al coordination and speciation in calcium aluminosilicate glasses effects of composition determined by 27al mq mas nmr and raman spectroscopy the structure and properties of glasses and melts in the cao al2o3 sio2 cas system play an important role in earth and material sciences aluminum has a crucial role in this ternary system and its environment is still questioned in this paper we present new results using raman spectroscopy and 27al nuclear magnetic resonance on cas glasses obtained by classic and rapid quenching methods we propose an al si tetrahedral distribution in the glass network in different qn species in this system we show that al and si are mainly in q4 species along the join r cao al2o3 1 and in depolymerized q2 and q3 units at high cao content for other joins r 1 57 and 3 five 5 al and six fold 6 al coordinated aluminum can be detected in the peraluminous glasses r 1 except for glasses with low silica and high cao content the presence of 5 al is related to viscous flow mechanisms while in highly depolymerized glasses the absence of 5 al may indicate different mechanisms for melts to flow this systematic study on the cas system modifies the simple picture of aluminosilicate glasses and the existence of 5 al should be included by geochemists geophysicists and glass scientists to model appropriately the physical properties of aluminosilicate glasses and melts

holocene and modern sediments in the seine estuary france a synthesis this synthesis of numerous studies on the holocene and modern sediments in the macrotidal setting of the seine estuary demonstrates their overall evolution in common with a number of estuaries the lower seine was an incised valley during the weichselian glacio eustatic sea level fall and infilling occurred during the subsequent lowstand the holocene sea level rise and the late holocene stillstand in the upper estuary above the basal gravel bed fluvial freshwater deposits filled the valley next fine sand and silts invaded the estuary upstream to rouen the sequence ends in loam resulting from an increase in the supply of sediment to the fluvial system in the upper estuary anthropogenic deepening of the modern channel results in erosion of the holocene sediments the only bedforms are thin and narrow sand sheets and some rare megaripples in the lower estuary above the weichselian basal gravel the holocene wedge records the change from a transgressed fluvial setting i e gravel beds to an open estuarine environment i e tidal delta the modern seine estuary has been progressively infilled by marine sands and silts now silts and clays supplied during high river flows accumulate at the outlet and offshore sands and gravel of the eastern bay of the seine are temporarily covered with veneers of mud these freshly deposited muds i e mud patches are periodically partly reworked by waves and strong tidal currents but silting of the inner shelf is noticeable copyright 2003 john wiley sons ltd

petrogenesis p t t path and tectonic significance of high pressure mafic granulites from the jiaobei terrane north china craton abstract high pressure hp mafic granulites in the jiaobei terrane are composed predominantly of garnet mafic granulites garnet hypersthene granulites and garnet amphibolites and they are found as irregular lenses or deformed dike swarms within tonalitic trondhjemitic granodioritic gneisses and granitic gneisses the hp mafic granulites contain four distinct metamorphic assemblages of which the early prograde assemblage m 1 is represented by the cores of garnets together with mineral inclusions of clinopyxene plagioclase quartz and it formed at 740 770 c and 0 90 1 00 gpa in contrast the peak assemblage m 2 consists of high ca cores in garnet high al cores in clinopyroxene and high na cores in plagioclase in the matrix which formed under p t conditions of 850 880 c and 1 45 1 65 gpa the peak metamorphism was followed by near isothermal decompression m 3 which resulted in the development of orthopyroxene clinopyxene plagioclase quartz amphibole magnetitie symplectites or coronas surrounding some garnet grains with p t conditions of 780 830 c and 0 65 0 85 gpa surrounding some garnet grains are symplectites of amphibole plagioclase quartz magnetitie which formed during a cooling retrograde stage m 4 with p t conditions of 590 650 c and 0 62 0 82 gpa an integrated study involving laser raman analysis of mineral inclusions cathodoluminescence imaging and in situ u pb dating of zircons shows that the protolith ages of the hp mafic granulites are mainly 2550 2500 ma and that the timing of the peak metamorphism of the hp mafic granulites ranges from 1900 to 1860 ma as recorded by the cores of metamorphic zircons on the other hand the medium to low pressure granulite amphibolite facies retrogression occurred mainly at 1860 1820 ma as recorded by the rims of some single zircon grains and the zircon grains that contain inclusions of garnet orthopyroxene plagioclase sphene the combination of petrography mineral compositions metamorphic reaction history thermobarometry and geochronology defines a near isothermal decompressional clockwise p t t path for the jiaobei hp mafic granulites suggesting that the jiaobei terrane underwent initial crustal thickening during 1950 1860 ma followed by relatively rapid exhumation cooling and retrogression in the period 1860 1820 ma this tectonothermal path was probably generated by subduction and collision related tectonic processes

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

petrochemistry and sr pb and nd isotopic geochemistry of the paleoproterozoic kuandian complex the eastern liaoning province china abstract a geochemical and isotopic study has been carried out on the paleoproterozoic kuandian complex and some associated granitoids in the eastern liaoning province china the kuandian amphibolite and granite give an imprecise 1 9 0 4 ga all errors are 2 rb sr errorchron with 87 sr 86 sr o 0 711 0 006 a 2 11 0 06 ga pb pb isochron with a first stage growth 8 43 and a 2 31 0 10 ga smnd isochron with 143 nd 144 nd o 0 50970 0 00009 or nd t 1 1 nd depleted mantle model dates tdm of amphibolite are 2 75 to 2 46 ga those of granite are 2 53 to 2 36 ga zircons from the kuandian granite give a minimum 2 14 0 05 ga upper intercept date the kuandian amphibolite is chemically similar to the high mg member of columbia river basalts and the kuandian granite is an anorogenic granite they are genetically related and formed 2 4 to 2 3 ga ago fractional crystallization of olivine pyroxene and plagioclase from precursor magma of the kuandian amphibolite can produce magma with composition of the kuandian granite the paleoproterozoic mantle source in the eastern liaoning province is less depleted than that inferred from the average mantle evolution curve in contrast with the archean mantle in the sino korean craton which is more depleted than the average this study also reveals that the lishan granite of the eastern liaoning province is older than 3 ga and that some granites and dykes previously mapped as proterozoic are of mesozoic age

alteration and geochemical patterns in the 3 7 3 8 ga isua greenstone belt west greenland abstract volcanic rocks of the 3 7 3 8 ga isua greenstone belt have undergone heterogeneous poly phase post magmatic alteration resulting in mobilisation of many elements including lree and th in contrast nb ta ti zr y and hree were relatively immobile during alteration processes the degree of element mobility appears to have been controlled by chemical composition primary volcanic structures carbonate and silica enrichment and proximity to ultramafic units and shear zones on the basis of the geochemical characteristics of the least altered samples two distinct associations have been recognised in structurally separated lithotectonic sequences these magmatic associations are a low hfse association tio2 0 20 0 40 wt zr 12 30 ppm nb 0 13 0 80 ppm y 6 14 ppm in the central arc sequence resembling tertiary boninites and a high hfse association tio2 0 50 1 14 wt zr 34 77 ppm nb 1 2 2 7 ppm y 11 28 ppm in the outer and inner arc sequences comparable to phanerozoic island arc basaltic to picritic volcanic rocks these two geochemically distinct sequences were likely to have been juxtaposed as a consequence of phanerozoic style plate tectonic processes operating in the early earth the isua volcanic rocks are characterised by sub chondritic nb ta 10 16 ratios post magmatic alteration can be ruled out as the cause of these low ratios rather these ratios reflect a compositional characteristic of the paleoarchean mantle source s the sub chondritic nb ta ratios may have resulted from either preferential sink of nb into the core as a weakly siderophile element or preferential retention of nb in the subducted oceanic crust during subduction zone petrogenetic processes alternatively the building blocks of the earth were not composed of ci like chondritic material

multiple mafic magmatic and high grade metamorphic events revealed by zircons from meta mafic rocks in the daqingshan wulashan complex of the khondalite belt north china craton abstract meta mafic rocks in the daqingshan wulashan complex in the central segment of the paleoproterozoic khondalite belt of the north china craton are composed predominantly of garnet bearing mafic granulites mafic granulites and amphibolites they occur mainly as irregular lenses and as a set of deformed dyke sill swarms within dioritic granitic orthogneisses and al rich paragneisses an integrated study involving laser raman and scanning electron microscope analyses of mineral inclusions from zircons cathodoluminescence imaging and la icp ms u pb dating of zircons shows that magmatic zircons in these meta mafic rocks record four age groups of 2500 2450 2300 2100 1970 1930 and ca 1850 ma indicating multiple mafic magmatic events occurred within the daqingshan wulashan complex in addition four groups of metamorphic zircons with ages of ca 2450 ca 1950 ca 1900 and ca 1850 ma are present within these meta mafic rocks zircons of the first oldest group contain medium to low pressure mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz and yield ages of ca 2450 ma representing the timing of the early mlp granulite facies metamorphic event within the daqingshan wulashan reworked basement complex in contrast zircons of the second group are free of mineral inclusions and yield ages of ca 1950 ma which is considered to be the timing of the regional high grade metamorphic and structural event probably caused by the collision of the yinshan and ordos blocks zircons of the third group contain mlp granulite facies mineral inclusions of orthopyroxene clinopyoxene amphibole plagioclase quartz similar to the zircons of the first group but yield younger ages of ca 1900 ma interpreted as the timing of the regional mlp granulite facies metamorphism that most likely occurred during the early stage of post orogenic exhumation of the daqingshan wulashan complex zircons of the fourth group contain mlp amphibolite facies mineral inclusions of clinopyoxene amphibole plagioclase quartz and yield the youngest ages of ca 1850 ma which probably represent the timing of the regional amphibolite facies metamorphism during the late stage of post orogenic exhumation of the daqingshan wulashan complex combined with previous geological data of the khondalite belt it is speculated that the multiple mafic magmatism and contemporaneous high grade metamorphism of the daqingshan wulashan complex from the khondalite belt were most likely generated by an orogenic process involving early subduction collision and late exhumation in an active continental margin arc

the submarine delta of the ganges brahmaputra cyclone dominated sedimentation patterns the ganges brahmaputra belongs to the world s largest rivers in terms of sediment discharge but little is known yet about the processes controlling sediment distribution on the shelf and the documentation of these processes in large and small scale sedimentary structures for this study the submarine delta of the river system was investigated by high resolution seismic reflection profiles and piston and gravity coring logged physical properties of the cores were combined with visual core description grain size analysis and radiography sedimentation rates were estimated by 210pb and 137cs gamma spectrometry and cross checked with evaluation of seismic profiles the data reveal that the broad delta topset 20 m waterdepth is formed by a thick layer of sand silt highest sedimentation rates about 10 cm a 1 occur at the centre of clinoform delta foreset beds where about 20 of the total riverine sediment load is deposited and thus cause an annual progradation of the subaqueous delta front by about 15 m the foreset beds consist of graded sand silt layers which are thought to be deposited by sediment laden flows generated during the surge of tropical cyclones tempestites interbedded with silty clay layers the head of a canyon the swatch of no ground that deeply incises into the shelf forms a sediment trap along the westward cyclonic transport path where sedimentation rate increases to about 50 cm a 1 episodically earthquakes or storms destabilize especially the rapidly accumulated foreset beds in the eastern delta creating up to 8 m thick mass flows on the outer shelf in water depth beyond 80 m no holocene sediment is deposited

quaternary tephrochronology and deposition in the subsurface sacramento san joaquin delta california u s a abstract we document characteristics of tephra including facies and geochemistry from 27 subsurface sites in the sacramento san joaquin delta california to obtain stratigraphic constraints in a complex setting analyzed tephra deposits correlate with 1 an unnamed tephra from the carlotta formation near ferndale california herein informally named the ash of wildcat grade 0 780 ma 2 the rockland ash bed 0 575 ma 3 the loleta ash bed 0 390 ma and 4 middle pleistocene volcanic ash deposits at tulelake california and pringle falls bend and summer lake oregon herein informally named the dacitic ash of hood 0 180 ma all four tephra are derived from cascades volcanic sources the rockland ash bed erupted from the southern cascades and occurs in up to 7 m thick deposits in cores from 40 m subsurface in the sacramento san joaquin delta tephra facies and tephra age constraints suggest rapid tephra deposition within fluvial channel and overbank settings likely related to flood events shortly following volcanic eruption such rapidly deposited tephra are important chronostratigraphic markers that suggest varying sediment accumulation rates in quaternary deposits below the modern sacramento san joaquin delta this study provides the first steps in a subsurface quaternary stratigraphic framework necessary for future hazard assessment

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

late quaternary floodplain development along the stung sen river in the lower mekong basin cambodia abstract the stung sen river the biggest tributary to lake tonle sap in the lower mekong basin in cambodia is characterized by large seasonal changes of water discharge under the asian monsoon climate and seasonal changes in water level that reach at least 7 m and are controlled by the water level of the lake the stung sen river floodplain consists of two geomorphic units meander belt along the river channel and backmarsh coupled observations of outcrops along the river channel and arrays of sediment cores across the floodplain north of kampong chheuteal village and kampong thom city c 150 km and c 70 km respectively reveal that floodplain environmental changes at c 11 ka were possibly associated with the holocene onset of the southeast asian monsoon and probably with the emergence of lake tonle sap these observations also show that the present backmarsh meander belt system was established about 5 5 ka along with the unique mekong tonle sap connection characterized by a reversal in flow direction during the monsoon season the meander belt materials are replaced as the river channel shifts on a decadal to centennial timescale backmarsh sediments at sites kampong chheuteal and kampong thom had a constant accumulation rate of about 0 5 mm y during the holocene contrasting with rates of 0 1 mm y during the late pleistocene at around 11 ka a sand layer was deposited over all of the valley around kampong chheuteal while wetlands enlarged around kampong thom probably because of increased rainfall triggered by an enhancement of the asian summer monsoon this 11 ka horizon has since been covered by clayey sediments keeping pace with the accumulation of lacustrine sediments in lake tonle sap

initiation of the mekong river delta at 8 ka evidence from the sedimentary succession in the cambodian lowland abstract modern deltas are understood to have initiated around 7 5 9 ka in response to the deceleration of sea level rise this episode of delta initiation is closely related to the last deglacial meltwater events and eustatic sea level rises the initial stage of the mekong river delta one of the world s largest deltas is well recorded in cambodian lowland sediments this paper integrates analyses of sedimentary facies diatom assemblages and radiocarbon dates for three drill cores from the lowland to demonstrate holocene sedimentary evolution in relation to sea level changes the cores are characterized by a tripartite succession 1 aggrading flood plain to natural levee and tidal fluvial channel during the postglacial sea level rise 10 8 4 ka 2 aggrading to prograding tidal flats and mangrove forests around and after the maximum flooding of the sea 8 4 6 3 ka and 3 a prograding fluvial system on the delta plain 6 3 ka to the present the maximum flooding of the sea occurred at 8 0 0 1 ka 2000 years before the mid holocene sea level highstand and tidal flats penetrated up to 20 50 km southeast of phnom penh after a period of abrupt 5 m sea level rise at 8 5 8 4 ka the delta progradation then initiated as a result of the sea level stillstand at around 8 7 5 ka another rapid sea level rise at 7 5 7 ka allowed thick mangrove peat to be widely deposited in the cambodian lowland and the peat accumulation endured until 6 3 ka since 6 3 ka a fluvial system has characterized the delta plain and the fluvial sediment discharge has contributed to rapid delta progradation the uppermost part of the sedimentary succession composed of flood plain to natural levee sediments reveals a sudden increase in sediment accumulation over the past 600 1000 years this increase might reflect an increase in the sediment yield due to human activities in the upper to middle reaches of the mekong as with other asian rivers

holocene interdependences of changes in sea surface temperature productivity and fluvial inputs in the iberian continental shelf tagus mud patch 1 sea surface temperature sst marine productivity and fluvial input have been reconstructed for the last 11 5 calendar cal ka b p using a high resolution study of c37 alkenones coccolithophores iron content and higher plant n alkanes and n alkan 1 ols in sedimentary sequences from the inner shelf off the tagus river estuary in the portuguese margin the sst record is marked by a continuous decrease from 19 c at 10 5 and 7 ka to 15 c at present this trend is interrupted by a fall from 18 c during the roman and medieval warm periods to 16 c in the little ice age river input was very low in the early holocene but increased in the last 3 cal ka b p in association with an intensification of agriculture and deforestation and possibly the onset of the north atlantic oscillation atlantic multidecadal oscillation modes of variability river influence must have reinforced the marine cooling trend relative to the lower amplitude in similar latitude sites of the eastern atlantic the total concentration of alkenones reflects river induced productivity being low in the early holocene but increasing as river input became more important rapid cooling of 1 2 c occurring in 250 years is observed at 11 1 10 6 8 2 6 9 and 5 4 cal ka b p the estimated age of these events matches the ages of equivalent episodes common in the ne atlantic mediterranean region this synchronicity reveals a common widespread climate feature which considering the twentieth century analog between colder ssts and negative north atlantic oscillation nao is likely to reflect periods of strong negative nao

holocene delta progradation into an epeiric sea in northeastern australia abstract progradation of the quaternary gilbert river megafan and holocene delta located in the low gradient intracratonic basin and epeiric sea of the gulf of carpentaria australia has been enhanced by the slight fall in sea level during the late holocene the monsoonal floods and channel avulsions on the megafan have controlled the rate of progradation and supply of sediment to the delta front the mixed influence delta can be classified as a tide dominated fluvially influenced and wave affected tfw delta palaeogeographic reconstruction of the gilbert river megafan delta and palaeoshorelines was created through gis analysis of beach and chenier ridges combined with field observations previous cross section data and radiocarbon and thermoluminescence dating progradation rates on the gilbert river delta are about 0 85 to 0 9 m yr in the northern and central parts of the delta and increase to 1 8 m yr in the southern part of the delta sedimentation rates vary from 0 2 to 1 0 mm yr with a total holocene delta volume of about 9 4 109 m3 and a sediment supply rate of 1 mm3 yr the low sediment supply rate is characteristic of most australian river systems but is about two orders of magnitude less than on many of the larger southeast asian deltas the low onshore and offshore accommodation space on the gilbert and mitchell river deltas is a function of the epeiric sea setting of these deltas and hence the thin succession of holocene sediments on these deltas also represent a significant difference from most southeast asian deltas

millennial scale stratigraphy of a tide dominated incised valley during the last 14 kyr spatial and quantitative reconstruction in the tokyo lowland central japan spatial and quantitative analysis of infilling processes of the tide dominated incised valleys beneath the tokyo lowland during the last 14 kyr was undertaken by using data from 18 sediment cores 467 radiocarbon dates and 6100 borehole logs the post last glacial maximum valley fills consist of braided river meandering river estuary spit and delta systems in ascending order the boundary between the estuary and delta systems is regarded as the maximum flooding surface the maximum flooding surface beneath the tokyo lowland is dated at 8 ka in the arakawa valley and 7 ka in the nakagawa valley this age difference is due to the migration of the tone river from the arakawa valley to the nakagawa valley at 5 ka and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers the meandering river system is dominated by sheet like sands that were deposited during lateral migration of channels during the younger dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the younger dryas the transition between these channel geometries is controlled by a threshold sea level rise of 4 to 7 mm yr 1 before migration of the tone river at 5 ka the tide dominated bay in the nakagawa valley was filled by upward fining laterally accreting muds the muds accreted from the margin to the axis of the bay such lateral accretion of suspended particles derived from outside the bay has been documented in other tide dominated coastal environments and is probably common in other similar settings after the migration of the tone river the bay was filled by upward coarsening deltaic sediments

the structure of y and la bearing aluminosilicate glasses and melts a combined molecular dynamics and diffraction study abstract to understand the behavior of rare earth elements ree in magmatic systems it is important to characterize in a systematic way their incorporation into silicate melts and glasses here we study the structural environment of the ree y and la in four aluminosilicate glasses and melts with varying ree content using a combined simulation and diffraction approach glasses are investigated by x ray and neutron diffraction as well as classical molecular dynamics simulations using two different polarizable ion potentials structure models of the corresponding melts are derived from classical and first principles molecular dynamics simulations we discuss the effect of temperature on coordination numbers and rationalize the structural changes in response to variations in melt glass composition in terms of cation field strengths we find robust evidence that ree and al coordination numbers decrease with increasing ree content in the investigated melts and glasses comparing the two classical potentials one of them is able to reproduce features of the experimental structure factors with a mixture of corner and edge sharing al o ree o polyhedra whereas the other potential predicts corner sharing al o ree o polyhedra only

the palaeoproterozoic boron deposits in eastern liaoning china a metamorphosed evaporite abstract we have carried out a field study of the palaeoproterozoic borate deposits of eastern liaoning province china the borates are hosted within mg silicate and mg carbonate rocks and have previously been interpreted as either skarns or metamorphosed volcanogenic exhalative deposits the deposits contain textures that are compatible with a sedimentary origin of the borates and there is a lack of the associated mineralization that is characteristic of magnesian skarns in addition preliminary boron isotope data indicate that the boron within the borates was not derived from the footwall rocks that have been proposed as the source of the skarn fluids a purely exhalative model can be dismissed on the basis of geochemical arguments and comparison with modern environments which show that borates are too soluble to precipitate directly from hydrothermal fluids the geology and field relationships show a number of similarities with recent non marine evaporite settings and young continental rifts in arid environments we conclude therefore that the liaoning deposits are metamorphosed evaporites in which the boron was originally present as primary evaporite borate minerals this model places the liaoning borates in the same category as the majority of other economic borate deposits in the world

depositional sequences on a late pleistocene holocene tropical siliciclastic shelf sunda shelf southeast asia this study describes and reviews the stratigraphic architecture of the world s largest but least known tropical siliciclastic shelf using the sequence stratigraphic concept the sunda shelf provides conditions particularly suited for reconstructing its depositional history due to a low gradient and extreme width the presence of huge paleo valley systems and abundant filled channels tectonic stability during the quaternary and high sediment input due to a large catchment area we investigated the subsurface along the most prominent paleo valley by shallow seismic surveying and 36 gravity cores controlled by 80 radiocarbon dates the deposits during sea level fall prior to the last glacial maximum lowstand and the subsequent deglacial rise correspond to four systems tracts a wide partly detached prograding deltaic clinoforms indicate forced regression related to a regressive systems tract b sparse shoreline deposits and widespread soil formation refer to a lowstand systems tract c rapidly backstepping coastline related deposits form a confined transgressive systems tract without stacking patterns and are mainly restricted to the paleo valley system d a thin marine mud cover extends as a condensed section over the whole shelf area the base of a highstand systems tract the stratigraphic architecture on the central sunda shelf strata over the past 50 000 years is the result of the interplay of three major factors 1 rapid sea level changes 2 locally pronounced physiography and 3 changes in sediment supply that determined the distribution and accumulation pattern c 2003 elsevier ltd all rights reserved

geochemistry and zircon u pb hf isotopic systematics of the neoarchean yixian fuxin greenstone belt northern margin of the north china craton implications for petrogenesis and tectonic setting abstract the yixian fuxin greenstone belt in the western liaoning metamorphic terrane is situated in the middle segment of the northern margin of the north china craton ncc and is composed mainly of plagioclase amphibolites pyroxene amphibolites and hornblende plagioclase gneisses la icpms zircon u pb isotopic dating of three representative samples of hornblende plagioclase gneisses reveals that the magmatic precursors of the yixian fuxin greenstone belt were formed during 2589 ma 2534 ma and subjected to subsequent 2490 ma metamorphism lu hf isotopic analyses of the zircons dated from the three samples yield positive ehf t values of 8 3 to 2 7 and tdm from 2 76 ga to 2 57 ga the youngest tdm value is close to their crystallization ages suggesting that they were mainly derived from partial melting of the depleted mantle materials these zircon chronological data and lu hf isotopic features indicate an important 2 5 ga episode of crustal growth in the western liaoning metamorphic terrane based on whole rock geochemical characteristics these meta volcanic rocks in the yixian fuxin greenstone belt may be subdivided into four groups samples in group 1 show high mgo contents from 7 19 to 7 93 and cr and ni contents of 208 395 ppm and 113 210 ppm with mg numbers mg of 53 4 to 55 1 and are characterized by slight lree depleted to flat ree patterns la sm n 0 77 1 05 flat patterns on the primitive mantle normalized multiple trace elements diagram and nb ta ratios between 12 3 and 15 9 implying that they were derived from partial melting of depleted mantle source samples in group 2 also display higher mgo 7 52 14 51 cr 372 570 ppm and ni 240 320 ppm contents with high mg 53 5 70 2 low tio2 contents 0 52 0 64 high nb ta ratios 15 8 19 9 and have right declined ree patterns with la sm n ratios from 1 73 to 3 6 and negative nb ta and ti anomalies indicative of their derivation from partial melting of a metasomatized refractory mantle source samples in group 3 show mgo content from 1 81 to 3 56 with mg of 35 9 to 43 5 and high cr 1179 1280 ppm and ni 712 721 ppm contents lower y and yb contents 6 7 9 42 ppm and 0 64 0 88 ppm respectively and higher nb ta ratios 18 4 21 8 and are characterized by the highest la yb n ratios 14 91 22 67 and negative nb ta and ti anomalies revealing that they formed from partial melting of garnet bearing oceanic slab and the slab melts were contaminated by mantle peridotite and subjected to crustal contamination during their ascent samples in group 4 exhibit high mgo content 5 98 10 52 with high mg numbers 52 4 70 8 cr 198 376 ppm and ni 112 177 ppm contents and lower nb ta ratios between 12 7 and 14 6 and have la yb n ratios ranging from 4 12 to 6 78 lower than those of the group 3 and strongly negative nb ta and ti anomalies suggesting that they were derived from partial melting of mantle peridotite metasomatized by slab derived fluids thus the yixian fuxin greenstones display geochemical features of the normal mid ocean ridge basalts n morbs group 1 boninite like rocks group 2 adakite like rocks group 3 and high magnesium andesites hma group 4 suggesting that the protoliths of the greenstone belt might have formed in an active continental margin similar to the andean type orogen

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

precise determination of phanerozoic zircon pb pb age by multicollector sims without external standardization 1 zircon has long been recognized as the best geochronometer and the most important timekeeper in geosciences modern microbeam techniques such as sims and la icpms have been successfully applied to in situ u pb zircon age determinations at spatial resolutions of 20 30 m or less matrix matched calibration by external standardization of well characterized natural zircon references is a principal requirement for precise microbeam u pb zircon age determination due to fractionation effects between pb and u which usually result in an external age error exceeding 1 alternatively zircons with a closed u pb system can be directly dated by measurement of 207pb 206pb isotopic ratio without external standardization which has been a common practice for zircons older than 1 0 ga but not for relatively young 1 0 ga and particularly phanerozoic ones because of limitations of analytical precision we describe in this paper a method of 207pb 206pb measurement on phanerozoic zircons using a new generation of large radius magnetic sector multicollector cameca ims 1280 sims in combination with multicollector mode a nuclear magnetic resonance nmr magnet controller and oxygen flooding techniques we achieve precisions of 207pb 206pb ratio of 0 1 and 0 1 0 2 propagating to pb pb age errors 0 4 and 1 3 excluding u decay constant uncertainties for zircons of latest neoproterozoic and late paleozoic to mesozoic age respectively therefore the multicollector sims is capable of direct determination of zircon pb pb ages as young as mesozoic age with uncertainties of geological significance this technique is useful for direct dating of zircons in thin sections moreover it has significance for dating of some other u rich minerals i e baddeleyite and zirconolite that are not suitable for sims u pb dating by external standardization

crustal uplift in the southern superior province canada revealed by paleomagnetism abstract a change in the polarity of magnetization with depth in the 2 45 ga matachewan dyke swarm is used to document vertical crustal movements that occurred at 1 9 2 3 ga along the kapuskasing structural zone a 500 km long fault zone that transects the archean superior province of canada at shallow crustal levels dykes have a primary magnetization dominantly of one polarity but at greater depths 20 km down a polarity change occurs associated with the growth of exsolved magnetite in feldspar due to slow crustal cooling after cessation of matachewan igneous activity regions of the dyke swarm with one dominant polarity are separated from those with opposite polarity by major faults using this polarity distribution and associated variations in the intensity of feldspar clouding and hydrous alteration maps of the southern superior province are produced that display regional crustal tilting on which are superimposed more local fault bounded blocks associated with the kapuskasing zone some of these blocks have been recognized for the first time as a result of this study the paleomagnetic work has also shown that the matachewan swarm is regionally distorted both within and north of the kapuskasing zone and originally had a more radial disposition this widespread distortion suggests that the lower crust was still relatively ductile at the time of deformation perhaps due to high heat flow associated with the waning stages of the matachewan mantle plume beneath

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

luminescence dating of beach ridges for characterizing multi decadal to centennial deltaic shoreline changes during late holocene mekong river delta abstract empirical understanding of decadal to centennial scale deltaic shoreline changes in the past is essential for understanding the fate of coasts in the coming decades and centuries we tested the effectiveness of quartz optically stimulated luminescence osl dating of beach ridges to constrain shoreline changes of the mekong river delta over the last 3500 years forty seven osl ages have been analyzed from the tra vinh delta plain central mekong river delta the tra vinh beach ridges are recurved and branching showing the hierarchy of shoreline changes which include discontinuous shifts c 5 km seawards caused by the emergence and elongation of a delta front bar island and subsequent downdrift accretion of spits the spit accretion is interrupted by changes of shoreline orientation each of the discontinuous shifts resulted in a cluster of beach ridges which is referred to as ridgeset the beach ridge sediments were found to have excellent luminescence properties resulting in low age uncertainties of c 5 the osl chronology agrees well with shoreline changes over recent decades and with radiocarbon ages of tidal flat sediment underlying the beach ridges the chronology clearly illustrates the coastal progradation from 3500 years relative to ad 2010 onwards two main types of beach ridge are present recurved and trunk ridges osl ages of recurved ridges are consistently younger both downdrift and seawards documenting decadal to centennial scale shoreline migration especially over the last 1500 years trunk ridges in contrast have less systematic ages because a trunk ridge is formed where the sediment is likely to have been reworked by waves ages of updrift trunk ridges characteristically show relatively young ages in each ridgeset representing the extensive erosion and resedimentation of the updrift coast major changes in shoreline orientation occurred around 400 500 years suggesting strengthening of the northeasterly winter monsoon at the beginning of the little ice age the rate of progradation of the tra vinh delta plain is described in two ways frequency of the discontinuous shift and growth rate of the delta plain area both suggest the coast has expanded regularly over the last 1000 years a decrease in sand supply to the coast in the last few decades due to river dam construction and fluvial sand dredging is inferred possibly affecting the behavior of the modern and future shorelines which can be compared with the less human influenced centennial to decadal scale past shoreline changes reconstructed in this study

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

river flow controls on tides and tide mean water level profiles in a tidal freshwater river 1 tidal rivers feature oscillatory and steady gradients in the water surface controlled by interactions between river flow and tides the river discharge attenuates the tidal motion and tidal motion increases tidal mean friction in the river which may act as a barrier to the river discharge time series of tidal water level amplitudes at five gauge stations along the river mahakam in indonesia and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis temporal variations in tidal damping coefficients for quaterdiurnal semidiurnal and diurnal tidal species were quantified from the observed amplitude profiles the analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb wavelet cross correlations between surface levels yielded empirical estimates of wave numbers an empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the mahakam the subtidal friction is decomposed into contributions from the river flow only from river tide interaction and from tidal asymmetry even for high river flow and low tidal velocity river flow enhances friction attributed to river tide interaction causing subtidal water level setup a simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream with a relatively good agreement between predictions and observations the explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity explaining the complex behavior of tidal mean surface level profiles

delta initiation and holocene sea level change example from the song hong red river delta vietnam abstract delta initiation and subsequent delta growth were investigated by using radiocarbon dated borehole cores from the song hong red river delta vietnam the sediments underlying the present delta plain record three depositional systems since the last glacial maximum fluvial estuarine and deltaic in ascending order the landward part of the initial delta was characterized by an active tide influenced accumulation of sandy sediments the seaward part of the initial delta is composed of muddy prodelta and seafloor sediments that accumulated slowly radiocarbon ages of molluscan shells and organic materials suggest that the transition from estuary to delta occurred at approximately 8500 cal years bp the transition was induced by deceleration of the postglacial sea level rise which was coeval with the delta initiation the stacking pattern of the delta system is very different from that of the estuary system the sediments of the estuary that developed during the rapid rise in sea level between 11000 and 8500 cal years bp display a retrogradational stacking pattern forming a thick transgressive systems tract on the other hand aggradational as well as progradational stacking with clinoform architecture characterized the delta system between 8500 and 6500 cal years bp as the sea level continued its slow rise progradation has been dominant during the last 6500 years because the cessation of sea level rise resulted in little accommodation being added the results of this study are similar to those for other major delta systems such as the changjiang and the ganges brahmaputra deltas despite large differences in sediment discharge tectonics basin size and coastal environment this implies that the postglacial sea level rise and the change in the rise rate markedly influenced the evolution of depositional systems at river mouths

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

holocene and modern sediment budgets for the ganges brahmaputra river system evidence for highstand dispersal to flood plain shelf and deep sea depocenters the partitioning of fluvial sediment load across continental margins is an important control on strata formation and sequence development however few quantitative sediment budgets that encompass entire dispersal systems exist for the ganges brahmaputra river system sediment discharge is estimated to be 10 9 t yr at gauging stations 300 km inland of the coast but little has been known of the downstream fate of this material geochronological geophysical and stratigraphic investigations of the lowland flood plain delta plain and shelf help to delineate the extent of holocene fill and allow calculation of a first order sediment budget results reveal that 1500 10 9 m 3 of sediment fill has been sequestered within the flood plain and delta plain since ca 7000 yr b p or about one third of the annual discharge the remaining load appears to be apportioned between the prograding subaqueous delta 1970 10 9 m 3 and transport to the deep sea bengal fan via a nearshore canyon modern 100 yr budget estimates based on short term accretion rates indicate a similar dispersal pattern and show that contemporaneous deposition continues within these disparate depocenters the roughly equal partitioning of sediment among flood plain shelf and deep sea settings reflects the respective influence of an inland tectonic basin a wide shelf and a deeply incised canyon system the findings also support new sequence stratigraphic models for these settings and indicate the important insight that modern river deltas can provide for ancient margin systems furthermore results affirm that values of riverine sediment flux to the oceans may be considerably overestimated by not accounting for loss to the flood plains downstream of the gauging stations

an introduction to the geological significance of sediment transport and accumulation on the amazon continental shelf in order to understand the formative processes and resulting stratigraphy on the amazon shelf and adjacent shoreline of amapa geological investigations were undertaken as part of a multidisciplinary amazon shelf sediment study amasseds the design of the study provided results of a multifaceted nature integrated with observations in other disciplines focused on sedimentary processes representative of fluctuating conditions on several time scales and broadly distributed on the shelf including regions not investigated in the past on short time scales most muddy sediment is transported northwest of the river mouth from there it moves seaward as fluid mud to cause rapid accumulation of foreset beds and moves northwestward to prograde the northernmost amapa shoreline and to supply sediment to the guianas fluid muds cover the shelf as far northward as 3 5 n and allow strong tides to propagate to shore where tidal currents cause most of the amapa shoreline to undergo erosion today averaged over decades and centuries about half of the amazon sediment discharge accumulates on the adjacent shelf and another significant fraction one sixth leads to accretion of the northernmost amapa shoreline and northwestward bypassing of sediment the remaining sediment is hypothesized to be trapped in deltaplain deposits of the lower amazon river system the foreset region and shoreline represent the two common loci of sediment accumulation that alternate their predominance on time scales of millennia and lead to a two stage progradation of coastal plain and subaqueous deltaic deposits this muddy regressive sedimentation during high sea level is replaced by formation of erosional sand layers during low sea level and transgressive conditions future research in the study area should address important considerations that were delineated by the present study including mechanisms of shoreline accretion the holocene history recorded in topset and coastal plain strata the role in local sedimentation played by the large shoal extending from cabo norte and the entrapment of amazon sediment by the delta plain

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

model shows that rivers transmit high frequency climate cycles to the sedimentary record rivers are a major component of sediment routing systems that control the transfer of terrigenous sediments from source to sink although it is widely accepted that rivers are perturbed by millennial scale climatic variability the extent to which these signals are buffered or transferred down river systems to be recorded in sediments at or beyond the river mouth remains debated here we employ a physically based numerical model to address this outstanding issue our model shows that river transport strongly amplifies high frequency sediment flux variations arising from changing water discharge due to positive feedback between discharge and the channel gradient this behavior is distinctly different from short period sediment flux signals with constant water discharge where the output sediment flux is strongly dampened within the river due to negative feedback between the channel gradient and sediment concentration we conclude that marine sedimentary basins may record sediment flux cycles resulting from discharge and ultimately climate variability whereas they may be relatively insensitive to pure sediment flux perturbations such as for example those induced by tectonics

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

ree geochemistry of carbonates from the guanmenshan formation liaohe group ne sino korean craton implications for seawater compositional change during the great oxidation event abstract the worldwide 2 33 2 06 ga positive 13 c carb excursion has been correlated with the great oxidation event goe and termed as the lomagundi event the 2 3 1 85 ga guanmenshan formation in the liaohe group of the northeastern sino korean craton is characterized by positive 13 c carb excursion and is a potential candidate to evaluate the lomagundi event using rey rare earth element and yttrium ree y chemical fingerprints here we present major and trace element analysis of 42 samples from the guanmenshan formation which are pure marine chemical sediments and use the data to trace the seawater composition during 2 3 1 85 ga 15 least altered dolomicrite samples 600 m strata have ree values of 0 739 4 175 ppm 2 414 1 184 ppm and the y ho ratios of 34 5 56 6 44 1 5 7 they show uniform positive la sn la sn 1 04 0 27 and gd sn gd sn 1 64 0 40 anomalies and notable lree depletions indicated by nd sn yb sn values of 0 24 0 92 average 0 56 0 19 these features are consistent with the geochemistry of well oxygenated shallow ambient seawater and suggest that these samples provide a robust record of the primary rey signature of seawater during the lomagundi event the rey patterns of 15 silicified dolomites marbles locally with veinlets from the pb zn mining camps in the region with average eu cn eu cn 1 56 0 95 are identical to those of high temperature hydrothermal fluids 250 c characterized by a flat pattern and marked positive eu anomalies indicating that these rocks were subjected to metasomatism by hydrothermal fluids the guanmenshan formation shows average ce sn ce sn of 0 93 0 09 and sm cn yb cn of 1 which are higher than those of the archean 2 33 ga chemical sediments generally f o 2 and p co 2 the rey in the dolomicrite were mainly sourced from fluxes of solutes from terrestrial weathering and also from seafloor hydrothermal processes on a subordinate scale the guanmenshan dolomicrites have eu sn eu sn values of 1 34 2 55 i e around 1 53 indicating that they were deposited during 2 33 2 06 ga as the eu sn eu sn 1 53 can be used as a proxy for the 2 33 2 06 ga marine chemical sediments our study shows that the guanmenshan formation was formed at a critical turning point in earth history when the global atmosphere hydrosphere system witnessed a dramatic change from reducing to oxidizing conditions

mesophotic coral buildups in a prodelta setting late eocene southern pyrenees spain a mixed carbonate siliciclastic system lower priabonian coral bioherms and biostromes encased in prodelta marls clays occur in the ainsa jaca piggyback basin in the south central pyrenean zone detailed mapping of lithofacies and bounding surfaces onto photomosaics reveals the architecture of coral buildups coral lithosomes occur either isolated or amalgamated in larger buildups isolated lithosomes are 1 to 8 m thick and a few hundred metres wide clay content within coral colonies is significant stacked bioherms form low relief buildups commonly 20 to 30 m thick locally up to 50 m these bioherms are progressively younger to the west following progradation of the deltaic complex the lowermost skeletal rich beds consist of bryozoan floatstone with wackestone to packstone matrix in which planktonic foraminifera are abundant and light related organisms absent basal coral biostromes and the base of many bioherms consist of platy coral colonies floating in a fine grained matrix rich in branches of red algae corals with domal or massive shape locally mixed with branching corals and phaceloid coral colonies dominate buildup cores these corals are surrounded by matrix and lack organic framework the matrix consists of wackestone to packstone locally floatstone with conspicuous red algal and coral fragments along with bryozoans planktonic and benthonic foraminifera and locally sponges coral rudstone and skeletal packstone with wackestone to packstone matrix also occur as wedges abutting the buildup margins integrative analysis of rock textures skeletal components buildup anatomy and facies architecture clearly reveal that these coral buildups developed in a prodelta setting where shifting of delta lobes or rainfall cycles episodically resulted in water transparency that allowed zooxanthellate coral growth the bathymetric position of the buildups has been constrained from the light dependent communities and lithofacies distribution within the buildups the process product analysis used here reinforces the hypothesis that zooxanthellate corals thrived in mesophotic conditions at least during the late eocene and until the late miocene comparative analysis with some selected upper eocene coral buildups of the north mediterranean area show similarities in facies components and textures and suggest that they also grew in relatively low light mesophotic and low hydrodynamic conditions

the influence of composition on the local structure around yttrium in quenched silicate melts insights from exafs abstract the structural environment around y in silicate and aluminosilicate glasses containing 5000 ppm y was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy the used glass compositions were taken from prowatke and klemme 2005 varying in the aluminum saturation index asi molar ratio of al 2 o 3 na 2 o k 2 o cao from 0 115 to 0 768 furthermore a set of glass compositions from the system cao al 2 o 3 sio 2 cas was used for which structural data from computer simulations are available haigis et al 2013 this issue structural parameters of the y o pair correlation of the first coordination shell were determined from the exafs based on a gamma like distribution function that accounts for the large static disorder and non gaussian pair distributions the analysis shows an increase in the coordination number from 6 to 8 along with an increase of the average y o distance by 0 13 a for the composition of prowatke and klemme 2005 for the cas composition an increase of the coordination number from 6 to 7 along with an increase of the average y o distance by 0 06 a is obtained the change of these parameters is associated with a considerable increase in the asymmetry and width of the y o pair distribution due to its size and charge 6 fold coordinated y will preferentially bond to non bridging oxygens of the polymeric melt network to form a stable configuration as is the case for the less polymerized melts with low asi in highly polymerized melts with asi values close to one 6 fold coordination of y is not possible because almost only bridging oxygens are available consequently over bonding of bridging oxygens around y is counterbalanced by an increase of coordination number and y o distance to satisfy local charge balance requirements

paleo pacific subduction accretion evidence from geochemical and u pb zircon dating of the nadanhada accretionary complex ne china the nadanhada terrane located along the eastern margin of eurasia contains a typical accretionary complex related to paleo pacific plate subduction accretion the yuejinshan complex is the first stage accretion complex that consists of meta clastic rocks and metamafic ultramafic rocks whereas the raohe complex forms the main parts of the terrane and consists of limestone bedded chert and mafic ultramafic rocks embedded as olistolith blocks in a weakly sheared matrix of clastic meta sedimentary rocks geochemical data indicate that the yuejinshan metabasalts have normal mid ocean ridge basalt n morb affinity whereas the raohe basaltic pillow lavas have an affinity to ocean island basalts oib sensitive high resolution ion microprobe shrimp u pb zircon analyses of gabbro in the raohe complex yield a weighted mean 206pb 238u zircon age of 216 5 ma whereas two samples of granite intruded into the complex yield weighted mean 206pb 238u zircon ages of 128 2 and 129 2 ma laser ablation inductively coupled plasma mass spectrometry la icpms u pb zircon analyses of basaltic pillow lava in the raohe complex define a weighted mean age of 167 1 ma two sandstone samples in the raohe complex record younger concordant zircon weighted mean ages of 167 17 and 137 3 ma these new data support the view that accretion of the raohe complex was between 170 and 137 ma and that final emplacement of the raohe complex took place at 137 130 ma the accretion of the yuejinshan complex probably occurred between the 210 and 180 ma suggesting that paleo pacific plate subduction was initiated in the late triassic to early jurassic

assessing the effect of sea level change and human activities on a major delta on the pacific coast of northern south america the patia river abstract this paper presents the main physical and human induced stresses that have shaped the recent evolution of the patia river delta the largest and best developed delta on the western margin of south america during the holocene the patia delta moved southward and the northern part became an estuarine system characterized by large extensions of mangrove ecosystems however a major human induced water diversion starting in 1972 diverted the patia flow to the sanguianga river and shifted the active delta plain back to its former holocene location this discharge diversion has led to sediment starvation of the southern delta lobe and changed the northern estuarine system into an active delta plain in addition coastal areas of the patia delta subsided as a result of a devastating tsunami in 1979 morphological changes along the delta coast are evidenced by 1 coastal retreat along the whole delta front during the period 1986 2001 2 coastal retreat along the abandoned delta lobe for the period 2001 2008 56 of the southern delta shoreline is retreating and only 4 of the coast shows signs of accretion 3 progradation of the northern delta region during the period 2001 2008 the discharge diversion of the patia river to the sanquianga has apparently balanced the observed trends in coastal erosion and sea level rise 5 1 mm yr 1 for the period 1984 2006 after the 1979 tsunami 4 formation of transgressive barrier islands with exposed peat soils in the surf zone and 5 abandonment of former active distributaries in the southern delta plain with associated inlet closure in the northern delta lobe major geomorphic changes include 1 distributary channel accretion by morphological processes such as sedimentation also in crevasses overbank flow increasing width of levees inter distributary channel fill and colonization of pioneer mangrove 2 freshening conditions in the sanguianga distributary channel a hydrologic change that has shifted the upper estuarine region salinity max q min 3 spatial switch of delta distributaries related to tectonic movements and subsidence 4 a relative sea level rise of 5 1 mm yr 1 after the occurrence of the 1979 tsunami 5 episodes of sea level rise associated with the enso cycle and 6 human induced discharge diversion the information presented here is valuable evidence for understanding the role of extreme events versus normal conditions in creating and shaping deltas

structural controls of co 2 on y la and sr incorporation in sodium rich silicate carbonate melts by in situ high p t exafs abstract carbonate rich silicate and carbonate melts play a crucial role in deep earth magmatic processes and their melt structure is a key parameter as it controls physical and transport properties carbon rich melts can be strongly enriched in trace elements but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses in this contribution we investigate the influence of co 2 on the local environments of trace elements contained in silicate glasses with variable co 2 concentrations and in silicate and carbonate melts the melts were studied in situ at high pressure and temperature conditions using the paris edinburgh press 2 2 to 2 6 gpa and 1200 to 1500 c the compositions studied include sodium rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at oldoinyo lengai volcano the local environments of yttrium y lanthanum la and strontium sr were investigated using extended x ray absorption fine structure exafs spectroscopy main findings of the study suggest 1 in peralkaline silicate glasses the local structure of y is unaffected by the co 2 content contrary a slight increase of oxygen bond lengths of sr and la is inferred with increasing co 2 content in peralkaline glasses while they remain constant in glasses of even higher peralkalinity independent of the co 2 content 2 in silicate melts of different co 2 contents y o bond lengths are constant while a slight increase within carbonate melt compositions is deduced on the other hand a steady bond lengths increase over the whole compositional range is inferred for la o and sr o this may well be explained by distinct preferences of these elements for specific local environments based on these new data we suggest potential mechanisms for the structural incorporation of these elements a key step towards understanding their partitioning behavior in natural magmatic systems

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

peat or no peat why do the rajang and mahakam deltas differ abstract coastal and deltaic holocene peat accumulations around the equatorial island of borneo southeast asia have served as models for economic coal bearing sequences in the stratigraphic record although climatic conditions vegetational communities and sedimentary regimes are comparable peat accumulations are not found on both the western and eastern sides of the island the rajang river delta and coastal plain sarawak east malaysia are covered in areally extensive thick peat deposits that have attained at least a thickness of 13 m in ombrogenous peat domes marudi baram river peat swamp biomass began to accumulate over pleistocene podzols when sea level stabilized 7 5 ka and delta progradation was initiated the mahakam river delta and coastal plain east kalimantan indonesia also began progradation at this time but there is no evidence in any part of the coastal region for peat accumulation rather poorly developed organic rich gleysols occur throughout the delta plain both the rajang river and mahakam river deltas are tidally influenced fine grained systems with a sediment provenance in the central massif sediment transported through the rajang river delta differs in that as much as 60 of the clay minerals deposited in the system are mixed layer i s and expandable k e clays that act to restrict pore water flow in the tidal and overbank deposits that comprise the delta plain these result in the development of an aquiclude above which paludal conditions develop promoting accumulation of organic matter in contrast there is a low proportion of mixed layer and expandable clays transported in the mahakam river system this precludes the development of a stilted water table within the delta allowing for organic matter recycling without peat accumulation the presence of a high proportion of expandable clay minerals on the western side of borneo is a reflection of the weathering and eroding source rocks on this side of the central borneo massif

episodic paleoproterozoic 2 45 1 95 and 1 85 ga mafic magmatism and associated high temperature metamorphism in the daqingshan area north china craton shrimp zircon u pb dating and whole rock geochemistry abstract in the daqingshan area within the khondalite belt of the north china craton paleoproterozoic gabbro and dolerite intrusions show amphibolite to granulite facies metamorphism u pb zircon dating and whole rock geochemistry were undertaken on these rocks in order to understand the timing of mantle magmatism and thermal processes ten samples yielded zircon u pb formation ages of 2 46 2 44 ga 1 97 1 92 ga and 1 84 ga and metamorphic ages of 1 95 1 83 ga they are variable in geochemical composition with some being enriched in light rare earth and large ion lithosphere elements but depleted in nb ta combined with previous results it is concluded that mafic magmatism at 2 45 2 37 ga and 1 97 1 92 ga indicates two paleoproterozoic extensional phases with the latter accompanied by ht uht metamorphism as a result of underplating of mantle magma

siliciclastic and volcaniclastic influences on equatorial carbonates insights from the neogene of indonesia in active tectonic areas of humid equatorial regions nearshore shallow water environments are commonly sites of near continuous siliciclastic influx and or punctuated volcaniclastic input despite significant clastic influence neogene carbonates developed in se asia adjacent to major deltas or volcanic arcs and are comparable with modern mixed carbonate clastic deposits in the region research into delta front patch reefs from borneo and fore arc carbonate platform development from java is described and used to evaluate the effects of siliciclastic and volcaniclastic influx on regional carbonate sedimentation local changes in carbonate producing biota and sequence development regional carbonate development in areas of high siliciclastic or volcaniclastic input was influenced by the presence of antecedent highs changes in the amounts or rates of clastic input delta lobe switching or variations in volcanic activity energy regimes and relative sea level change a variety of carbonate producing organisms including larger benthic foraminifera some corals coralline algae echinoderms and molluscs could tolerate near continuous siliciclastic or volcaniclastic influx approximately equal to their own production rates these organisms adopted various strategies for coping with clastic input including a degree of mobility morphologies adapted to unstable substrate inhabitation or shedding sediment and shapes adapted to low light levels local carbonate production was also affected by energy regime clastic grain sizes and associated nutrient input clastic input influenced the inhabitable depth range for photoautotrophs the zonation of light dependent assemblages and the morphology and sequence development of mixed carbonate clastic successions this study provides data on the dynamic interactions between carbonate and non carbonate clastic sediments and when combined with information from comparable modern environments allows a better understanding of the effects of siliciclastic and volcaniclastic influx on carbonate production

late holocene evolution of the mahakam delta east kalimantan indonesia abstract the late holocene mahakam delta located along the tropical eastern shore of kalimantan indonesia is considered to be a textbook example of a mixed tide fluvial dominated delta system the delta prograded about 60 km during the past 5000 years which led to the development of a distinct network of distributary and tidal channels wave action is low due the limited fetch in the narrow strait of makassar mahakam river discharge is about a quarter of the mississippi river discharge and is characterized by absence of flood surges therefore natural levees crevasse splays and avulsions are absent in the delta plain for the past four decennia both modern and ancient mahakam delta deposits have been studied in detail in order to better understand subsurface miocene and tertiary mahakam deposits which host large volumes of hydrocarbons this study focuses on the dynamics and stratal patterns of delta plain delta front platform deposits and suspended sediments due to the predominance of semi diurnal tides and the associated flow reversals depositional patterns are highly variable which has resulted in the formation of characteristic sand mud couplets the distribution of the sand mud couplets found in this study differs from previously proposed conceptual models they are limited to the fluvial domain and form in the distributary channels lateral channel bar or at the fluvial dominated delta front platform which flanks the mouth bar deposits in offshore direction the sand mud couplets which formed as delta front platform and lateral channel bar deposits are similar and can only be identified based on their 14 c age the sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments some 22 new ams 14 c dates show that late holocene sea level history resembles the eustatic sea level curve giving a first approximation of the late holocene sea level history for east kalimantan the dates suggest that the progradational delta system evolved under conditions of slowly rising sea level which compares well to the eustatic sea level curve in addition calculated averaged deposition rates of the sand mud couplets indicate that deposition is driven by the spring neap tide cycles instead of the daily tidal cycle

predicting the terrestrial flux of sediment to the global ocean a planetary perspective a new model for predicting the long term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins the model is based on relief basin area or averaged discharge and basin averaged temperature basinaveraged temperature is determined from basin location latitude longitude and the lapse rate across the basin relief hypsometric approximation the sediment flux model incorporates climate through basin temperature and hydrologic runoff solutions are provided for each of the major hemispheric climate regions polar temperate and tropic the model successfully predicts the pre anthropogenic flux of sediment to within the uncertainties associated with the global observations within a factor of two for 75 of rivers that range across five orders of magnitude in basin area and discharge most of the problem rivers are associated with low observational loads often smaller rivers where anthropogenic impacts are often magnified and temporal variability is high model predictions provide a baseline for researchers 1 to question the quality of observational data where available and disagreement is greatest 2 to examine a river basin for unusually large anthropogenic influences i e causes of erosion or causes of hinterland sediment retention and 3 to uncover secondary factors not addressed by our model lithology lakes the model provides a powerful tool to address the impact of paleo climate fluctuations warmer colder wetter drier on the impact of sediment flux to the coastal ocean d 2003 elsevier b v all rights reserved

the paths and timing of late paleozoic ice revisited new stratigraphic and paleo ice flow interpretations from a glacial succession in the upper itarare group parana basin brazil abstract this paper examines a glacial diamictite bearing succession from the upper itarare group taciba formation in eastern parana basin brazil the object of study provides the opportunity to investigate in detail the late stages of glacial sedimentation during the late paleozoic ice age lpia in this sector of sw gondwana with implications for glacial cyclicity and regional paleo ice flow reconstructions sedimentology geological mapping and palynological analysis allowed the recognition of four facies associations comprising subaqueous outwash mass transport tide influenced delta front and tide influenced delta plain deposits the succession records at least two episodes of ice margin advance and retreat into a marine influenced environment and can be placed in the earliest permian based on the palynomorph assemblage cross stratification in outwash facies and deltaic deposits indicate sediment transport to the sw the same revealed by deformational structures in mass transport diamictites derived from downslope resedimentation of glaciomarine sediments during deglaciation a glacial source to ne is therefore indicated and is in agreement with paleo ice flow directions obtained from previously studied localities to the north this north derived early permian glaciation contrasts with glacial sources to the se recognized in the lower and middle intervals of the itarare group the scenario suggests a geometric reconfiguration of the parana basin during the lpia and the migration of ice centers with time during the late paleozoic ice age in sw gondwana

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

zircon ages and geochemistry of late neoarchean syenogranites in the north china craton a review abstract at the end of the neoarchean continental evolution voluminous syenogranites were emplaced in the north china craton together with other magmatic rocks trondhjemite tonalite granodiorite ttg monzogranite diorite gabbro syenogranites are widely distributed in anshan benxi qinhuangdao and western shandong and also occur in southern jilin northern liaoning northwestern hebei and central henan based on geological relationships degree of metamorphism deformation and magmatic zircon ages two phases of syenogranite magmatism are recognized rocks produced during the first phase show a gneissic texture and were formed between 2 53 and 2 52 ga and locally comprise abundant ttg rocks of the second phase cut late neoarchean ttg and supracrustal rocks display a massive structure and mainly formed between 2 52 and 2 50 ga all syenogranites share the same features in major element compositions being high in sio2 and low in cao total feo mgo tio2 and p2o5 however they are different in trace and ree compositions and can be subdivided into three types 1 type 1 shows a large variation in total ree contents low la yb n ratios strong negative eu eu anomalies and ba depletion 2 type 2 is similar to type 1 but has higher la yb n ratios 3 type 3 shows a large variation in total ree and la yb n ratios and significantly do not show strongly negative eu eu anomalies and ba depletion whole rock sm nd isotopic compositions show large variations in nd t values and tdm nd modal ages ranging from 9 49 to 4 72 and 3 70 to 3 25 ga type 1 0 55 1 03 and 2 77 2 71 ga type 2 and 2 35 to 1 23 and 2 93 2 66 ga type 3 respectively hf isotopic compositions of zircons from three samples have hf t values and tdm1 hf ages of 0 7 7 2 and 2 84 2 56 ga type 1 2 6 7 4 and 2 74 2 56 ga type 2 and 2 1 6 3 and 2 76 2 60 ga type 3 it is concluded that syenogranites were generated by melting of continental crust with different mean crustal residence ages and most of them were emplaced during the second phase 2 52 2 50 ga in an extensional tectonic regime the formation of these voluminous syenogranites marks a tectono magmatic event resulting in stabilization of the north china craton at the end of the neoarchean

is the ordos block archean or paleoproterozoic in age implications for the precambrian evolution of the north china craton the ordos block is a large but poorly exposed crustal segment in the western part of the north china craton little is known about its precambrian basement rocks and their evolution because of an extensive cover by younger sedimentary rocks we report shrimp zircon ages and hf in zircon isotopic compositions for five samples recovered from drill holes that penetrated into the ordos basement based on these data two age groups of rocks can be distinguished an early paleoproterozoic group that is represented by one sample from the northern margin of the ordos block and a late or middle late paleoproterozoic group consisting of the remaining four samples the early paleoproterozoic sample contains zircon cores and metamorphic rims with ages of 2 4 ga and 2 28 ga respectively the cores have ehf t values of 8 8 to 6 2 and hf crustal model ages of 2606 to 3221 ma the remaining rocks of late or middle late paleoproterozoic age contain zircons that may also show a core rim structure but with the cores having ages of 2 08 ga and the metamorphic rims recording ages of 1 9 ga the zircon cores have ehf t values of 9 1 to 10 1 and hf crustal model ages of 2039 to 3068 ma combined with data from earlier studies we draw the conclusion that late paleoproterozoic metasedimentary rocks are widespread in the ordos basement there is no evidence from our samples of an archean component and this calls into question the prevailing view that the ordos basement is an archean cratonic block the fact that the ordos basement was involved in a widespread late paleoproterozoic tectono thermal event indicates that most current models for the tectonic evolution of the western portion of the north china craton need to be revised

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

refining the eustatic sea level curve since the last glacial maximum using far and intermediate field sites the eustatic component of relative sea level change provides a measure of the amount of ice transferred between the continents and oceans during glacial cycles this has been quantified for the period since the last glacial maximum by correcting observed sea level change for the glacio hydro isostatic contributions using realistic ice distribution and earth models during the last glacial maximum lgm the eustatic sea level was 125 5 m lower than the present day equivalent to a land based ice volume of 4 6 4 9 107 km3 evidence for a non uniform rise in eustatic sea level from the lgm to the end of the deglaciation is examined the initial rate of rise from ca 21 to 17 ka was relatively slow with an average rate of ca 6 m ka 1 followed by an average rate of ca 10 m ka 1 for the next 10 ka significant departures from these average rates may have occurred at the time of the younger dryas and possibly also around 14 ka most of the decay of the large ice sheets was completed by 7 ka but 3 5 m of water has been added to the oceans since that time

controls on river delta formation insights from numerical modelling abstract primary hydraulic and sedimentary controls on river deltas were previously postulated in classification schemes in the field of sedimentary geology based on many field observations however detailed mechanistic models were restricted to the river dominated delta class analogous to the concept of morphological conditioning here we show that antecedent stratigraphy controls morphometrics of prograding river dominated delta distributary networks under steady sea level further we use coupled hydrodynamic morphodynamic stratigraphic detailed numerical modelling to assess the influence of wind generated waves and tides on clastic river delta formation our synthetic simulations show that deltas forming under mere riverine forcing prograde via sequences of mouth bar induced flow bifurcation and upstream channel shifting windwave action suppresses sequestration of fine sediments on the developing delta plain entailing relatively smooth shorelines perturbed by a limited number of distributary channels in contrast tide influenced river deltas are found to prograde mainly via lengthening of initially formed relatively stable distributaries as well as being characterized by cyclicity in deposits interbedding of sands and silts these results provide a framework for physics based river delta modelling under various environmental conditions particularly our findings suggest that relatively low energetic basin conditions can already significantly impact morphological and stratal patterns of prograding river deltas

mixed energy process interactions read from a compound clinoform delta paleo orinoco delta trinidad preservation of river and tide signals by mud induced wave damping

two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton petrogenesis and tectonic implications abstract mafic dyke swarms constitute a common occurrence within the cratonic provinces in the world since the archean proterozoic boundary and their geneses harbor critical information for facilitating regional tectonic and supercontinental reconstruction this zircon u pb dating and geochemical study documents two episodes of paleoproterozoic mafic intrusions from liaoning province north china craton ncc the haicheng suite hcs with an emplacement age of ca 2125 ma from the liaodong peninsula and the guohua suite ghs with an age of ca 1816 ma from the western liaoning terrane the hcs meta gabbros are tholeiitic in composition with an sio 2 range from 46 to 52 modest enrichment in light rare earth elements lree and depletion in high field strength elements hfse and possess radiogenic whole rock nd nd t 1 91 to 4 21 and zircon hf hf t 4 02 to 8 48 isotopic compositions these features endow the hcs with a juvenile subduction fluid metasomatized lithospheric mantle source by contrast the ghs exhibits a meta gabbroic to dioritic composition and a transitional character from tholeiitic to calc alkali with variably enriched lrees and more evolved isotopic signatures nd t 0 20 to 5 82 zircon hf t 0 09 to 4 91 than the hcs while the relatively intact high fe gabbroic samples are supposed to represent partial melts from a fertile cratonic sub continental lithospheric mantle source in the garnet spinel stability field the low fe dioritic ones tend to bear the imprints of subsequent assimilation and fractional crystallization process apart from making an important contribution to the present archive of the paleoproterozoic mafic dyke swarms in the ncc the present two mafic magmatic suites witnessed a shift in tectonic setting from a subduction related continental arc environment to a post orogenic extensional regime synthesizing two suites with coeval felsic igneous episodes as well as concomitant episodic metamorphic events in the jiao liao ji belt leads to the characterization of a possible divergent double subduction system in the eastern ncc during the time span of ca 2 2 1 80 ga synchronized beating of episodic magmatic and metamorphic pulses in the constituent mobile belts of the ncc carries further implication of attesting to the ubiquity and importance of divergent double subduction system in the cratonic amalgamation and its incorporation within the supercontinent columbia

partial melting of a refractory subducted slab in a paleoproterozoic island arc implications for global chemical cycles this study focuses on the rare occurrence of high fe low si tholeiitic basaltic rocks of a paleoproterozoic 1 9 ga backarc arc succession amisk lake flin flon greenstone belt canada and their implications for subarc mantle processes and the global elemental budget of ta nb and ti volcanism at amisk lake is characterized by interbedded tholeiitic and boninite like backarc basalts overlain by intermediate to felsic calc alkalic arc volcanic rocks the change from dominantly backarc to arc volcanism is marked by picritic flows overlain by the high fe tholeiites the high fe tholeiites are characteristically high in fe 2 o 3 t 15 21 wt low in sio 2 39 45 wt and slightly light rare earth element enriched la sm n 1 3 1 93 they are unusually high in ta nb and ti normally depleted in arc related rocks and low in zr hf and y relative to normal type mid ocean ridge basalt the petrogenesis of these rocks requires high degrees of partial melting of a dehydrated subducting slab at low pressure the high fe tholeiites represent either direct partial melts of the slab or partial melts of the overlying mantle wedge which has been metasomatized by this slab melt these rocks provide evidence for the retention of ta nb and ti in subducting slabs and the subsequent isolation of these elements in the deep mantle thus explaining the lack of complementarity of ta nb and ti between the continental crust and depleted mantle conditions of higher heat flow and rapid subduction of young oceanic crust during the paleoproterozoic could have resulted in partial melting of the subducted slab at shallow depths

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

structural environment around th4 in silicate glasses implications for the geochemistry of incompatible me4 elements the structural environment around th4 in several silicate glasses containing 1 3 wt th4 was investigated as a function of melt composition and polymerization using extended x ray absorption fine structure exafs spectroscopy one set of glasses had the bulk chemical composition of monticellite mo diopside di anorthite an albite al olivine basalt o bas tholeiitic basalt t bas calc alkaline dacite dac and calc alkaline rhyolite rhy a second set of th bearing glasses had the bulk al composition but also contained either 5 5 wt f or 2000 ppm cl in glasses containing 3 wt th th coordination varies from 8 d viiith o 2 41 0 02 a in mo and di to a mixture of 8 and 6 coordinations d vi viiith o 2 35 2 36 0 02 a in all other compositions the presence of viiith is related to the thorianite tho2 saturation in the glass in al glasses containing 1 wt th 6 fold coordinated th dominates d vith o 2 32 0 02 a no clear evidence for f or cl complexes around th is observed in any of the halogen containing glasses weak but significant interactions of th with tetrahedral si al network and or alkali elements are observed especially in highly polymerized compositions rhy in which th si ai na k contributions are detected between 3 25 and 3 50 0 05 a these results suggest that in this set of glasses th does not form complexes but rather acts as a weak network modifier the presence of vith in silicate glasses an unusual low coordination for th suggests that the ionic radius of th in magmatic systems is lower than previously reported rth 0 94 a the resulting high th o bond strength 0 7 vu unknown in minerals may explain the observed low crystal melt partition coefficients of th4 i e its incompatible character during magmatic differentiation increasing polymerization is predicted to favor higher coordination around th viii ix as a result of a shortage of nbo to which th preferentially bonds hence dramatic changes in the crystal chemistry of th are predicted i e the incorporation of th in minerals comparison with u4 suggests that vith is less abundant in similar glass melt systems compared with viu this may explain the u th fractionation often observed in zircon as well as the preferential incorporation of th in accessory minerals containing large sites in which th4 can be substituted e g the ca2 site in titanite apatite or zirkelite

experimental study of avulsion frequency and rate of deposition in existing models of alluvial architecture it is typically assumed that mean avulsion frequency is independent of sedimentation rate however if avulsion is driven by superelevation of a river bed above its surrounding flood plain one might expect avulsion rate to increase with sedimentation rate we have carried out a series of experiments with laboratory scale fluvial fans in which we measured the frequency of apical avulsions as a function of mean sedimentation rate on the fan avulsion frequency increased strongly with increasing sedimentation rate and then stabilized as mass flows began to influence deposition in the regime of increasing avulsion frequency the added volume of sediment needed to trigger an avulsion decreased with increasing sedimentation rate although our experimental results cannot simply be scaled up to natural rivers they suggest the possibility of coupling between avulsion frequency and sedimentation rate that would be strong enough to change qualitatively the results of existing models of alluvial architecture these models should be applied with caution until avulsion mechanics are better understood

lutetium incorporation in magmas at depth changes in melt local environment and the influence on partitioning behaviour abstract the structure of two lu doped 4000 ppm model end member silicate liquids a highly polymerised haplogranite si al na k o and a less polymerised anorthite diopside si al mg ca o have been studied up to 8 gpa using in situ x ray diffraction techniques the results are the first to identify trace rare earth element incorporation in silicate melts at high pressure at pressures below 5 gpa the bonding environment of lu o was found to be dependent on composition with coordination number cn lu o 8 and bond distance r lu o 2 36 a in the haplogranite melt decreasing to cn lu o 6 and r lu o 2 29 a in the anorthite diopside melt this compositional variance in coordination number at low pressure is consistent with observations made for y o in glasses at ambient conditions and is coincident with a dramatic increase in the partition coefficients previously observed for rare earth elements with increasing melt polymerisation with increasing pressure we find that cn lu o and r lu o remain constant in the haplogranite melt however an abrupt change in both lu o coordination and bond distance is observed at 5 gpa in the anorthite diopside melt with cn lu o increasing from 6 to 8 fold and r lu o from 2 29 to 2 39 a this occurs over a similar pressure range where a change in the p dependence in the reported rare earth element partition coefficients is observed for garnet clinopyroxene and olivine melt systems this work shows that standard models for predicting trace elements at depth must incorporate the effect of pressure induced structural transformations in the melt in order to realistically predict partitioning behaviour

late quaternary paleoenvironments of the mahakam delta kalimantan indonesia abstract in order to trace the evolution of paleoenvironments within deltaic zones under an equatorial climate present day ecosystem tracers have been defined namely biological tracers benthic foraminifera and ostracods we thus obtained information with regards to salinity mainly with the help of foraminifera and carbonate equilibrium at the water sediment interfaces and thereby the intensity to which bottom organic matter degraded information was also obtained on the mixing of continental and marine waters as well as on the positioning of environments with respect to nlets mainly with the use of ostracods in the first 200 m of a core drilled along a length of 650 m these biomarkers clearly show four transgressive marine sequences since 125 000 yr b p becoming more intense towards the top they also show the sharp asymmetry existing in a transgression progradation cycle finally their importance in the impact of the deltaic plain s size is indicated all these characteristics contribute to the understanding of the evolutionary trend of such a system with respect to changes in parameters controlling the environment

a comparison of u pb and hf isotopic compositions of detrital zircons from the north and south liaohe groups constraints on the evolution of the jiao liao ji belt north china craton the jiao liao ji orogenic belt is one of the important paleoproterozoic mobile belts in the north china craton ncc and its central segment consists of the north and south liaohe groups and the liaoji granitoids the north and south liaohe groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies and the liaoji granitoids are divisible into 2 2 2 1 ga pre tectonic monzogranitic gneisses and 1 88 1 85 ga post tectonic porphyritic monzogranites and alkaline syenites combined with cathodoluminescence cl imaging we report la icp ms laser ablation inductively coupled plasma mass spectrometry u pb and hf isotopic data for detrital zircons from the north and south liaohe groups zircons grains from both groups have igneous zircon cores that yielded two u pb age populations at 2 0 2 2 ga major and 2 5 ga minor indicating that their provenances were similarly dominated by paleoproterozoic liaoji granitoids and late archean basement rocks some structureless zircon rims in both groups yield concordant or upper intercept ages 1 9 ga interpreted as the peak metamorphic age of the two groups these results suggest that both groups were deposited in the period 2 0 1 9 ga shortly after the emplacement of the liaoji granitoids moreover zircons from both groups have similar hf model age peaks t c dm peaks at 2 66 2 75 ga and 2 80 3 00 ga

dynamic particle segregation and accumulation processes in time and space revealed in a modern river dominated delta a spatiotemporal record of the kiso river delta central japan abstract the holocene succession of the kiso river delta a sand rich river dominated delta in central japan was analyzed at high temporal and spatial resolution the results demonstrate how the spatiotemporal distribution of sedimentary facies gross sediment accumulation rates and accumulation rates of mud versus sand relate to the geomorphic development of the delta and the post glacial sea level history the centers of peak mud and sand accumulation have migrated seaward in parallel during a regressive stage from 6 5 ka to the present at the rate of 3 9 m y the mud and sand accumulation centers mark the bottom and top respectively of the delta front slope the sediments of the prograding delta show strong sorting and clear upward coarsening because of the steep slope of the delta front such internal topographic control redistributes and separates the coarse and fine fractions of the fluvial input during regression the topographic controlled sedimentary segregation constructs delta front topography in reverse therefore the proportion of sand to mud in the fluvial input controls the stability of the delta front morphology our modeling of the kiso river delta may have implications for prediction of coastal flooding adjacent to deltas in other parts of the world

sediment trapping in deltas of small mountainous rivers of southwestern taiwan and its influence on east china sea sedimentation abstract taiwan s setting of high mountains steep gradients frequent earthquakes erodible lithology and heavy rainfall represents an ideal site to focus on sedimentary processes of the deltas of small mountainous rivers smrs several smrs in southwestern taiwan have deposited a thick sedimentary succession in the composite southwest taiwan delta swtd since the middle holocene evidence from the swtd can help to determine its trapping efficiency and assess the role of smrs in sediment transport to the sea we used historical nautical charts bathymetric data satellite radar data and 14c dates to calculate the sediment volume of the swtd on millennial and decadal scales the 14c dates of core samples indicate deposition of thick deltaic sediment in subsiding areas since the time of the maximum flooding surface about 7 cal ka bp the paleo shoreline changes of the swtd suggest a steady westward progradation since 7 cal ka bp in contrast the nautical charts suggest minor volume reduction of the offshore part of the swtd with a deepening trend and retreating shorelines during the last seven decades the results show that at least 201 72 13 90 km3 3 23 105 mt of sediment has been trapped in the swtd since 7 cal ka bp and that the delta has shifted to a destructive phase during the past seven decades as human influences such as construction of reservoirs dams and weirs in the hills have reduced the sediment supply the birth of the taiwan warm current and following continuous sediment supply from the western rivers of taiwan to the east china sea since 7 3 cal ka bp have played a crucial role in the sedimentation of the east china sea particularly in the okinawa trough and the japan sea through the tsushima warm current