tectonics of the paleoproterozoic jiao liao ji orogenic belt in the liaodong peninsula north china craton a review abstract a global collisional orogenic event that formed the columbia supercontinent occurred during 2100 1800 ma in the eastern north china craton ncc the paleoproterozoic jiao liao ji orogenic belt jljob composed of metamorphosed volcanic sedimentary rocks and intrusions may have preserved records of the collisional event tectonics of the jljob thus becomes the key to the understanding of the tectonic evolution of the ncc and may provide important information on assembly of the columbia supercontinent two classical models i e the rift closure model and arc continent collision model have been widely cited for the tectonic evolution of the jljob the former is based on occurrence of a type granites and bimodal volcanics within the orogenic belt and comparable archean blocks to the south and north of it while the latter is supported by occurrence of calc alkaline volcanics i type granites paired metamorphic belts and detrital zircon age constraints integration of literature results and our data we suggest that the jljob was formed by closure of a back arc basin at an active continental margin tectonic evolution of the jljob is subdivided into four stages i e pre orogenic stage at 2200 2060 ma transitional stage at 2060 1940 ma orogenic stage at 1940 1860 ma and post orogenic stage after 1860 ma

archean basement components and metamorphic overprints of the rangnim massif in the northern part of the korean peninsula and tectonic implications for the sino korean craton abstract the geology of the korean peninsula s northern part is little known to the international community even though this area is a critical link between various eastern asia terranes its tectonic architecture and geochronological framework are still gaps in knowledge this study reports integrated field geochemical and geochronological characteristics of the precambrian gneissic rocks from this region focusing on the rangnim massif the studied samples are divisible into three groups according to their field occurrence as granitic gneiss fine grained biotite gneiss and leuco veins the essential mineralogy of all these rocks is biotite bt muscovite mu plagioclase pl k feldspar kf and quartz the analyzed samples show high sio2 65 92 77 63 wt and al2o3 10 23 to 17 56 wt contents low mgo and cao their k2o contents is mostly higher than na2o sims secondary ion mass spectrometry zircon u pb dating of the eleven samples yields magmatic protolith ages of 2454 2567 ma and multiple metamorphic overprintings during the earliest paleoproterozoic 2 45 ga paleoproterozoic 1 87 1 93 ga and jurassic 160 ma the presence of these potassic granitoids in different locations indicate the high extent maturation of neoarchean continental crust in the rangnim massif zircon lu hf isotopic results of these samples show large variations mostly plotting between the depleted mantle linear model line and chondritic uniform reservoir chur line but some have negative ehf t values considering that their protoliths are all crust melting products it can be concluded that the neoarchean magmatism incorporated both juvenile crustal components as well as a reworking of older crust this is supported by the detection of rare early archean xenocrysts based on juvenile crust having ehf values of 0 before 3500 3600 ma it is concluded that the reworked components were eoarchean in age not hadean magmatic as well as precambrian metamorphic pulses of the rangnim massif show broad similarities with the eastern north china craton gyeonggi and yeongnam massifs and southwest japan which seem to suggest that they might share a coherent precambrian basement and evolutionary history at least before the end of late paleoproterozoic

multiple 3 8 3 1 ga tectono magmatic events in a newly discovered area of ancient rocks the shengousi complex anshan north china craton abstract near anshan city in the north china craton the oldest rocks in asia 3300 ma have been thoroughly documented at two localities baijiafen and dongshan in this paper we report the full geological context for more ancient rocks from a third anshan locality the polyphase migmatite shengousi complex shrimp u pb zircon dating indicates a protracted tectono magmatic history for the shengousi complex the oldest recognised component is banded trondhjemitic gneiss 3773 6 ma which is veined by strongly deformed granitic pegmatite these occur with a second generation of trondhjemitic rocks 3454 8 and 3448 9 ma the next generation of plutonic rocks is a composite suite of iron enriched mafic dykes 3332 6 and 3331 8 ma with broadly coeval felsic veins 3311 4 ma finally there was intrusion of monzogranite 3129 6 ma strong deformation has generally brought these 3773 3129 ma plutonic phases into close concordance to form banded rocks however locally cross cutting relationships are preserved in small lower strain domains that give a relative chronology agreeing with the absolute zircon u pb chronology all of this complex history is recorded in a single some of the the 3450 ma igneous phases discovered in the shengousi complex are new ages for igneous rocks in the anshan area the precambrian geology of the anshan area is thus marked by polyphase eoarchaean orthogneisses the newly recognised 3450 ma phases widespread 3360 3300 magmatic activity found in association with mesoarchaean plutonic rocks and the neoarchaean anshan group and palaeoproterozoic liaohe group metasedimentary rocks this shows that the geology of the anshan area has a strong similarity with the narryer gneiss complex of western australia which contains the polyphase eoarchaean meeberrie gneisses the 3490 3440 ma eurada gneiss association 3300 ma granites and migmatisation and is intercalated with younger precambrian metasedimentary rocks of different ages containing hadean detrital zircons no other ancient gneiss complexes in the world show such a close match in their history with the anshan area rocks this means that the anshan area is prospective for locating new occurrences of hadean crustal components intercalated with younger sedimentary rocks

neoproterozoic granitoid in northwest sulu and its bearing on the north china south china blocks boundary in east china 1 middle neoproterozoic granitoid rocks are found in the wulian region that is located in the northwestern part of the sulu orogen and is approximately bounded by the wulian yantai fault in southeast zircon u pb dating yields concordant ages of 738 10 to 758 5 ma for three granites and one gabbro hornblende ar ar dating on the gabbro gives consistent plateau and isochron ages of 719 1 3 7 and 717 9 7 2 ma respectively this suggests that the wulian granitoids correspond to bimodal magmatism during the mid neoproterozoic in the northern margin of the south china block in response to the breakup of rodinia supercontinent they were tectonic slices scraped off from the upper part of the south china block during the triassic continental subduction this demonstrates that the suture location between the north china block and the south china block lies north of the wulian and penglai groups rather than along the wulian yantai fault that marks the northern margin of ultrahigh pressure metamorphic belt

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

arc generated metavolcanic rocks in the anshan benxi greenstone belt north china craton constraints from geochemistry and zircon u pb hf isotopic systematics abstract the anshan benxi granite greenstone belt abgb in the eastern block of the north china craton mainly comprises supracrustal rocks of amphibole plagioclase gneisses plagioclase amphibolites chlorite schists biotite schists quartzites and banded iron formations bifs and intrusive monzogranitic to syenogranitic gneisses based on geology spatial distributions lithologies and zircon u pb geochronology the metavolcanic rocks of the southern abgb can be divided into the 2527 ma southern plagioclase gneiss group 2536 ma southern amphibolite group 2574 to 2560 ma northern chlorite schist group and northern amphibolite group from south to north these rocks outcrop as stratified and stratoid beds whereas some occur as enclaves within later intrusive k rich granitic gneisses the southern plagioclase gneiss group exhibits calc alkaline andesite compositions with high mgo cr and ni fractionated ree patterns and depletion in nb ta which resemble high magnesian andesite hma and are derived from the partial melting of sub arc mantle peridotite that was previously metasomatized by slab melts the southern amphibolite group has tholeiitic basalt compositions with slight enrichment in lrees and high nb ti concentrations but low nb la pm ratios which coincide with nb enriched basalt and are generated by the remelting of residues of sub arc mantle after the extraction of hma melts the northern schist group shows high k calc alkaline andesite dacite compositions and have highest silica and potassium and obvious enrichment in lrees and liles and depletion in nb ta which are comparable to the sanukitoid series rocks these rocks probably formed by low degree partial melting of a sub arc mantle wedge that was metasomatized by slab derived fluids the northern amphibolite group exhibits tholeiite compositions with unfractionated ree patterns and low nb la pm ratios which are consistent with back arc basin basalts babb and are produced by partial melting of depleted mantle combined with lithological associations of the hma neb sanukitoid like rocks and babb like rocks the anshan benxi granite greenstone belt was produced under a convergent plate environment both the zircon ehf values and petrogenesis indicate that the four groups of the metamorphic volcanic rocks directly contributed to continental crustal growth integrating with the widespread 2 5 ga syenogranites and subordinate k rich granitoids that were derived from reworking of ancient crust we propose that the abgb experienced a significant episode of continental growth dominated by a subduction related lateral accretion accompanied with contemporaneously strong reworking of ancient crustal materials

geochronological constraints on the genesis of high grade iron ore in the gongchangling bifs from the anshan benxi area north china craton abstract the gongchangling iron deposit located in the northeast of the north china craton is hosted in late neoarchean algoma type bifs it is famous for the major production of high grade iron ore in the gongchangling no 2 mining area in china with regard to the genesis of high grade iron ore more and more evidences indicate that it was related with hydrothermal enrichment of bifs however the hydrothermal nature was argued for meteoric metamorphic or migmatitic fluid in this study the trace element compositions of garnet from the altered wall rock of high grade iron ore obtained by la icp ms show compositional zoning indicating it is a metamorphic origin these garnets yield a sm nd isochron age of 1888 77 ma interpreted as the time of metamorphism in this area la icp ms u pb dating of zircon from the upper migmatite zone shows that the migmatitic granite was formed at 2478 36 ma since the ree patterns of garnet suggest that it was formed in the nearly neutral fluid rather than the acid meteoric fluid in the paleoproterozoic hence combined the ages of metamorphism and migmatization with high grade iron ore of 1840 7 or 1860 7 ma obtained by previous studies it indicates that the genesis of the high grade iron ore derived from the enrichment of bifs by metamorphic hydrothermal fluid

patterns of water 87sr 86sr variations in oil gas and water saturated rocks implications for fluid communication processes distances and timescales abstract this study reviews 87sr 86sr depth profiles of formation waters sampled by sr residual salt analysis sr rsa from 100 oil gas wells and research sites including reservoirs with clastic and carbonate host rocks and with gas oil and water as the continuous fluid phase globally the water data form a smooth trend between low seawater like 87sr 86sr ratios 0 706 at shallow depths and high 0 724 ratios in deeply buried rocks where water rock interaction dominates we test the hypothesis that 87sr 86sr depth profiles in individual wells could be influenced by diffusional mixing processes by developing 1d diffusion mixing equations to simulate compositional patterns through time and comparing them with observed profiles different combinations of boundary and initial conditions generate various patterns characteristic of diffusion including non steady state curves relating to incomplete mixing and steady state patterns such as vertical or inclined straight lines where initial heterogeneities have fully mixed the dataset yielded 193 occurrences of these patterns steady state patterns are more common and longer in water zones while non steady state patterns are more common and longer in oil and gas zones the detection of diffusional mixing patterns in hydrocarbon saturated rocks suggests that diffusion is active although on average a factor of 13 18 slower than in comparable water saturated rocks pattern generation and equilibration times were modelled for each non steady state pattern and compared with the time since reservoir filling with oil gas revealing that 90 of them could have been generated since filling but 60 of them would already have mixed to steady state had the initial compositional heterogeneities arisen during or before reservoir filling this is critical evidence that at least some of the initial heterogeneities must have arisen and subsequently partially mixed after filling these patterns tend to be short the evidence for post fill water rock interaction and diffusive transport has important implications for porosity permeability prediction indicating that key diagenetic processes like quartz cementation may be inhibited by hydrocarbon filling but not stopped altogether compositional differences of water within oil gas zones reveal the folly of using one aquifer water sample as the basis for interpreting water saturations from well resistivity logs for in place resource estimation sr rsa studies may thus be useful in designing water sampling strategies

late archean sm nd isochron age for mafic ultramafic supracrustal amphibolites from the northeastern sino korean craton china isotopic data published by previous workers document the presence of early archean 3 5 ga metabasaltic enclaves in grey gneisses west of bohai bay eastern hebei province p r c metabasaltic and metakomatiitic amphibolites crop out as lower supracrustal members of the archean section northeast of bohai bay in southern jilin eastern liaoning provinces six analyzed specimens of the latter unit contain more magnesium on analysis averaging approximately 13 vs 7 wt percent mgo but although they exhibit a wider range of ree concentrations they average a similar range of ree abundance patterns la lu 24 7x chondrite as the former 24 9 chondrite new sm nd isotopic and ree analyses combined with available petrologic geologic information indicate that metakomatiitic amphibolites from the sino korean craton northeast of bohai bay are late archean in emplacement age a wholerock sm nd isochron age of 2660 75 2 ma was obtained with nd t 4 4 0 5 as in many parts of the sino korean craton the highly positive nd t value suggests a prior extended history 1 0 ga of depletion of subcontinental mantle sources in some incompatible elements and in lree relative to hree a seventh analyzed sample a mafic inclusion in tonalitic gneiss of unknown age has an unusual chemical composition with strong enrichment in lree sr and zr and severe depletion in ni and cr judging from isotopic data which yield a much younger depleted mantle model age of 1 67 ga it could represent a cognate xenolith in a mid proterozoic tonalitic intrusion shown on present maps as archean in age the protolith might have been an evolved alkali basalt

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

a strontium oxygen and hydrogen isotopic composition of brines michigan and appalachian basins ontario and michigan abstract 87 sr 86 sr ratios of brine from samples from the michigan and appalachian basins in ontario and michigan covering the stratigraphic interval from the cambrian to mississippian vary from 0 708 to 0 711 with the exception of the salt units of the salina formation silurian most values are greater than seawater for the time in question indicating water rock interaction the sources of the radiogenic sr has not been identified all samples plot below the gmwl in 18 o 2 h space with the cambrian and ordovician samples closest to the line mixing of brines meteoric and glacial pleistocene water is indicated in some cases the more concentrated brines from each stratigraphic unit show a very narrow spread in values all the ordovician brines show a narrow range over a 200 km area for sr o and h isotopes indicating extensive lateral migration of the fluids strontium in the brine has not equilibrated isotopically with its host rock in some cases the late stage minerals saddle dolomite calcite and anhydrite have the same 87 sr 86 sr ratios as the brine indicating that they precipitated from the brine in isotopic equilibrium

deformation history of the paleoproterozoic liaohe assemblage in the eastern block of the north china craton the paleoproterozoic liaohe assemblage and associated liaoji granitoids represent the youngest basement in the eastern block of the north china craton various structural elements and metamorphic reaction relations indicate that the liaohe assemblage has experienced three distinct deformational events d1 to d3 and four episodes of metamorphism m1 to m4 the earliest greenschist facies event m1 is recognized in undeformed or weakly deformed domains wrapped by the s1 schistosity suggesting that m1 occurred before d1 the d1 deformation produced small mostly meter scale isoclinal and recumbent folds f1 an associated penetrative axial planar schistosity s1 a mineral stretching lineation l1 and regional scale ductile shear zones concurrent with d1 was m2 metamorphism which occurred before d2 and produced low to medium pressure amphibolite facies assemblages regionally divergent motion senses reflected by the asymmetric f1 folds and other sense of shear indicators together with the radial distribution of the l1 lineation surrounding the liaoji granitoids imply that d1 represents an extensional event the d2 deformation produced open to tight f2 folds of varying scales s2 axial crenulation cleavages and ene ne striking thrust faults involving broadly nw se compression following d2 was m3 metamorphism that led to the formation of sillimanite and cordierite in low pressure type rocks and kyanite in medium pressure rocks the last deformational event d3 formed nw wnw trending folds f3 axial planar kink bands spaced cleavages s3 and strike slip and thrust faults which deflect the earlier d1 and d2 structures d3 occurred at a shallow crustal level and was associated with or followed by a greenschist facies retrograde metamorphic event m4 the liaohe assemblage and associated liaoji granitoids are considered to have formed in a paleoproterozoic rift the late spreading of which led to the occurrence of the early extensional deformation d1 and the m1 and m2 metamorphism and the final closing of which was associated with the d2 and d3 phases of deformation and m3 and m4 metamorphism

use of historical elevation data to calculate surface elevation and volume changes of ha iltzuk icefield southwest british columbia canada 1970 to mid 1980s investigations into glacial changes including understanding variations in the rates of glacial volume and surface elevation changes have increased over the past decade this study uses historical glacier elevation data in the form of topographic maps from 1970 and a digital elevation model from the mid 1980s to calculate surface elevation and volume changes for ha iltzuk icefield southwest british columbia canada results indicate that the icefield thinned at an average rate of 0 76 0 25 m a 1 during this period a previous study of ha iltzuk icefield also using the geodetic method found a thinning rate of 1 0 0 20 m a 1 between the mid 1980s and 1999 indicating a slight increase in the amount of icefield thinning within the ablation zone thinning increased with decreasing elevation at a rate of 1 9 0 68 m a 1 km 1 between these two periods 1970 to mid 1980s versus mid 1980s to 1999 analysis of meteorological data suggests that increases in both temperature and rainfall as well as decreases in snowfall likely contributed to the increased thinning rate

archean to paleoproterozoic evolution of the north china craton preface abstract as one of representative cratons in china the north china craton records a long term and complicated tectonic history including the formation of eoarchean continental nucleus neoarchean continental crustal growth and reworking paleoproterozoic amalgamation of micro blocks and formation of orogenic belts related to the columbia supercontinent and formation of late paleoproterozoic to early neoproterozoic rifts in recent years extensive geochemical geochronological magmatic and metamorphic structural and geophysical investigations have been carried out on the north china craton which have resulted in a series of new achievements and some percussive interpretations of the precambrian continental crustal formation and evolution these new data and results allow us to make a correct judgment for organizing this special issue in which representative and creative experts currently working in the craton exhibit outcomes of their research on the craton thirty nine contributions have been collected in this special issue which provide insightful understanding of the components magmatism and metamorphism metallogeny and tectonic evolution of the north china craton and give an insight into discussion about some key issues on the basis of new data and interpretation such a special issue will not only make a timely addition to the literatures on the precambrian research field but will also open a new window through which the international geological community will adequately understand what major advancements have been obtained in the precambrian geology of the north china craton and what issues are still unresolved and controversial at present

short term flow dynamics of a retreating tidewater glacier leconte glacier alaska u s a an analysis of motion in the terminus region of leconte glacier alaska u s a delineates mechanisms that are important to tidewater glacier stability this glacier is undergoing rapid retreat since 1995 it has retreated 2 km and thinned 125 m at the present location of the terminus ice velocities in this region are quite high at the terminus they exceed 27 m d 1 our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides surface melt and precipitation the near terminus ice speed is 180 out of phase with the tide such that high tide corresponds to low speed smaller melt forced diurnal variations in speed are present throughout the lowermost 7 km speed ups in excess of 10 of the mean often occur after rainstorms as a result of increased basal water pressure and storage but the relation is not simple the velocity does not vary over the spring and summer seasons

saline groundwaters in the canadian shield a first overview abstract the chemical and isotopic compositions of saline groundwaters and brines in the canadian shield are described the occurrence of such waters is very widespread not related to any specific rock type or mineralization and generally can be expected at depths below 1 km the most saline brines have salinities exceeding 200 g l 1 dissolved solids and their chemistries tend to suggest that in the past saline waters penetrated the canadian shield the original chemistry of these solutions was subsequently modified through strong rock water interactions and it appears that their final chemical compositions are independent of the original chemistries stable isotope analyses indicate that these waters are not simple evaporated seawater sedimentary basin brines hydrothermal solutions or residual ore forming fluids although any of these could be a precursor of the brines secondary isotope exchange reactions and the hydration of primary silicates accompanied by the formation of clay minerals could have modified not only the primary isotopic composition but may have also profoundly influenced the chemistries of these brines to be effective these processes would have had to occur in closed systems

surge of bering glacier and bagley ice field alaska an update to august 1995 and an interpretation of brittle deformation patterns in the summers of 1993 1994 and 1995 video and global positioning system location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the bering glacier and bagley ice field system alaska in an effort to characterize surge crevasse patterns and surge propagation during survey flights in late august 1995 we observed that the 1993 94 bering glacier surge was continuing and still expanding affecting new areas farther up in bagley ice field new crevasse fields similar in pattern to the first surge crevasses we had observed in june 1993 below khitrov hills and in other isolated areas of central bering glacier and in july 1994 near the head of bering glacier near the junction of bering glacier and bagley ice field in both upper bering glacier and bagley ice field were opening in eastern bagley ice field and in the steller side of bagley ice field the type of crevasses seen in the new fields suggested that the surge was propagating into these areas by analysis and interpretation of the brittle deformation patterns apparent in the crevasse patterns some aspects of the past kinematic framework of the surge can be deduced this approach may lead to a more general classification of ice surface structures and to their linkage to ongoing processes

nd isotopic constraints on crustal formation in the north china craton abstract recent tectonic analysis suggests that the north china craton consists of two archean continental blocks called the eastern and western blocks separated by the paleoproterozoic trans north china orogen although the published geochronological data are not sufficient to constrain the detailed tectonothermal evolution of the craton the available nd isotopic data show some important differences in nd model ages between the tectonic units the eastern block shows two main nd model age peaks one between 3 6 and 3 2 ga and the other between 3 0 and 2 6 ga limited nd isotopic data from the western block show a large range of model ages between 3 2 and 2 4 ga these differences are consistent with the recently proposed model the nd isotopic data from mantle derived mafic rocks indicate that the mantle beneath the north china craton was depleted in the archean consistent with major crustal growth during this period in the paleoproterozoic however the mantle derived mafic rocks show negative end t values implying crustal contamination this may have resulted from subduction and collision between the eastern and western block implying that the mechanisms of crustal formation and evolution may have been different between the archean and paleoproterozoic the north china craton was re activated by addition of mantle derived magma into the lower crust in the late mesozoic resulting in rejuvenation of the lower crust this indicates that underplating is also an important mechanism for continental addition although in this case it may not equate to crustal growth since it was preceded by removal of lithospheric mantle and possible some lower crust

the nature of groundwater flow in fractured rock evidence from the isotopic and chemical evolution of recrystallized fracture calcites from the canadian precambrian shield abstract the isotope geochemistry of fracture calcites in three precambrian plutons on the canadian shield has been investigated in order to understand the paleohydrogeological conditions in fractured crystalline rock fracture calcites of ancient hydrothermal origins in the chalk river and east bull lake plutons exhibit 18o enrichment and 13c depletion trends resulting from recent low temperature calcite recrystallization under open system conditions for oxygen but semiclosed for carbon and under extremely variable time integrated water rock calcite ratios this process causes recycling of elements with calcite distribution coefficients 1 rare earths manganese and possibly iron from the precursor calcite to younger calcites as well as calcite control over the 87 sr 86 sr ratio of the groundwater within the chalk river pluton the large but variable water rock calcite mole ratios calculated from the shifts in the stable isotopic compositions of fracture calcites are compatible with fracture flow models that invoke flow channeling within single fractures that also contain regions of immobile porosity quantification of isotopic shifts resulting from recrystallization requires that the initial isotopic composition of the precursor hydrothermal calcite be well constrained unlike the chalk river and east bull lake plutons hydrothermal fracture calcites in the white lake pluton which intrudes marble rich country rocks of the grenville supergroup have highly variable 13c and 18o values this is attributed to mixing of carbon from magmatic and sedimentary reservoirs and to oxygen isotopic exchange between hydrothermal fluids and carbonate country rocks at the time of intrusion convective circulation of meteoric groundwater from the surrounding 13c rich carbonate rocks up to 6 6 resulted in 13c values as heavy as 3 0 for the fracture calcites in the pluton

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

measurement of ice sheet topography using satellite radar interferometry detailed digital elevation models dems do not exist for much of the greenland and antarctic ice sheets radar altimetry is at present the primary in many cases the only source of topographic data over the ice sheets but the horizontal resolution of such data is coarse satellite radar interferometry uses the phase difference between pairs of synthetic aperture radar sar images to measure both ice sheet topography and surface displacement we have applied this technique using ers 1 sar data to make detailed i e 80 m horizontal resolution maps of surface topography in a 100 km by 300 km strip in west greenland extending northward from just above jakobshavns isbrae comparison with a 76 km long line of airborne laser altimeter data shows that we have achieved a relative accuracy of 2 5m along the profile these observations provide a detailed view of dynamically supported topography near the margin of an ice sheet in the final section we compare our estimate of topography with phase contours due to motion and confirm our earlier analysis concerning vertical ice sheet motion and complexity in ers 1 sar interferograms

multiple alteration events in the east bull lake anorthosite gabbro layered complex ne ontario canada evidence from fracture mineralogy and40ar 39ar dating abstract the east bull lake anorthosite gabbro layered complex contains a variety of alteration minerals some of the more common ones are calcic amphiboles biotite epidote adularia quartz chlorite calcite prehnite pumpellyite laumontite gypsum iron hydroxides and clays the mode of occurrence and the data related to the stability of the alteration minerals suggest that they were formed under pressure temperature conditions of 1 epidote amphibolite greenschist facies 2 prehnite pumpellyite facies 3 zeolite facies and 4 low temperature mineral facies 40 ar 39 ar data of hornblende and adularia indicate that the pluton is affected by distinct alteration events two mafic dyke intrusions that overlap the alteration events are recognised in the pluton synthesis of available radiometric ages suggests that the pluton intruded at 2472 70ma and was subjected to alteration as late as the paleozoic and cenozoic eras

estimating volume change of mountain glaciers using srtm and map based topographic data this paper describes a method for estimating the volume change of mountain glaciers using the shuttle radar topography mission srtm c band data 2000 and a digital elevation model dem generated from topographic maps this approach was developed with srtm data and topographic maps of 1 25 000 scale 1977 from the akshiirak glaciers tien shan central asia the dem for 1977 was generated using 10 m contour lines from 18 map sheets covering the akshiirak massif and surrounding area the nominal vertical accuracy of the maps is 3 3 m the standard deviation of the differences between the map derived dem and the srtm data on glacier free areas of less than 25deg is 6 3 m a single localized region in the western periphery of the study area with systematic error in the srtm data from 20 to 12 m on a 30 km spatial scale was found and excluded from the error analysis assuming a 10 m map error on the upper snow covered glacier areas the estimated root mean square error of the glacier surface change is 8 2 m from 1977 to 1999 the average glacier surface thinning is 15 1 m and the estimated volume loss is 6 15 km3 the rate of the akshiirak glacier volume loss has increased by 2 7 times compared with historical data from 1943 to 1977 the srtm data show an opportunity for quantifying climatic and dynamic surface elevation changes in mountain glaciers ice cloud and land elevation satellite icesat laser altimetry and srtm data could also be used for the estimation of short term surface changes of mountain glaciers

the use of strontium isotopes in determining groundwater mixing and brine fingering in a playa spring zone lake tyrrell australia j hydrol 167 225 239 playas in arid and semi arid regions can be important regional groundwater discharge zones located in the northwestern portion of victoria australia lake tyrrell is a large playa that serves as a major discharge zone of regional groundwater the chemistry of the regional groundwater is unique having salinities of approximately 30 g 1 1 and ph values as low as 2 8 as the regional groundwater is discharged along the western edge of the playa in the spring zone it is evapo concentrated into a dense brine which sinks through the playa sediments macumber s pioneering work on the geohydrology of this region established that this denser reflux brine below the playa surface has evolved from the evaporation of regional groundwaters we have measured the 87sr 86sr ratio of a number of groundwater samples taken at shallow depths along the spring zone at the playa edge and compared them with the regional groundwaters and the reflux brine our data reveal a rather complex pattern of mixing of the various water masses associated with the playa system most probably the result of density driven convective plumes two types of regional groundwater can be identified based on their 87sr 86sr values with groundwater from the south being less radiogenic than that flowing from the north i e 0 7108 vs 0 7142 vertical variations in 87sr 86sr in the regional groundwaters observed in wells adjacent to the spring zone can also be identified along a vertical gradient in the spring zone besides the hydrogeological information provided by these measurements the strontium isotope variations allow us to evaluate the source of strontium to these waters the regional groundwaters south of the lake are very similar in 87sr 86sr ratio to the reflux brines whereas the northern regional groundwaters are comparatively enriched in 87sr this enhanced 87sr signature indicates the addition of sr along the flow path via the weathering of the aquifer material the miocene parilla sand the southern waters have 87sr 86sr values closer to that of present day seawater and or miocene seawater indicating that the major source of sr to the system is from one or both of these sources our results demonstrate that strontium isotopes can be extremely useful in studying the dynamics as well as the geochemistry of surface water groundwater interactions

geochemical and isotopic evidence for a genetic link between canadian shield brines dolomitization in the western canada sedimentary basin and devonian calcium chloridic seawater hypersaline brines of marine origin deep within fractured crystalline rocks of the canadian shield are characterized by calcium chloride compositions with relatively low concentrations of magnesi

in situ zircon u pb dating and whole rock geochemistry of metasedimentary rocks from south liaohe group jiao liao ji orogenic belt constraints on the depositional and metamorphic ages and implications for tectonic setting abstract the liaohe group is an important paleoproterozoic lithostratigraphic unit of the jiao liao ji orogenic belt and traditionally subdivided into the north and south liaohe groups however their tectonic setting and evolution are still a matter of debate the precise depositional and metamorphic data of the studied metasedimentary rocks from the south liaohe group provide important information on the controversial discussion of the tectonic setting and evolution based on cathodoluminescence cl imaging and connecting la icp ms u pb geochronology zircon grains separated from metasedimentary rocks of different formations of the south liaohe group were subdivided into detrital and metamorphic zircons or zircon domains igneous zircon cores of detrital zircons of the li eryu gaojiayu dashiqiao and gaixian formations yield u pb age peaks at 2130 ma 2520 ma 2160 ma 2500 ma and 2040 ma indicating that their sediments were transported from the liaoji granitoids the archean basement rocks of the adjacent complex in addition deposition age of the sedimentary precursors was investigated which must have taken place at some time after 2 05 ga 2 07 ga 2 04 ga and 1 92 ga respectively these new geochronological data can be well explained by 1 a continent arc collision model which suggests that the south liaohe group formed an intervening island arc and foreland basin sandwiched between the longgang and nangrim complexes and 2 a northward subduction of the nangrim complex source rocks of the south liaohe group these source rocks were successively deposited along the margin of the two complexes

structural deformation and mineralization in the early proterozoic liaojitite suite eastern liaoning province china abstract the liaojitite suite located in eastern liaoning province china formed in the eugeosyncline of an early proterozoic mobile zone structural deformation occurred during several orogenic episodes especially during the second deformation of the third episode the luliang orogeny 1900 2000 ma ago superposed dome shaped structures and their unevenly distributed groups formed during the luliang orogeny constitute the principal tectonic style in the mobile zone the tectonic style may be considered transitional in the evolution from an oval style in archean granite greenstone terrains to a linear style in phanerozoic terrains the superposed dome shaped structures contain the liaoji granite in the cores ringed successively by the boron bearing series and the outer turbidite series the simple appearances of the dome shaped structures mask their complicated multiply deformed nature which is revealed by tracing their formation and evolution from primary volcanic domes to granitic diapirs and finally to superposed dome shaped structures the evolution of the superposed dome shaped structures represents a change in crustal activity from simple shear to horizontal compression mineralization in the liaojitite suite was closely related to the three deformations of the luliang orogeny metallogenic elements were concentrated during the first deformation physical re emplacement of orebodies occurred during the second and third deformations

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

are the south and north liaohe groups of north china craton different exotic terranes nd isotope constraints abstract the liaohe group is an important paleoproterozoic stratigraphic unit in the northeastern part of the north china craton and is traditionally subdivided into the north and south liaohe groups associated with both the north and south liaohe groups are voluminous paleoproterozoic granitoid rocks named the liaoji granitoids different tectonic models including terrane amalgamation continent arc collision and rift closure have been proposed to interpret the tectonic setting and evolution of the north and south liaohe groups and associated liaoji granitoids at the centre of the controversy between these models is whether or not the north and south liaohe groups developed on the same archean basement nd isotopic geochemistry of the liaoji granitoids provides important constraints on this controversial issue the liaoji granitoids associated with the north and south liaohe groups display similar e nd values restricted to a narrow range from 0 to 2 implying that these granitoid rocks were derived from the same or a similar magma source moreover the liaoji granitoids associated with the north and south liaohe groups have similar nd model ages t dm ranging from 2 4 to 2 6 ga suggesting that the protoliths of the liaoji granitoids associated with both groups may have formed simultaneously and that the basement rocks underneath the liaoji granitoids and associated north and south liaohe groups belong to the same continental block rather than two different blocks combining lithological structural and geochronological considerations we interpret the north and south liaohe groups as having developed on a single late archean basement that underwent paleoproterozoic rifting associated with the intrusion of the liaoji granitoids and the formation of the liaohe group and closed upon itself in the paleoproterozoic

strontium isotope geochemistry and its geochemical implication from hot spring waters in south korea abstract despite being a non volcanic area the southern korean peninsula has a number of hot water springs with temperatures more than 40 c most of which are commercially used for spa the hot springs are located at the fringes of the granite body rather than the center of the mesozoic granite here we report on the geochemical characteristics of the hot water springs the hot springs in the jurassic granite area are mainly of na ca hco 3 type whereas those in the cretaceous granite area are of na cl so 4 type the stable isotope composition of o and h suggests a meteoric origin of the hot spring water further the chemical components of the hot spring waters indicate that they were all derived from hot spring water rock interaction rather than through anthropogenic input the 87 sr 86 sr ratio of the hot spring waters in the jurassic granite area ranges from 0 711088 to 0 729034 and that in the cretaceous granite area ranges from 0 705652 to 0 707912 such 87 sr 86 sr ratio distribution of hot spring waters corresponds with the distribution of the initial 87 sr 86 sr ratios for the emplacement age of the jurassic and cretaceous granites in the hot spring occurrence area the 87 sr 86 sr ratios in the hot spring waters were also divided into three groups according to their geographical location eastern western and southern groups the constant 87 sr 86 sr ratio of hot spring water from one hot spring area during the last 6 years strongly suggests that the hot spring bearing aquifer system in south korea should be separated from the upper cold shallow groundwater system this indicates that the 87 sr 86 sr ratio of the hot spring waters in the granite area of south korea originates from an equilibrium because of long term water rock interaction rather than short term water rock interaction due to the input of recent meteoric water hence it may be concluded that hot spring water in the granite area may be a limited deep groundwater resource that might deplete with overuse

airborne and spaceborne dem and laser altimetry derived surface elevation and volume changes of the bering glacier system alaska usa and yukon canada 1972 2006 using airborne and spaceborne high resolution digital elevation models and laser altimetry we present estimates of interannual and multi decadal surface elevation changes on the bering glacier system alaska usa and yukon canada from 1972 to 2006 we find 1 the rate of lowering during 1972 95 was 0 9 0 1 m a 1 2 this rate accelerated to 3 0 0 7 m a 1 during 1995 2000 and 3 during 2000 03 the lowering rate was 1 5 0 4 m a 1 from 1972 to 2003 70 of the area of the system experienced a volume loss of 191 17 km 3 which was an area average surface elevation lowering of 1 7 0 2 m a 1 from november 2004 to november 2006 surface elevations across bering glacier from mcintosh peak on the south to waxell ridge on the north rose as much as 53 m up glacier on bagley ice valley about 10 km east of juniper island nunatak surface elevations lowered as much as 28 m from october 2003 to october 2006 nasa terra modis observations from may to september 2006 indicated muddy outburst floods from the bering terminus into vitus lake this suggests basal englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006

strontium isotope geochemistry of groundwaters and streams affected by agriculture locust grove md the effects of agriculture on the isotope geochemistry of sr were investigated in two small watersheds in the atlantic coastal plain of maryland stratified shallow oxic groundwaters in both watersheds contained a retrievable record of increasing recharge rates of chemicals including no3 cl mg ca and sr that were correlated with increasing fertilizer use between about 1940 and 1990 the component of sr associated with recent agricultural recharge was relatively radiogenic 87sr 86sr 0 715 and it was overwhelming with respect to sr acquired naturally by water rock interactions in the oxidized non calcareous portion of the saturated zone agricultural groundwaters that penetrated relatively unoxidized calcareous glauconitic sediments at depth acquired an additional component of sr from dissolution of early tertiary marine caco3 87sr 86sr 0 708 while undergoing o2 reduction and denitrification ground water discharge contained mixtures of waters of various ages and redox states two streams draining the area are considered to have higher 87sr 86sr ratios and no3 concentrations than they would in the absence of agriculture however the streams have consistently different 87sr 86sr ratios and no3 concentrations because the average depth to calcareous reducing denitrifying sediments in the local groundwater flow system was different in the two watersheds the results of this study indicate that agriculture can alter significantly the isotope geochemistry of sr in aquifers and streams and that the effects could vary depending on the types sources and amounts of fertilizers added the history of fertilizer use and groundwater residence times

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

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

tectonothermal history of the basement rocks in the western zone of the north china craton and its tectonic implications the basement of the north china craton can be divided into the eastern central and western zones based on lithological structural metamorphic and geochronological data the western zone comprises two different petrotectonic units archaean tonalitic trondhjemitic granodioritic ttg grey gneisses and metamorphic mafic rocks and palaeoproterozoic khondalite series the former is characterized by isobaric cooling ibc type anticlockwise p t paths in the north northwestern part of the zone and near isothermal decompression itd type clockwise p t paths in the eastern part adjacent to the central zone on the other hand the tectonothermal evolution of palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling defining clockwise p t paths the archaean ttg gneisses and associated mafic rocks with anticlockwise metamorphic p t paths reflects an origin related to underplating and intrusion of mantle derived magmas which may be derived from mantle plumes they represent a late archaean continental block in the western part of the north china craton the palaeoproterozoic khondalite series rocks represent passive continental margin deposits they were metamorphosed and deformed in the late palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the north china craton the itd type clockwise p t t paths of the palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the north china craton at c 1800 ma

comparison of the sr isotopic signatures in brines of the canadian and fennoscandian shields abstract a synthesis of sr isotope data from shallow and deep groundwaters and brines from the fennoscandian and canadian shields is presented a salinity gradient is evident in the water with concentrations varying from approximately 1 75 g l 1 below 1500 m depth in the fennoscandian shield and from 10 up to 300 g l 1 below 650 m depth in the canadian shield strontium isotope ratios were measured to assess the origin of the salinity and evaluate the degree of water rock interaction in the systems in both shields the sr concentrations are enriched relative to cl defining a positive trend parallel to the seawater dilution line and indicative of sr addition through weathering processes the depth distribution for sr concentration increases strongly with increasing depth in both shields although the variation in sr isotope composition does not mirror that of sr concentrations strontium isotope compositions are presented for surface waters and groundwaters in several sites in the fennoscandian and canadian shields numerous mixing lines can be drawn reflecting water rock interaction a series of calculated lines links the surface end members surface water and shallow groundwater and the deep brines these mixing lines define a range of 87 sr 86 sr ratios for the deep brines in different selected sites all sites show a specific 87 sr 86 sr signature and the occurrence of large 87 sr 86 sr variations is site specific in both shields in canadian shield brines the sr isotope ratios clearly highlight large water rock interaction that increases the 87 sr 86 sr ratio from water that could have been of marine origin in contrast to the canadian shield groundwater does not occur in closed pockets in the fennoscandian and the well constrained 87 sr 86 sr signatures in deep brines should correspond to a large well mixed and homogeneous water reservoir whose sr isotope signature results from water rock interaction

age and evolution of a late archean to paleoproterozoic upper to lower crustal section in the wutaishan hengshan fuping terrain of northern china abstract the taihangshan wutaishan area forms part of the central north china craton and consists of three main components the hengshan and fuping complexes containing predominantly ductilely deformed late archean to paleoproterozoic high grade granitoid orthogneisses intruded by mafic dykes of gabbroic composition and the low grade late archean wutai greenstone belt developed between the high grade terrains and consisting of bimodal volcanic rocks and metasediments associated with coeval granitoids zircon dating shows that both the hengshan and fuping complexes were intruded by major granitoid bodies between 2 52 and 2 48 ga with rare occurrences of 2 7 ga gneisses wutai granitoids adjacent to the fuping complex also contain 2 7 ga xenocrysts all possibly reflecting the same older basement rare granitic gneisses in the hengshan have emplacement ages of 2 35 ga and show the same structural features as the older rocks indicating that the main deformation occurred after 2 3 ga deposition of supracrustal rocks and emplacement of mafic dykes occurred in the paleoproterozoic together with intrusion of granitic bodies at 2 1 2 0 ga and all underwent regional metamorphism at 1 88 1 85 ga we interpret the hengshan and fuping granitoid gneisses as the lower plutonic part of a late archean to early paleoproterozoic japan type magmatic arc with the upper volcanic part represented by the wutai complex components of this arc may have evolved at a continental margin as indicated by the 2 7 ga zircons virtually all magmatic events are recorded in all three complexes however the 1 85 ga metamorphic event is only recorded in the higher grade portions of the wutai since low grade and presumably high crustal level precluded metamorphic zircon growth shear zones in the hengshan are interpreted as major lower crustal discontinuities post dating the peak of high pressure granulite metamorphism we suggest that they formed during orogenic collapse and uplift of the hengshan complex in the late paleoproterozoic 1800 ma

implications based on the first shrimp u pb zircon dating on precambrian granitoid rocks in north korea abstract precambrian basement rocks in north korea consist of supracrustals and granitoid rocks of which the former comprise the late archean nangrim group and the paleoproterozoic jungsan and machollyong groups whereas the latter include four major types grey ttg gneisses garnet sillimanite bearing s type granites massive porphyritic granites and hornblende bearing granites 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 precambrian history of north korea and its relations to north china shrimp u pb zircon analyses on two grey gneiss samples po501 and k14 reveal that they were emplaced at 2538 14 ma and 2636 49 ma respectively and metamorphosed at 2462 2433 ma these data for the first time confirm the existence of late archean rocks in the korean peninsula moreover one grey gneiss sample k14 contains several zircons with ages of 3 1 3 4 ga suggesting possible middle archean crust in north korea rocks with such ages are widely distributed in north china implying that north china and north korea have similar archean basement one grey gneiss sample r53 yielded a shrimp zircon age of 1933 12 ma indicating that some grey gneisses in north korea formed during the paleoproterozoic two garnet and or sillimanite bearing s type granite samples gave 207 pb 206 pb ages of 1908 31 ma and 1903 49 ma interpreted to reflect the time of metamorphism of the paleoproterozoic jungsan and machollyong groups since these s type granites are considered to be derived from the partial melting of pelitic rocks from these groups the 1 9 ga metamorphic event has also been revealed in paleoproterozoic rocks in south korea and north china shrimp zircon data also show that massive porphyritic monzogranites in north korea evolved over a protracted interval from 1865 ma to 1843 ma similar aged porphyritic monzogranites are also found in north china and south korea and their origin is considered to be related to a post tectonic extensional event of regional extent the last phase of precambrian magmatism recognized in north korea is grenvillian aged represented by the hornblende bearing granite that yields a shrimp zircon age of 1195 4 ma and is considered to be the source rock of the adjacent yushulazi group north china that contains numerous 1 1 1 2 ga old detrital zircons

deformation history of the hengshan wutai fuping complexes implications for the evolution of the trans north china orogen abstract the trans north china orogen separates the north china craton into two small continental blocks the eastern and western blocks as one of the largest exposure in the central part of the orogen the hengshan wutai fuping complexes consist of four lithotectonic units the wutai hengshan and fuping complexes and the hutuo group the hengshan complex contains high pressure mafic granulites and retrograded eclogites structural analysis indicates that most of the rocks in these complexes underwent three distinct episodes of folding d 1 to d 3 and two stages of ductile thrust shearing stz 1 between d 1 and d 2 and stz 2 after d 3 the d 1 deformation formed penetrative axial planar foliations s 1 mineral stretching lineations l 1 and rarely preserved small isoclinal folds f 1 in the hengshan and fuping complexes in the wutai complex however large scale f 1 recumbent folds with sw vergence are displayed by sedimentary compositional layers penetrative transposition resulted in stacking of thrust sheets which are separated by ductile shear zones stz 1 the kinematic indicators of stz 1 in the hengshan and wutai complexes show top to the s230 w thrusting likely related to northeastward oblique pre collisional subduction d 1 resulted in crustal thickening with resultant prograde peak metamorphism the hutuo group did not undergo the d 1 deformation either because sedimentation was coeval with the d 1 deformation or because it was at a high structural level and was not influenced directly by the early deformation the d 2 deformation produced nw verging asymmetric and recumbent folds the d 2 deformation is interpreted to have resulted from collision between the eastern and western blocks of the north china craton in the hutuo group and the fuping complex the development of ese verging asymmetric tight folds is associated with d 2 the structural pattern resulting from superimposition of d 1 and d 2 is a composite synform in the hengshan wutai fuping complexes all four lithotectonic units were superposed during the later d 3 deformation the d 3 deformation developed nw trending open upright folds ongoing collision led to development of transpressional ductile shearing stz 2 forming the transpressional zhujiafang dextral ductile shear zone between the northern hengshan complex and the southern hengshan complex and generating the sinistral longquanguan ductile shear zone between the fuping complex and the wutai complex respectively the stz 1 and d 2 deformation were possibly responsible for fast syn collisional exhumation of the high pressure mafic granulites and retrograded eclogites the structural patterns and elucidation of the deformation history of the hengshan wutai fuping complexes places important constraints on the tectonic model suggesting that an oceanic lithosphere between the eastern and western blocks underwent northeastward directed oblique subduction beneath the western margin of the eastern block and that the final closure of this ocean led to collision between the two blocks to form the coherent basement of the north china craton

geochronology and geochemistry of metamorphic rocks in the jiaobei terrane constraints on its tectonic affinity in the sulu orogen abstract tectonic affinity of tectono lithological units close to ultrahigh pressure metamorphic belt is a key issue for understanding the geodynamics of continental collision this is particularly so for the jiaobei terrane northeast of the dabie sulu orogenic belt in china new data from la icpms zircon u pb dating whole rock elements and nd sr isotopes and mineral o isotopes are presented for metamorphic rocks from this terrane the results place geochronological and geochemical constraints on their protolith nature and metamorphic timing and thus on its tectonic affinity to one of the two triassic collided continents the north and the south china blocks protolith ages for ttg gneiss amphibolite and mafic granulite are 2 7 2 5 and 2 4 ga respectively regional metamorphism took place extensively at 1 76 ga protolith of the ttg gneiss was generated by partial melting of mantle derived rocks at the root of a thickened crust protolith of the amphibolite was probably a product of arc like magmatism protolith of the mafic granulite was derived from a depleted mantle source both of them were locally contaminated by supracrustal materials protoliths of paragneiss and schist in the fenzishan group were mostly derived from supracrustal sources but protolith of amphibolite in the fenzishan group is of mantle derived signature unlike the uhp metaigneous rocks in the dabie sulu orogenic belt that show unusual 18 o depletion the jiaobei metamorphic rocks have basically preserved their original mantle like o isotope compositions in general the nature and timing of geological events recorded in the metamorphic rocks from the jiaobei terrane are comparable with those from the north china block rather than the south china block thus the jiaobei terrane is concluded to have tectonic affinity to the former but behave like a micro continent during the triassic continental collision the 1 76 ga regional metamorphism in the jiaobei terrane is likely related to reworking of the arc continent collisional orogen in the periphery of the north china block rather than the 1 85 ga collision event between the eastern and western north china blocks the present study lends support to the common assumption that the suture boundary between the north and south china blocks in the sulu orogen is located along the wulian yantai fault tectonic mingling along the wulian yantai fault is probably related to subduction erosion during the continental collision

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

strontium isotopic composition of hot spring and mineral spring waters japan abstract in japan hot springs and mineral springs are distributed in quaternary and neogene volcanic regions as well as in granitic sedimentary and metamorphic regions lacking in recent volcanic activity the87sr 86sr ratio was determined in hot spring and mineral spring waters obtained from 47 sites the ratios of waters from quaternary and neogene volcanic regions were in the range 0 703 0 712 which is lower than that from granitic sedimentary and metamorphic regions 0 706 0 712 the geographical distribution of the ratios coincides with the bedrock geology and particularly the ratios of the waters in quaternary volcanic regions correlate with those of surrounding volcanic rocks these features suggest that subsurface materials control the87sr 86sr ratios of soluble components in the hot spring and mineral spring waters

the location and evolution of the tectonic boundary between the paleoproterozoic jiao liao ji belt and the longgang block northeast china abstract in this paper we discuss the location nature and evolution of the tectonic boundary between the jiao liao ji belt and the longgang block northeast china the boundary in terms of paleogeography which involves a study of the liaohe group or tectonics employing non seismic geophysical data e g gravity data and magnetotelluric soundings existing geological data and the differences in physical properties between the jiao liao ji belt and the longgang block we clarified the spatial distribution of the tectonic boundary and characterized the geological bodies at different depths on either side of the boundary we analyzed the most recently updated bouguer gravity anomaly gravity magnetic and electrical profile data as well as comprehensive data on the physical properties of the rocks in the research area thus providing information on the geological nature of the boundary at deep levels the results indicate that during the early period of formation of the jiao liao ji belt a basin controlling boundary fault developed that constituted the original tectonic boundary between the jiao liao ji belt and the longgang block this fault extended from shuangtaling to sandaoling lian shanguan dawanggou balidianzi and erhulai to guaimozi following a roughly east west trend most previous studies have considered that the liaohe group which extends from benxi city to benxi county and huanren county is the paleo geographic boundary of the jiao liao ji belt

br cl ratios and o h c and b isotopic constraints on the origin of saline waters from eastern canada saline groundwaters were recovered from undisturbed restigouche deposit and active brunswick 12 mine zn pb volcanogenic massive sulfide deposits in the bathurst mining camp bmc northern new brunswick canada these groundwaters along with fresh to brackish meteoric ground and surface waters from the bmc have been analyzed to determine their major trace element and stable isotopic o h c and b compositions saline groundwaters total dissolved solids 22 45 g l are characterized by relatively high na ca ratios compared to brines from the canadian shield and low na clmolar and d 11 b isotopic compositions 2 5 to 11 1 compared to seawater although saline waters from the canadian shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line those from the bmc fall close to the water line fracture and vein carbonate minerals at the restigouche deposit have restricted carbon isotopic compositions of around 5 to 6 the carbon isotopic compositions of the saline waters at the restigouche deposit 12 d 13 cdic are the result of fractionation of dissolved inorganic carbon by methanogenesis we suggest that unlike previous models for shield brines the composition of saline waters in the bmc is best explained by prolonged water rock reaction with no requirement of precursor seawater we suggest that elevated br cl ratios of saline waters compared to seawater may be explained by differential uptake of br and cl during groundwater evolution through water rock reaction 2007 elsevier ltd all rights reserved

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

the inner zone of the liaoji paleorift its early structural styles and structural evolution abstract a suite of eugeosynclinal formations together with common occurrence of extensional granitic rocks constitutes the major part of the inner zone of the liaoji paleorift in liaodong peninsula china two characteristic associations of deformation structures formed under different crustal conditions have been recognized in the liaoji paleorift zone from macro meso and micro structural studies and tectono thermal analyses magmatic core complex mcc a special structural style of extensional regime inherited from early rifting is constituted by the spatial temporal and genetic associations of magmatic cores bedding parallel ductile shear zones and extensional nappes such complexes are widely developed in the rift zone superposed on the mccs thrust nappes and thrusting related brittle ductile shear zones dominate a compressional event in the later evolution of the rift zone early structures were strongly deformed and transformed by later structures and meanwhile also exerted control on the latter e g the thrust nappes are often related to early folds and represented by fold nappes with extensive reactivation and reemplacement of granitic rocks in the cores a schematic evolutionary model for the early structural evolution of the early proterozoic in the inner zone is presented which indicates a different evolution of early rift zones from those of younger ones

characterizing multiple water rock interactions in the critical zone through sr isotope tracing of surface and groundwater abstract here we report on sr isotopes from shallow and deep groundwater from catchments located on granite and schist around the world this extensive approach of sr isotope tracing initiated in france on areas impacted by intensive agricultural activities was enlarged to africa granite gneiss and schists 2200 700 ma of the congo basin archean granitoid gneisses and sedimentary greenstone 3700 2500 ma of the orange river india and nepal archean granites 2500 ma and palaeoproterozoic granodiorite and schists 3100 1600 ma for india himalaya metamorphic silicate metasediments and gneisses 630 to 490 ma north america 3500 2500 ma silicate rocks in the mackenzie basin 1000 to 70 ma silicate rocks in the fraser basin in canada and 1760 to 1430 ma anorthosite and granite in the laramie aquifer in wyoming south america in french guiana archean gneiss 3400 to 2700 ma and granite gneiss rocks 2300 to 1900 ma australia 65 ma arenaceous and argillaceous rocks and considering both surface and groundwater in this extensive approach the sr and mg contents are well correlated and both are partly related to agricultural and weathering inputs the relationship between sr isotope and mg sr ratios allows definition of the relative impact on surface and groundwater of processes occurring in the critical zone mainly rain agricultural practices and water rock interactions

multi decadal elevation changes on bagley ice valley and malaspina glacier alaska 1 digital elevation models dems of bagley ice valley and malaspina glacier produced by i intermap technologies inc iti from airborne interferometric synthetic aperture radar insar data acquired 4 13 september 2000 ii the german aerospace center drl from spaceborne insar data acquired by the shuttle radar topography mission srtm 11 22 february 2000 and iii the us geological survey usgs from aerial photographs acquired in 1972 73 were differenced to estimate glacier surface elevation changes from 1972 to 2000 spatially non uniform thickening 10 7 m on average is observed on bagley ice valley accumulation area while non uniform thinning 47 5 m on average is observed on the glaciers of the malaspina complex mostly ablation area even larger thinning is observed on the retreating tidewater tyndall glacier these changes have resulted from increased temperature and precipitation associated with climate warming and rapid tidewater retreat

the importance of silicate weathering of a sedimentary aquifer in arid central australia indicated by very high 87sr 86sr ratios with the exception of brine systems and crystalline rock aquifers groundwater 87sr 86sr ratios rarely differ by more than 0 01 from the phanerozoic seawater value of 0 70923 groundwater 87sr 86sr ratios from central australia 0 72562 0 76248 are the highest ever recorded for a low salinity sedimentary aquifer we propose a model for the evolution of these 87sr 86sr ratios and demonstrate how the lowest 87sr 86sr ratios reflect water rock interactions with predominantly carbonate minerals while the highest 87sr 86sr ratios are ultimately controlled by weathering of old primary silicate minerals detailed analysis of aquifer core material identified albite and microcline as the most prevalent primary silicates and where these minerals were abundant relatively high rb concentrations were measured high rb combined with long time scales since deposition has produced very high 87sr 86sr ratios in the rocks and subsequently the groundwater therefore strontium isotopes can provide further constraints for chemical models of arid zone groundwater systems particularly when silicate hydrolysis is believed to significantly contribute to dissolved solute compositions

chemical interaction of aqueous solutions with epidote feldspar mineral assemblages in geologic systems ii equilibrium constraints in metamorphic geothermal processes thermodynamic analysis of the system na sub 2 o k sub 2 o cao feo fe sub 2 o sub 3 al sub 2 o sub 3 sio sub 2 h sub 2 o hcl co sub 2 at pressures and temperatures to 5 kb and 600 sup 0 c affords quantitative description and interpretation of phase relations among epidote garnet plagioclase and alkali feldspar solid solutions in hydrothermal systems comparison of computed and observed compositions of these minerals and coexisting fluids suggests that the calculations afford close approximation of equilibrium and mass transfer in metamorphic geothermal processes the standard molal enthalpies of decomposition reactions for plagioclase are of the order of 4 to 50 kcal mole sup 1 which requires the activity of the anorthite component of plagioclase coexisting with epidote solid solutions to increase with increasing temperature at constant pressure in contrast because the standard molal volumes of these reactions are also negative a sub caal sub 2 si sub 2 o sub 8 decreases with increasing pressure at constant temperature either stoichiometric epidote or clinozoisite is compatible with plagioclase quartz calcite and an aqueous phase but only at x sub co sub 2 less than or equal to 0 2 the complex zoning commonly exhibited by both plagioclase and epidote solid solutions in geologic systems can be attributed to minor isothermal isobaric changes in the composition of coexisting aqueous solutions logarithmic activity and fugacitymore diagrams constructed with provision for solid solution permit documentation of such changes and facilitate thermodynamic interpretation of mineral and fluid compositions in metamorphic geothermal systems less

strontium isotopic composition of some brines from the precambrian shield of canada abstract twenty four groundwater samples from seven operating mines at sudbury yellow knife and thompson ontario north west territories and manitoba resp all from depths greater than 1 km and ranging in total dissolved solids tds from 1900 to 250 000 mg l 1 were measured for their 87 sr 86 ar values each geographic location gives a limited range in values and each location is distinct from the others this is interpreted as the result of extensive water rock interaction on a local scale for most of the time these brines were isolated and only recently have been exposed to surface water as a result of the mining operations the extent of the isolation is shown by the contrasting isotopic values of two pockets of water 0 711 vs 0 716 located on opposite sides of the same fault system on the north range at sudbury the exchange at all sites probably has continued until the present as indicated by the close agreement between water and present day 87 sr 86 sr whole rock values if so it suggests that there is no single age for such brines but it may be possible to date stages in the water s evolution by determining the age of secondary minerals that equilibrated with the water

a strontium isotopic study of mineral and surface waters from the cezallier massif central france implications for mixing processes in areas of disseminated emergences of mineral waters abstract surface and mineral waters from a geothermal area cezallier in the centre of the massif central france were analysed for sr isotopes sr and major elements in order to use sr isotopes to investigate the discharge of a mineralised water area especially in the case of disseminate mineralised water emergences the 87 sr 86 sr ratios of mineralised waters ranged from 0 715541 to 0 716773 the variation in 87 sr 86 sr values was small for the 5 mineral springs sampled over two periods 5 10 6 14 10 6 regarding the reproductivity of the 87 sr 86 sr ratio measurements no differences can be seen and the 87 sr 86 sr ratio of mineral waters can be considered to be constant with time the 87 sr 86 sr ratios of surface waters collected along the zagat river ranged from 0 705303 to 0 715091 the lowest values were always observed in the headwaters the difference in the 87 sr 86 sr ratios between the two sampling periods was 22 10 4 and can be related to the hydrological situation low or high flow the 87 sr 86 sr ratios of surface waters collected in the drain ranged from 0 715072 to 0 716585 the difference in the 87 sr 86 sr ratios between the two sampling periods is 11 10 4 for the drain headwaters and 13 10 5 at the outlet of this area likewise these variations can also be related to the hydrological situation plots of 87 sr 86 sr vs 1 sr ratios show two distinct binary mixing trends and the existence of at least four end members a mixing parameter f giving the proportions of the two components can be estimated for assumed 87 sr 86 sr ratio and sr content values of the pure end members an estimate of the mineral water discharge can be calculated using the results of the mixing model and the measured flow in the drain area the mixing model gives an estimate 0 5 1 l s 1 or 10 13 of mineral water in the total flow a similar calculation was done for the river where the mineral water flow was 0 96 l s 1 3 5 m3 h 1 100 m downstream from the bridge in april 1994 and 6 m3 h 1 20 m downstream from the bridge in september 1994

single zircon grains record two paleoproterozoic collisional events in the north china craton abstract the western block of the north china craton consists of the yinshan block in the north and the ordos block in the south which were amalgamated along the east west trending khondalite belt at 1 95 ga the western block then collided with the eastern block to form the coherent basement of the north china craton along the north south trending trans north china orogen at 1 85 ga the huaian complex a high grade terrrane located at the conjunction of the khondalite belt and trans north china orogen records metamorphic events associated with both collisions the complex consists of lithologies from both the khondalite belt and trans north china orogen of which the former consist of graphite garnet sillimanite gneiss garnet quartzite felsic paragneiss calc silicate rock and marble together called the khondalite series zircons in the graphite garnet sillimanite gneiss can be divided into three types 1 spherical grains without internal structures 2 grains with a core and rim structure and 3 grains with a dark core surrounded by double rims except for the dark core in type 3 all other types of zircon domains are structureless and highly luminescent with very low th u ratios typical of a metamorphic origin analyses on the cores of type 2 and the inner rims of type 3 from two samples yield upper intercept ages of 1946 26 and 1947 22 ma similar to previously determined metamorphic ages from the khondalite belt and thus interpreted as the time of collision between the yinshan and ordos blocks analyses on type 1 zircons rims of type 2 and the outer rims of type 3 from the same two samples give ages of 1850 15 and 1857 16 ma interpreted as the time of collision between the eastern and western blocks thus zircons in the graphite garnet sillimanite gneiss of the huaian complex record both of the paleoproterozoic collisional events in the north china craton

insar observations of the 1993 95 bering glacier alaska u s a surge and a surge hypothesis time varying accelerations were observed on bagley icefield during the 1993 95 surge of bering glacier alaska u s a using repeat pass synthetic aperture radar interferometry observations were from datasets acquired during winter 1991 92 pre surge winter 1993 94 during the surge and winter 1995 96 post surge the surge is shown to have extended 110 km up the icefield from bering glacier to within 15 km or less of the flow divide acceleration and step like velocity profiles are strongly associated with an along glacier series of central phase bull s eyes with diameters of 0 5 4 km these bull s eyes are interpreted to represent glacier surface rise fall events of 3 30 cm during 1 3 day observation intervals and indicate possible migrating pockets of subglacial water we present a surge hypothesis that relates late summer climate to englacial water storage and thence to the subglacial water dynamics pressurization hydraulic jacking depressurization and migration suggested by our observations

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

87sr 86sr values in groundwaters of the east bull lake pluton superior province ontario canada abstract the east bull lake pluton is a 2 48 ga old layered mafic intrusion located on the southern margin of the superior province precambrian shield in ontario canada the groundwaters have been studied as part of a detailed geological mapping and geochemical study of the pluton for the canadian nuclear fuel waste management program all groundwater samples are dilute the most concentrated na cl type water contains 3 1 g l total dissolved solids present day87sr 86sr values of the rock samples varies from 0 705 to 0 714 and the groundwaters from 0 711 to 0 720 the ca hco3 recharge waters show the greatest range in values in contrast to the deeper na hco3 and deep na cl waters where a narrow range of 0 712 0 713 is found fracture filling laumontite calcite and gypsum have the same isotopic signature as the deep water the ca hco3 water is the youngest component of the groundwater system and its spread in isotopic values reflects local conditions at the surface the na cl water is considered to be the oldest component and its sr isotopic ratio value indicates equilibration with silicate fracture mineral phases the isotopic data suggest that laumontite calcite and gypsum fracture phases have either crystallized from this water or are currently controlling its isotopic composition by dissolution no age can be assigned to the deep waters except that the na cl component may date from the early paleozoic based on geological arguments or more likely be 104 106 years old based on kinetic studies of rock water interaction and other isotopic data if seawater was one component of the na cl water history there is no record of this in the87sr 86sr ratios

palaeoproterozoic assembly of the north china craton the basement of the north china craton consists of the eastern and western blocks separated by the central zone both the eastern and western blocks are dominated by late archaean tonalitic trondhjemitic granodioritic gneiss complexes interdigitated with minor supracrustal rocks metamorphosed at 2 5 ga with anticlockwise p t paths the central zone is composed of reworked late archaean components and palaeoproterozoic juvenile crustal materials that underwent regional metamorphism at 1 85 ga with clockwise p t paths involving isothermal decompression as a result of collision between the eastern and western blocks which resulted in the final assembly of the north china craton

geochemistry zircon u pb dating and tectonic implications of the palaeoproterozoic ji an and laoling groups northeastern jiao liao ji belt north china craton abstract the jiao liao ji belt is located between the longgang and langrim blocks in the eastern block of the north china craton ncc the belt comprises palaeoproterozoic volcanic sedimentary successions that are divided into the ji an south liaohe and jingshan groups in the south and the laoling north liaohe and fenzishan groups in the north the tectonic setting and depositional environments of the liao ji area are debated this paper presents geochemical and detrital zircon u pb data for the boron bearing graphite bearing aluminum rich ji an group and the clastic sediments and carbonates of the laoling group in southern jilin province in order to constrain their depositional ages provenance and tectonic setting zircon geochronology for both the ji an and laoling groups yields age peaks of 2 57 2 41 2 23 2 09 and 2 04 2 02 ga indicating that the sediments were derived from the longgang and or liaonan block s the 2 2 2 1 ga liaoji granitoids and 2 0 ga igneous rocks respectively on the basis of the youngest detrital zircons and the oldest metamorphic zircon peaks depositional ages can be constrained to the period of 2 13 1 94 2 10 1 94 and 1 95 1 90 ga for the mayihe huangchagou and dadongcha formations of the ji an group and 2 18 1 90 2 08 1 91 1 99 1 90 1 96 1 90 and 1 94 1 90 ga for the dataishan zhenzhumen huashan linjiang and dalizi formations of the laoling group respectively the zircon age spectra of each formation indicate that deposition of the ji an and laoling groups was related to the opening and closing of a back arc during the period 2 2 1 9 ga the dataishan formation laoling group was deposited in the rift environment during opening of the back arc during the early stage the mayihe and huangchagou formations ji an group were deposited on the side of the magmatic arc and the zhenzhumen formation laoling group was deposited on the passive margin side during the late stage both ji an and laoling groups were deposited in a pre orogenic setting including the dadongcha huashan linjiang and dalizi formations detrital zircon age spectra of the ji an group are similar to those of the south liaohe group with the exception of the gaojiayu formation indicating that the two groups had a similar provenance

u pb and hf isotopic study of detrital zircons from the yejishan group of the luliang complex constraints on the timing of collision between the eastern and western blocks north china craton abstract the trans north china orogen is a recently recognized continent continent collisional belt along which the discrete eastern and western blocks amalgamated to form the coherent basement of the north china craton however there is a hot debate on the timing of the collision between the two blocks with one school of thought arguing the collision occurred at 2 5 ga whereas others believe it took place at 1 85 ga u pb ages and hf isotopic data of detrital zircons from foreland basins in the trans north china orogen can provide rigorous constraints on this controversial issue one of such foreland basins is represented by the yejishan group in the luliang complex in the middle sector of the western margin of the trans north china orogen the group consists of conglomerates quartz wackes sandstones and minor limestones most of which contain large amounts of detrital zircons cl images reveal that nearly all detrital zircons from the yejishan group possess oscillatory zoning with th u ratios of 0 2 2 34 typical of an igneous origin the 207 pb 206 pb ages of detrital zircons range between 3 24 and 1 81 ga with most having paleoproterozoic ages of which the youngest group ages are around 1 87 1 81 ga this indicates that the foreland basin in which the yejishan group was deposited must have formed not earlier than 1 87 1 81 ga thus supporting the collision between the eastern and western blocks at 1 85 ga not at 2 5 ga

zircon geochronology and metamorphic evolution of mafic dykes in the hengshan complex of northern china evidence for late palaeoproterozoic extension and subsequent high pressure metamorphism in the north china craton abstract magmatic and metamorphic zircons have been dated from ductilely deformed gabbroic dykes defining a dyke swarm and signifying crustal extension in the northern part of the hengshan complex of the north china craton these dykes now occur as boudins and deformed sheets within migmatitic tonalitic trondhjemitic granodioritic and granitic gneisses and are conspicuous due to relics of high pressure granulite or even former eclogite facies garnet pyroxene bearing assemblages shrimp ages for magmatic zircons from two dykes reflect the time of dyke emplacement at 1915 ma whereas metamorphic zircons dated by both shrimp and evaporation techniques are consistently in the range 1848 1888 ma the youngest granitoid gneiss yet dated in the hengshan has an emplacement age of 1872 17 ma these results complement recent geochronological studies from the neighbouring wutai and fuping complexes to the se of the hengshan showing that a crustal extension event occurred in the late palaeoproterozoic this preceded a major high pressure collision type metamorphic event in the central part of the north china craton that occurred in the palaeoproterozoic and not in the late archaean as previously thought our data support recent suggestions that the north china craton experienced a major craton wide orogenic event in the late palaeoproterozoic after which it became cratonized and acted as a stable block

petrogenesis and tectonic implications of two types of liaoji granitoid in the jiao liao ji belt north china craton abstract two types of granitoid monzogranite and granodiorite are recognized within the paleoproterozoic liaoji granitoids of the jiao liao ji belt jljb in the hupiyu and simenzi areas north china craton we conducted zircon u pb geochronological geochemical and hf isotopic analyses of these granitoids zircon u pb dating indicates an emplacement age of 2180 14 ma for the monzogranite hupiyu granitoids and ages of 2130 24 and 2173 11 ma for the fangjiaweizi and dadingzi granodiorites at simenzi respectively the hupiyu monzogranite samples are enriched in zr ga and y and depleted in nb and ti low nb y ratios and high zr saturation temperatures 849 884 c indicate that the hupiyu monzogranites have an affinity with a2 subtype granitoids the fangjiaweizi and dadingzi granodiorites have high sr y and low k2o na2o ratios indicating an affinity with adakitic rocks geochemical compositions and wide variation in ehf t values suggest that the monzogranites and granodiorites were derived from thinned and thickened lower crust respectively and that magmatism was accompanied by input of mantle material this study represents the first identification of pre tectonic adakitic rocks in the jljb the assemblage of pre tectonic a2 type granitoids and adakitic rocks indicates a continental back arc basin as the initial tectonic setting of the jljb these new data combined with results of previous studies support an arc continent collision model for the jljb

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

the interglacial glacial cycle and geochemical evolution of canadian and fennoscandian shield groundwaters abstract results from cryogenic column experiments are compared with the geochemical data collected in the canadian and fennoscandian shields over the past 25 years to investigate the relative influence of the glacial interglacial cycle specifically the impact of continental glaciers permafrost and methane hydrate on the evolution of groundwater from crystalline shield environments several different geochemical indicators of freezing processes either glacial or permafrost related were utilized comparisons of na cl and br cl ratios 18 o and 2 h values and 18 o values and cl concentration during freezing fluids with different dominant cations follow distinctly different linear trends when na cl and br cl ratios are compared significantly none of the freezing trends follows the trend hypothesized by herut et al 1990 for the evolution of seawater chemistry during freezing intrusion of glacial meltwater and in situ freezing i e permafrost formation result in a similar end member when comparing 18 o values and cl concentration the geochemical influence of a freezing process on fresh brackish and some saline fluids was identified at some but not all canadian shield sites regardless of site location with respect to modern day permafrost appreciably physical and geochemical data do not support the formation of brines through any freezing process in the canadian and fennoscandian shields as hypothesized by starinsky and katz 2003 rather on all diagnostic freezing plots brines are an end member indicating a different evolutionary pathway significant depletions in 18 o with respect to modern precipitation an indication of either glacial meltwater or a freezing process were identified at depths of up to 1 km at some sites in the canadian shield and to shallower depths in the fennoscandian shield the potential of this fluid to reach such depths could be attributable to artificial gradients and mixing glacial recharge permafrost or paleo permafrost formation or methane hydrate or paleo methane hydrate formation at most locations it was not possible to distinguish between the different scenarios using the current geochemical database

the geochemistry age and origin of groundwater in a mafic pluton east bull lake ontario canada abstract the geochemistry of groundwater in the east bull lake gabbro anorthosite pluton near elliot lake ontario canada has been investigated three chemical types of groundwater are present to depths of about 650 m and are controlled by the nature of the groundwater flow systems and the water rock interactions in the fractures ca hco 3 water is present in the recharge area of the local flow system and evolves rapidly along the direction of groundwater flow to a high ph na hco 3 water primarily by cation exchange reactions saline na cl water is present below a depth of about 350 m on the basis of its chemistry and hydraulic head measurements the na cl water is believed to be part of a deep regional groundwater flow system carbon 14 measurements of the na hco 3 water suggest that this water was recharged shortly after the last pleistocene deglaciation this is supported by 18o values that are as much as 6 lighter than shallow modern groundwater despite the high mg content of the enclosing rocks mg2 concentrations in the groundwater of this unit are na hco 3 and na cl waters and hence could still be forming under the present low temperature conditions the stable isotope composition of the na cl water suggests that this water type is not a geochemically evolved product of the overlying waters although present day albitization of the anorthosite could be responsible for the increased ca na ratio in the na cl water compared to the other water types the salinity of this water appears to have been derived outside the pluton possibly as an ancient infiltration into crystalline basement rocks of saline formation waters present in paleozoic sedimentary rocks which formerly overlay the pluton or from nearby proterozoic formations this hypothesis is supported by br cl ratios that are similar to sea water and many present day formation waters and the isotopic composition of the dissolved sulphate the he age of the saline water is of the order of 108 years therefore both the saline water and many of its solutes appear to have ancient origins

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

87sr 86sr of brines from the fennoscandian shield a synthesis of groundwater isotopic data from the baltic sea region high salinity ca na cl brines occur in sweden and finland the complex geological history of the fennoscandian shield is reflected by the wide range of saline waters whose chemical compositions have been explained by local water rock interaction simple evolution of relict sea water or freezing of sea water during glacial periods this study deals with the present knowledge of sr isotopes in groundwater from the fennoscandian shield to better constrain the origin of their deep saline component two different mixing trends are seen between aspo island groundwater and the baltic sea the first trend links the north sea to rivers through various dilution levels in the baltic the second trend is a simple linear relationship through aspo groundwaters agreeing with a binary mixing between a baltic end member and a highly sr concentrated fluid strontium isotope compositions are presented for precipitation in finland and sweden the baltic sea and the river waters draining the fennoscandian shield and for g

paleo water rock interaction determined through isotopic tracing sr o c u in fracture fill minerals evidence from the vienne granitoids france abstract based on the concepts a that the stable c and o isotopes combined with the sr isotope ratios of fracture fills should reflect the source groundwater from which the solid phases precipitated and b that u series disequilibria usd enable the calculation of residence time for the u by using fe oxides as the best candidate an isotopic toolbox was applied to fracture fill from the crystalline basement of the vienne district the fracture fills are formed mainly of carbonates clays and fe oxides the isotope data indicate two main generations of carbonate that originated from hydrothermal circulation and equilibrium with present day groundwaters but the sr isotope ratios highlight another component with a higher 87 sr 86 sr ratio reflecting the complexity of the water rock interactions for the usd the fe hydroxides located at 207 m depth yield an age of 102 5 ka st germain i interglacial stage whereas those located at 277 m and 300 m yield respective ages of 173 15 ka and 181 10 ka these corresponding to the transition between the penultimate glacial period isotopic stage 6 and the end of the preceding interglacial stage isotopic sub stage 7a investigating water rock interaction 87 sr 86 sr 18 o 13 c usd in the fracture fill minerals from the crystalline basement has shown that such an approach is relevant to developing an understanding of how the groundwater system has changed over time

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

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

deformation history of the hengshan complex implications for the tectonic evolution of the trans north china orogen structural analysis indicates that the hengshan complex underwent five distinct episodes of deformation d1 d5 the d1 episode formed small isoclinal folds f1 penetrative axial planar foliations s1 and mineral stretching lineations l1 d1 fabrics were reworked by following d2 deformation associated with d2 was the development of nw verging asymmetric folds and accompanying thrust faults both d1 and d2 resulted from crustal thickening and coherent with prograde and peak metamorphism d2 deformation was followed by transpressional dextral shearing d3 including top to nw oblique slip shearing and nne ssw dextral strike slip shearing ongoing collision led to development of the zhujiafang ductile shear zone d4 a near e w trending high strain belt across the hengshan complex d5 deformation is characterized by f5 open folds and associated normal faults probably related to exhumation of the complex structural patterns of the hengshan complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the eastern and western blocks underwent eastward directed subduction beneath the western margin of the eastern block and closure of this ocean finally led to collision between the two blocks to form the coherent north china craton

3800 to 2500 ma crustal evolution in the anshan area of liaoning province northeastern china shrimp u pb zircon geochronology has revealed several generations of granitoids and gneisses from the anshan area of northeastern china two samples of the baijiafen granite sensu lato 3804 5 and 3812 4 ma chentaigou granite 3306 13 ma lishan granite 3142 7 ma east and west anshan granites 3001 4 and 2994 8 ma tiejiashan granite 2962 4 and 2964 6 ma and qidashan granite 2475 ma the 3800 ma baijiafen granite consists of banded migmatitic trondhjemitic gneisses and forms only a small part of the area nonetheless they are the oldest known rocks in asia and are one of very few locations in the world where rocks of this antiquity have been found the younger suites are predominantly granite sensu stricto in composition and although foliated they have not been transformed into banded gneisses nd isotopic data suggest that the 3800 ma granites were produced at least in part by remelting of very ancient lree enriched sources perhaps like the exposed remnants of the 3800 ma rocks the chentaigou supracrustals contain layered mafic and ultramafic rocks banded iron formation bif and siliceous layered rocks of probable volcanogenic origin a sample of the latter has yielded a concordant u pb zircon age of 3362 5 ma interpreted as the age of deposition a trondhjemitic sheet cutting these rocks has yielded a u pb zircon age of 3342 6 ma the chentaigou supracrustals are the oldest recognised in the area younger supracrustal sequences collectively known as the anshan group contains the main economic bif units in the area bif is intruded by the 2475 ma qidashan granite indicating that the anshan group is archaean or earliest proterozoic in age

synchronous a type and adakitic granitic magmatism at ca 2 2 ga in the jiao liao ji belt north china craton implications for rifting triggered by lithospheric delamination abstract the jiao liao ji belt jljb underwent back arc or intra continental rifting during the early palaeoproterozoic but the underlying mechanism remains unclear to address this issue this study focuses on the petrogenesis of widespread palaeoproterozoic granitoids on liaodong peninsula china zircon u pb dating and geochemical and hf isotopic data suggest that these granitoids were formed at ca 2 2 ga and they can be divided into a type and adakitic granites the a type granites have relatively high sio2 k2o zr ga nb and y contents and low cao mgo al2o3 and sr contents based on these characteristics ehf t values 0 8 to 2 8 and tdm2 ages 2797 2569 ma the a type granites are inferred to be derived from neoarchaean tonalite trondhjemite granodiorites in a rift setting in contrast the coeval adakitic granites have relatively high na2o al2o3 and sr contents and high sr y and lan ybn ratios but low mgo ni yb and y contents suggesting a magma source with garnet but no plagioclase in the residue beneath thickened lower crust their variable ehf t values 8 5 to 6 9 and tdm2 ages 3276 2305 ma indicate that the adakitic magmas were mainly generated by the partial melting of meso neoarchaean crust the co existence of contemporaneous ca 2 2 ga adakitic and a type granites provides evidence that the jljb underwent regional rifting in the palaeoproterozoic most likely due to delamination of a thickened lithosphere as follows 1 in the neoarchaean the lower crust of the longgang block underwent granulite and or eclogite facies metamorphism due to continuous thickening which resulted in increasing lower crustal density 2 the thickened lower crust became unstable and delaminated at ca 2 2 ga asthenospheric upwelling following this lithospheric delamination triggered the thinning of the overlying lithosphere the upper crust and remnant thickened lower crust were partially melted to form the a type and adakitic granites respectively the rifting likely resulted in the separation of the longgang and nangrim blocks prior to their amalgamation in the late palaeoproterozoic to form the jljb

polyphase deformation of the fuping complex trans north china orogen structures shrimp u pb zircon ages and tectonic implications abstract the fuping complex is located in the central part of the trans north china orogen tnco a paleoproterozoic collisional belt along which the eastern and western blocks were assembled to form the north china craton three stages of deformation d 1 d 3 have been identified in the fuping complex d 1 formed tight to isoclinal folds f 1 penetrative foliation s 1 and mineral lineation l 1 which resulted from the early nw se orientated thrusting and shearing d 2 progressively overprinted d 1 and was dominated by mostly nw se shortening and top to the se e thrusting under a compressive environment d 1 and d 2 occurred in association with the peak metamorphism m 1 d 3 occurred during the exhumation after the crustal thickening producing regional scale nww see trending open folds f 3 and associated low angle detachment faults and was responsible for the isothermal decompression m 2 metamorphism of the complex following the d 3 deformation the complex was exhumed to shallow crustal levels where the rocks underwent the retrogressive cooling m 3 metamorphism syn tectonic leucocratic dykes are widespread in the fuping complex two leucocratic dykes that did not experience d 1 but underwent d 2 yield shrimp zircon ages of 1843 12 ma and 1844 18 ma which indicate that d 1 must have occurred at some time earlier than 1844 ma whereas d 2 must have occurred at some time later than this age two weakly deformed post d 2 leucocratic dykes yield shrimp zircon ages of 1817 14 ma and 1815 45 ma suggesting that the d 2 deformation occurred in the period 1843 1815 ma the new shrimp data indicate that the collision related deformation of the fuping complex must have occurred in the paleoproterozoic not in the late archean structural and geochronological data presented in this study in association with previous lithological and geochemical data suggest that the fuping complex may have been located in the hinterland of an eastward subduction zone and underwent intensive deformation and metamorphism involved in the final collision between the western and eastern blocks at 1 85 ga

formation and evolution of paleoproterozoic orogenic belt in southern jilin jiao liao ji belt north china craton constraints from geophysics abstract the tectonic setting and depositional environments of the laoling and ji an groups in the northeastern jiao liao ji belt northeastern china are controversial these paleoproterozoic stratigraphic units are exposed sporadically in baishan and tonghua beneath a thick cover of quaternary basalts meaning that only limited information can be obtained by traditional geological methods therefore using geophysical techniques in this region is pertinent here we present new data on the petrophysical properties density magnetic susceptibility and specific resistivity obtained from 2d cross gradient joint inversion profiles the results allow us to establish the relationships between the laoling and ji an groups interpret the tectonic setting of deposition and locate the subsurface margins of the jiao liao ji belt petrophysical parameters from the dataishan formation density of 2 58 g cm3 zero magnetic susceptibility and specific resistance of 103 04 m indicate that these rocks were derived predominantly from the longgang block in the north for the zhenzhumen formation the petrophysical parameters high density weak magnetic susceptibility and high specific resistivity are consistent with deposition in a passive margin that received detrital material sediments from the longgang block and the liaoji granitoids the mayihe and huangchagou formations intermediate to high density strong magnetic susceptibility and intermediate specific resistivity were deposited closer to a magmatic arc with the detritus derived from the liaoji granitoids the low to intermediate density stronger magnetic susceptibility and intermediate specific resistivity of the huashan linjiang dalizi and dadongcha formations indicate that these rocks were deposited in a pre orogenic setting with the detritus derived from the longgang block liaoji granitoids and other felsic igneous rocks based on the geophysical profiles we conclude that the jiao liao ji belt extends under quaternary basalt from linjiang to baishan and eastward towards north korea two basin controlling faults f1 and f2 represent the northern and eastern boundaries between the longgang block and the jiao liao ji belt we interpret geophysical anomalies and variations in the petrophysical parameters in the context of subduction and collision processes