an outline of the plate tectonics of china china is principally a part of the eurasian plate but the margins of the indian and philippine sea plates are involved in the himalayas and in the coastal range of taiwan respectively within the eurasian plate the cathaysian paleoplate is separated from the angaraian paleoplate by the junggar hegen suture which contains paleozoic ophiolites and rare blueschists the three microplates of the cathaysian paleoplate consist of precambrian cratons and or phanerozoic accretionary fold belts these coalesced precambrian cratons record at least six stages of intense orogeny before cratonization the paleozoic to cenozoic accretionary fold belts of china can be correlated with similar events now found in west pacific andean and atlantic type active continental margins ophiolites occupying many of these tectonic zones provide evidence for the age and igneous history of oceanic crust formed during the paleozoic to cenozoic the presence of blueschist in some of these chinese sutures reveals evidence of large scale subduction and tectonic exhumation during consolidation of the eurasian plate cenozoic collision of the eurasian and indian plates produced deformation and uplift of the himalayas strongly influencing the tectonics of western china in contrast mesozoic tertiary evolution of eastern china is typical basin range geology similar to that of the western united states which included development of deep sedimentary basins along with calc alkaline plutonic and volcanic activity associated with crustal thinning and high heat flow the complicated tectonic evolution of china is greatly illuminated by the presence of ophiolites and blueschists in proterozoic to tertiary convergent boundaries these petrotectonic assemblages provide evidence of an extremely mobile history of plate movement in china

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part ii xenotime xenotime from a geochemically heterogeneous series of mildly to strongly peraluminous granites of the erzgebirge germany displays extended compositional variability with respect to abundances of hree y u and th with few exceptions the maximum and minimum concentrations for the lanthanides and actinides exceed those noted for this mineral from other geologic environments xenotime chemistry is dominated by the theoretical end members hree po 4 and ypo 4 90 mol in total typical xenotime grains from the erzgebirge granites and from other granites worldwide contain 70 80 mol ypo 4 and 16 25 mol hree po 4 this study documents the occurrence of xenotime abnormally rich in hree in place of y with up to 45 mol hree po 4 substitutions of thorite coffinite th u pb sio 4 brabantite ca th u po 4 2 and monazite la sm po 4 are of minor importance reaching maximum levels of 5 6 mol each with a total contribution typically th u super 4 ca super 2 the total lanthanide and actinide contents in xenotime and host granite are not strongly correlated however formation of xenotime unusually rich in hree occurs only in the a type limica granites that are strongly enriched in these elements the shapes of hree patterns of xenotime and host rock are similar which combined with mass balance calculations indicate the importance of this mineral in affecting the hree as well as y evolution of late stage granitic melts late xenotime may show strong y ho fractionation thus recording the decoupling of y and the hree which can occur in the latest stages of crystallization of evolved granites and which may be associated with deuteric alteration

tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

petroleum in basement rocks basement reservoirs are a special type of important oil reservoirs that until recently have generally been neglected as targets for exploration most basement reservoirs occur either on platforms or in intermontane basins they are rare in foredeep basins the basement reservoirs always occur on highs or uplifts within the basin and have been subjected to long periods of weathering and erosion younger sediments presumably source beds directly overlie basement providing opportunity for entrapment of oil in the basement rock almost all basement reservoirs occur below a regional unconformity all source beds of basement reservoirs lie above the reservoir rock but all source beds lying above the reservoir rock do not necessarily form basement reservoirs although most source beds lie above an unconformity some lie below it and form a so called second crop unconformities play an important role in basement reservoirs as they are the passageway for oil migration provide conditions for long distance migration and connect source and reservoir rocks which may lie on opposite sides of the unconformity and at great distances from each other the unconformity surface provides evidence that basement rocks have undergone weathering erosion solution and leaching for so long a time that porosity and permeability have increased greatly and the accumulation of petroleum was facilitated oil may accumulate in any igneous metamorphic or sedimentary rocks with secondary fissures dissolved interstices and caverns or in sandstone and carbonate rocks with primary porosity carbonates form the best basement reservoirs because being hard and brittle they not only develop secondary fissures but are readily dissolved by ground water so that original pores are enlarged and new porosity produced basement reservoirs are characterized by thick reservoir rocks porosity and permeability are irregular production from basement reservoirs is usually high and reserves are large

alteration of crystalline basement rocks by hydrocarbon bearing fluids moinian of ross shire scotland abstract moinian proterozoic gneisses in easter ross shire scotland exhibit pronounced alteration where they have been subjected to the flow of hydrocarbon bearing fluids from an adjacent devonian sedimentary basin comparison of the petrography of altered and unaltered gneiss indicates that element redistribution accompanied the alteration process the alteration involved creation of secondary porosity by dissolution of primary minerals in the gneiss chloritization of biotite and precipitation of authigenic orthoclase cross cutting veinlets include bitumen authigenic quartz orthoclase albite monazite and titanium oxides attesting to redistribution of all the major components of the gneiss evidence for bitumen being coeval with albite quartz and an association of high porosity with bitumen indicate that hydrocarbon bearing fluids were present during the alteration process bitumen also penetrated beyond the visible alteration zone and accreted around radioelement bearing accessory minerals organic geochemical data indicate that there is a local source for the bitumen in the devonian sequence bitumen veining also occurs within the devonian sequence fluid inclusion data from quartz associated with bitumen in the gneiss and the devonian indicate minimum trapping temperatures of 120 140 and 100 120 c respectively the alteration was probably a result of a fluid flow episode relating to fault movement during basin subsidence

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

textural chemical and isotopic insights into the nature and behaviour of metamorphic monazite monazite is a mineral of choice for dating metamorphism in amphibolite and granulite grade metapelites however there exist a number of difficulties that complicate the interpretation of monazite geochronological data and prevent its application to many geological problems the two main obstacles addressed in this contribution are firstly the minor but significant e g 1 30 ma dispersal in duplicate isotope dilution thermal ionisation mass spectrometry id tims u pb age data commonly recorded from a single rock and secondly the difficulty of attaching monazite age data to pressure and temperature information through a multidisciplinary approach utilising tims and laser ablation multicollector inductively coupled plasma mass spectrometry la mc icpms isotope data quantitative and qualitative emp chemical analyses of monazite and textural studies we assess the significance of pb loss older components and continuous and episodic monazite growth in the generation of dispersed age data three samples from the canadian cordillera and one sample from the himalaya of pakistan are examined each sample exhibits an age dispersion of between 1 and 12 ma for single crystal and multi grain tims u pb monazite age determinations consideration of the closure temperature for pb diffusion in monazite and the metamorphic temperatures experienced by these samples suggests diffusive pb loss did not play a significant part in generating this age dispersal the la mc icpms study indicates that an older component 100 ma older than the tims ages contributed to the age dispersal in three of the four samples in all the samples however chemical analyses identified that the majority of monazites examined exhibited significant intra crystalline zoning in y content the la mc icpms analysis of one sample that was constrained to zones of distinct y content indicates that these zones are of distinct age we suggest that monazite grown before the appearance of garnet and during garnet breakdown is relatively rich in y whereas monazite grown after garnet is relatively poor in y a combination of these chemical data with textural observations suggests that once monazite had entered the mineral assemblage it grew or recrystallised episodically throughout the prograde and retrograde paths of the metamorphic event this behaviour contributes to and in one of the samples controls the observed age dispersal this recognition allows the generation of pressure temperature time points by combining textural and chemical information of monazite with in situ age determinations and pressure temperature information from garnet thus the episodic growth of compositionally distinct monazite throughout a metamorphic event provides the geochronologist with a very valuable chronological tool

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

adakitic signature formed by fractional crystallization an interpretation for the neo proterozoic meta plagiogranites of the ne jiangxi ophiolitic melange belt south china article i nfo the low temperature high pressure metamorphic rocks which are exposed as exotic blocks within the serpentinite matrix of the ne jiangxi ophiolitic melange belt consist of enclave bearing and free meta plagiogranites both rock types are characterized by a metamorphic mineral assemblage consisting of ab rich plagioclase quartz clinopyroxene amphibole while rutile titanite and zircon occur as accessories the former primary magmatic mineral parageneses for the meta mafic enclaves and the meta plagiogranites are similar and consist of an rich plagioclase hornblende ilmenite monazite apatite however the ab rich plagioclase abundance of the meta mafic enclave is much lower and the hornblende and accessory mineral abundances are higher compared with those of the meta plagiogranite host rocks meta plagiogranites with mafic enclaves have a chemical composition similar to that of typical adakites with elevated al2o3 15 86 wt mg 53 5 and sr contents 485 ppm and a positive eu anomaly the rare earth element patterns are highly fractionated with la yb nn12 and low y b4 ppm and yb b0 4 ppm the mafic enclave has a basaltic composition with a negative eu anomaly and has ca 10 times higher hree and y concentrations than the plagiogranite host rocks enclave free meta plagiogranites also have high al2o3 16 08 wt na2o 8 88 wt and mg 52 3 values without obvious eu enrichment or depletion the yand yb concentrations 13 and 1 33 ppm respectively are higher than those of the enclave bearing meta plagiogranites and slightly lower than those of the mafic enclave zircon of the enclave bearing meta plagiogranites gives a weighted mean 206 pb 238 u crystallization age of 970 21 ma these meta plagiogranites have low 87

understanding mesozoic accretion in southeast asia significance of triassic thermotectonism indosinian orogeny in vietnam results from a zircon u pb study of the metamorphic basement of vietnam reveal that a large part of the continental crust was affected by a short lived episode of ductile deformation and high temperature metamorphism between 258 6 ma and 243 5 ma although coincident with final stages of north south china collision qinling orogenesis the thermotectonism in vietnam was caused by accretion of sibumasu to indochina south china this accretion event indosinian orogeny has regional significance because it contributed to the final stages of north south china collision an aspect not explicitly recognized in qinling orogenic models

significant role of structural fractures in renqiu buried hill oil field in eastern china renqiu oil field is in a buried hill of sinian late precambrian rocks located in the jizhong depression of the western bohai bay basin in eastern china the main reservoir consists of sinian dolomite the buried hill is a fault block bounded on the west side by a large growth fault that trends north northeast and has throws of up to 1 km 3 300 ft the source rocks for the oil are tertiary sediments that overlie the sinian dolomite structural fractures are the main factor forming the reservoir of the buried hill oil field three dominant structural trends northeast north northeast and northwest form the regional fracture system the fractures are best developed along the north northeast fault zones and at the intersections of other structural trends because the regional stress field altered during the late mesozoic the mechanical properties of north northeast fault zones were changed from compressional shear to extensional shear consequently the enlargement of the structural fractures provided good channels for the circulation of meteoric water the north northeast growth fault controlled the structural development of the fault block the block was raised and eroded before the tertiary sediments were dep sited so the sinian dolomite was exposed and underwent a long period of weathering and leaching during the eocene the jizhong depression subsided but deposition faulting and relative uplift of the block occurred simultaneously as the block was gradually submerged at the same time several horizontal and vertical karst zones were formed along the fracture system by the circulating water the eocene source rocks lapped onto the block therefore the buried hill with many developed karst fractures was surrounded by a great thickness of source rocks as the growth fault developed the height of the fault block increased from 400 m 1 300 ft before the oligocene to 1 300 m 4 300 ft after as petroleum was generated it migrated immediately along the growth fault into the karst fracture system of the buried hill the karst fracture block reservoir has 800 m 2 625 ft of oil bearing closure and has good interconnected porosity between the leached fracture zones renqiu buried hill oil field offers a high yield

fluid inclusion evidence of petroleum migration through a buried metamorphic dome in the pannonian basin hungary some of the petroleum currently produced in the pannonian basin in hungary stems from buried metamorphic basement domes that form structural highs between neogene sedimentary sub basins in the bekes sedimentary sub basin the source rocks of the petroleum are known to be of middle to late miocene age whereas at least part of the petroleum in the adjacent szeghalom basement dome appears to be of lower miocene age or even older virtually nothing is known about the compositions distribution sources and migration history of this older petroleum although such variables are crucial to future exploration strategies this study addresses the first two of these gaps in knowledge by providing a basic characterization of the older petroleum trapped as fluid inclusions in fracture hosted quartz crystals within the szeghalom dome szd fluid inclusion samples from 9 wells at depths of 1900 to 2200 m were analysed by visible and cie calibrated uv microscopy microthermometry laser raman and 1 h nmr spectroscopy two major types of early miocene oils were found distributed over 5 distinct temporal generations an earlier immature brown oil succeeded by a light gas condensate the early petroleum was undersaturated with respect to methane gas and it migrated through the fracture network at temperatures between about 160 to 130 c entraining blebs of bitumen and flushed by weakly saline water the later gas condensate migration consisted of a heterogeneous mixture of volatile oil methane rich gas weakly saline water at slightly lower temperatures between 135 and 120 c the temperature evolution was caused by cooling of the metamorphic wall rocks during basement uplift culminating in middle miocene exhumation the various hydrocarbons are unevenly distributed across the szeghalom dome showing that pre middle miocene fluid migration through the fracture network was compartmentalized at the km scale 2007 elsevier b v all rights reserved

from water to tillage erosion dominated landform evolution while water and wind erosion are still considered to be the dominant soil erosion processes on agricultural land there is growing recognition that tillage erosion plays an important role in the redistribution of soil on agricultural land in this study we examined soil redistribution rates and patterns for an agricultural field in the belgian loess belt 137cs derived soil erosion rates have been confronted with historical patterns of soil erosion based on soil profile truncation this allowed an assessment of historical and contemporary landform evolution on agricultural land and its interpretation in relation to the dominant geomorphic process the results clearly show that an important shift in the relative contribution of tillage and water erosion to total soil redistribution on agricultural land has occurred during recent decades historical soil redistribution is dominated by high losses on steep midslope positions and concavities as a result of water erosion leading to landscape incision and steepening of the topography in contrast contemporary soil redistribution is dominated by high losses on convex upperslopes and infilling of slope and valley concavities as a result of tillage resulting in topographic flattening this shift must be attributed to the increased mechanization of agriculture during recent decades this study shows that the typical topographical dependency of soil redistribution processes and their spatial interactions must be accounted for when assessing landform and soil profile evolution

mesozoic overthrust tectonics in south china whether south china was a platform or a para platform after the mid paleozoic deformation or whether the mountains of huanan south china form a mesozoic collision type orogen depends upon whether the ophiolite melange in the yangtze region is precambrian basement or was overthrust onto a foreland thrust belt during the mesozoic this paper presents evidence of tectonic windows under the melange and basement klippes above the melange in the yangtze region

subsurface biodegradation of crude oil in a fractured basement reservoir shropshire uk subsurface biodegradation of crude oil in current oil reservoirs is well established but there are few examples of ancient subsurface degradation biomarker compositions of viscous and solid oil residues bitumen in fractured precambrian and other basement rocks below the carboniferous cover in shropshire uk show that they are variably biodegraded high levels of 25 norhopanes imply that degradation occurred in the subsurface lower levels of 25 norhopanes occur in active seepages liquid oil trapped in fluid inclusions in mineral veins in the fractured basement confirms that the oil was emplaced fresh before subsurface degradation a triassic age for the veins implies a 200 myr history of hydrocarbon migration in the basement rocks the data record microbial biodegradation of hydrocarbons in a fractured basement reservoir and add to evidence in modern basement aquifers for microbial activity in deep fracture systems buried basement highs may be especially favourable to colonization through channelling fluid flow to shallow depths and relatively low temperatures and are therefore an important habitat within the deep biosphere

shrimp zircon u pb geochronological and whole rock geochemical evidence for an early neoproterozoic sibaoan magmatic arc along the southeastern margin of the yangtze block abstract it has been generally accepted that the south china block was formed through amalgamation of the yangtze and cathaysia blocks during the proterozoic sibaoan orogenesis but the timing and kinematics of the sibao orogeny are still not well constrained we report here shrimp u pb zircon geochronological and geochemical data for the taohong and xiqiu tonalite granodiorite stocks from northeastern zhejiang southeastern margin of the yangtze block our data demonstrate that these rocks dated at 913 15 ma and 905 14 ma are typical amphibole rich calc alkaline granitoids formed in an active continental margin combined with previously reported isotopic dates for the 1 0 ga ophiolites and 0 97 ga adakitic rocks from northeastern jiangxi the timing of the sibao orogenesis is thus believed to be between 1 0 and 0 9 ga in its eastern segment it is noted that the sibao orogeny in south china is in general contemporaneous with some other early neoproterozoic 1 0 0 9 ga orogenic belts such as the eastern ghats belt of india and the rayner province in east antarctica indicating that the assembly of rodinia was not finally completed until 0 9 ga

thermobarometric modelling of zircon and monazite growth in melt bearing systems examples using model metapelitic and metapsammitic granulites u pb age data collected from zircon and monazite are used to draw fundamental inferences about tectonic processes in the earth despite the emphasis placed on zircon and monazite ages the understanding of how to relate the timing of growth of zircon and monazite to an evolving rock system remains in its infancy in addition few studies have presented large datasets of geochronological data from zircon and monazite occurring in the same metamorphic rock sample such information is crucial for understanding the growth of zircon relative to monazite in a systematic and predictive manner as per this study the data that exist support the generally held conception that zircon ages tend to be older than monazite ages within the same rock here experimental data for zircon and monazite saturation in melt bearing rocks are integrated with phase diagram calculations the calculations constrain the dissolution and growth behaviour of zircon and monazite with respect to evolving pressure temperature and silicate mineral assemblages in high grade melt bearing metasedimentary rocks several key results emerge from this modelling first that in aluminous metapelitic rocks i e garnet cordierite sillimanite assemblages zircon ages are older than monazite ages in the same rock second that the growth rate of accessory minerals is nonlinear and much higher at and near saturation than at lower temperatures and third that the difference in zircon and monazite ages from the same rock may be ascribed to differences in the temperature s at which zircon and monazite grow rather than differences in closure temperature systematics using our methodology the cooling rate of granulites from the reynolds range central australia have been constrained at 4 c myr 1 this study serves as a first pass template on which further research in applying the technique to a field study can be based

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

structural development of the lower paleozoic belt of south china genesis of an intracontinental orogen abstract an extensive structural study of wuyishan and surrounding areas south china brings data on the structures formed prior to the devonian unconformity building the lower paleozoic belt an ordovician tectonic event was responsible for i south directed structures in the wuyishan proper and its southern border related to both thin and thick skinned tectonics accompanied by metamorphism and crustal thickening ii north directed structures to the west of ganjiang fault and north of jiangshan shaoxing fault where only thin skinned tectonics is visible the southward deformation accommodating the shortening includes emplacement of thrust sheets involving deep crustal material and some mantle peridotite and likely repetition of continental material both responsible for crustal thickening the orogeny was due to the underthrusting of the southern part of the south china block beneath the northern part of this block closing the pre existing nanhua rift created at around 850 800 ma and involving the rift sedimentary fill in the southward thrusting the syn metamorphic tectonic piling was followed by anatexis and granite emplacement at around 440 390 ma our new u th pb epma monazite dating gives ages of 433 9 ma and 437 5 ma early silurian for the main anatectic event and a younger age of 412 5 ma late silurian early devonian for a late re heating process the lower paleozoic belt is an intracontinental orogen without oceanic suture record it shows some similarities with the cenozoic european pyrenees chain with a strong asymmetry

redistribution of rare earth elements thorium and uranium over accessory minerals in the course of amphibolite to granulite facies metamorphism the role of apatite and monazite in orthogneisses from southwestern norway the amphibolite to granulite facies transition has been studied in a high k calc alkaline hornblende biotite k feldspar megacrystic augen gneiss series from the rogaland vest agder rog va sector of the sveconorwegian province southwest norway hornblende begins to break down mainly to clinopyroxene at the cpx in isograd and biotite mainly to orthopyroxene at the opx in isograd abbreviations for minerals following kretz 1983 the magmatic accessory mineral association comprises titanite and allanite which begin to break down before the cpx in isograd titanite is preserved as relict inclusions in other minerals at higher grade monazite and thorite formed in the breakdown of allanite monazite abundance reaches a maximum between the cpx in and opx in isograds the middle and heavy rare earth element m hrees except eu content of apatite steeply increases with increasing metamorphic grade and is directly correlated to the decrease of the modal abundances of titanite hornblende and biotite the u contents of apatite are low and do not increase with metamorphic grade the light rare earth elements lrees and th content of apatite are not correlated to the breakdown of allanite around the cpx in isograd but increase around the opx in isograd a simplified equation is proposed for monazite crystallisation in the vicinity of the cpx in isograd that accounts for the allanite titanite and hornblende breakdowns and the m hree substitution in apatite 3 m hree 2o3in hornblende and litanite 3 lree 2in allaniteo3 2ca5 po4 3apatite f oh 6sio2quartz 6 lree pmonaziteo4 2ca2 m hree 3 sio4 3 f oh lessingite in apatite 6caoin plagioclase at the opx in isograd the increase of lrees and th content of apatite results either from the breakdown of some monazite 3 lree po4monazite 3sio2quartz 4caoin plagioclase f2 h2o fluid ca5 po4 3 f oh apatiteca2 lree 3 sio4 3 f oh less ingite in apatite or the breakdown of the remaining allanite 3 lree 2o3in allanite 6sio2quartz 4caoin plagioclase f2 h2o fluid 2ca2 lree 3 sio4 3 f oh lessingite in apatite the release of fluorine from the breakdown of biotite at the opx in isograd may increase apatite stability relatively to monazite in the granulite facies when compared to amphibolite facies the granulite facies augen gneisses do not show any u or th depletion this means that changes in the accessory mineral associations and the simultaneous breakdown of hydrous minerals at the amphibolite granulite facies transition do not inevitably result in depleted granulite facies rocks but rather to an isochemical element redistribution the coexistence of small amounts of metamorphic monazite and of relict inclusions of titanite in upper amphibolite facies augen gneisses suggests that high k calc alkaline orthogneisses are a suitable material to date with the u pb method prograde path of amphibolite facies regional metamorphism on monazite and the cooling path on titanite

landform change due to soil redistribution by intense tillage based on high resolution dems tillage erosion is considered to be one of the most widespread forms of soil erosion on sloping agricultural land yet little attention has been paid to the impact of tillage erosion on landform change this study assessed the rates of tillage erosion caused by manual hoeing and evaluated the impacts of medium term tillage erosion on landform change on slopes with linear and complex forms in the three gorges reservoir region china to quantify the tillage erosion rate without the influence of water erosion a series of tillage experiments were set up and an on site survey was conducted during the dry season of 2008 the tillage erosion rates on the linear and complex slopes were assessed using high resolution digital elevation models dems a step profile method and a tillage erosion model the erosion rates from the step profile method were 16 8 and 36 6 mg ha 1 tillage pass 1 on the linear and complex slopes respectively and those deduced from the tillage erosion model were 17 6 and 41 7 mg ha 1 tillage pass 1 after intense tillage the most notable changes in soil depth occurred at the summit and toe positions with a decrease of 100 at the 0 m position summit and an increase of 13 1 and 30 9 after 5 and 15 operation tillage respectively at the toeslope position on the linear slope on the complex slope a 100 reduction in soil depth was observed at the summit the largest increase in soil depth appeared at the toeslope position after 5 and 15 operation tillage by 23 1 and 48 2 respectively and a significant decrease in soil depth at the shoulder slope also occurred for the linear slope the slope gradient gradually decreased due to intense tillage and the landform could be referred to as slow forming terraces where no severe water erosion occurred at the lower slope positions additionally insignificant changes in the slope gradient occurred at the flat summit slope positions whereas significant soil accumulation at the toeslope positions caused an obvious reduction of the slope gradients on the complex slope this indicates that intensive tillage results in a gradual smoothening of the slopes furthermore tillage erosion altered the soil profiles leading to the truncation the mixing of soil profiles and the formation of new soil profiles at different slope positions overall these results clearly indicate that tillage erosion is one of the important soil redistribution processes and hoeing tillage plays a dominant role in landform change c 2012 elsevier b v all rights reserved

electron microprobe dating of monazite because monazite is extremely rich in u and th radiogenic pb pb accumulates very quickly and reaches in about 100 ma a level where it is possible to analyse it with the electron probe assuming that common pb is negligible and that partial loss of pb has not occurred the simultaneous measurement of u th and pb allows to obtain a geologically meaningful age from a single electron probe analysis here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method a specific statistical method to deal with the large number of data which can be obtained on a single sample is described and several guidelines illustrated by examples are suggested to optimize the method electron probe measurements carried out on samples of known age from 200 ma to 3 1 ga yield ages that always fall inside the confidence interval of the isotopically determined age demonstrating that this method is reliable the younger age limit is approximately 100 ma although it can be younger in some favourable cases in old monazites extremely high pb contents have been found up to 5 wt indicating that monazite can tolerate high radiation doses without experiencing lead loss the final precision on the age for a normal monazite is 30 50 ma for a total counting time of 600 s a complete dating procedure can be completed in less than 1 h first results indicate that old ages can be preserved in monazite either in small relict cores in crystals or by the coexistence of several generations of monazites in a sample this method has all the advantages of the electron probe it is non destructive has an excellent spatial resolution monazites as small as 5 i m can be dated and because it is possible to work on normal polished thin sections the petrographical position of the dated crystal is known this method offers a large number of geologists access to an in situ dating technique at moderate cost

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

carbon redistribution by erosion processes in an intensively disturbed catchment abstract understanding how organic carbon oc moves with sediments along the fluvial system is crucial to determining catchment scale carbon budgets and helps the proper management of fragile ecosystems especially challenging is the analysis of oc dynamics during fluvial transport in heterogeneous fragile and disturbed environments with ephemeral and intense hydrological pulses typical of mediterranean conditions this paper explores the catchment scale oc redistribution by lateral flows in extreme mediterranean environmental conditions from a geomorphological perspective the study area is a catchment carcavo in se spain with a semiarid climate erodible lithologies and shallow soils which is highly disturbed by agricultural terraces land levelling reforestation and construction of check dams to increase our understanding of catchment scale oc redistribution induced by erosion we studied in detail the subcatchments of eight check dams distributed along the catchments main channel we determined 137 cs physicochemical characteristics and the oc pools of the catchment soils and sediments deposited behind each check dam performed spatial analysis of catchment properties and buffer areas around the check dams and carried out geomorphological analysis of the slope channel connections the soils showed very low total organic carbon toc values oscillating between 15 2 and 4 4 g kg 1 for forest and agricultural soils respectively sediments mobilized by erosion were poor in toc 6 6 0 7 g kg 1 compared to the eroded forest soils and the redistribution of oc through the catchment especially of the mineral associated organic carbon mac pool showed the same pattern as clay particles and 137 cs the toc erosion rates estimated for the carcavo watershed are relatively low 0 031 0 03 mg ha 1 y 1 but similar to those reported for subhumid mediterranean catchments that are less fragile and more conducive to plant growth the toc erosion total erosion ratio was lower 0 06 than other estimates although the average oc concentration of the sediments was higher than that of the agricultural soils of the catchment underlining the problem of maintaining sustainable soil oc contents the oc in deposited sediments came not only from surface erosion processes but also from deeper soil or sediment layers mobilized by concentrated erosion processes sediment richer in oc came from the surface soil of vegetated reforested areas close and well connected to the channels subcatchments dominated by laminar erosion processes showed a toc erosion total erosion ratio that was two times higher than that of subcatchments dominated by concentrated flow erosion processes the lithology soils and geomorphology exert a more important control on oc redistribution than land use and vegetation cover in this geomorphologically very active catchment

deep seated abiogenic origin of petroleum from geological assessment to physical theory the theory of the abyssal abiogenic origin of petroleum is a significant part of the modern scientific theories dealing with the formation of hydrocarbons these theories include the identification of natural hydrocarbon systems the physical processes leading to their terrestrial concentration and the dynamic processes controlling the migration of that material into geological reservoirs of petroleum the theory of the abyssal abiogenic origin of petroleum recognizes that natural gas and petroleum are primordial materials of deep origin which have migrated into the earth s crust experimental results and geological investigations presented in this article convincingly confirm the main postulates of the theory and allow us to reexamine the structure size and locality distributions of the world s hydrocarbon reserves

fractured basement play development on the uk and norwegian rifted margins fractured crystalline basement reservoirs basement on the uk continental shelf ukcs and the norwegian continental shelf ncs have been underexplored over the last 12 years hurricane energy has deliberately set out to explore basement potential by exploring and appraising the rona ridge west of shetland and the rona ridge lancaster field is now being progressed towards being the first uk basement field development the norwegian basement play is also recognized as a potentially material resource through serendipitous oil discoveries with the 16 1 15 well drilled in 2011 being the first successful full scale basement test on the ncs building on this success the 2018 rolvsnes appraisal well 16 1 28 s has demonstrated the significant basement potential of the extensive utsira high and confirmed the materiality of a norwegian basement play the rona ridge and utsira basement discoveries are used as a comparison with two other yet to be evaluated prospective basement plays on the ncs with the objective of establishing technical subject areas where future ukcs and ncs collaboration would aid in accelerating understanding of the ukcs ncs basement play

an improved u th pb age calculation for electron microprobe dating of monazite abstract determination of u th pb ages using the electron probe microanalyser epma is an inexpensive alternative method for dating monazite the method is rapid and reliable both for simple monogenenetic monazite and for complex polygenetic monazite having undergone metamorphic events involving fluid interaction and recrystallization the main limitation of the method is its rather poor precision i e 45 to 120 ma for ages ranging from 300 to 3000 ma calculated on each spot the precision is limited by pb content and by counting statistics which cannot give precision better than 2 for individual determinations on u th and pb even at high levels a procedure that uses the new th pb vs u pb diagram to improve the calculated precision on u th pb ages gives results to within 5 to 15 ma for ages ranging from 300 to 3000 ma with complex polygenetic monazite in which either the points show large scattering indicated by a large mswd or the regression line exhibits a slope very different from neighbour theoretical isochrons the procedure must be applied separately on homogeneous domains only this makes it possible to distinguish between events separated by a gap of 20 to 60 ma according to the range of ages concerned i e 300 to 3000 ma several examples are given to illustrate these systematics

formation of uranium thorium rich bitumen nodules in the lockne impact structure sweden a mechanism for carbon concentration at impact sites the ordovician lockne impact structure is located in central sweden the target lithology consisted of limestone and black unconsolidated shale overlaying a precambrian crystalline basement the precambrian basement is uranium rich and the black shale is both uranium and organic rich this circumstance makes lockne a good candidate for testing the occurrence of u th rich bitumen nodules in an impact structure setting u th rich bitumen nodules are formed through irradiation hence the increase in the complexity of organic matter by a radioactive uranium and thorium rich mineral phase u th rich bitumen nodules were detected in crystalline impact breccia and resurge deposits from the impact structure but samples of non impact affected rocks from outside the impact structure do not contain any u th rich bitumen nodules this implies that in the lockne impact structure the nodules are associated with impact related processes u th rich bitumen nodules occur throughout the geological record and are not restricted to an impact structure setting but our studies at lockne show that this process of irradiation can readily occur in impact structures where fracturing of rocks and a post impact hydrothermal system enhances fluid circulation the irradiation of organic matter by radioactive minerals has previously been proposed as a process for concentration of carbon on the early earth impact structures are suggested as sites for prebiotic chemistry and primitive evolution and irradiation by radioactive minerals could be an important mechanism for carbon concentration at impact sites

hydrocarbon downward accumulation from an upper oil source to the oil reservoir below in an extensional basin a case study of chezhen depression in the bohai bay basin abstract there is a disputable theory that hydrocarbon can be injected into the reservoir and migrate downward in an oil reservoir with an upper oil source which is still questioned now however although some examples are previously found questions still remain about the theory regarding oil sources oil migration pathways and migration forces that related to downward hydrocarbon migration for this reason the chezhen graben in the bohai bay basin is selected to study all the problems above geo chemical evidence show that lower es3 source rock t6 in seismic profiles has a close genetic relationship with the underlying es4 t7 in seismic profiles and ordovician oil therefore the upper source lower reservoir type can be formed inside the lower gentle slopes and sag zones and inside the cambrian and permian reservoirs the fluid inclusion experiment shows that the lower es3 source rock underwent 3 over pressure evolution stages meanwhile there is a huge pressure difference between the lower es3 source rock and underlying es4 reservoirs which is the migration force of downward migration in the lower areas of gentle slopes and sags the early generated and early ended faults are terminated at the source rock of es3 member and can be re opened under the over pressure influence of the source rock and regional tensile stress then they become the pathways of the so called downward migration the distance of downward migration can be calculated through the accumulation dynamic which is obtained by hydrocarbon pressure subtracting the reservoir hydrostatic pressure pressure attenuation and displacement pressure the research result on downward migration process is of great significance to broaden the hydrocarbon exploration fields

the nature and age of basement host rocks and fissure fills in the lancaster field fractured reservoir west of shetland hosting up to 3 3 billion barrels of oil in place the upfaulted precambrian crystalline rocks of the lancaster field offshore west of shetland give key insights into how fractured hydrocarbon reservoirs can form in such old rocks the neoarchean c 2700 2740 ma charnockitic basement is cut by deeply penetrating oil mineral and sediment filled fissure systems seen in geophysical and production logs and thin sections of core mineral textures and fluid inclusion geothermometry suggest that a low temperature supplementary material analytical methods and isotopic compositions and ages are available at https doi org 10 6084 m9 figshare c 4763237 thematic collection this article is part of the geology of fractured reservoirs collection available at https www lyellcollection org cc the geology of fractured reservoirs

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

u pb dating of high temperature metamorphic episodes in the kon tum massif vietnam abstract in vietnam recent studies demonstrated that the kon tum massif was part of the indosinian mountain system together with the truong son belt one sector of the kon tum massif song ba valley is a granulite facies terrain for which ar ar and u pb ages cluster around 245 250 ma in the area of song bien river also metamorphosed under granulite facies conditions ar ar ages of 410 ma are displayed by biotite in this study u pb dating of monazite and zircon has been used to understand the reason for these two groups of ages taking into account the metamorphic mineral assemblages related to granulite facies metamorphism in the two districts for granulites of song ba valley ages of 245 250 ma are confirmed from monazites in the song bien district ages of 465 470 ma displayed by monazites are interpreted to correspond to the metamorphic climax zircons from one of these samples record the age of anatexis that has affected the granulitic rocks the younger age recorded in the song ba valley is considered to reflect high temperature related to charnockitic intrusions emplaced near the end of the indosinian orogeny overprinting the earlier formed granulites and resetting the u pb and ar ar ages for the first time two ht events are dated in the kon tum massif one occurring during the ordovician and the other during the permo triassic

catastrophic debris flows on 13 august 2010 in the qingping area southwestern china the combined effects of a strong earthquake and subsequent rainstorms in the wenchuan area in sw china an abundance of loose co seismic landslide debris was present on the slopes after the wenchuan earthquake which in later years served as source material for rainfall induced debris flows or shallow landslides slopes composed of cambrian sandstones and siltstones intercalated with slates appeared to be most susceptible to co seismic landsliding a total of 20 debris flows are described in this paper all were triggered by heavy rainfall on 13th of august 2010 field reconnaissance and measurements supported by aerial photo interpretation were conducted to identify the locations and morphological characteristics of the debris flow gullies in order to obtain information about surface area and volume of landslides and the debris flows the debris flows in the study area were initiated by two processes a run off erosion on co seismic landslide material and concentrated erosion of landslide debris in steep channels b new landslides that transform into debris flows the volume of debris flow deposits on individual fans varies by many orders of magnitude the smallest deposit has a volume of from 5760 to 3 1 million m3 a comparison of the measured volumes deposited on the fan with the volumes of debris stored in the catchment shows the huge potential for future debris flow activity whilst there is a weakly significant positive correlation between these two volumes no significant statistical correlation could be established between volumes of debris flow deposits and other morphometric parameters of the catchment a catastrophic debris flow catchment the wenjia catchment was selected as an extreme case to show in detail the mechanism of debris flow formation as a result of intensive erosion in loose material which was deposited by a rock avalanche during the 2008 earthquake event analyses of the meteorological conditions that triggered these debris flows show one day antecedent precipitation varying between 67 7 and 137 6 mm with a mean rainfall intensity of about 7 3 to 22 5 mm h a rainfall event with peak intensity of 38 7 mm h triggered the largest debris flow event rainfall data related to five debris flow events in the wenjia torrent was used to establish a primary rainfall intensity duration relationship for the triggering of debris flows which was compared to other rainfall duration thresholds from other parts of the world in the discussion emphasis is laid on the need to unravel the process mechanisms which initiated the debris flows for a better understanding and assessment of meteorological thresholds

formation and tectonic evolution of southeastern china and taiwan isotopic and geochemical constraints abstract the southern part of china consists of the proterozoic yangtze craton and the phanerozoic south china foldbelts including the himalayan foldbelt of taiwan models for continental growth have been many and controversial isotopic and geochemical data from mesozoic and younger granitoids and sediments are used here to place constraints on the tectonic evolution of southeastern china and to evaluate whether the young phanerozoic foldbelts are representative of old rejuvenated landmass whether they characterize crustal accretion through successive subduction processes hence suggesting a net growth of continental mass or whether they represent some intermediate situation available sm nd isotopic data for phanerozoic granitoids and metasediments from the south china foldbelts and taiwan invariably show proterozoic model ages t dm ranging from 1 to 2 5 ga with a mean of 1 54 0 30 1 ga all rocks have negative nd t values 2 to 15 suggesting variable but important contributions of old continental materials to the sources of the phanerozoic rocks obviously they do not represent wholesale growth of continental mass the granitoids of the south china foldbelts have multiple origins as viewed from their chemical and isotopic characteristics secular geochemical variation has been established for inland granitoids of proterozoic to mesozoic age their high i sr values 0 710 0 737 suggest that most granitoids are essentially anatectic products of ancient continental crust this is compatible with remelting via microcontinental collision or terrane accretion repeated intracrustal reprocessing by partial fusion and differentiation has undoutedly contributed to important mineralization mesozoic granitoids excluding a type alkaline granites in the coastal region and taiwan show relatively low i sr 0 705 0 710 and high nd values implying that greater amounts of mantle components have been added to ancient continental material in the generation of these rocks this means that mesozoic magmatism in the coastal region resulted from subduction of a paleo pacific plate kula beneath the asian continent the overall geochemical evidence seems to be consistent with a model of serial collisions between microcontinental blocks for the bulk of the south china foldbelts the latest arc continent collision began about 4 ma ago in eastern taiwan

migration of biogenic hydrocarbons into granites a review of hydrocarbons in british plutons abstract the occurrence of hydrocarbons bitumens senso lato in granite plutons and other basement rocks is not per se evidence of an abiogenic origin for the hydrocarbons on the contrary plutons are thermal foci and often highly fractured and therefore are hosts to the migration of fluids from outside the plutons including water and biogenic hydrocarbons hydrocarbons are associated with several british granites in all cases they can be attributed to biogenic sedimentary source rocks the occurrences are particularly related to hydrothermal mineralized veins in granites including the cornish hercynian granites the mountsorrel granodiorite and the weardale granite

early mesozoic thrust tectonics of the northwest zhejiang region southeast china the nw zhejiang region of south china occupies a key tectonic position near the suture zone of the yangtze and cathaysian blocks and is of critical importance for the assembly of east asia sedimentological and tectonic analyses indicate that the region had a se dipping paleoslope in the late paleozoic to early triassic a transitional sedimentary environment from deep sea to continental molasse is documented in the early triassic late triassic interval associated structures are nw vergent folds and thrusts that root southeastward beneath the high grade chencai metamorphic complex the structural styles of this foreland fold and thrust belt are characterized by multifold duplexes and individual folds that are together zoned from se to nw as follows 1 core zone characterized by shear folds and ductile thrusts 2 se belt with out of sequence thrusting of multifold duplexes and an average shortening of 50 3 central belt with duplexes imbricate fans and an average shortening of 40 and 4 nw belt with jura type folds and a shortening of 10 a tectonic model for the foreland fold and thrust belt is discussed in relation to the early mesozoic archipelago paleogeography of south china

electron microprobe observations of pb diffusion in metamorphosed detrital monazites electron microprobe analyses have been made on monazite grains from paragneiss samples in the andalusite sillimanite transition 620 15 c and sillimanite orthoclase 680 15 c zones of the cretaceous ryoke metamorphic belt southwest japan monazites from pelitic gneisses are of metamorphic origin euhedral to subhedral and chronologically homogeneous giving chemical th u total pb isochron chime ages of 98 8 3 3 98 0 3 2 ma two psammitic gneisses of individual metamorphic grade contain both metamorphic monazite grains and detrital ones as old as ca 1700 ma most detrital monazite grains are heterogeneous in the tho2 and uo2 concentrations and have multiple or single rims as young as ca 100 ma several detrital monazite grains are well rounded in form exhibit homogeneous th and u distributions and show a pb diffusion profile in the margin the width of the diffusion zones is approximately constant throughout grains from each psammitic gneiss 18 22 m for 620 c and 48 58 m for 680 c assuming the isothermal diffusion of pb from homogeneous monazite spheres during a 5 ma duration of peak metamorphism we obtain diffusion coefficients of 1 9 0 3 10 21 and 1 5 0 3 10 20 cm2 s at 620 c and 680 c respectively these data derive an activation energy of 2 44 2 85 1 26 105 j mol and a frequency factor of 3 4 10 7 8 5 10 12 2 2 107 cm2 s taking account of uncertainties of 15 c in the temperatures and of 20 in the diffusion coefficients the diffusion parameters obtained from natural samples in this study provide a reliable insight into the closure temperature for pb in monazite that has been poorly understood so far

crustal structure of china from deep seismic sounding profiles abstract more than 36 000 km of deep seismic sounding dss profiles have been collected in china since 1958 however the results of these profiles are not well known in the west due to the language barrier in this paper we summarize the crustal structure of china with a new contour map of crustal thickness nine representative crustal columns and maps showing profile locations average crustal velocity and pn velocity the most remarkable aspect of the crustal structure of china is the well known 70 km thickness of the crust of the tibetan plateau the thick 45 70 km crust of western china is separated from the thinner 30 45 km crust of eastern china by the north south trending seismic belt 105 e the average crustal velocity of china ranges from 6 15 to 6 45 km s indicating a felsic to intermediate bulk crustal composition upper mantle pn velocities are 8 0 0 2 km s equal to the global continental average we interpret these results in terms of the most recent thermo tectonic events that have modified the crust in much of eastern china cenozoic crustal extension has produced a thin crust with a low average crustal velocity similar to western europe and the basin and range province western usa in western china mesozoic and cenozoic arc continent and continent continent collisions have led to crustal growth and thickening inferences on the process of crustal thickening are provided by the deep crustal velocity structure as determined by dss profiles and other seismological studies a high velocity 7 0 7 4 km s lower crustal layer has been reported in western china only beneath the southernmost tibetan plateau we identify this high velocity layer as the cold lower crust of the subducting indian plate as the indian crust is injected northward into the tibetan lower crust it heats and assimilates by partial melting a process that results in a reduction in the seismic velocity of the lower crust in the central and northern tibetan plateau

buried hill play jizhong subbasin bohai bay basin a review and future prospectivity as one of the six subbasins in the lacustrine bohai bay basin the jizhong subbasin is characterized by a dominance of the petroleum reserves located in buried hill traps of paleozoic and proterozoic marine carbonates particularly the latter this paper documents the revitalization of exploration of the buried hill play and discusses other play fairways not previously considered through use of case studies discovery of the largest field renqiu field in 1975 led to the establishment of the buried hill play in this play oil derived from the paleogene lacustrine source rocks charged into and accumulated in the underlying proterozoic marine carbonate reservoirs a number of buried hill fields were discovered within a time span of ca 10 yr in the subbasin with more and more large buried hill structures at depths of less than 5000 m 16 400 ft being drilled the annual reserve addition showed a rapid decline until 2006 the application of new technologies including reprocessing of merged three dimensional seismic data improved logging and testing techniques together with innovative exploration ideas made it possible to revitalize the buried hill play the exploration success lies with the focus change from targeting the conventional shallow to moderately buried hills to the unconventional buried hill pools which include deeply buried hilltop hillslope and intrahill pools case studies of one conventional buried hill field renqiu field and three unconventional buried hill fields chang 3 wengu 3 and niudong 1 fields together with modern geological investigations indicate that there still exists significant exploration potential for the buried hill play in the jizhong subbasin the potential largely lies with the unconventional buried hills the baxian wuqing and baoding depressions are favorable fairways for the deeply buried hill pools represented by the niudong 1 field the wenan slope is the favorable fairway for the intrahill pools represented by the chang 3 and wengu 3 fields

quantifying the spatial distribution of soil mass wasting processes after the 2008 earthquake in wenchuan china a case study of the longmenshan area the beautiful longmenshan area is one of the main tourist attractions in sichuan province china the epicenter of a catastrophic earthquake measured at 8 0 ms china seismological bureau occurred within this area at wenchuan 31 degrees 01 16 n 103 degrees 22 01 e at 14 28 may 12 2008 beijing time the earthquake triggered numerous types of landslide transport and hazards including soil and debris avalanches rockfalls slumps debris flows creation of barrier lakes and slope fattenings this paper examines the landslide hazards in the longmenshan area caused by the earthquake using remotely sensed images mainly beijing 1 microsatellite data before and after the earthquake compared to digital elevation maps and slope gradient maps land use and vegetation cover maps areas of erosion and loss of vegetation were compared from pre and post earthquake data from which were calculated changes in vegetated areas bare slopes and mass movement during the earthquake these events occurred over altitudes from 1000 to 4000 m and on slope angles between 25 and 55 degrees the results show that the total area of erosion and land movement due to the earthquake increased by 86 3 km 2 19 2 of the study area compared with pre earthquake the areas of very low intensity soil erosion and moderate intensity soil erosion were respectively reduced by 3 6 km 2 24 3 km 2 and 30 9 km 2 on the other hand the areas of severe and very severe intensity soil erosion were substantially increased by 45 8 km 2 and 99 2 km 2 in the post earthquake stage the bare areas vegetation cover 15 have increased by 65 8 km 2 without vegetation the denuded earthquake damaged slopes and other high risk sites have become severe erosion problems thus it is essential to continue long term monitoring of mass wasting in the denuded areas and evaluate potential risk sites for future landslides and debris flows we anticipate that these results will be helpful in decision making and policy planning for recovery and reconstruction in the earthquake affected area c 2009 elsevier inc all rights reserved

phanerozoic high pressure eclogite and intermediate pressure granulite facies metamorphism in the gyeonggi massif south korea implications for the eastward extension of the dabie sulu continental collision zone abstract petrological analysis zircon trace element analysis and shrimp zircon u pb dating of retrogressed eclogite and garnet granulite from bibong hongseong area sw gyeonggi massif south korea provide compelling evidence for triassic 231 4 3 3 ma high pressure hp eclogite facies m1 metamorphisms at a peak pressure temperature p t of ca 16 5 20 0 kb and 775 850 c this was followed by isothermal decompression itd with a sharp decrease in pressure from 20 to 10 kb and a slight temperature rise from eclogite facies m1 to granulite facies m2 followed by uplift and cooling granitic orthogneiss surrounding the baekdong garnet granulite and the ophiolite related ultramafic lenticular body near bibong records evidence for a later silurian 418 8 ma intermediate high pressure ihp granulite facies metamorphism and a prograde p t path with peak p t conditions of ca 13 5 kb and 800 c k ar ages of biotite from garnet granulites amphibolites and granitic orthogneisses in and around the bibong metabasite lenticular body are 208 219 ma recording cooling to about 310 c after the early triassic metamorphic peak neoproterozoic zircon cores in the retrogressed eclogite and granitic orthogneiss provide evidence that the protoliths of these rocks were 800 and 900 ma old respectively similar to the ages of tectonic episodes in the central orogenic belt of china this and the evidence for triassic hp uhp metamorphism in both china and korea is consistent with a regional tectonic link within northeast asia from the time of rodinia amalgamation to triassic continent continent collision between the north and south china blocks and with an eastward extension of the dabie sulu suture zone into the hongseong area of south korea

the chemical composition of ree y th u rich accessory minerals in peraluminous granites of the erzgebirge fichtelgebirge region germany part i the monazite ce brabantite solid solution series peraluminous granites of the erzgebirge fichtelgebirge germany are hosts of various members of the monazite group of minerals that display an unprecedented compositional diversity the eibenstock s type granite constitutes the third reported occurrence worldwide of brabantite and the first occurrence of this mineral in a granite many new occurrences of cheralite ce as well as a monazite group mineral intermediate between monazite ce and huttonite for which the term huttonitic monazite is proposed were discovered even common monazite ce may show extreme ranges of actinide and lanthanide element concentrations the granites that host brabantite and cheralite ce are highly differentiated strongly peraluminous low temperature residual melts of s type affinity which are rich in fluorine and other volatile constituents but depleted in thorium and the light rare earth elements such highly evolved volatile rich compositions resemble rare element pegmatites and appear favorable for the precipitation of cheralite ce and brabantite but not of monazite with large amounts of huttonitic substitution instead these minerals occur preferentially in f poor biotite and f rich li mica granites of a type affinity irrespective of the level of uranium in silicate melts which may exceed that of thorium the substitution of uranium in monazite remains limited the compositional data reported here are consistent with complete miscibility in the monazite ce brabantite solid solution series under magmatic conditions these granites contain monazites that span almost the entire compositional range reported for monazite group minerals worldwide and therefore granites appear to be ideal rocks in which to study the crystal chemistry of this mineral group in general

oil and gas production from basement reservoirs examples from indonesia usa and venezuela abstract basement rocks are important oil and gas reservoirs in various areas of the world such reservoirs include fractured or weathered granites quartzites or metamorphics in south america basement reservoirs occur in venezuela and brazil in north africa basement oil and gas production occurs in morocco libya algeria and egypt significant basement reservoirs occur in the west siberia basin as well as in china in the usa basement derived oil production occurs in a number of areas including california wilmington and edison fields kansas el dorado and orth fields and texas apco field in southeast asia basement reservoirs are the main contributor of oil production in vietnam in indonesia to date oil and gas production from basement rocks has been minimal however the recent large gas discovery in pre tertiary fractured granites in southern sumatra has led to a focusing of exploration in indonesia for basement reservoirs

mesozoic tectonic evolution of the southeast china block new insights from basin analysis abstract in order to better understand the mesozoic tectonic evolution of southeast china block secb in short this paper describes geological features of mesozoic basins that are widely distributed in the secb the analyzed data are derived from a regional geological investigation on various mesozoic basins and a recently compiled 1 1 500 000 geological map of mesozoic cenozoic basins two types of basin are distinguished according to their tectonic settings namely the post orogenic basin type i and the intracontinental extensional basin type ii the latter includes the graben and the half graben or faulted depression basins our studies suggest that the formation of these basins connects with the evolution of geotectonics of the secb the post orogenic basin type i was formed in areas from the piedmont to the intraland during the interval from late triassic to early jurassic and the formation of the intracontinental extensional basin type ii connects with an intracontinental crustal thinning setting in the late mesozoic the graben basin was generated during the middle jurassic and is associated with a bimodal volcanic eruption and the half graben or faulted depression basin filled mainly by the rhyolite tuff and sedimentary rocks during early cretaceous is occupied by the late cretaceous paleogene red colored terrestrial clastic rocks we noticed that the modern outcrops of numerous granites and basins occur in a similar level and the mesozoic granitic bodies contact with the adjacent basins by large normal faults suggesting that the modern landforms between granites and basins were yielded by the late crustal movement the modern basin and range framework was settled down in the cretaceous abundant sedimentary structures are found in the various basins from that the deposited environments and paleo currents are concluded during the late triassic early jurassic time the source areas were situated to the north and northeast sides of the outcrop region in this paper we present the study results on one geological and geographical separating unit and two separating fault zones the wuyi orogenic belt is a late mesozoic paleo geographically separating unit the ganjiang fault zone behaves as the western boundary of early cretaceous volcanic rocks and the zhenghe dapu fault zone separates the se china coastal late mesozoic volcanic sedimentary basins and the wuyi orogenic belt finally we discuss the geodynamic mechanisms forming various basins proposing a three stage model of the mesozoic sedimentary evolution

paleocene eocene record of ophiolite obduction and initial india asia collision south central tibet 1 uppermost cretaceous to eocene marine sedimentary sequences occur both to the south and north of the yarlung zangbo suture in south central tibet they consist of indian margin strata of the northern tethyan himalaya and asian margin strata of the gangdese forearc both assemblages are characterized by major changes in depositional environment and sedimentary provenance at 65 ma and an appearance of detrital chromium rich spinel of ophiolite affinity tio2 generally 0 1 wt during the paleocene ophiolitic melange exposed along the suture could have provided a source for detrital spinel the melange occurs in the hanging wall of a north dipping south directed mylonitic shear zone which includes a tectonic sliver of mafic schist amphibole from the schist yields 40ar 39ar ages of 63 ma which we attribute to cooling during slip along the shear zone and southward obduction of the melange melange obduction was coeval with the development of an angular unconformity within the gangdese forearc basin to the north between late maastrichtian time and 62 ma upper paleocene to middle eocene sandstones in the northern tethyan himalaya yield 200 120 ma u pb detrital zircon ages and 190 170 ma 40ar 39ar detrital mica ages these detrital grains were most likely sourced from regions north of the yarlung zangbo suture suggesting that onset of india asia collision in south central tibet is middle eocene or older in age collectively our results support previous suggestions that oceanic rocks were obducted onto the northern margin of india during latest cretaceous earliest tertiary time coeval changes in gangdese forearc sedimentation raise the possibility that this obduction event marks onset of tectonic interaction between india and asia at 65 ma alternatively in concert with the conventional view of eocene collision initiation the obducted oceanic rocks may be of intraoceanic origin while coeval changes in gangdese forearc sedimentation may be a consequence of an increase in the rate of ocean continent convergence following the demise of the intraoceanic subduction zone

relict proterozoic basement in the nanling mountains se china and its tectonothermal overprinting 1 the basement beneath the caledonian belt in se china has been overprinted by indosinian and yanshanian events and is poorly known in situ u pb and hf isotope analysis of zircons from granites and surrounding rocks in the nanling mountains area of the fold belt reveal that the lanhe felsic gneiss is an outcrop of mesoproterozoic basement probably with a partly late archean protolith this is consistent with nd model ages of granites in this region and exposures of cathaysia basement in the coastal area of se china in the nanling mountains this basement was reactivated to generate granitoid rocks during the caledonian indosinian and yanshanian tectonothermal events the caledonian overprint is documented in extensive exposures of the zhuguang migmatites 425 470 ma and by previous u pb zircon dating of adjacent granites the jiangnan granite may be of similar age but strongly reworked the indosinian overprint resulted in the formation of granites such as the luxi and xiazhuang bodies 233 246 ma in the guidong complex the yanshanian overprint produced the most widely distributed granites circa 160 ma such as the jiufeng and fogang bodies and parts of the guidong complex hf isotope data show that all of the phanerozoic magmatic rocks were derived from the mesoproterozoic basement and minor archean components without obvious contributions from juvenile sources the presence of zircons with archean age 2 5 2 7 ga in both the lanhe gneiss and devonian sediments indicates that the badu and mayuan groups may not be the oldest basement of the cathaysia block some archean basement circa 2 5 2 7 ga may still be exposed but unrecognized in this region and cathaysia may include archean microcontinental fragments

electron microprobe dating as a tool for determining the closure of th u pb systems in migmatitic monazites high spatial resolution dating of monazite by the electron probe microanalyzer epma enables systematic and detailed studies of small minerals like zircon monazite records the complex history undergone by the host rocks recent improvements in the statistical treatment of many in situ data now make it possible to decipher the related thermal events and so obtain reliable and precise ages our work shows that a significant number of individual spot analyses is required to reach such precise information i e more than 30 40 data using the examples of monazites from three migmatites and one granite we show how to select the most efficient method of age calculation according to the u and th geochemistry of the grains or grain domains that we are trying to date three situations may be met 1 monazites exhibiting significant th u ratio variation 2 monazites exhibiting a fairly constant th u ratio but significant u th heterogeneity and 3 monazites of constant u and th concentrations for the first case a precise mean age can be calculated using a method of data reduction in the th pb f u pb diagram whereby a precision of 5 10 ma 2 is commonly achieved for the second case an isochron age can be calculated according to the pb f th method with a common precision of around 20 ma 2 whereas for the third case a simple weighted average age can be calculated using these approaches coupled with a back scattered electron image study we demonstrate that inheritance is probably as common for monazite as for zircon in addition the combination of high spatial resolution and precise age determination show the limited extent of pb diffusion in monazite finally an example from a migmatite from southern french guiana demonstrates the especially robust behavior of the th u pb system in monazite this system remains closed during late migmatization and during the subsequent zircon crystallization and zircon overgrowth of protolith zircons the monazite yielded exactly the same age as the protolith zircons

tectonics of south china key to understanding west pacific geology abstract south china is not a post caledonian platform but a composite of orogenic belts this late proterozoic mesozoic orogen is a collage of three continental fragments the three blocks are yangzi huanan and dongnanya and they are separated by the banxi nanpanjiang formerly xianggangzhe and gunanhai suture zones yangzi was separated from gondwanaland during late precambrian when an open ocean called banxi was present between the two continents tectonic processes at an active margin during sinian and early paleozoic time led to the genesis of an accretionary wedge complex the banxi melange and the huanan flysch nappes on the northern margin of huanan which was then the northern margin of the gondwana continent reorganization of plates during the devonian suspended subduction at the huanan active margin huanan was uplifted and unconformably overlain by transgressive deposits of devonian and or carboniferous age a remnant ocean the nanpanjiang sea still existed between yangzi and huanan and deep water sedimentation continued both at the southern margin of yangzi and at the northwestern margin of huanan the latter again became an active margin during late paleozoic when permian and triassic flysch sediments were deposited in foredeeps ahead of advancing nappes huanan and yangzi collided during the triassic and resulted in the deformation of the passive margin of the latter to form the yangzi deformed belt huanan was separated from a more southerly continent dongnanya in the devonian by seafloor spreading which created a late paleozoic and early mesozoic ocean gunanhai ocean a continuously deposited sequence ranging in age from devonian to triassic was laid down on the southern passive margin of huanan on the other side of the ocean the dongnanya permian strata include glacial marine deposits of gondwanaland affinity dongnanya became separated from gondwanaland during the late permian when it marched northward to be reunited with huanan the huanan passive margin sequence was deformed by folding and overthrusting after the late mesozoic collision of huanan and dongnanya scattered outcrops of the suture melange resulting from this collision occur at a few localities in coastal fujian dongnanya in our model was the mesozoic continent of southeast asia peripheral to mainland asia this may or may not have been the eastern continuation of the microcontinent sibumasu siam thailand burma malaysia sumatra the collision of dongnanya and asia gave rise not only to the gunanhai melange of coastal fujian but also to the ophiolite melanges parts of which are present in taiwan tailuko the philippines and western malaysia

the crust of cathaysia age assembly and reworking of two terranes abstract u pb dating and hf isotope data from detrital zircons have been used to analyse the crustal evolution of the eastern and western parts of the cathaysia block in se china zircons from the oujiang river in eastern cathaysia indicate that the basement is dominantly paleoproterozoic 1850 1870 ma 2100 2400 ma in age with minor archean components it was extensively reworked in jurassic cretaceous time 100 155 ma to produce the widespread yanshanian magmatic suite both the 1850 1870 ma event and the yanshanian magmatism show wide ranges in hf isotope composition consistent with mixing between crustal and juvenile magmas marked downstream changes in the relative proportions of zircon age populations emphasize the care required in using detrital zircon data to estimate continental growth rates zircons from the north river indicate that the crust of western cathaysia was generated mainly during neoproterozoic time although it contains some archean 2500 3500 ma to mesoproterozoic components this crust was strongly reworked during caledonian ca 450 ma indosinian ca 240 ma and early yanshanian ca 160 ma thermal events there is little evidence for juvenile crustal growth in any of these events although the yanshanian granitoids of the eastern and western parts of the cathaysia give similar mean hf model ages consistent with published nd model ages this is a coincidence they have different crustal sources the distinct patterns of crustal evolution suggest that eastern and western cathaysia may represent separate microcontinents accreted to the older yangtze craton and transposed by extensive strike slip faults

palaeomagnetism of early triassic limestones from the huanan block south china no evidence for separation between the huanan and yangtze blocks during the early mesozoic summary there has been extensive debate on the timing of the collision between the huanan and yangtze blocks ever since hsu and co workers hsu et al 1987 1988 proposed a mesozoic collision model for south china tectonics we report new rock and palaeomagnetic data from an early triassic limestone formation from the huanan block that help to constrain its tectonic history the samples are from two localities jiupi jt and huangben lt in lianzhou county northern guangdong province only thermal demagnetization is eective in decomposing a multicomponent remanent magnetization the majority of samples show three components a low temperature component a an intermediate temperature component b and a high temperature characteristic remanent magnetization chrm the a component has a steep inclination and is probably drilling induced the b component clusters around the present geomagnetic field direction and is a brunhes age viscous remanence fold test results suggest that the jt chrm is pre tectonic and that the lt chrm is a syn or prefolding remagnetization samples from the two localities show quite similar acquisition and thermal demagnetization of the isothermal remanent magnetization irm and suggest that magnetite carries the chrm component however partial anhysteretic remanent magnetization parm spectra anisotropy of anhysteretic remanence aar rock fabric and morphology of magnetic extracts are quite dierent for the two localities the aar of jt samples shows low anisotropy average 2 per cent and reflects a composite compaction and strain fabric the aar of lt samples shows a high degree of anisotropy average 10 per cent and is clearly consistent with rock deformation fabrics the magnetic extracts of lt samples are dominated by spherical botryoidal ti poor magnetite which is probably precipitated from tectonic fluids during deformation while the jt magnetic extracts are dominated by rod shaped ti poor magnetite probably derived from the erosion of igneous rocks although minor amounts of botryoidal magnetite and rod like magnetite particles can be seen in jt and lt extracts respectively the rock fabric and magnetic fabric data and sem observations of magnetic extracts corroborate the results of the fold test the best clustered lt chrm direction is d 294 i 12 a 95 12 its pole position is 187 e 19 s dp 6 dm 12 the assumption of a reversed polarity for the jt chrm direction d 198 i 20 a 95 9 implies that the huanan block was in the northern hemisphere during the early triassic and its pole position 239 e 68 n dp 5 dm 10 is close to early triassic pole positions from the yangtze block a normal polarity for the jt site chrm would require tectonic movements inconsistent with the local geology therefore the huanan and yangtze blocks were not separated in the early triassic the rotation of the lt locality may have been caused by the collision of the southeast china coastal terranes and or subduction of the pacific plate in the late mesozoic

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

spatial variation in soil soc and total n redistribution on affected and non affected slope terraces due to the 8 0 wenchuan earthquake in 2008 by using 137cs technique abstract using the 137 cs technique we assessed spatial variation in soil erosion and its impact on lateral movements of soil organic carbon soc and total nitrogen total n in a terraced series and a complex slope in the longmenshan fault zone china the complex slope derived from three terraced fields with damaged banks resulting from the 8 0 wenchuan earthquakes in 2008 the terraced series and complex slope are the dominant sloping farmland patterns in this area which represent for earthquake non affected and affected sloping farmland respectively soil loss occurred over the upper parts of slopes and deposition occurred towards the downslope boundary of each terrace also soil loss occurred on upper terraces and soil accumulation on lower terraces net soil erosion rates for the terraced toposequence were estimated at 3 70 14 38 mg ha 1 yr 1 indicating the terraced toposequence played an important role in soil conservation for the complex slope higher soil erosion rates occurred at the summit and other slope positions with greater slope curvature and soil accumulation occurred at the toe slope and other slope positions with lower slope curvature 15 m 25 m and 40 m in addition to water erosion collapses resulting from earthquake and tillage erosion were also important soil erosion processes for the complex slope moreover net soil erosion rate on the complex slope 4 89 18 03 t ha 1 yr 1 was significantly higher than on the terraced series soc and total n inventories showed similar patterns to the 137 cs inventory such results confirm that 137 cs can help to trace soc and total n dynamics on sloping farmland in this area

assessing soil redistribution in a complex karst catchment using fallout 137cs and gis abstract caesium 137 derived from nuclear testing in the past century has been widely used as a sediment tracer of soil redistribution providing information on medium term 40 50 years erosion rates to date most studies have focused on individual fields of limited extent but estimated rates and patterns of soil redistribution require upscaling to catchment level an attempt to assess soil redistribution processes with strong geomorphic control on complex terrain such as an internally drained karst catchment is presented in this work a comprehensive geomorphological survey of the estanya lake catchment spanish pyrenees enabled the main geomorphic elements to be identified with a grid resolution of 5 5 m which was the basis for the terrain analyses a detailed dem was constructed and improved after field identification of the drainage system and point measures on gentle slopes with total topographic station a 100 100 m sampling grid was established to derive point data of 137 cs inventories across the catchment geostatistical interpolation of point samples of 137 cs inventories in soil was carried out to identify and assess the areas of sediment gain and loss by comparing with 137 cs reference inventories profile activity models were used to calibrate 137 cs data and to derive estimates of soil redistribution gis was used to provide spatially distributed erosion and deposition rates in the landscape for the whole catchment the median values of soil erosion and deposition of 4 7 and 3 1 mg ha 1 year 1 respectively showed a large variability and reveal coupling between erosional and depositional forms in the catchment the highest erosion and deposition rates were found in cultivated fields at the southern sector of the catchment the spatial analysis of the results supports the importance of taking into account geomorphological features in karst catchments as relevant controlling factors in soil redistribution processes

neoproterozoic bimodal magmatism in the cathaysia block of south china and its tectonic significance shrimp u pb zircon age geochemical and sm nd isotopic results are reported for the mamianshan volcanic rocks in the cathaysia block of southeastern south china the mamianshan volcanic rocks are bimodal in composition and are dominantly transitional to mildly alkaline basalts and subordinate alkaline rhyolite with an eruption age of 818 9 ma the basaltic samples are characterized by lree enriched and humped trace element patterns similar to many alkali basalts in continental rifts variablend t values between 3 33 and 4 35 indicate that the primary magma of these basalts was derived from an oib like mantle source and underwent fractional crystallization plus crustal contamination the rhyolitic rocks are highly enriched in th ta nb ree zr hf and y and depleted in sr p eu and ti sharing affinity to a 1 type granites combined with their slightly positive nd t values 0 22 to 0 92 the mamianshan felsic rocks were most likely generated by partial melting of the regional paleoproterozoic mayuan amphibolites the mamianshan bimodal volcanic rocks in the cathaysia block are coeval with the widespread intraplate magmatism around the yangtze block our results support the idea that a coherent south china craton was formed during the ca 1 0 ga sibao orogeny and it subsequently underwent extensive continental rifting related to mantle plume or superplume activities beneath rodinia since ca 825 ma 2004 elsevier b v all rights reserved

soil erosion rates on sloping cultivated land on the loess plateau near ansai shaanxi province china an investigation using 137cs and rill measurements sediment yields from the rolling hills area of the loess plateau in northern china 10 000 25 000 t km 2 yr 1 are amongst the highest in the world the sediment is believed to derive from both the deep gullies that dissect the rolling plateau and the steep cultivated fields on the slopes of the mounds between the gullies however there are few reliable data for erosion rates on the cultivated fields and it is suspected that current estimates 10 000 16 000 t km 2 yr 1 based on empirical relationships derived from erosion plot studies exceed the true values this study sought to address the need for more information concerning erosion of the cultivated fields through derivation of erosion rates from measurements of rill volume and caesium 137 cs 137 inventories for typical fields near the village of ansai shaanxi province the derived erosion rates are discussed and compared with estimates based on empirical relationships derived from erosion plot data where erosion rate estimates based on both rill volume data and cs 137 inventories are available they show good agreement in the pattern of downslope variation both show a sharp decline in erosion rates at a slope length of c 50 m this is tentatively attributed to a change from transport limited to detachment limited conditions where rill incision reaches the undisturbed loess at the base of the plough layer no such decline is visible in the predictions based on empirical relationships derived from erosion plot data further evidence is presented that supports the suggestion that these empirical relationships overestimate erosion rates at slope lengths in excess of c 50 m it is tentatively suggested that the rates of soil erosion from sloping cultivated fields in the rolling hills area are more likely to lie in the range 8000 10 000 t km 2 yr 1 than in the higher range suggested by the empirical relationships c 1998 john wiley sons ltd

geodynamic significance of the kontum massif in central vietnam composite 40ar 39ar and u pb ages from paleozoic to triassic abstract the kontum massif of south central vietnam has long been classified as lower continental crust of precambrian archean age u pb zircon and 40ar 39ar biotite ages from charnockites and amphibolite facies rocks from this basement however yield much younger ages and imply at least two paleozoic thermal events syntectonic charnockites from the kannack complex and the southern kontum massif record permo triassic magmatism u pb documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 249 pm 2 end document 2 ma and docume

basement exploration west of shetlands progress in opening a new play on the ukcs abstract commercial production of hydrocarbon from fractured crystalline basement is well documented with petroleum basins across the globe hosting fractured basement fields the uk is an anomaly within this global phenomenon as despite numerous serendipitous discoveries of basement oil in the north sea and the west of shetlands there is currently no commercial field on the united kingdom continental shelf ukcs that is reliant on oil production from fractured basement recognizing that this situation presented an exploration niche hurricane energy plc hurricane was formed to focus on ukcs basement exploration and concentrated its efforts in acquiring exploration acreage in the west of shetlands in 2009 hurricane drilled the first well designed to explore the basement play on the ukcs leading to the lancaster discovery with a contingent resource range 1c 3c of 62 456 million barrels of oil equivalent mmboe the lancaster discovery is presented to summarize the challenges and processes that have been applied in the exploration and evaluation of the west of shetlands basement play conclusions from this work indicate that basement hydrocarbon resource potential is of such significance that it may represent a strategic resource for the uk with over 1154 mmboe of 2c and mean unrisked prospective resources so far identified

crust upper mantle seismic velocity structure across southeastern china abstract one in line wide angle seismic profile was conducted in 1990 in the course of the southeastern china continental dynamics project aimed at the study of the contact between the cathaysia block and the yangtze block this 380 km long profile extended in nw se direction from tunxi anhui province to wenzhou zhejiang province five in line shots were fired and recorded at seismic stations with spacing of about 3 km along the recording line we have used two dimensional ray tracing to model p and s wave arrivals and provide constraints on the velocity structure of the upper crust middle crust lower crust moho discontinuity and the top part of the lithospheric mantle p wave velocity s wave velocity and v p v s ratio are mapped the crust is 36 km thick on average albeit it gradually thins from the northwest end to the southeast end offshore of the profile the average crustal velocity is 6 26 km s for p waves but 3 6 km s for s waves a relatively narrow low velocity layer of about 4 km of thickness with p and s wave velocities of 6 2 km s and 3 5 km s respectively marks the bottom of the middle crust at a depth of 23 km northwest and 17 km southeast at the crust mantle transition the p and s wave velocity change quickly from 7 4 to 7 8 km s northwest and 8 0 to 8 2 km s southeast and from 3 9 to 4 2 km s northwest and 3 9 to 4 5 km s southeast respectively this result implies a lateral contrast in the upper mantle velocity along the 140 km sampled by the profile approximately the average v p v s ratio ranges from 1 68 1 8 for the upper crust to 1 75 for the middle and 1 75 1 85 for lower crust with the interpretation of the wide angle seismic data jiangshan shaoxin fault is considered as the boundary between the yangtze and the cathaysia block

age and origin of the tanghu granite southeast china results from u pb single zircon and nd isotopes u pb single zircon and sm nd whole rock isotopic data for the tanghu granite of the zhuguangshan batholith suggest that a basement either composed of or derived from middle proterozoic to late archean rocks underlies southeast china the granite contains two kinds of inherited zircon components whole anhedral zircons and small cores within younger magmatic zircons the u pb data for a single analysis of four magmatic zircons yielded a concordant age of 433 2 ma whereas single zircons yielded two linear arrays with lower intercepts of 435 1 and 434 14 ma and upper intercepts of 1415 3 and 2516 6 ma respectively xenocrystic zircons of archean age had not previously been recognized in any rocks from southeast china two whole rock samples from the granite yielded nd values of 7 1 and 8 3 at 434 ma and nd model ages of 1750 ma relative to a depleted mantle we conclude from this isotope data that the tanghu granite crystallized at 434 1 6 ma weighted average and was derived from a source of unknown age but had an average crustal residence age of 1750 ma and was partially composed of a mixture of continental crustal material of at least two ages 1400 and 2500 ma

shrimp u pb zircon geochronology and geochemistry of metavolcanic and metasedimentary rocks in northwestern fujian cathaysia block china tectonic implications and the need to redefine lithostratigraphic units abstract northwestern fujian province is one of the most important pre palaeozoic areas in the cathaysia block of south china metavolcano sedimentary and metasedimentary rocks of different types ages and metamorphic grades granulite to upper greenschist facies are present and previously were divided into several formations and groups tectonic contacts occur between some units whereas deformed unconformities have been reported between others new shrimp u pb zircon ages presented here indicate that the original lithostratigraphy and the old group and formation terminology should be abandoned thus the tianjingping formation was not formed in the archaean or palaeoproterozoic as previously considered but must be younger than its youngest detrital zircons 1790 ma but older than regional metamorphism 460 ma besides magmatic zircon ages of 807 ma obtained from metavolcano sedimentary rocks of the nanshan formation and 751 728 ma for the mamianshan group many inherited and detrital zircons with ages ranging from 1 0 to 0 8 ga were also found in them these ages indicate that the geological evolution of the study area may be related to the assembly and subsequent break up of the rodinia supercontinent the new zircon results poorly constrain the age of the mayuan group as neoproterozoic to early palaeozoic 728 458 ma and not palaeoproterozoic as previously thought many older inherited and detrital zircons with ages of 3 6 2 8 2 7 2 6 2 5 2 0 1 8 and 1 6 ga were found in this study a 3 6 ga detrital grain is the oldest one so far identified in northwestern fujian province as well as throughout the cathaysia block nd isotope tdm values of eight volcano sedimentary and clastic sedimentary rock samples centre on 2 73 1 68 ga being much older than the formation ages of their protoliths and thus showing that the recycling of older crust played an important role in their formation these rocks underwent high grade metamorphism in the early palaeozoic 458 425 ma during an important tectono thermal event in the cathaysia block