yr from 245 to 230 ma the mountain range is a warped extensional footwall within which white mica cooled from 225 to 205 ma locally younger extension is recorded by white mica recrystallization at 198 194 ma after which the entire block had cooled to below 300 c early cretaceous 40ar 39ar ages from the tongbai shear zone indicate that dextral shear along the southwest boundary of the orogen was contemporaneous with normal to sinistral oblique slip along the xiaotian mozitan fault along the northern boundary coeval dextral and sinistral shear zones along the northern and southwestern margins of the hong an and dabie shan would have caused eastward lateral extrusion of these two blocks perhaps driven by collision of the lhasa block with eurasia

where is the north china south china block boundary in eastern china the qinling dabieshan belt results from the collision of the north china and south china blocks the eastern extension of the belt the sulu area consists of several stacked units from top to bottom these are 1 a weakly metamorphosed slate sandstone unit of neoproterozoic paleozoic age 2 a gneiss quartzite unit metamorphosed under high pressure p conditions 3 a marble amphibolite unit 4 an ultrahigh p unit that was very deeply subducted and then exhumed and 5 a migmatitic dome resulting from the melting of ultrahigh p rocks all these units underwent the same deformation which was characterized by a top to the northwest extensional ductile shearing during their exhumation granulite facies restites in the migmatite are not significantly different from granulitized eclogites derived from the ultrahigh p rocks the migmatite exhibits the same structural and petrologic evolution as that determined for the other units the resemblance of petrologic and structural features and the lack of ocean basin rock shows that the boundary between the north china block and south china block must be placed north of the sulu area

geological controls on the sulphur content of coal seams in the northumberland coalfield northeast england the sulphur content of coal is an important consideration when developing reserves for exploitation driven by emission limits from power stations becoming more stringent variations in the sulphur content of westphalian a and b coals from the predominantly freshwater northumberland coalfield northeast england were studied according to their regional stratigraphic and in seam location the observed variation in sulphur content spatially increases towards the source area away from more marine influenced areas with increased sulphur content through time linked to changes in the general depositional environment as conditions became more marine influenced a model of basinal surface water and groundwater flow driven by post depositional source area tectonism is thought to have played only a minor role in contributing secondary sulphur to the coal however the isotopic composition of coal pyrite shows a similar range in composition to that of pyrite and other sulphides from the north pennine orefield along the southern margin of the coalfield suggesting an additional potential source of secondary sulphur as sulphur rich fluids were expelled northwards through the coal measures during early permian variscan transpression from the south the westphalian a and b are interpreted as third order depositional sequences defined by third order maximum flooding surfaces each sequence is made up of several coal bearing fourth order parasequences which tend to be more brackish to marine in character on either side of the third order maximum flooding surfaces when base level was relatively high the lowest sulphur coals are confined to the lower to middle relative low stand part of the westphalian a third order base level curve and the lowest part of the westphalian b third order base level curve this difference is attributed to a more rapid rise of base level in the westphalian b the stratigraphic and spatial distribution of coal sulphur has been used as a guide to prediction of reserve identification for surface mining operations

from passive margins to orogens the link between ocean continent transition zones and ultra high pressure metamorphism a lithostratigraphic association consisting of serpentinized mantle rocks continent derived allochthons mid oceanic ridge gabbros of jurassic age and post rift sediments typical of an ocean continent transition is found in the eclogitic piemonte units in the western alps in situ u pb geochronology was performed on zircons from an orthogneiss sampled at the bottom of a sliver of continental basement in contact with serpentinites primary magmatic zircons of permian age were overgrown by a second generation of zircon at ca 166 150 ma likely related to melt infiltration associated with the intrusion of the underlying gabbroic body this indicates that continental basement slices and oceanic basement rocks were already juxtaposed in the jurassic and they were probably part of hyper extended crust related to the opening of the tethys therefore the complex lithological association described here which is also characteristic of several ultra high pressure melange zones worldwide was acquired prior to the orogenic event during which it was only partly reworked ocean continent transitions are in positions favorable to reach ultra high pressure conditions following negatively buoyant oceanic lithosphere into subduction and then being accreted to the orogen in response to the arrival of more buoyant continental lithosphere resisting subduction the ocean continent transition is now found in the immediate footwall of a 500 m thick shear zone which accommodated multiple episodes of deformation during eocene oligocene time suggesting an important link between alpine deformation and rift related structures

high pressure ultrahigh pressure eclogites from the hong an block east central china geochemical characterization isotope disequilibrium and geochronological controversy the hong an block western dabieshan exposes a series of hp uhp metamorphic rocks with a s to n distribution from blueschist greenschist kyanite free to kyanite and coesite bearing eclogites the available age data are inconclusive that hinder our understanding of the tectonic evolution of the block the metamorphic temperatures in the hong an block tmeta 700 to 500 c are lower by 50 150 c than that of the dabie and sulu terranes in this work we undertook new trace element and sr nd o isotopic analyses on minerals in order to gain more insight into the geochronological problems the results are as follows 1 trace element distribution patterns suggest that garnet and omphacite in many cases are out of chemical equilibrium and the presence of high temperature lree rich mineral inclusions e g epidote in garnet and omphacite has contributed to isotope disequilibrium 2 sm nd isotope analyses yielded no isochron ages for the hong an eclogites 3 rb sr isotope analyses gave mixed results in some cases coexisting minerals are completely out of isotope equilibrium and in others isochron relationship is established yielding ages from 210 ma to 225 ma the pattern of rb sr isotope disequilibrium appears to be independent of the petrological and o isotope temperatures 4 in contrast to the unequilibrated sm nd isotopic systems oxygen isotopes of the eclogite minerals seem to have attained isotope equilibrium or near equilibrium oxygen isotope temperatures are comparable with petrological temperatures however this is an apparent feature due to mass balance constraints 5 whole rock 18o values show a large variation from 10 to 8 suggesting that their protoliths have undergone very different processes of water rock interaction in view of the overall geochronological information we conclude that the hp uhp metamorphism in the hong an block took place in the triassic at about 220 230 ma as observed in the dabie and sulu terranes the significance of published paleozoic dates 450 300 ma for the xiongdian eclogite is not clear however any hypotheses advocating two periods of uhp metamorphic events for the same tectonic unit or in the same locality are not constrained by the geochronological data

subduction followed by collision alpine and himalayan examples abstract the high mountains of the himalaya and alps are both the result of ongoing continental collision following closure by subduction of neo tethys and related ocean basins during the mesozoic and tertiary the high topography is associated in both areas with a thickened crustal root of up to 70 km thickness as deduced from various geophysical investigations in the himalayan region where several thousand kilometres of ocean crust was consumed below the lhasa block southern margin of the asian continent both continental trans himalayan batholith and oceanic kohistan ladakh arc accreted to asia in the jurassic magmatic arcs are recognisable in the alps where much smaller oceanic rifts and basins were consumed such arc sequences are absent in the area of the high mountains regardless of this major difference in volume of subducted oceanic lithosphere seismic tomography in both regions has identified several anomalous regions in the mantle interpreted as the remnants of detached slabs of oceanic crust metamorphosed rocks of continental crust sequences in both the himalaya and alps record evidence of subduction to depths exceeding 90 km coesite stability field as well as rapid exhumation to shallower depths at rates of 4 mm a or more this subduction related metamorphism of the eclogite and blueschist facies is clearly distinguishable from subsequent younger lower pressure greenschist amphibolite facies metamorphic overprints related to imbricate stacking of continental crust slices thermal relaxation and final exhumation dragging of buoyant upper crust down to upper mantle depths requires an attached root of oceanic lithosphere but the rapid exhumation stage may well be a consequence of slab break off this process appears to have been equally effective in the alps and the nw himalaya despite the significant differences in duration of subduction and the volumes of oceanic lithosphere involved

high pressure metamorphic rocks from tongbaishan central china u pb and 40ar 39ar age constraints on the provenance of protoliths and timing of metamorphism abstract the tongbaishan area is situated at the junction between the paleozoic north qinling orogen and the mesozoic south qinling dabie sulu orogen the area contains an important geological section for understanding the assembly of the sino korean and yangtze cratons two eclogite zones were recently recognized in this area the peak metamorphic conditions are estimated to be 530 610 c and 17 20 kbar for the northern eclogite zone and 460 560 c and 13 19 kbar for the southern eclogite zone shrimp u pb analyses on zircons of eclogite metagabbro and orthogneiss indicate that their protoliths were formed during the neoproterozoic and experienced high pressure hp recrystallization during the permian triassic period therefore the tongbaishan area belongs to the western extension of the dabieshan hp uhp terrane in addition u pb ages of detrital zircons from quartzite paragneiss and schist show three age populations of 2 49 ga 1 93 ga and 1 85 1 82 ga suggesting that extensive paleoproterozoic orogeny or tectonothermal events took place in the northern margin of the yangtze craton the shrimp dating and complementary 40ar 39ar dating of muscovite from quartzofeldspathic gneiss and quartzite reveal that the crustal rocks were subducted to great depths and underwent hp eclogite facies metamorphism at ca 255 ma slightly earlier than the timing of deep subduction of the uhp slice the hp rocks were later exhumed to mid to upper crustal levels and suffered from retrograde recrystallization at ca 238 ma the dating also discloses a still later phase of deformation and recrystallization at ca 215 ma the available age data throughout the tongbai dabie sulu orogen reflect diachronous exhumation from ca 238 ma for the hp slice to ca 213 ma for the uhp slice such a phenomenon could be explained by successive subduction and exhumation of the broken slices of the subducting yangtze slab

a remote coal deposit revisited middle jurassic coals at kulhoj western germania land northeast greenland abstract in 1908 members of the danmark expedition discovered a coal deposit in a very remote area in western germania land close to the margin of the inland ice in northeast greenland the deposit was however neither sampled nor described and was revisited in 2009 for the first time since its discovery the outcrops found in 2009 amount to approximately 8 m of sediment including a coal seam of 2 m thickness more outcrops and additional coal deposits most certainly are to be found pending further fieldwork the deposits are middle jurassic callovian in age and were deposited in a floodplain environment related to meandering river channels spores and pollen in the lower fluvial deposits reflect abundant vegetation of ferns along the river banks in contrast a sparse spore and pollen flora in the coals show a mixed vegetation of ferns and gymnosperms based on proximate and petrographic analyses the coals are classified as medium rank high grade coal their composition is dominated by inertinite and vitrinite and they represent deposits laid down in a freshwater mire no evidence of marine incursion has been found the coal seam studied does not include liptinite rich coals such as those present in the same lithostratigraphic unit elsewhere in northeast greenland but loose blocks in the area suggest their presence in unknown parts of the succession

trace elements in the lower pliocene fossiliferous kangal lignites sivas turkey abstract the kangal lignite basin which is one of the most productive lignite basins in eastern anatolia turkey includes two lignite seams containing abundant gastropoda shells in the lower pliocene kalburcayiri formation the seams are currently exploited in an open cast mine in the kalburcayiri field and supply feed coal to a power plant with 300 mw capacity the average thickness of each of the two seams in this mine is about 10 m and they are separated by about 20 m of tuffaceous sedimentary rocks a 15 20 cm thick tuff bed occurs within the upper seam the purpose of the study was to understand mineralogy and trace element concentrations of the two lignite seams in the kalburcayiri formation which were affected by volcanic ashes fifty nine core samples of the lignites from seven boreholes across the basin and eight channel samples from the working lignite seams were collected and analysed by proximate analysis x ray powder diffraction xrd inductively coupled plasma mass spectrometry icp ms and scanning electron microscopy sem with energy dispersive x ray microanalysis techniques the samples show that the worked lignite seams on an as received basis contain high moisture contents 43 4 57 8 all the samples on an air dried basis have high ash yields from 19 5 to 81 7 and a broad range of total sulfur contents from 1 16 to 7 04 and calorific values 684 to 4621 kcal kg except for two samples with no temperature rise due to high ash yield the mineral matter of the studied samples is made up of calcite quartz feldspar pyrite opal ct clay minerals gypsum and traces of aragonite the trace element analyses on a whole coal dry basis indicate that most of the borehole samples showed enrichment in specific elements including zn 15 1394 g g mo 13 368 g g and u 5 5 131 g g when compared to the range of these elements for most coals in the world the contents of zn mo and u for the samples from the worked lignite seams are respectively 38 187 54 161 and 28 55 g g the sem studies show that zn is hosted mainly in micron sized zn bearing mineral sphalerite but no mo and u bearing minerals have been detected during these studies except for monazites containing th and u traces the mo and u concentrations are negatively correlated with the ash yields and these elements are contained mainly within organic matter

quality palynology and palaeoenvironmental interpretation of the ilgin lignite turkey the ilgin lignite field can be subdivided into the haramikoy and kurugol areas which are separated by an area of basement and a fault the lignite bearing sequence consists mainly of fluvial and lacustrine neogene deposits the ilgin lignite averaging 8 m up to 25 m thick is blackish brown and dark brown in colour the lignite contains abundant brown wood plant remains and white gastropod shells samples have an average of 38 9 moisture on an as received basis and a mean of 3 9 total sulphur on an air dried basis geochemical analysis using an icp ms was undertaken thirteen lignite core samples from three boreholes drilled in the kurugol area were ashed at 750 c the average trace element contents of the lignite show a higher concentration of u average 43 ppm when compared to the range for most coals in the world while the others ti p sc be mn co cu zn ga as rb sr zr nb mo cs ba y ta w tl pb bi th la ce pr nd sm eu gd tb dy ho er yb lu agree with the global ranges the ilgin lignite is identified as of middle miocene middle serravallian age and occurs within lacustrine sediments deposited under subtropical climatic conditions

differential subduction and exhumation of crustal slices in the sulu hp uhp metamorphic terrane insights from mineral inclusions trace elements u pb and lu hf isotope analyses of zircon in orthogneiss based on new evidence the sulu orogen is divided from south east to north west into high pressure hp crustal slice i and ultrahigh pressure uhp crustal slices ii and iii a combined set of mineral inclusions cathodoluminescence images u pb shrimp dating and in situ trace element and lu hf isotope analyses was obtained on zircon from orthogneisses of the different slices zircon grains typically have three distinct domains that formed during crystallization of the magmatic protolith hp or uhp metamorphism and late amphibolite facies retrogression respectively i oscillatory zoned cores with low pressure lp mineral inclusions and th u 0 38 ii high luminescent mantles th u 0 10 with hp mineral inclusions of qtz grt arg phe ap for slice i zircon and coe grt phe kfs ap for both slices ii and iii zircon iii low luminescent rims with lp mineral inclusions and th u 0 08 zircon u pb shrimp analyses of inherited cores point to protolith ages of 785 770 ma in all seven orthogneisses the ages recorded for uhp metamorphism and subsequent retrogression in slice ii zircon c 228 and c 215 ma respectively are significantly older than those of slice iii zircon c 218 and c 202 ma respectively while slice i zircon recorded even older ages for hp metamorphism and subsequent retrogression c 245 and c 231 ma respectively moreover ar ar biotite ages from six paragneisses interpreted as dating amphibolite facies retrogression gradually decrease from hp slice i c 232 ma to uhp slice ii c 215 ma and uhp slice iii c 203 ma the combined data set suggests decreasing ages for hp or uhp metamorphism and late retrogression in the sulu orogen from south east to north west thus the hp uhp units are interpreted to represent three crustal slices which underwent different subduction and exhumation histories slice i was detached from the continental lithosphere at 55 65 km depth and subsequently exhumed while subduction of the underlying slice ii continued to 100 120 km depth uhp before detachment and exhumation slice iii experienced a similar geodynamic evolution as slice ii however both uhp metamorphism and subsequent exhumation took place c 10 myr later magmatic zircon cores from two types of orthogneiss in uhp slices ii and iii show similar mid neoproterozoic crystallization ages but have contrasting hf isotope compositions ehf 785 2 7 to 2 2 and 17 3 to 11 1 respectively suggesting their formation from distinct crustal units mesoproterozoic and paleoproterozoic to archean respectively during the breakup of rodinia the uhp and the retrograde zircon domains are characterized by lower th u and 176 lu 177 hf but higher 176 hf 177 hf t than the neoproterozoic igneous cores the similarity between uhp and retrograde domains indicates that late retrogression did not significantly modify chemical and isotopic composition of the uhp metamorphic system

high pressure blueschists and eclogites in hong an a framework for addressing the evolution of high and ultrahigh pressure rocks in central china the hong an region in the qinling dabie collisional zone in eastern china hosts a series of metamorphic rocks exposing a south to north distribution from blueschist blueschist greenschist amphibolite eclogite kyanite free and kyanite eclogite to coesite eclogite facies rocks that represent progressively deeper levels of the mesozoic subduction collision complex the hong an area is interesting for three reasons 1 it escaped the thermal and structural overprint imparted on much of the dabie mountains during early cretaceous intrusion of voluminous granites and granodiorites 2 the high pressure hp hong an eclogites are widely distributed often preserve prograde crystallization histories and can be directly linked in time and space to the blueschist blueschist greenschist rocks exposed to the south 3 the blueschist blueschist greenschist facies rocks are generally better exposed than their equivalents in the southeastern dabie mountains and offer some opportunity for simultaneous structural and metamorphic analysis the hong an area hp rocks offer perhaps the closest approximation to a preserved snapshot of mesozoic pressure temperature p t conditions attending early subduction exhumation in the region and are thus essential to generating a coherent picture of the dynamics attending both metamorphism and exposure of the coeval ultrahigh pressure uhp rocks the purpose of this contribution is twofold 1 to document previously unpublished metamorphic and structural data characterizing these hp sequences and their relative continuity in hong an 2 to incorporate these data with recent geochronologic structural and paleomagnetic information in the context of protracted late paleozoic through mesozoic subduction collision and exhumation metamorphism and exhumation of some of the southern hong an hp sequences appear to have occurred concomitant with oceanic subduction immediately to the west and thus may have preceded widespread continental subduction collision moreover all of the hp uhp sequences in the region were exhumed before the end of collision between the sino korean and yangtze cratons at ca 160 ma exhumation of hp uhp rocks both before and during continental plate collision is neither novel for central china nor for other hp uhp zones but is important to take into account when reconstructing the evolution of such orogens

stratigraphic and geophysical integrated methodologies for the interpretation of sulphur water formational environment in salento italy abstract the salento coal deposits south eastern italy are unutilized because these deposits are thin and nearly uneconomic but they have a high scientific and economic value due to their high organic sulphur content the studied area is located in the western salento peninsula where wells used by a fish farm ittica ugento have shown high concentrations of hydrogen sulphide data from surface and boreholes stratigraphic surveys integrated with electrical resistivity tomography ert allow us to define the structure depths and geometry of the aquifer and its relationship with saltwater intrusion induced polarization ip with pole dipole array survey has been carried out near the coastline the value measured was over 50 msec a direct relationship is shown to exist between ip values and the aquifer containing sulphur water the high resolution of the data obtained with the applied methods not only shows the validity of the methodology but is the key to evaluating the groundwater resources of the area the proposed mechanism is that of entrapment of sulphur water in a graben structure when sulphate enriched waters of marine origin come into contact with organic substances and lignite deposits galatone formation oligocene they are deprived not only of free oxygen but also generate hydrogen sulphide as a result of the reduction of sulphates

shrimp u pb dating trace elements and the lu hf isotope system of coesite bearing zircon from amphibolite in the sw sulu uhp terrane eastern china abstract in this study we link mineral inclusion data trace element analyses u pb age and hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi stage metamorphic evolution of amphibolites from the sulu ultrahigh pressure uhp terrane eastern china zircon grains separated from amphibolites from the ccsd mh drill hole g12 and niushan outcrop g13 were subdivided into two main types based on cathodoluminescence cl and laser raman spectroscopy big dusty zircons with inherited cores and uhp metamorphic rims and small clear zircons weakly zoned grey white luminescent inherited cores preserve mineral inclusions of cpx pl ap qtz indicative of a mafic igneous protolith dark grey luminescent overgrowth rims contain the coesite eclogite facies mineral inclusion assemblage coe grt omp phe ap and formed at t 732 839 c and p 3 0 4 0 gpa in contrast white luminescent small clear zircons preserve mineral inclusions formed during retrograde hp quartz eclogite to lp amphibolite facies metamorphism t 612 698 c and p 0 70 1 05 gpa inherited zircons from both samples yield shrimp 206 pb 238 u ages of 695 520 ma with an upper intercept age of 800 31 ma the uhp rims yield consistent triassic ages around 236 225 and 239 225 ma for g12 and g13 with weighted means of 229 3 and 231 3 ma respectively small clear zircons from both samples give 206 pb 238 u ages around 219 210 ma with a weighted mean of 214 3 ma interpreted as the age of retrograde quartz eclogite facies metamorphism matrix amphibole from both samples indicate ar ar ages of 209 0 7 and 207 0 7 ma respectively probably dating late amphibolite facies retrogression the data suggest subduction of neoproterozoic mafic igneous rocks to uhp conditions in middle triassic 230 ma times and subsequent exhumation to an early hp 214 ma and a late lp stage 208 ma over a period of 16 and 6 myr respectively thus early exhumation from a mantle depth of 120 100 km to about 60 km occurred at an average rate of 0 3 cm y while subsequent exhumation to a middle crustal level took place at approximately 0 54 cm y these exhumation rates are considerably slower than those obtained for uhp rocks in the dora maira and kokchetav massifs 2 3 cm y based on similar p t estimates and trace element and hf isotope compositions sulu amphibolites can be identified as retrograde uhp eclogites the ehf 800 of 8 implies a significant input from the depleted mantle to the sulu dabie terrane during the middle neoproterozoic overgrown rims are characterized by a distinct trace element composition with low lu hf and th u and significantly higher 176 hf 177 hf ratios than inherited cores consistent with formation during after garnet re crystallization and fractionation of the lu hf system during uhp metamorphism the combined dataset suggests homogenization of the 176 hf 177 hf ratio within the metamorphic mineral assemblage and during protolith formation observed variations are explained by mixing of material from both domains during laser ablation e g due to partial recrystallization of inherited cores

metamorphic growth and recrystallization of zircon distinction by simultaneous in situ analyses of trace elements u th pb and lu hf isotopes in zircons from eclogite facies rocks in the sulu orogen simultaneous in situ analyses of trace elements u th pb and lu hf isotopes were carried out on distinct domains of zircons in ultrahigh pressure uhp eclogite facies metamorphic rocks from the main hole of the chinese continental scientific drilling ccsd in the sulu orogen for the first time trace elements are directly linked to lu hf isotopes in metamorphic zircons with reference to their u pb dates this enables methodological integration to distinguish four types of metamorphic zircon solid state replacement and dissolution recrystallizations of protolith zircons and new growth from the aqueous fluid metamorphically grown zircons are characterized by concordant u pb ages for the metamorphism flat hree patterns typical of the garnet effect low contents of ree especially hree y nb ta and th u high contents of hf low lu gd n lu hf and th u 0 1 ratios and elevated 176hf 177hf ratios relative to solid state recrystallized zircons this suggests the effects of both garnet and fluid on the growth of metamorphic zircons in contrast metamorphic recrystallization has reset the u th pb isotope system of protolith zircons to different extents depending on the extents of fluid action during metamorphism solid state recrystallized zircons exhibit the lowest degrees of resetting and thus almost inherit all geochemical features from the protolith zircons which are characterized by discordant u pb ages close to or below the protolith age steep mree hree patterns typical of magmatic origin high contents of trace elements and their ratios and low 176hf 177hf ratios on the other hand dissolution recrystallized zircons show the highest degrees of reworking and thus have concordant or nearly concordant u pb ages for the metamorphism steep mree hree patterns lowered contents of trace elements such as ree th u y nb ta and ti relative to the protolith zircons and almost unchanged hf isotope ratios replacement recrystallized zircons display intermediate degrees of reworking and thus have their many features of elements and isotopes in between while the metamorphic growth in the presence of both garnet and fluid is characterized by both depletion of hree with flat pattern and the low contents of trace elements the metamorphic recrystallization in the presence of aqueous fluid is indicated by gradual decreases of mree to hree without the flat hree pattern therefore the simultaneous in situ analyses of metamorphic zircons have the advantage over single term analyses in making distinction between the new growth and the different types of recrystallization

tracing two orogenic cycles in one eclogite sample by lu hf garnet chronometry the adula nappe central alps was thought to be a melange of rock fragments some of which were subducted and then exhumed from the mantle lu hf dating of two populations of garnets in one rock sample instead indicates that the nappe twice experienced subduction and exhumation as one coherent unit

precipitation gradients during the miocene in western and central turkey as quantified from pollen data abstract in the present paper we have analyzed thirty five palynofloras covering the time span from the early miocene aquitanian to the late miocene middle tortonian in turkey the results obtained are presented in tables and maps showing temporal palaeoprecipitation values the mean annual precipitation map exceeds 1200 mm during the aquitanian and early middle serravallian it is suggested to have been between 1000 and 1300 mm in the latest serravallian earliest tortonian in western and central turkey in the early middle tortonian the lower boundary of map decreases to below 1000 mm in central and eastern turkey today maps are represented by lower values around 600 1000 mm in western and 400 600 mm in central turkey for the driest month lmp the rainfall was not distributed homogeneously in the aquitanian the calculations are between 36 and 48 mm with humid conditions in western and eastern turkey during the burdigalian and middle miocene the driest month precipitation varied with respect to locations however it is clear that there was a reduction in precipitation during the early middle tortonian with values around 26 27 mm in central and eastern turkey the same pattern is observed for the wettest month precipitation hmp with estimates higher than 200 mm during the aquitanian and earliest tortonian although some areas received low rainfall hmp was reduced between 130 and 140 mm in the early middle tortonian the warmest month precipitation wmp varied from 96 to 140 mm except for konya ilgin kirsehir hacibektas and manisa soma that received 88 mm during the early middle miocene in the early middle tortonian the amount of summer rainfall lay between 58 and 88 mm the reason of the decrease in all rainfall parameters during the early middle tortonian could be related to several factors such as climatic cooling altitude aridification palaeotopograhy or continentality however it is necessary to indicate that the tortonian cooling had previously been proposed by akgun et al 2007 as the explanation using a large number of palynological assemblages in turkey we also observe a decrease in precipitation parameters during the middle miocene this could be related to fact that either low species diversity can result in wide coexistence intervals or the monterey cooling event was related to a cooling during the langhian and serravallian

occurrence and distribution of sulfur in peat forming environments of southern florida abstract cores and surface samples of peats from the everglades mangrove region of southern florida were analyzed for total sulfur and pyritic sulfur these values were compared with the petrographic botanical components of the peats as determined from point counts of oriented microtome sections pyrite occurs as individual euhedral crystals loosely packed framboids and lenses or crusts of minute crystals framboids and minute crystals are often associated with organic matter and sometimes with bacteria and fungi pyrite tends to selectively occur in void spaces in or between peat tissues in samples containing very small amounts of pyrite framboidal pyrite is the prevalent form marine to brackish peats contain the highest pyrite and total sulfur contents with brackish peats generally containing more pyrite than marine peats pyrite tends to be lower in all peats within 30 cm of the surface whether marine or brackish burial of freshwater peats beneath marine or brackish peats tends to increase the total sulfur and pyritic sulfur in the underlying peats burial beneath brackish water clay rich deposits such as splays tends to increase total sulfur and pyritic sulfur in the underlying deposits more than burial beneath less clay rich deposits

quality parameters of lignite of the north bohemian basin in the czech republic in comparison with the world average lignite abstract sulfur is considered to be the most harmful element in atmospheric emissions and fall out which originate from coal combustion total sulfur content std in lignites of the north bohemian basin nbb has a geometric mean of 1 61 wt at n 12 979 and is mostly influenced by the presence of iron disulfides the distribution of sulfur and many trace elements is log normal a non uniform distribution of sulfur in lignite was found within the basin with the lowest std contents i e not exceeding 1 wt s confined to the eastern and southeastern margin of the nbb contents between 1 and 1 5 wt s are most common in lignites of the south central nbb lower sulfur contents were identified in the area of the atec delta and its northern extension in contrast high contents of sulfur in lignite exceeding 1 5 wt are found along the northern margin of the basin at the foot of the krusne hory mts and in the westernmost part of the nbb three genetically different types of iron disulfides occur in lignite of the nbb synsedimentary early diagenetic diagenetic and epigenetic among those forms synsedimentary disulfides mostly pyrite appear to be most abundant they form finely dispersed microscopic framboids or veinlets that commonly parallel the coal bedding the other iron disulfide forms are much less abundant dissolved sulfate which was supplied to the nbb during the miocene is likely to have been derived from sulfides of the krusne hory mts crystalline complex this unit has an isotopic composition of sulfide sulfur varying between 1 and 5 consequently the sulfate supplying the nbb should exhibit slightly positive 34 s values syngenetic pyrites forming microframboids or veinlets in coal show 34 s values close to 0 these values are similar those of sulfur dioxide in gases of power stations burning nbb coal this implies that no considerable shifts in sulfur isotopic composition occur during thermal oxidation of the dominant pyrite arsenic is positively correlated with sulfur r2 0 89 its total content astd is 20 53 ppm at n 9172

u pb hf and o isotope evidence for two episodes of fluid assisted zircon growth in marble hosted eclogites from the dabie orogen abstract a combined study of internal structure u pb age and hf and o isotopes was carried out for metamorphic zircons from ultrahigh pressure eclogite boudins enclosed in marbles from the dabie orogen in china cl imaging identifies two types of zircon that are metamorphically new growth and recrystallized domain respectively the metamorphic zircons have low th and u contents with low th u ratios yielding two groups of 206 pb 238 u age at 245 3 to 240 2 ma and 226 4 to 223 2 ma respectively anomalously high 18 o values were obtained for refractory minerals with 9 9 to 21 4 for garnet and 16 9 for zircon this indicates that eclogite protolith is sedimentary rocks capable of liberating aqueous fluid for zircon growth during continental subduction zone metamorphism most of the zircons are characterized by very low 176 lu 177 hf ratios of 0 000001 0 000028 indicating their growth in association with garnet recrystallization a few of them falling within the older age group have comparatively high 176 lu 177 hf ratios of 0 000192 0 000383 suggesting their growth prior to the formation of garnet in the late stage of subduction the variations in the lu hf ratios for zircons can thus be used to correlate with garnet growth during eclogite facies metamorphism in either case the zircons have variable e hf t values for individual samples suggesting that their protolith is heterogeneous in hf isotope composition with localized fluid availability in the bulk processes of orogenic cycle nevertheless a positive correlation exists between 206 pb 238 u ages and lu hf isotope ratios for the metamorphically recrystallized zircons suggesting that eclogite facies metamorphism in the presence of fluid has the identical effect on zircon lu hf and u th pb isotopic systems we conclude that the zircons of the older group grew in the presence of fluid during the subduction prior to the onset of peak ultrahigh pressure metamorphism whereas the younger zircons grew in the presence of fluid released during the initial exhumation toward high pressure eclogite facies regime

mineralogical and geochemical characterization of the saray and pinarhisar coals northwest thrace basin turkey abstract this study investigates the mineralogical and geochemical characteristics of coals from the saray and pinarhisar coalfields in the northwest thrace basin using optical microscopy scanning electron microscopy x ray diffraction and inductively coupled plasma mass spectrometry the saray and pinarhisar coals were deposited in a limnic environment the sulfur content of the coals ranges from 0 3 to 15 3 and high sulfur contents may originate from both seawater and volcanism pyritic and organic sulfur are the dominant sulfur forms 1 2 and 2 7 on average respectively the mineral matter of the coals consists mainly of pyrite barite gypsum muscovite and kaolinite with minor amounts of quartz butlerite tamarugite and rozenite the coals are enriched in trace elements including v 61 ppm on average co 5 85 ppm on average ni 79 ppm on average as 39 2 ppm on average th 3 6 ppm on average and u 6 7 ppm on average based on pearson correlation coefficients ti v cr fe co ni cu se rb au hg pb and th have mainly inorganic affinities r ash elements 0 5 in the pinarhisar coals fe as and au also have inorganic affinities r ash elements 0 5 in the saray coals the element contents and correlation coefficients indicate that the strandja massif the tethyan ophiolite belt and the oldest basement sediments were included in the sediment source region for both coalfields while the strandja massif was the prevailing sediment source region for pinarhisar coalfield

petrology and geochemistry of the high sulphur coals from the upper permian carbonate coal measures in the heshan coalfield southern china abstract the heshan coals with very high organic sulphur content are found in the upper permian marine carbonate successions heshan formation in the heshan coalfield central guangxi southern china the petrography mineralogy and geochemistry of coals and non coal partings from the suhe and lilan coal mines of the heshan coalfield have been investigated using proximate petrographic inductively coupled plasma mass spectrometry icp ms x ray fluorescence xrf x ray diffraction xrd and scanning electron microscopy with an energy dispersive x ray sem edx techniques the sulphur content in the coals with ash less than 50 ranges from 5 3 to 11 6 of which more than 90 is organic sulphur reflecting a strong marine water influence on the palaeomire the high vitrinite reflectance 1 89 2 18 romax indicates that the coals in the heshan coalfield are mainly low volatile bituminous coal microscopic observation has revealed that the coal is mainly composed of vitrinite and inertinite macerals with relatively low tpi and high gi values suggesting an unusual strongly alkaline palaeomire with high ph xrd analysis plus optical and scanning electron microscopy show that the minerals in these coals are mainly quartz calcite dolomite kaolinite illite and pyrite although marcasite strengite and feldspar as well as some oxidised weathering products such as gypsum are also present most trace elements in the heshan coals are enriched with respect to their world mean with mo u and w highly enriched more than 10 times their world means the trace elements are believed to be associated either with organic compounds mo and u or minerals such as aluminium iron silicates sc ge and bi aluminium silicates cs be th pb ga and ree iron phosphates zn rb and zr iron sulphides as cd cr cu ni tl and v and carbonates sr mn and w abnormally high organic sulphur content high ash yields relatively high gi values very low tpi values very high u contents and very low th u ratios suggest that the heshan coals accumulated in low lying marine influenced palaeomires developed on carbonate platforms many of these characteristics have also been recorded in the tertiary coals of the circum mediterranean coal basins where no marine influence is present the similarities are thought to be produced by strongly alkaline groundwater chemistry common to both environments

palaeoenvironmental reconstruction of the eastern part of the karapinar ayranci coal deposit central turkey abstract regional tectonic movements during the neogene period resulted in the development of several fault controlled basins in central anatolia many of these basins host economic coal deposits the recently discovered karapinar ayranci coal deposit is the most important one due to its large reserves c 1 8 gt and location in the vicinity of important urban areas the paper aims to reconstruct the palaeoenvironmental conditions before during and after coal formation in the eastern part of karapinar ayranci deposit by means of coal petrography and mineralogical data combined with sedimentological and palaeontological data the basinal infilling consists of mainly lacustrine fluvial and alluvial sediments the coal seams comprise several beds intercalating with claystone mudstone and marl the coal being lignite in rank displays high ash yield 36 4 wt on dry basis and high total sulphur content avg 7 7 wt on dry ash free basis facies diagrams and lithological features of the coal seams suggest that peat was accumulating under pure telmatic to limnotelmatic conditions however peat accumulation ceased several times due to a rise in water level therefore clastic e g quartz clay minerals and authigenic e g pyrite mineral contents are variable along the seam profile gastropod and ostracod fauna points to freshwater conditions in the palaeomire high total sulphur and evaporite mineral e g halite contents usually point to brackish saline conditions during peat accumulation however in case of the karapinar ayranci deposit high sulphur contents can be related to sulphate rich karstic aquifer which contributed to the palaeomire water supply

coal geology and coal quality of the miocene mugla basin southwestern anatolia turkey abstract this work focuses on the relationship between the coal geology and coal quality of the miocene mugla basin southwestern anatolia turkey to this end detailed petrographical mineralogical and geochemical studies were performed on composite profile samples from the nine coal fields in the mugla basin alatepe bagyaka bayir cakiralan ekizkoy eskihisar husamlar sekkoy and tinaz coal fields the mugla lignite is a high ash from 16 to 56 and sulphur from 2 1 to 5 7 lignite which is petrographically characterised by a high huminite content mainly gelinite macerals the mineral matter of the studied lignite samples is made up mainly of clay minerals and quartz with the exception of the sekkoy and ekizkoy lignites in which calcite is the dominant mineral phase with minor amounts of quartz clay minerals pyrite and gypsum and traces of aragonite syngenetic opal is also frequently identified in these samples the differentiation of these two types of lignite with specific mineralogical patterns is attributed to the contemporaneous development of peatlands with a high detrital input dominated by the quartz and clay mineral setting and peatlands with low detrital supply and a dominant carbonate rich lacustrine environment the higher water table of the latter allowed the precipitation of micritic carbonates and the development of lakes with abundant mollusc fauna this differentiation is also evidenced by the geochemical data thus the sekkoy ekizkoy husamlar bayir and alatepe lignites are characterised by relatively low al and fe contents

on the evolution of orogens pressure cycles and deformation mode switches abstract evidence of two burial exhumation cycles that took place during a single orogeny has been found in rocks belonging to the piemonte unit of the western alps an early high pressure event which resulted from tectonic burial down to pressures of 1 5 gpa was followed by exhumation to ca 0 20 0 35 gpa as a result of extensional deformation renewed shortening culminated in a second burial episode down to pressures of 0 65 0 80 gpa before the final exhumation took place existing geochronological data allow only ca 13 19 ma for the completion of both burial exhumation cycles therefore we suggest that the evolution of orogens is characterized by multiple short lived burial exhumation cycles related to orogen scale alternance between shortening and extensional deformation

post breakup burial and exhumation of passive continental margins seven propositions to inform geodynamic models despite many years of study the processes involved in the post breakup development of passive margins remain poorly understood integration of apatite fission track analysis afta and stratigraph

postrift history of the eastern central atlantic passive margin insights from the saharan region of south morocco the passive margin of south morocco is a low elevated passive margin it constitutes one of the oldest margins of the atlantic ocean with an early jurassic breakup and little geological data are available concerning its postrift reactivation so far we investigated the postrift thermal history of the onshore part of the margin with low temperature thermochronology on apatite crystals fission track and u th sm he ages we obtained are significantly younger than the breakup 190 ma fission track ages range from 107 8 to 175 16 ma with mean track lengths from 10 7 0 3 to 12 5 0 2 m u th sm he ages range from 14 1 to 185 15 ma using inverse modeling of low temperature thermochronological data we demonstrate that the south moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases the first exhumation event occurred during late jurassic early cretaceous and we attribute this to mantle dynamics rather than to intrinsic rifting related processes such as flexural rebound the second event from late cretaceous to early paleogene might record the onset of africa europe convergence we show a remarkably common behavior of the whole moroccan passive margin during its early postrift evolution the present day differences result from a segmentation of the margin domains due to the africa europe convergence finally we propose that varying retained strengths during rifting and also the specific crustal lithospheric geometry of stretching explain the difference between the topographical expressions on the continental african margin compared to its american counterpart

geological controls on the coal quality of the mequinenza subbituminous coal deposit northeast spain abstract the results of geological petrographical geochemical and mineralogical studies performed to determine the coal forming paleo environmental conditions which gave rise to anomalous enrichments in organic sulphur molybdenum and uranium in the oligocene mequinenza subbituminous coal deposit of northeastern spain are summarized this paper demonstrates the major influence exerted by the paleohydrology of the depositional framework on the early diagenetic evolution of the precursor peat deposits the s mo and u enrichments the preservation of aragonite and chlorophillinite and the high degree of gelification of the mequinenza coal are a consequence of alkaline syngenetic conditions in the depositional environment similar conditions can be inferred for many mesozoic and tertiary coal deposits in the mediterranean region mallorca sardinia hungary bulgaria serbia greece and turkey however the source of sulphur may have been different and have included triassic and early jurassic sulphate recycling scenarios or volcanic sources whatever the source sulphur enrichment is always influenced by the alkaline depositional environments developed in basins generated during the alpine cycle in circum mediterranean mobile belts

early miocene climate and biomes of turkey evidence from leaf fossils dispersed pollen and petrified wood abstract the early miocene was a period of major palaeogeographic reorganization in the eastern mediterranean region during which time the anatolian plateau became subaerial and several intracontinental basins intermittently became connected to the paratethys and mediterranean seas in this paper we analyse early miocene vegetation and climate using leaf records palynological assemblages and fossil wood at 36 localities from western and central turkey most of which have precise age control based on radiometric dating and mammal faunal ages using the leaf flora of guvem bes konak kesekoy climate leaf analysis multivariate program clamp analyses and koppen signatures were employed to infer a palaeoclimate typical of modern laurel forest regions based on the palynological records abundance of various pollen taxa was used as a measure of openness of vegetation and regional presence of major tree taxa most pollen floras are dominated by tree pollen ranging from 85 to 98 and indicated widespread afforestation in the pollen diagrams shifts in dominance from swamp forest elements taxodioideae to well drained forests pinaceae indicate changes in lake levels or phases of basin development such shifts may have been associated with the development of more xeric forest vegetation wood anatomical features such as false tree rings further may indicate seasonal climate pollen diagrams and macrofossils reflect zonal and azonal broadleaf and needleleaf forest and extrazonal open vegetation the latter occurred in areas with shallow soils on volcanic rocks or limestone e g cycads dracaena or coastal areas herb dominance taxonomic composition and biogeographic affinities suggest laurel forest as a major forest biome on well drained soils and ecotones between laurel forest and broadleaf deciduous forest biomes a comparison with younger floras shows that these are neither more diverse nor more warmth loving despite an increase in global temperature mid miocene climatic optimum suggesting bottlenecks during previous oligocene cooler times for warmth loving taxa

characterization of turkish coals a nationwide perspective abstract the u s geological survey usgs and the turkish general directorate of mineral research and exploration maden tetkik ve arama genel mudurlugu mta are working together to provide a better understanding of the chemical properties of turkish coals from major turkish lignite producing areas the coals in turkey are generally low rank lignite or subbituminous formed in several different depositional environments at different geologic times and have differing chemical properties eocene coals are limited to northern turkey oligocene coals found in the thrace basins of northwestern turkey are intercalated with marine sediments miocene coals are generally located in western turkey the coal deposits which have limnic characteristics have relatively abundant reserves pliocene pleistocene coals are found in the eastern part of turkey most of these coals have low calorific values high moisture and high ash contents analysis of 143 coal channel samples most are lignite and subbituminous in rank but a few are bituminous and one is anthracitic in rank has been completed for up to 54 elements and other coal properties using a variety of analytical techniques including inductively coupled plasma emission and mass spectrometry instrumental neutron activation analysis and various single element techniques and astm standard procedures many of these coals have elemental concentrations similar to u s lignites found in the gulf coast and fort union regions however maximum or mean concentrations of b cr cs ni as br sb cs and u in turkey are higher than the corresponding maximum or mean values found in either the fort union or gulf coast regions

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

evolution of topography of post devonian scandinavia effects and rates of erosion abstract the mechanisms and timing of mountain growth in scandinavia remain enigmatic given that the region has not been involved in active orogenesis since the devonian and in any large scale tectonic activities after the ne atlantic breakup during the early cenozoic in this study we combine analysis of the vertical motions of the region caused by dominantly glacial erosion during the quaternary with apatite fission track aft analysis of rocks from the area using numerical models we first quantify how fluvial and glacial erosion carved out the fjords and valleys to a depth of 2 km below the paleosurfaces this erosional episode represents a major local weight loss and results in up to a 0 8 km uplift of rocks and up to a 0 5 km rise of local topography these estimates only marginally depend on the effective elastic thickness of the lithosphere and thus are robust we show then that no correlation exists between sample altitude and published aft data but that a correlation does exist between aft age and the depth below our constructed pre glacial summit surface this correlation demonstrates the robustness of the numerical erosional model quantifies average erosion rates during carboniferous cretaceous at

episodic burial and exhumation in ne brazil after opening of the south atlantic it is a common assumption that elevated passive continental margins have remained high since rifting and breakup here we show that the atlantic margin of ne brazil has undergone a more complex history our synthesis of geological data landscape analysis and paleothermal and paleoburial data reveals a four stage history 1 after early cretaceous breakup the margin under went burial beneath a thick sedimentary cover 2 uplift episodes in the campanian and eocene led to almost complete removal of these deposits 3 the resulting large scale low relief erosion surface peneplain was deeply weathered and finally reburied at the oligocene miocene transition and 4 miocene uplift and erosion produced a new lower level peneplain by incision of the uplifted and re exposed paleogene peneplain previous studies have identified aspects of this interpretation but we have defined the absolute timing and magnitude of discrete events of burial and exhumation that followed early cretaceous rifting and eocene oligocene peneplanation we suggest that a late sedimentary cover protected paleogene weathering profiles until the present day the uplift phases in brazil are synchronous with uplift phases in africa and the andes the andean phases coincided with rapid convergence on the western margin of south america and the campanian uplift coincided with a decline in spreading rate at the mid atlantic ridge consequently we suggest that both vertical movements and lateral changes in the motion of the plates have a common cause which is lateral resistance to plate motion

the relationship between macerals and sulphur content of some south african permian coals abstract there is a positive correlation between sulphur concentration and the vitrinite maceral group content in permian vryheid formation coals in south africa the reverse is true for the inertinite maceral family this relationship is evident at intraseam interseam and intercoalfied levels vitrinite precursors formed where the water table in peat forming environments was high and eh low these conditions favoured bacterial sulphate reduction and resulting h 2 s reacted with fe 2 and organic peat compounds to form pyrite and organic sulphur components inertinite precursors formed when the water table was low and eh high aerobic respiration prevailed and little h 2 s was produced organic sulphur derived from peat forming plant tissue is dominant in intertinite rich low sulphur coal pyritic sulphur exceeds organic sulphur in high sulphur coals dur to preferential reaction of h 2 s with fe 2

properties of a lacustrine subbituminous k1 seam with special reference to the contact metamorphism soma turkey abstract the subbituminous k1 seam in the middle miocene soma formation of western turkey reaches a thickness of 24 m typical samples on an air dried basis have 9 5 14 2 moisture 4 3 13 8 ash and 0 57 2 54 total sulphur the coal rank parameters and non agglomerating behaviour show that the coals are of subbituminous a rank the k1 seam is huminite rich coal with a mean random ulminite reflectance rr between 0 46 and 0 49 fluorescence emission measurements show that the sporinite cutinite resinite and alginite present have typical fluorescence spectra between 460 and 700 nm the soma formation was intruded by an olivine basalt during the pliocene pleistocene which caused local contact metamorphism at the top of the k1 seam on the basis of proximate ultimate and petrographic analyses the intruded seam can be divided into normal coal transition zone and natural coke intervals each differing in their degree of metamorphism moisture volatile matter hydrogen and oxygen contents very rapidly decrease close to the contact point with the intrusion whilst calorific value carbon content and mean random reflectance value increase a diagram ofo c versus h c also shows a distinct increase in rank caused by the intrusion minor illite siderite and plagioclase feldspar are present in the natural coke samples butpyrrhotite is not observed mineralogical geochemical and reflectance studies indicate that the general temperature during formation of natural coke was probably relatively low

geological controls on the mineralogy and geochemistry of the beypazari lignite central anatolia turkey abstract the raw coal from the cayirhan mine beypazari basin turkey contains an average of 28 5 mineral matter consisting up to 80 zeolites the coal seam is split by a 1 m thick tuffaceous siltstone into the upper first tv and lower second tb seams which contain essentially different zeolites the first seam contains ca rich zeolites clinoptilolite heulandite whilst the second seam contains na rich zeolites analcime experimental work has shown that a na rich activation solution will produce na rich zeolites when the original volcanic glass is na rich but will produce ca rich zeolites when the volcanic material is ca rich it is thought that a na rich activation solution derived from contemporaneous volcanics in the beypazari basin reacted with volcanic tuffs of different chemical composition to produce the vertical variability in the mineral matter of the two seams trace element analyses of the raw coal showed that they are enriched in as b cr ni and zr when compared to world wide averages of coal they are also enriched in the major elements na and k these elements are probably also derived from a volcanic source barium and sr show a clear affinity for analcime whilst li cr ni cu zn co and ga show a clear affinity for clinoptilolite heulandite trace elements showing a positive correlation with the organic matter are mn b be ge y zr nb hf w and u manganese u th sc ge and hree heavy rare earth elements show correlations with phosphate trace elements showing correlation with both fe and s contents are co mo ta pb and iree intermediate rare earth elements arsenic and v seem to have mixed affinities with sulphides and zeolites and organic matter and zeolites respectively although a proportion of the as b and s are retained in the ash during coal combustion due to the sorption mechanism of cao derived from the clinoptilolite heulandite decomposition significant emissions of these elements may arise from the cayirhan thermal power station due to the anomalously high concentrations of these elements in the beypazari coal the high total alkali metal content of these coals exceeds the recommended maximum for steam coal but it is believed that sodium occurring in a mineralogical form such as analcime is not as likely to contribute to boiler fouling as organically associated sodium

zircon u pb and hf evidence for coupled subduction of oceanic and continental crust during the carboniferous in the huwan shear zone western dabie orogen central china both oceanic and continental hp rocks are juxtaposed in the huwan shear zone in the western dabie orogen and thus provide a window for testing the buoyancy driven exhumation of dense oceanic hp rocks the hp metamorphic age of the continental rocks in this zone has not been well constrained and hence it is not known if they are of the same age as the exhumation of the hp oceanic rocks in situ laser ablation multiple collector inductively coupled plasma mass spectrometry la mc icp ms u pb trace element and hf isotope analyses were made on zircon in a granitic gneiss and two eclogites from the huwan shear zone u pb age and trace element analysis of residual magmatic zircon in an eclogite constrain its protolith formation at 411 4 ma the zircon in this sample displays ehf t values of 6 1 to 14 4 the positive ehf t values up to 14 4 suggest that the protolith was derived from a relatively depleted mantle source most likely palaeotethyan oceanic crust a granitic gneiss and the other eclogite yield protolith u pb ages of 738 6 and 700 14 ma respectively which are both the neoproterozoic basement rocks of the yangtze block the zircon in the granitic gneiss has low ehf t values of 14 2 to 10 5 and old tdm2 ages of 2528 2298 ma suggesting reworking of palaeoproterozoic crust during the neoproterozoic the zircon in the eclogite has ehf t values of 1 0 to 7 4 and tdm1 ages of 1294 966 ma implying prompt reworking of juvenile crust during its protolith formation metamorphic zircon in both eclogite samples displays low th u ratios trace element concentrations relatively flat heavy rare earth element patterns weak negative eu anomalies and low 176lu 177hf ratios all these features suggest that the metamorphic zircon formed in the presence of garnet but in the absence of feldspar and thus under eclogite facies conditions the metamorphic zircon yields u pb ages of 310 3 and 306 7 ma therefore both the oceanic and continental type eclogites share the same episode of carboniferous eclogite facies metamorphism this suggests that high pressure continental type metamorphic rocks might have played a key role in the exhumation and preservation of oceanic type eclogites through buoyancy driven uplift

formation uplift and dissection of planation surfaces at passive continental margins a new approach the usefulness of large scale low relief high level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists we argue that the formation of low relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels in the absence of other options the most likely base level is sea level we have analysed west greenland landscapes in a recent study by combining the cooling history from apatite fission track analysis afta data with the denudation history from landscape analysis and the stratigraphic record an important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed the present day high level plateau in west greenland is the remnant of a planation surface that was formed by denudation that lasted c 20 million years during which up to 1 km of cover was removed after maximum burial at the eocene oligocene transition here we present additional afta data to show that the planation surface is the end product of cenozoic denudation even in basement areas and argue that phanerozoic sediments most likely of cretaceous palaeogene age must have been present prior to denudation the planation surface was offset by reactivated faults and uplifted to present day altitudes of up to 2 km the uplift occurred in two late neogene phases that caused incision of valleys below the planation surface and their subsequent uplift we therefore find that the elevated and deeply dissected plateau is evidence of episodic post rift uplift that took place millions of years after cessation of sea floor spreading west of greenland we suggest that other margins with similar morphology may also be characterized by episodic post rift uplift unrelated to the processes of rifting and continental separation rather than being permanently uplifted since the time of rifting as is commonly assumed copyright 2009 john wiley sons ltd

trace element signature and u pb geochronology of eclogite facies zircon bergen arcs caledonides of w norway secondary ion mass spectrometry sims u pb and trace element data are reported for zircon to address the controversial geochronology of eclogite facies metamorphism in the lindas nappe bergen arcs caledonides of w norway caledonian eclogite facies overprint in the nappe was controlled by fracturing and introduction of fluid in the proterozoic sveconorwegian granulite facies meta anorthosite norite protolith zircon grains in one massive eclogite display a core rim structure sveconorwegian cores have trace element signatures identical with those of zircon in the granulite protolith i e 0 31 th u 0 89 heavy rare earth element hree enrichment and negative eu anomaly weakly zoned to euhedral oscillatory zoned caledonian rims are characterized by th u 0 13 low lree content minimum normalized abundance for pr or nd variable enrichment in hree and no eu anomaly a decrease of ree towards the outermost rim especially hree is documented this signature reflects co precipitation of zircon with garnet and clinozoisite in a feldspar absent assemblage and consequently links zircon to the eclogite facies overprint the rims provide a mean 206pb 238u crystallization age of 423 4 ma this age reflects eclogite forming reactions and fluid rock interaction this age indicates that eclogite facies overprint in the lindas nappe took place at the onset of the scandian silurian collision between laurentia and baltica

processes in continental collision zones preface abstract formation and exhumation of high pressure hp to ultrahigh pressure uhp metamorphic rocks in continental subduction zones are the two fundamental geodynamic aspects of collisional orogensis this volume is based on the session 08c titled geochemical processes in continental collision zones at goldschmidt 2010 in knoxville usa it focuses on micro to macro scale processes that are temporally and spatially linked to different depths of crustal subduction exhumation and associated mineralogical changes they are a key to understanding a wide spectrum of phenomena involving hp uhp metamorphism and syn post collisional magmatism papers in this volume report progresses in petrological geochronological and geochemical studies of uhp metamorphic rocks and their derivatives in china with tectonic settings varying from arc continent collision to continent continent collision microbeam in situ analyses of metamorphic and magmatic minerals are successfully utilized to solve various problems in the study of continental deep subduction and uhp metamorphism in addition to their geochronological applications to dating of hp to uhp metamorphic events during continental collision microbeam techniques have also served as an efficient means to recognize different generations of mineral growth during continental subduction zone metamorphism furthermore metamorphic dehydration and partial melting of uhp metamorphic rocks during subduction and exhumation are highlighted with respect to their effects on fluid action and element mobilization these have provided new insights into chemical geodynamics in continental subduction zones

dynamics of exhumation and deformation of hp uhp orogens in double subduction collision systems numerical modeling and implications for the western dabie orogen abstract the dynamics of formation and exhumation of high pressure hp and ultra high pressure uhp metamorphic orogens in double subduction collision zones remain enigmatic here we employ two dimensional thermo mechanical numerical models to gain insights on the exhumation of hp uhp metamorphic rocks as well as their deformation during the collision of a micro continent with pro and retro continental margins along two subduction zones a three stage collisional process with different convergence velocities is tested in the initial collisional stage a fold and thrust belt and locally rootless superimposed folds are developed in the micro continent and subduction channel respectively in the second exhumation stage of hp uhp rocks a faster convergence model results in upwelling of the asthenosphere which further leads to a detachment between the crust and lithospheric mantle of the micro continent a slower convergence model results in rapid exhumation of hp uhp rocks along the north subduction channel and a typical piggy back thrusting structure in the micro continent a non convergence model produces a slab tear off leading to the rebound of residual lithosphere of the micro continent in the third and final stage a series of back and ramp thrusts are formed in the micro continent with the pro continent re subducted based on an analogy of our numerical results with the western dabie orogen wdo we suggest that 1 slab tear off results in a rebound of residual lithosphere which controls the two stage syn collisional exhumation process of hp uhp rocks in the wdo and 2 in contrast to the single subduction collision system the exhumation range of the partially molten rocks with lower viscosity and density is restricted to a specific region of the micro continent by the mianlue and shangdan subduction zones which generated the complex deformation features in the wdo

carboniferous and triassic eclogites in the western dabie mountains east central china evidence for protracted convergence of the north and south china blocks shrimp u pb dating and laser ablation icp ms trace element analyses of zircon from four eclogite samples from the north western dabie mountains central china provide evidence for two eclogite facies metamorphic events three samples from the huwan shear zone yield indistinguishable late carboniferous metamorphic ages of 312 5 307 4 and 311 17 ma with a mean age of 309 3 ma one sample from the hong an group 1 km south of the shear zone yields a late triassic age of 232 10 ma similar to the age of ultra high pressure uhp metamorphism in the east qinling dabie orogenic belt ree and other trace element compositions of the zircon from two of the huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase namely in the eclogite facies an interpretation supported by the presence of garnet omphacite and phengite inclusions zircon also grew during later retrogression zircon cores from the huwan shear zone have ordovician to devonian 440 350 ma ages flat to steep heavy ree patterns negative eu anomalies and in some cases plagioclase inclusions indicative of derivation from north china block igneous and low pressure metamorphic source rocks cores from hong an group zircon are neoproterozoic 780 610 ma consistent with derivation from the south china block in the western dabie mountains the first stage of the collision between the north and south china blocks took place in the carboniferous along a suture north of the huwan shear zone the major triassic continent continent collision occurred along a suture at the southern boundary of the shear zone the first collision produced local eclogite facies metamorphism in the huwan shear zone the second produced widespread eclogite facies metamorphism throughout the dabie mountains sulu terrane and a lower grade overprint in the shear zone

distribution of environmental sensitive trace elements in the eocene sorgun coals turkey abstract the distribution of trace elements in the lower eocene coal seam mined in the yeniceltek kucukkohne and ayridam coal mines from the sorgun basin was investigated in relation to ash content and maceral composition the coal seam is mainly composed of huminite in the present study 35 samples from five seam sections were collected on the basis of megascopic characteristics results were determined using an energy dispersive polarised x ray fluorescence edp xrf spectrometer on a whole coal dry basis most of the major and trace elements studied are enriched in high ash samples while ba br mn and w show relative enrichments in low ash samples most of elements studied such as ga ce la th nb rb zr v cu u pb sb cs sn cr se y and zn are primarily associated with mineral matter clay minerals arsenic and a part of zn se and sb are probably concentrated in pyrites in the samples element concentrations show statistically significant negative correlations with many macerals and positive relationships with only attrinite that is mainly mixed with mineral matter clay minerals and small quartz grains in the samples nine trace elements as cr mn ni pb sb se th and u considered as potentially hazardous air pollutants are present in low to moderate concentrations the mean values of trace element concentrations display relative enrichments in se 2 8 ppm th 21 ppm and w 26 ppm in the investigated samples in comparison with other coals in the world

quality variations in the high sulphur lignite of the neogene beypazari basin central anatolia turkey abstract during the miocene a number of fault bounded basins developed in central anatolia turkey one such basin at cayirhan near beypazan contains thick laterally extensive lignite seams this basin was filled initially with coarse clastic material upward fining of the clastics during basin fill with an increase in the amount of clay and carbon content led to the development of relatively shallow linmic basins in which extensive peat deposits accumulated in low lying mires these lignites are characterized by their high sulphur and ash contents up to 8 2 s and 68 3 ash on an air dried basis studies of the sulphur and ash contents reveal three types of distribution namely vertical variation within individual seams variation between the seams and lateral variation across the basin in the case of the sulphur content vertical variation within and between the seams is related to variations in the amount and source of the sulphate in the mire water and the lateral variation is probably related to structural topographic control of the mire at the time of formation variation in the ash content within the seams is probably the result of depositional processes at the time of mire development variation between seams is recognized due to the presence of ubiquitous zeolites in the mineral matter namely heulandite in the first seam and analcime in the second seam this is probably the result of variations in the chemistry of the original volcanoclastic or clastic material associated with the lignite or of variations in the chemistry of the circulating fluid there is a broad east west lateral variation across the basin in the ash content of the seams probably resulting from variations in the amount and rate of clastic or volcanoclastic influx into the mire at the time of formation related to structural topographic controls

triassic high pressure metamorphism in the huwan shear zone tracking the initial subduction of continental crust in the whole dabie orogen abstract la mc icpms trace element u pb and hf isotope analyses were performed on zircons from continental derived retrograde high pressure metamorphic rocks which were attested by the occurrence of hp mineral inclusions in metamorphic zircons from the huwan shear zone in the western dabie orogen zircons in a schist sample are mostly detrital and gave u pb ages from 1212 to 2312 ma suggesting that the detritus were derived from multiple sources or suffered partial pb loss during subsequent metamorphism magmatic zircons in an amphibolite sample yielded an upper intercept u pb age of 1806 63 ma which was interpreted as its protolith formation age the zircons in the amphibolite show a weighted e hf t value of 16 3 and a weighted hf model age of 3455 ma suggesting that the protolith was derived from reworking of ancient continental materials metamorphic zircons in a quartz rich leucosome sample and the amphibolite sample gave weighted mean 206 pb 238 u ages of 241 1 and 243 4 ma respectively these metamorphic zircons contain mineral inclusions of garnet and omphacite and are characterized by relatively flat hree patterns with slight negative eu anomalies this indicates that they formed in the presence of garnet but the absence of plagioclase and thus under eclogite facies conditions the u pb age of ca 243 ma is consistent with eclogite facies metamorphic ages of the juvenile oceanic crust in the western dabie orogen suggesting that the initial continental subduction for high pressure metamorphism of the whole dabie orogen can be traced back to ca 243 ma in addition the western dabie hp uhp orogenic belt might have suffered multi slice subduction and exhumation during the triassic

distribution of forms of sulfur in peats from saline environments in the florida everglades abstract although there is published information on the mechanism of sedimentary pyrite formation resulting from bacterial reduction of sulfate little is known about the distribution of forms of sulfur including organic in peats in order to increase understanding of the geochemistry of sulfur in coals we have determined distributions of forms of sulfur in five cores of saline peat and one of brackish peat all from areas near the shark river and whitewater bay in the coastal swamps of south florida all concentrations vary widely with depth total sulfur concentrations range up to 6 of dry solids minor amounts of sulfur are present as h2s s0 so42 and acid soluble sulfide but the principal forms are usually pyritic and organic the ratio organic pyritic is highly variable but at a majority of levels in a profile is considerably greater than unity it is inferred that topochemical factors are important in determining the distribution of sulfur forms in any element of volume

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

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

composition and organic maturity of middle jurassic coals north east greenland evidence for liptinite induced suppression of huminite reflectance abstract middle jurassic coals from kuhn o north east greenland may contain up to 85 vol liptinite principally resinite up to 68 6 vol the coals are thus petrographically comparable to the middle jurassic muslingebjerg formation coals at hochstetter forland approximately 40 50 km to the north and they are inherently excellent petroleum source rocks liptinite poor 6 0 vol coal samples from both kuhn o and hochstetter forland yield mean random huminite reflectance values of 0 49 0 53 ro implying a rank of sub bituminous a above a threshold value somewhere between 3 and 24 vol resinite and 6 and 35 vol total liptinite significant reflectance suppression is induced and between 24 and 69 vol resinite and 35 and 85 vol total liptinite a nearly linear inverse relationship exists between the content of liptinite resinite and the mean random reflectance values at the highest liptinite resinite contents reflectance suppression may be up to 0 23 ro the reflectance suppression is related to bitumen adsorption caused by bitumen expulsion from resinite and total reflectance distributions of the huminite fractions suggest that the reflectance of all huminite macerals is lowered with increasing liptinite resinite content

zircon u pb age and trace element evidence for paleoproterozoic granulite facies metamorphism and archean crustal rocks in the dabie orogen abstract zircon u pb ages and trace elements were determined for granulites and gneiss at huangtuling which are hosted by ultrahigh pressure metamorphic rocks in the dabie orogen east central china cl images reveal core rim structure for most zircons in the granulites the cores show oscillatory zoning relatively high th u ratios and hree enriched patterns consistent with a magmatic origin they gave a weighted mean 207pb 206pb age of 2766 9 ma interpreted as dating magma emplacement of the protolith the rims are characterized by sector or planar zoning low th u ratios negative eu anomalies and flat hree patterns consistent with their formation under granulite facies metamorphic conditions zircon u pb dating yields a weighted mean 207pb 206pb age of 2029 13 ma which is interpreted to record a metamorphic event possibly during assembly of the supercontinent columbia the gneiss has a protolith age of 1982 14 ma which is younger than the zircon age of the granulite facies metamorphism suggesting a generally delay between ht metamorphism and the intrusion of post collisional granites a few inherited cores with igneous characteristics have 207pb 206pb ages of 2 90 3 28 and 3 53 ga suggesting the presence of mesoarchean to paleoarchean crustal remnants in the yangtze craton a few cretaceous metamorphic ages were also obtained suggesting the influence of post collisional collapse in response to cretaceous extension of the dabie orogen it is inferred that the recently discovered archean basement of the yangtze craton occurs as far north as the dabie orogen

values of δ34s in iron disulphides of the north bohemian lignite basin czech republic three main genetically different types of iron disulphides occur in lignite of the north bohemian basin synsedimentary diagenetic and epigenetic among them the synsedimentary disulphide appears to be the most abundant it forms fine dispersed microscopic framboids or veinlets mostly parallel with the coal bedding this disulphide is mostly represented by pyrite the other types are much less abundant the epigenetic variety consists of large macroscopic clusters of crystals of marcasite twins or crystalline filling of fractures the shift in sulphur isotopic composition between the original sulphate and the derived sulphides which originated through bacterial reduction may vary considerably depending on conditions particularly on the open or closed nature of the system with respect to sulphate the largest shifts in the isotopic composition between sulphate and sulphide sulphur are typical for an open system dissolved sulphate which supplied the north bohemian basin during the miocene is likely to have been derived from weathered sulphides of the krugn6 hory crystalline complex this unit has isotopic compositions of sulphide sulphur varying between 1 and 5 0 and assuming no significant shifts in sulphur isotope compositions the sulphate supplying the basin should exhibit a slightly positive 534s value organic sulphur is thought to have played a much less important role synsedimentary pyrites which form microframboids or veinlets in coal show 634s values close to 0 0 these values when compared with those of sulphur dioxide in gases exhaled by power stations burning lignite of the north bohemian basin indicate that they correspond to mean values for synsedimentary pyrite this also implies that no considerable shifts in isotopic composition take place during thermal oxidation in power plants

subduction ultrahigh pressure metamorphism and regurgitation of buoyant crustal slices implications for arcs and continental growth abstract intracontinental collisional belts that retain mineralogic relics of phanerozoic ultrahigh pressure uhp metamorphism are increasingly being recognized adjacent regions generally lack evidence of coeval calcalkaline volcanism plutonism following consumption of intervening oceanic lithosphere each orogen marks the site of a deeply subducted microcontinental promontory fragments of which later returned to midcrustal levels mafic and ultramafic rocks are volumetrically minor pressures in uhp complexes approached or exceeded 2 8 gpa at 600 900 c subduction zones involve low t prograde gradients and constitute the only plate tectonic realm where such conditions exist although internal portions of descending plates may have even lower geothermal gradients crustal upper margins are typified by p t trajectories of 5 10 c km attending underflow clinoamphibole rich metabasaltic rocks dehydrate at pressures 2 2 2 5 gpa this accounts for the kinetically favorable solid state production of mafic eclogites and partial fusion of morbs to form hydrous andesitic melts devolatilization of partly serpentinized mantle lithosphere also introduces h 2 o to the magmagenic zone as large masses of continental crust enter deeper portions of subduction zones mineralogic transformations slow or cease because micas the major oh bearing phases in such rocks retain volatile contents to pressures 4 gpa persistence of hydroxyl bearing layer silicates may explain the metastable preservation of low density assemblages in continental crust subjected to uhp conditions and the dearth of calcalkaline magmatism in most collision belts exhumed uhp terranes are intensely deformed and disaggregated all consist dominantly of quartzofeldspathic compositions mafic eclogites garnet peridotites constitute only a few volume percent eventual decoupling of the relatively low density subducted crust promotes buoyancy propelled transport to shallow depths along the subduction channel with the hanging wall lithosphere acting as a stress guide extensional collapse and erosional unroofing of rising masses result in the continued ascent of deeply subducted but buoyant crustal material although equidimensional massifs must return surfaceward large volume to surface areas render the contained uhp phase assemblages virtually unquenchable surviving uhp terranes thus consist of relatively thin slabs of continental crust allochthons that retain uhp relics apparently lost heat by conduction across both upper normal fault and lower reverse fault contacts based on present exposures estimated thicknesses of uhp sheets are qinling dabie sulu belt 5 km kokchetav complex 1 3 km dora maira massif 1 2 km western gneiss region 1 km slices evidently rose to midcrustal levels at exhumation rates approaching 10 mm per year back reaction attending decompression in all cases was nearly complete where uhp mineral inclusions persisted retrogression apparently was limited by the relative impermeability of the rocks to catalytic aqueous fluids and by declining temperatures the coarse grain size of host phases also disfavored complete retrogression

timing of uhp metamorphism in the hong an area western dabie mountains china evidence from zircon u pb age trace element and hf isotope composition the hong an area western dabie mountains is the westernmost terrane in the qinling dabie sulu orogen that preserves uhp eclogites the ages of the uhp metamorphism have not been well constrained and thus hinder our understanding of the tectonic evolution of this area la icpms u pb age trace element and hf isotope compositions of zircons of a granitic gneiss and an eclogite from the xinxian uhp unit in the hong an area were analyzed to constrain the age of the uhp metamorphism most zircons are unzoned or show sector zoning they have low trace element concentrations without significant negative eu anomalies these metamorphic zircons can be further subdivided into two groups according to their u pb ages and trace element and lu hf isotope compositions one group with an average age of 239 2 ma show relatively high and variable hree contents 527 lun 14 and 176lu 177hf ratios 0 00008 0 000931 indicating their growth prior to a great deal of garnet growth in the late stage of continental subduction the other group yields an average age of 227 2 ma and shows consistent low hree contents and 176lu 177hf ratios suggesting their growth with concurrent garnet crystallization and or recrystallization these two groups of age are taken as recording the time of prograde hp to uhp and retrograde uhp hp stages respectively a few cores have high th u ratios high trace element contents and a clear negative eu anomaly these features support a magmatic origin of these zircon cores the upper intercept ages of 771 86 and 752 70 ma for the granitic gneiss and eclogite respectively indicate that their protoliths probably formed as a bimodal suite in rifting zones in the northern margin of the yangtze block young hf model ages tdm1 of magmatic cores indicate juvenile mantle derived materials were involved in their protolith formation