the resolving power of cross borehole tomography the data collected in a cross borehole tomography problem is inherently incomplete since the boreholes do not completely surround the media under study the ability of the experiment to resolve structure is therefore limited by poor experimental geometry we use the method of backus and gilbert to investigate the ability of this technique to resolve variations in acoustic velocity and attenuation between the two boreholes both integrals that appear in the backus gilbert formulation can be performed analytically thus expediting the calculations the resolving kernels have significant horizontal width demonstrating that the horizontal position of structures can be only poorly resolved

magnetotelluric evidence for serpentinisation in a cambrian subduction zone beneath the delamerian orogen southeast australia abstract the delamerian orogen in southeast australia represents a proterozoic continental rift margin overprinted by convergent margin andean style subduction in the cambrian a detailed 150 km east west magnetotelluric transect was collected across the orogen to investigate the electrical resistivity structure the magnetotelluric transect follows an existing full crustal reflection seismic transect of which interpretations support a westward dipping cambrian subduction model as derived from field mapping and geochemistry a 2d inversion of the data from the 68 station broadband magnetotelluric transect imaged a heterogeneous crust with lateral changes as large as 10 000 m occurring over 15 km the crust within the western glenelg zone is resistive in contrast to the eastern glenelg zone and the grampians stavely zone above the paleo subduction zone which host three conductive pathways the main low resistivity regions 1 10 m reside at mid lower crustal depths 10 30 km extending up to the surface with a higher resistivity 300 m but still much less than surrounding resistivity mantle 1000 m crust 10 000 m fluids released from the upper mantle during the cambrian west dipping subduction are interpreted to have moved up crustal faults to create the observed low resistivity pathways by serpentinisation and magnetite creation in mafic ultramafic rocks the electrical conductivity of hand samples of serpentinised mafic ultramafic rocks in the region was found to be much greater than most other rock types present in addition to adding insight into the crustal structure the magnetotelluric data also supports geological surface mapping as the major lawloit and yarramyljup faults that bound different geological domains also mark domains of different electrical structure

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

komatiites from west shandong north china craton implications for plume tectonics the mengyin komatiites are located at the base of the taishan complex 2 7 ga in the western shandong greenstone belt of the eastern block of north china craton the mengyin komatiites have high magnesian low titanium and aluminum undepleted chemical characteristics although the ultramafic rocks underwent amphibolite to greenschist facies metamorphism they preserve remnant igneous spinifex textures some komatiite samples even preserve rare fresh olivine according to the mass equilibrium between the olivine and melt the potential eruption temperature of the mengyin komatiites at 1 atm is about 1270 c which might indicate a plume tectonic setting it is inferred that komatiites in mengyin west shandong may be part of a plume related global magmatic event related to the break up of a supercontinent that included the eastern block of the north china craton 2006 international association for gondwana research published by elsevier b v all rights reserved

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

is the paleoproterozoic jiao liao ji belt north china craton a rift as a typical example of the paleoproterozoic crust in the eastern block of the north china craton the paleoproterozoic jiao liao ji belt consists principally of the liaohe group and its equivalents liaoji granites and mafic intrusions previous studies indicate that the evolution of the jiao liao ji belt has been mainly attributed to the opening and closing of an intracontinental rift along the eastern continental margin of the north china craton here we synthesize the paleoproterozoic magmatism sedimentation metamorphism and metallogeny against the rift model and propose a process of arc continent collision between the northern longgang and the southern nangrim blocks this conclusion is consistent with the observations including that a the 2 0 to 2 2 ga magmatism shows a typical subalkaline series rather than a bimodal distribution since the mafic rocks mostly have arc affinities and the acidic intermediate rocks belong to the calc alkaline series b the main source of the 1 9 to 2 0 ga sedimentary rocks is the paleoproterozoic arc materials indicating a fore arc or back arc basin setting c a couple of big borate deposits occur in the boron rich volcanic rocks that were formed in convergent continental margins d the north and south liaohe groups show different rock associations and metamorphic histories p t paths and e the nangrim and longgang blocks vary in lithological units geochronology and metamorphic features thus an arc continent collision tectonic scenario for the paleoproterozoic jiao liao ji belt is involved a a southward subduction in the period 2 0 2 2 ga b sedimentation during the period 1 9 2 0 ga c arc continent collision at ca 1 9 ga and d post collisional extension at 1 82 1 87 ga marking the end of the paleoproterozoic tectonothermal event

a widespread paleoproterozoic partial melting event within the jiao liao ji belt north china craton zircon u pb dating of granitic leucosomes within pelitic granulites and its tectonic implications abstract in the southern zone of the paleoproterozoic jiao liao ji belt jljb north china craton ncc abundant granitic leucosomes are widespread within migmatites as irregular layers lenses and blocks they are parallel to or as cross cut foliations in the host rocks on various scales and show distinct evidence of migmatization in the formation of these centimeter to decimeter scale segregations the migmatites extend at least 1100 km in length spreading over the whole jljb from the ji an group in south jilin through the south liaohe group in liaodong peninsula to the jingshan group in jiaodong peninsula rather than as sporadic outcrops limited to the jiaobei terrane as reported in previous studies the granitic leucosomes are comprised mainly of quartz k feldspar and antiperthitic plagioclase albite with secondary minerals of garnet biotite zircon etc they are enriched in sio 2 74 65 75 54 wt al 2 o 3 13 25 14 87 wt and k 2 o na 2 o 8 19 8 95 wt but have a lower tio 2 fe 2 o 3 feo mgo mno content 0 42 1 34 wt the major element components are similar to those of granitic leucosomes of pelitic granulites in typical orogenic belts around the world a combined study of whole rock geochemistry mineral inclusions cathodoluminescence cl images and laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dates of zircons revealed the nature and timing of partial melting of the host pelitic granulites all dated anatectic zircons from various granitic leucosomes display magmatic zones with distinct cores and rims and contain mineral inclusions of qtz kfs ab ap in both domains both the cores and rims exhibit unusually high u and th contents and anomalously low th u ratios

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

anisotropic velocity tomography a case study in a near surface rock mass cross borehole data were acquired in the surface crown pillar of a massive sulfide ore mine the data consist of five two dimensional 2 d cross borehole panels each with approximately 900 source receiver pairs the panels were located within the crown pillar at either side of and within a major subvertical fault zone that intersects the orebody an initial analysis of the data indicates that the bedrock containing the orebody is seismically anisotropic a rigorous analysis of the traveltimes using anisotropic velocity tomography confirms the initial assessment that anisotropy exists within the crown pillar rock mass anisotropic velocity tomography is the generalization of tomographic methods to anisotropic media as in any geophysical problem the data are insufficient to completely resolve the distributions of the rock properties at all scale lengths we use external constraints on the roughness of the final solution to ensure an algebraically well posed problem plots of the data residuals the t

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

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

target oriented interferometric tomography for gpr data an interferometric form of fermat s principle and traveltime tomography is used to invert ground penetrating radar gpr data for the subsurface velocity distribution the input data consist of gpr traveltimes of reflections from two buried interfaces a reference and b target where the data are excited and recorded by gpr antennas at the surface fermat s interferometric principle is then used to redatum the surface transmitters and receivers to interface a so the associated reflection traveltimes correspond to localized transit times between interfaces a and b the overburden velocity model above interface a is not required the result after tomographic inversion is a high resolution estimate of the velocity between interfaces a and b that does not depend on the velocity model above interface a a motivation for introducing interferometric traveltime tomography is that typical layer stripping approaches will see the slowness error increase with depth as the layers are inverted this suggests that

u pb dating of zircons from granitic leucosomes in migmatites of the jiaobei terrane southwestern jiao liao ji belt north china craton constraints on the timing and nature of partial melting abstract in the jiaobei terrane of the jiao liao ji belt eastern china layers and irregular lenses of granitic leucosomes are widely distributed within high pressure hp mafic granulites medium pressure mp granulites amphibolites ttg gneisses and hp and mp pelitic granulites the layers and lenses may be parallel to or cross cut the foliation in the host rocks on different scales and they show evidence of coalescence and migration in the formation of centimeter to decimeter scale segregations the migmatized rocks extend over an area of at least 120 km 75 km from laixi through laiyang and qixia to sw yantai a combined study of mineral inclusions cathodoluminescence cl images and zircon u pb la icp ms dates provides clear evidence on the nature and timing of the partial melting in these granulite facies metamorphic rocks most zircons from the granitic leucosomes are either inherited crystals igneous or detrital with distinct overgrowths or are simply new euhedral crystals both the overgrowths and the new crystals commonly exhibit perfect euhedral shapes pronounced oscillatory zoning and contain mineral inclusions of qtz kfs pl ap in contrast the inherited cores are rounded or irregular in shape and exhibit signs of dissolution these observations suggest that the new zircons are anatectic in origin and that they crystallized from melts derived from dehydration melting reactions and partial melting of the host granulite facies rocks numerous u pb spot analyses of anatectic zircons reveal that the jiaobei terrane experienced a major episode of partial melting in the paleoproterozoic with crystallization of the melt occurring in two distinct periods from 1860 9 2 2 to 1852 1 2 8 ma and 1839 9 2 9 to 1833 3 5 3 ma as represented respectively by the magmatic cores and rims of the anatectic zircons the first age group probably represents the initial crystallization of melts derived from partial melting within the jiaobei terrane while the second age group may represent the completion of migmatization and crystallization of granitic leucosomes this significant partial melting event was genetically associated with the paleoproterozoic mp granulite facies hot stage of exhumation of the southwestern part of the jiao liao ji belt and it induced extensive retrogression of the ttg gneisses and mafic and pelitic granulites as well as the formation of regional migmatites

seasonal temperature salinity changes and thermocline development in the mid atlantic bight as recorded by the isotopic composition of bivalves stable isotope records across annual growth increments in specimens of the surf clam spisula solidissima from the mid atlantic bight shelf from 10 m and 45 m depths reflect the changes in temperature and nutrient concentrations on the shelf over the year the 18 o and 13 c records from clams at the two depths record well mixed conditions in the water column during the winter months and the development of a thermocline during the summer spring high productivity and a transient salinity excursion in surface waters are also recorded reconstructing the paleoceanography of late cenozoic temperate continental shelves may be possible using stable isotope records from fossil spisula solidissima and other bivalves

nature of three episodes of paleoproterozoic magmatism 2180 ma 2115 ma and 1890 ma in the liaoji belt north china with implications for tectonic evolution abstract three episodes of paleoproterozoic magmatism with distinctively different nature in the liaoji belt of the eastern north china craton are discussed here the 2200 2140 ma liaoji a type granites the 2160 2110 ma haicheng mafic sills and the 1890 ma qingchengzi i type granites the mafeng monzogranitic pluton representative of the liaoji a type granites gives a sims u pb zircon age of 2181 6 ma n 20 mswd 4 3 the qingchengzi plagiogranitic pluton representative of the qingchengzi i type granites gives a sims u pb zircon age of 1891 10 ma n 8 mswd 1 8 the mafeng monzogranites are high in fe ti k but low in mg al and ca they have high abundance of total rees ree 213 346 ppm they are relatively depleted in feldspar compatible elements e g eu and sr and hfses e g nb ta p and ti they have high 10000 ga al ratios of 3 19 3 61 and zr nb ce y concentrations of 472 656 ppm which are typical for a type granite the qingchengzi plagiogranites have relatively high al ca na but low fe ti and k contents they have low abundance of total rees ree 17 6 21 6 ppm they are enriched in liles e g ba k and sr but depleted in hfses e g nb ta p ti and y these features combined with extremely high sr y ratios 327 413 are comparable with those of typical modern adakites the liaoji a type granites show a source same to that of the haicheng mafic sills and they originated from the archean subcontinental lithospheric mantle plus with contamination from the archean granites however the qingchengzi i type granites are interpreted to originate from subducted oceanic crust with significant contributions from sediments the liaoji a type granites and the coeval bimodal volcanism in the liaohe group as well as the haicheng mafic sills may represent episodic magmatism which was related to a protracted intra continental rifting caused by lithospheric extension the ca 1890 ma qingchengzi i type granites and coexisting s type granites as well as the coeval regional metamorphism are favored to represent an active continental magmatism linked to paleoproterozoic subduction

pbsl dating of garnet and staurolite constraints on the paleoproterozoic crustal evolution of the eastern block north china craton abstract it is well accepted that the north china craton formed by assembly of the eastern and western blocks along the trans north china orogen with cratonization in the paleoproterozoic 1 85 ma however there is controversy about the formation of the eastern and western blocks themselves especially the timing of cratonization of the eastern block the jiao liao ji orogenic belt is the most important paleoproterozoic orogenic belt in the eastern block and consists mainly of the north and south liaohe groups and the liaoji granitoids the timing of metamorphism of the liaohe group is the key to understanding the evolution of the eastern block of the north china craton because the isotope systematics of metamorphic minerals can be used to date parts of the prograde thermal histories of metamorphic belts dating of minerals such as garnet and staurolite has the distinct advantage that time information can be related directly to the pressure temperature deformation history recorded by the same mineral in this paper we present results of precise 207pb 206pb stepwise leaching pbsl dating of garnet and staurolite from the metasedimentary rocks of the south liaohe group the primitive pb and radiogenic pb are selectively extracted from garnet and straurolite by leach steps and determined by multiple collector mc icp ms the garnet and staurolite record two groups of 207pb 206pb ages at 1 93 1 91 ga and 1 86 ga respectively these constrain the time of peak metamorphism of the liaohe group during collision between the longgang block in the north and the liaonan nangrim block in the south and a subsequent post collisional event respectively our data for the south liaohe group and previously published data for the liaoji granite combined with key lithological structural and metamorphic information indicate that the cratonization of the eastern block of the north china craton occurred at 1 93 1 91 ga

high resolution aquifer characterization using seismic cross hole tomography an evaluation experiment in a gravel delta we performed field experiments at a well studied aquifer test site to evaluate the geophysical method of seismic cross hole tomography for high resolution aquifer characterization we address the challenge of finding meaningful relationships between seismic velocity and hydraulic conductivity at the field scale for hydraulic conductivity estimation the resolution of seismic cross hole data is limited by inversion ambiguities and diffraction effects which are not accounted for using conventional ray based inversion algorithms for velocity reconstruction we investigate the impact of diffraction effects on seismic velocity inversion and implications for hydraulic modelling our ray based seismic tomograms correlate well with sedimentary cores and hydraulic conductivity logs allowing us to interpret a zone model with distinct geophysical hydraulic zones we use this zone model to constrain seismic inversions using two approaches for forward modelling ray tracing infinite frequency approximation and wavefield modelling at a realistic frequency which accounts for diffraction we show that using the common ray tracing approach seismic velocities in low velocity zones may be significantly overestimated based on the available data we observe a negative linear relationship between logarithmic hydraulic conductivity and seismic velocity this relationship is used to parameterize hydraulic models based on seismic velocity models computer simulations of advective contaminant transport demonstrate that their results are extremely sensitive to an accurate determination of seismic low velocity zones we conclude that seismic tomography is indeed very useful for high resolution aquifer characterization however an inversion approach that accounts for diffraction effects a priori knowledge of the subsurface structure and additional well data should be applied for quantitative interpretations

multiple sources for the origin of granites geochemical and nd sr isotopic evidence from the gudaoling granite and its mafic enclaves northeast china geochemical and sr and nd isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china the rocks include monzogranite porphyric granodiorite and quartz diorite monzogranites have relatively high 87rb 86sr ratios 0 672 0 853 low initial 87sr 86sr ratios 0 7052 0 7086 and e nd t values 18 5 to 20 9 indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time quartz diorites have high initial 87sr 86sr ratios 0 7118 0 7120 and negative e nd t values 13 2 to 18 1 coupled with high al2o3 and mgo contents indicating they were derived from enriched lithospheric mantle with contributions of radiogenic sr from plagioclase rich metagreywackes or meta igneous rocks i e ancient lower crust two groups of enclaves with igneous textures and abundant acicular apatites are distinguished dioritic enclaves and biotite monzonitic enclaves dioritic enclaves have low al2o3 13 5 16 4 wt and high mgo mg 72 3 concentrations low initial 87sr 86sr ratios 0 7058 0 7073 and negative e nd t values 7 2 and are enriched in liles and lrees and depleted in hfses suggesting they were derived from an enriched lithospheric mantle source biotite monzonitic enclaves have sr and nd isotopic compositions similar to the monzogranites indicating they were crystal cumulates of the parental magmas of these monzogranites granodiorites have transitional geochemistry and nd and sr isotopic compositions intermediate between the monzogranites quartz diorites and the enclaves geochemical and sr and nd isotopic compositions rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead magma mixing of mafic mantle derived and juvenile crustal derived magmas coupled with crystal fractionation and assimilation of ancient lower crust is compatible with the data this example shows that at least some calc alkaline granitoids are not produced by pure intracrustal melting but formed through a complex multi stage hybridization process involving mantle and crustal derived magmas and several concomitant magmatic processes crystal fractionation crustal assimilation and crustal anatexis

broad band trajectory mechanics author s vasco dw nihei k abstract 2019 published by oxford university press on behalf of the royal astronomical society we present a trajectory based solution to the elastodynamic equation of motion that is valid across a wide range of seismic frequencies that is the derivation of the solution does not invoke a high frequency assumption or require that the medium have smoothly varying properties the approach adopted from techniques used in quantum dynamics produces a set of coupled ordinary differential equations for the trajectory the slowness vector and the elastic wave amplitude along the ray path the trajectories may be determined by a direct solution of the governing equations or derived as the by product of a numerical wavefield simulation synthetic tests with interfaces and layers containing increasingly narrow transition zones indicate that the conventional high frequency trajectories associated with the eikonal equation bend too sharply into high velocity regions as the wavelength exceeds the transition zone width tests in a velocity model based upon mapped structural surfaces from the geysers geothermal field in california indicate that discrepancies between high frequency and broad band trajectories can exceed several hundred metres at wavelengths of 1 hz an application to a crosswell tomographic imaging experiment demonstrates that the technique provides a basis for the seismic monitoring of fluid flow along narrow features such as fracture zones

crosswell seismic imaging in a contaminated basalt aquifer multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at idaho national engineering and environmental laboratory most of these surveys used a high frequency 1000 10 000 hz piezoelectric seismic source to obtain p wave velocity tomograms the p wave velocities range from less than 3200 m s to more than 5000 m s additionally a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site this source known as an orbital vibrator allows simultaneous acquisition of p and s waves at frequencies of 100 to 400 hz and acquisition over larger distances the velocity tomograms show a relationship to contaminant transport in the groundwater zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows the orbital vibrator data show high vp vs values from 1 8 to 2 8 in

zircon u pb and lu hf isotopic and whole rock geochemical constraints on the lanhe and heichashan groups implications for the paleoproterozoic tectonic basin evolution of the luliang complex abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks collided to form the north china craton the complex mainly consists of metamorphosed granitic plutons and supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan lanhe and heichashan groups the lanhe group is composed of meta conglomerates quartzites and phyllites with minor meta basalts whereas the heichashan group consists of molasse like meta conglomerates and coarse grained quartzites geochemistry of the yejishan meta sedimentary rocks indicates weak source weathering and dominantly chemical immature features whereas the lanhe and heichashan samples display opposite features u pb ages of detrital zircons from the lanhe groups yield four age peaks at 2180 ma 2370 ma 2520 ma and 2700 ma the former three peaks coincide with ages of the chijianling guandishan ttg gneisses 2199 2151 ma and meta volcanic rocks from the luliang and yejishan groups 2213 2156 ma age of the gaijiazhuang porphyritic gneisses 2375 2364 ma and age of the yunzhongshan ttg gneisses 2499 ma respectively whereas detrital zircons forming the oldest age peak were most likely derived from the early neoarchean crust of the eastern block for the heichashan group the dominant 2 2 2 0 ga detrital zircons were probably recycled from the underlying jiehekou group and the minority is directly derived from the early paleoproterozoic granitoids in the luliang complex the youngest detrital zircon age peaks of 2 17 ga and 1 82 ga place maximum depositional ages on the lanhe and heichashan groups respectively whereas the local 1 81 1 79 ga massive granites place constraint on their minimum depositional ages taking into account the lithostratigraphic features provenance and formation ages we suggest that the lanhe group formed in a shrinked remnant back arc basin and the heichashan group was deposited in a foreland basin conversion of the tectonic basin from the middle paleoproterozoic back arc basin to the late paleoproterozoic foreland basin is well consistent with the model that the single collision to form the basement of the north china craton happened at 1 85 ga

the liaohe group an insight into the paleoproterozoic tectonic evolution of the jiao liao ji belt north china craton abstract the jiao liao ji belt represents one of the largest exposed regions of paleoproterozoic rocks along the eastern margin of the north china craton paleoproterozoic basement material in this area is dominated by deformed and metamorphosed volcano sedimentary successions with minor amounts of granitic and mafic intrusions this study presents the results of a systematic zircon u pb geochronological whole rock geochemical and sm nd isotopic analysis of the volcano sedimentary successions within the liaohe group of the jiao liao ji belt these data provide insights into the multiple paleoproterozoic tectonothermal events that have affected the belt as well as the petrogenesis of the paleoproterozoic meta volcanics and metasedimentary rocks on the liaodong peninsula accurate u pb age and trace element determinations of zircons from the meta volcanics in this region using laser ablation inductively coupled plasma mass spectrometry indicate that these units formed at ca 2 2 ga and were metamorphosed at ca 1 9 ga respectively these data indicate that the paleoproterozoic geochronological framework of this region is dominated by 2 2 2 0 ga magmatic 1 98 1 90 ga sedimentary ca 1 90 ga metamorphic and 1 87 1 82 ga post tectonic magmatic events the meta volcanics can be split into basalt basaltic andesite andesite dacite and rhyolite units that define a continuous calc alkaline dominated magmatic sequence that is similar to the sequences commonly found within phanerozoic magmatic arcs the meta basalts are enriched in the light rare earth elements cr co and ni and are depleted in the heavy rare earth elements and the high field strength elements e g nb ta and ti indicating that they formed from magmas generated by the partial melting of lithospheric mantle material that was previously metasomatized by subduction zone derived fluids melts the large geochemical and isotopic variations within the metamorphosed andesite dacite and rhyolite units all provide evidence of magma mixing between felsic melts generated by the partial melting of paleoarchean neoarchean basement material and the mafic melts that may also formed the meta basalts within the liaohe group or evolve via fractional crystallization prior to mixing the geochemistry of the metasedimentary rocks indicate that the pre metamorphism sedimentary units ranged from being compositionally mature to being immature and poorly sorted and were weakly to moderately weathered these sediments were derived primarily from metamorphosed felsic volcanics within the liaohe group as well as the paleoproterozoic liaoji granites they also contain archean continental crustal material that is derived mainly from ancient intermediate mafic basement units the combined geochronological geochemical and geological data indicate that a paleoproterozoic arc continent collision model can well explain the nature and formation of the jiao liao ji belt

acoustic velocities in heated block of granite subjected to uniaxial stress acoustic velocities have been measured within a 38 cm cubic block of granite isolated from the surrounding rock the block was subjected to uniaxial stresses in the range 0 24 mpa and to heating in the range 14 sup 0 to 98 sup 0 c an increase in temperature from 14 sup 0 to 72 sup 0 c in the unstressed block resulted in an increase in velocities in directions parallel and perpendicular to the applied stress a further increase in temperature to 98 sup 0 c in the unstressed block resulted in a decrease in velocities application of uniaxial stress with the block at a temperature of 98 sup 0 c resulted first in uniform increases in velocity to an applied stress of mpa and then sharp decreases from 10 to 14 mpa followed by uniform increases in velocity to a maximum stress of 24 mpa a reduction in temperature to 16 sup 0 c resulted in a sharp reduction in velocity 25 percent less than originally measured at ambient temperature it is concluded that at temperatures rising to 72 sup 0 c anisotropic thermal expansion of the crystals comprising the granite causes the closure of microcracks present in the unheated rock between 72 sup 0 and 98 supmore 0 c particularly when stress was applied irreversible mechanical changes occurred in the block less

applications of algebraic reconstruction techniques to crosshole seismic data tomographic imaging techniques were applied to two crosshole data sets to determine the velocity structures and the reliability and resolution of the algorithms on real data the experiments were carried out at the retsoff salt mine in new york and at the underground radioactive waste study site at the stripa mine facility in sweden the traveltimes at restoff were high quality and were obtained over raypaths of up to 500 m in length the structure was quite complicated with velocity contrasts up to 50 percent the stripa site was in granitic rock with velocity contrasts of only a few percent the dimensions of the experiment were small with maximum ray lengths of just over 10 m the data at this site were collected with very high accuracy source and receiver locations were measured to better than 1 0 mm and traveltimes were read to 0 001 ms a number of algorithms similar to the algebraic reconstruction techniques art used in medical imaging have been applied to the data some modifications of the algorithms such as the application of weighting schemes damping parameters and curved raypaths were performed the resulting velocity fields were compared to the known fields and with each other to determine an optimal method the algorithms were found to be a rapid reliable means of reconstructing the slowness field of real data low velocity zones were recovered with accuracy in location and value it was also found that great care was necessary in application of the techniques to ensure that proper damping parameters are used and the proper number of iterations taken otherwise poor reconstructions will result

mid late triassic metamorphic event for changhai meta sedimentary rocks from the se jiao liao ji belt north china craton evidence from monazite u th pb and muscovite ar ar dating abstract the precise constraints on the timing of metamorphism of the changhai metamorphic complex is of great importance considering the prolonged controversial issue of the north margin and the extension of the sulu dabie hp uhp belt while the monazite u th pb and muscovite 40 ar 39 ar techniques are widely accepted as two of the most powerful dating tools for revealing the thermal histories of medium low grade metamorphic rocks and precisely constraining the timing of metamorphism the changhai metamorphic complex at the se jiao liao ji belt north china craton consists of a variety of pelitic schist and grt ky bearing paragneiss and minor quartzite and marble analyses of mineral inclusions and back scattered electric bse images of monazites combined with la icp ms u th pb ages for monazites and 40 ar 39 ar ages for muscovites provide evidence of the origin and metamorphic age of the changhai metamorphic complex monazites separates from various grt mus schists and grt ky st mus paragneisses exhibit homogeneous bse images from cores to rims and contain inclusion assemblages of grt mus qtz ctd ky in schist and grt ky st mus pl kfs qtz inclusions in paragneiss these inclusion assemblages are very similar to matrix minerals of host rocks indicating they are metamorphic rather than inherited or detrital in origin la icp ms u th pb dating reveals that monazites of schist and paragneiss have consistent 206 pb 238 u ages ranging from 228 1 3 8 to 218 2 3 7 ma in contrast muscovites from various schists show slightly older 40 ar 39 ar plateau ages of 236 1 1 5 to 230 2 1 2 ma these geochronological and petrological data conclude that the pelitic sediments have experienced a metamorphic event at the mid late triassic 236 1 218 2 ma rather than the paleoproterozoic 1950 1850 ma commonly regarded as the precambrian basement for the jiao liao ji belt hence the changhai metamorphic complex should be considered as a discrete lithotectonic group this newly recognized mid late triassic metamorphic event 236 1 218 2 ma for the changhai metamorphic complex is coeval with the hp uhp metamorphic event 235 220 ma for sulu dabie rocks this leads us to speculate that the metamorphism of the changhai complex belt along the se margin of the north china craton was genetically related to the mid late triassic collision of the north china and south china cratons by the same token the sulu dabie hp uhp belt may have extended through yantai and the southern yellow sea and to the southern side of the changhai metamorphic complex

reconstructing past upwelling intensity and the seasonal dynamics of primary productivity along the peruvian coastline from mollusk shell stable isotopes 1 we present here a potential new method to evaluate past variations of the mean intensity of peruvian coastal upwelling and of the seasonal timing of phytoplankton blooms this method uses a combination of the monthly carbon and oxygen isotopic signals preserved in fossil mollusk shells and a series of corrections to extract the variations of the dissolved inorganic carbon dic 13c based on the analysis of five shell samples 85 shells in total from the southern peruvian coast we suggest that the mean coastal upwelling intensity can be determined from a linear relationship between average values of corrected shell 13c and 18o this new potential proxy would bring additional independent information valuable to interpret paleoproductivity changes reconstructed from marine sediment of the nearby continental shelf results obtained on fossil samples from the middle holocene show an increase in upwelling intensity during this period associated to a spatial reorganization of upwelling centers along the south peruvian coast at the seasonal scale corrected shell 13c enrichment indicates a phytoplankton bloom seasonal timing of phytoplankton blooms can be estimated by the lag with the annual temperature cycle reproduced by shell 18o monthly variations the results obtained with two modern shell samples indicate phytoplankton blooms occurring during summer and fall consistently with in situ productivity observations our method relies on revisited assumptions about the influence of temperature and metabolism in mollusk shell 13c we further discussed the validity of these assumptions and the potential implications for the interpretation of similar data sets

crosshole seismology and seismic imaging in crystalline rocks a borehole to borehole audiofrequency seismic system using piezoelectric transducers as active elements has been developed and used to investigate crystalline rocks in canada high quality seismograms have been recorded for transmitter receiver distances of up to 230 meters it has been found that both travel times and signal amplitudes provide diagnostic information about rock quality two dimensional images of seismic velocity and transparency distributions between two boreholes derived from observed arrival times and amplitudes by simple back projection tomography reflect lithology and geological structure the results indicate the potential usefulness of crosshole seismic imaging as a tool for rock mass characterization

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

near surface and crustal scale images of the nechako basin british columbia canada from magnetotelluric investigations1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2geological survey of canada gsc contribution no 20100129 two dimensional 2 d models of audio and broadband magnetotelluric mt data collected throughout the southern nechako basin in south central british columbia canada provide electrical resistivity images of the cretaceous to oligocene volcanic and sedimentary packages and underlying crustal scale features analysis of distortion effects and structural dimensionality indicate that the mt responses are primarily one dimensional 1 d at periods less than 0 1 s departures from a 1 d response occur with maximum phase differences occurring between 0 1 and 10 s the upper crustal resistivity models reveal a low resistivity layer at near surface depths interpreted as chilcotin basalts that blankets portions of the region to depths less than 50 m but locally thicken up to 200 m cretaceous sedimentary units those showing the highest potential for hydrocarbons are characterized by moderately low resistivities that are laterally variable more uniform lower resistivities appear to be associated with the e

convolutional back projection imaging of physical models with crosshole seismic data1 the development of crosshole seismic tomography as an imaging method for the subsurface has been hampered by the scarcity of real data for boreholes in excess of a few hundred metres depth crosshole seismic data acquisition is still a poorly developed and expensive technology a partial solution to this relative lack of data has been achieved by the use of an ultrasonic seismic modelling system such ultrasonic data obtained in the laboratory from physical models provide a useful test of crosshole imaging software in particular ultrasonic data have been used to test the efficacy of a convolutional back projection algorithm designed for crosshole imaging the algorithm is described and shown to be less susceptible to noise contamination than a simultaneous iterative reconstruction technique sirt algorithm and much more computationally efficient

isotope paleontology growth and composition of extant calcareous species abstract isotope paleontology uses the isotopic composition of fossil remains of organisms to make inferences about the physical surroundings of growth of the organisms especially temperature and to obtain clues about life history and modes of growth in calcareous fossils oxygen isotopes are mainly used in the former and carbon isotopes in the latter however since physical surroundings and organism response are intimately associated both types of information are contained in each of the isotopic signals to explore the potential of isotope paleontology and to provide a basis for reconstruction a broad range of extant organisms has been studied taking the pioneering work of epstein and associates as a starting point results are summarized for a representative sampling of these studies with emphasis on work at the laboratories of the authors from the mid seventies to the present the organisms considered are nannoplankton benthic algae planktonic and benthic deep sea foraminifera larger foraminifera sponges corals bryozoans polychaetes arthropods bivalves gastropods cephalopods and vertebrates fish otoliths the survey broadly suggests that regarding oxygen isotopes materials tend to be precipitated close to equilibrium with the surrounding seawater as postulated by urey and that for carbon isotopes disequilibrium is the rule life spans growth rates differential seasonal growth and age of reproductive activity can be extracted under favorable circumstances from individual shells and skeletal parts in detail the interpretation of isotope records of individual shells is quite complicated and simple models will fail to give satisfactory results in many or most cases

rapid climate change in the north atlantic during the younger dryas recorded by deep sea corals research on global climate change has increasingly focused on rapid century scale and decadal changes one such climate shift the younger dryas cooling event1 took place during the last deglaciation from 13 000 to 11 700 years bp climate records from greenland ice cores and north atlantic sediment cores show high frequency fluctuations implying significant 5 c shifts in temperature at this time taking place within 50 100 years ref 2 the origin of the younger dryas has recently been attributed to a reduction or cessation of deep water production in the north atlantic and a concurrent lessening of the heat flux from low latitudes3 4 the role of intermediate waters 1 000 2 000 m depth is less certain however because climate proxies for this ocean reservoir are rare and ambiguous here we report on the use of a new climate archive deep sea corals from orphan knoll 1 600m depth in the northwestern atlantic ocean the oxygen isotope ratios in the coral skeletons accurately dated by the 230th 234u chronometric method change markedly coincident with the initiation of the younger dryas suggesting that there were profound changes in intermediate water circulation at this time

location of the tectonic boundary between the paleoproterozoic jiao liao ji belt and the archean longgang block in the lianshanguan area northeastern china abstract the tectonic evolution of the paleoproterozoic jiao liao ji belt which is located in the north china craton in northeastern china is the subject of ongoing debate most previous studies on this belt have been based on traditional geological methods with most of the data being obtained from the surface leading to uncertainties regarding the deep geological structure of the belt this has restricted our understanding of the tectonic character and development of the belt however this limitation could be overcome by geophysical studies here we analyze and interpret newly collected rock physical property data density magnetic susceptibility and resistivity and non seismic geophysical data gravity magnetic and magnetotelluric sounding data for the lianshanguan area to infer the location configuration and nature of the tectonic boundary between the paleoproterozoic jiao liao ji belt and the archean longgang block the lianshanguan rock mass which belongs to the archean longgang block shows a weak gravity anomaly 0 6 mgal and high resistivity 103 6 to 104 m the area south of the lianshanguan rock mass consists of the paleoproterozoic liaohe group and displays an intermediate magnetic anomaly 0 200 nt and low resistivity 10 102 5 m we therefore infer that the tectonic boundary of the jiao liao ji belt is located along the southern margin of the lianshanguan intrusion we also show that the tectonic boundary in the eastern liaoning southern jilin area trends e w and extends from shuangtaling through lianshanguan caohecheng balidianzi and to guaimozi the boundary between the longgang block and the jiao liao ji belt dips predominantly to the south suggesting an extensional tectonic regime during the paleoproterozoic time

shifts in oxygen and carbon isotope signals in marine molluscs from the central paratethys europe around the lower middle miocene transition abstract stable isotope data of mollusc shells from two adjacent time slices karpatian badenian from the central paratethys were investigated to detect differences in environmental parameters and to depict shifts in the isotope signature of the paratethyan seawater around the early middle miocene transition altogether seventeen different gastropod species and one bivalve species from the karpatian korneuburg basin and the badenian northern alpine foreland basin were selected representatives of various ecological guilds yielded different isotope patterns especially in 13c reflecting different original habitats or nutrition although molluscs precipitate their shells in oxygen isotopic equilibrium we preferred to compare isotope data of shells of the same genus of the family turritellidae from the karpatian and badenian the badenian turritella shells from the northern alpine foreland basin yielded distinctly higher 18o and 13c values than the respective karpatian shells from the korneuburg basin as the main factors controlling 18o values in gastropod shells are temperature and 18o of the water during precipitation the differences between the oxygen isotope data of the two time slices can only be explained by these factors good independent palaeotemperature proxies exist for the early to middle miocene of central europe they do not indicate a significant temperature variation therefore different 18o values of the seawater in the different basins of the central paratethys must be responsible for the contrasting 18o values when calculated with commonly assumed 18o seawater values for the miocene badenian turritella shells indicate too cold temperatures these data clearly document the danger of palaeotemperature interpretations based solely on stable isotopes as smaller and marginal marine settings such as the paratethys sea can be seriously influenced by regional differences in the isotope composition of the seawater only a thorough consistent control by other climate proxies e g palaeoecology of molluscs as in this study allows a sensible interpretation

paleoproterozoic structural evolution of the southern segment of the jiao liao ji belt north china craton abstract the paleoproterozoic jiao liao ji belt separates the eastern block of the north china craton into two small sub blocks the northern longgang and the southern rangrim blocks however it still remains unknown or controversial about the subduction polarity collisional deformation and kinematics between two sub blocks the southern segment of the belt consists of the paleoproterozoic fenzishan and jingshan groups and paleoproterozoic high pressure mafic granulites and serpentinites blocks which are located in the jiaodong complex all of which are separated from the jiaodong complex of neoarchean ttg gneisses by stz1 ductile shear zones structural analysis in this study indicates that most of the rocks in all the units of the southern segment of the jiao liao ji belt underwent three distinct episodes of folding d1 to d3 and two stage of ductile thrust shearing stz1 coeval to d1 and d2 stz2 between d2 and d3 the d1 deformation formed penetrative axial planar foliations s1 bedding parallel ductile shear zone mineral stretching lineations l1 and rarely preserved small isoclinal d1 folds in the jingshan and fenzishan groups in the jingshan group however penetrative deformational transposition resulted in stacking of sedimentary compositional layers which are separated by bedding parallel ductile shear zones stz1 at a period of about 1956 ma to 1914 ma the kinematic indicators of stz1 in the jingshan group with resultant prograde peak metamorphism up to granulite facies grade and the fenzishan group with peak metamorphism up to amphibolite facies grade indicate nw directed compression d2 resulted in crustal thickening with retrograded medium pressure granulite facies grade at about 1914 1893 ma the d2 deformation produced nw verging asymmetric and recumbent folds interpreted to have resulted from basement involved thicken skin structures the jiaodong complex was also involved into the development of wnw verging asymmetric tight folds associated with d2 in the jingshan and the fenzishan groups ongoing collision led to the development of transpressional ductile shearing stz2 forming the transpressional taipingzhuang dextral ductile shear zone between the jingshan group and the southern archean complex and the transpressional tading xiadian sinistral ductile shear zone between the jingshan group and the northern archean complex all three lithotectonic units were superposed during the late d3 deformation with amphibolite facies metamorphism the d3 deformation developed wnw trending open to tight upright folds at about 1893 1875 ma the structural pattern resulting from superimposition of d2 and d3 is a composite synform in the fenzishan and jingshan groups the structural events of d1 and stz1 and d2 and stz2 deformation were possibly responsible for fast syn collisional exhumation of the high pressure mafic granulites the structural patterns and deformational history of the fenzishan and jingshan groups suggest a southeastward directed oblique subduction beneath the northwestern margin of the rangrim block and that the final scissor shaped closure of the rift led to collision between the two blocks to form the coherent basement of the eastern block 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

response of infaunal macrobenthos to the sediment granulometry in a tropical continental margin southwest coast of india abstract surficial sediment samples collected from the continental margin of the southwest coast of india in july 2004 were examined for the grain size and soft bottom macrobenthic fauna to understand the sediment granulometry and its effect on the faunal distribution samples were collected using smith mcintyre grab from 20 to 200 m depth range consisting of mid shelf outer shelf and slope fine grained sediment located in the mid shelf and supported low faunal abundance polychaetes constituted the bulk of the fauna feeding guild changed with depth and sediment granulometry coexistence of deposit feeders and carnivores in outer shelf and deposit feeders and filter feeders in the slope region indicated the effective utilization of different food resources in general richness and diversity were high in the southern region depth wise the diversity and abundance were relatively high in the 50 75 m depth range correlation and bio env analysis showed that combination of different factors such as sediment texture sediment sorting and depth were found to influence the distribution of macrobenthos hence spatial variations observed in benthic community were presumably linked to the variations in sediment granulometry and the energy level conditions prevailing in the area

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

the use of oxygen isotope variation in shells of estuarine mollusks as a quantitative record of seasonal and annual colorado river discharge abstract we describe a new method for the calculation of river flow that uses the oxygen isotope composition of bivalve mollusk shells that grew in the river water seawater mixing zone of the colorado river estuary sclerochronological techniques are used to identify tidally induced fortnight scale bundles of daily growth increments within shell cross sections these fortnightly markers are used to establish a chronology for samples taken for 18 o analysis a composite seasonal 18 o profile derived from five shells that grew in the absence of river water flow is used as a baseline against which profiles of river influenced shells are compared because this comparison is between matched fortnights within a year the temperature of shell growth is likely to be very similar the difference in 18 o between the river influenced shell and the no flow composite shell therefore represents the change in the 18 o of the water due to the presence of river water in the mixing zone the river water end member is also determined within a fortnightly context so that the change in the 18 o of mixing zone water can be used to calculate the relative proportions of seawater and fresh water the fresh water end member is calculated from the 18 o of bivalves alive prior to the emplacement of dams and water diversions on the colorado river the marine end member is based on direct measurements of the 18 o of northern gulf of california water during times of no colorado river flow the system has been calibrated to absolute flow amounts using recent releases of known volume and rate

stable isotope profiles of last interglacial pelukian transgression mollusks and paleoclimate implications in the bering strait region abstract the marine paleoclimate during the last interglaciation in the bering strait region is inferred from the stable oxygen and carbon isotope profiles of fossil bivalve mollusks specimens were collected from the marine highstand deposits of the pelukian transgression from the arctic alaskan coastal plain the nome coastal plain st lawrence island and the val katlen suite on the chukotka peninsula as a calibration modern mollusks were obtained from the major water masses in the bering chukchi seas system and from coastal environments near the fossil localities the 18 o composition of the modern mollusks accurately reflects the seawater 18 o differences among the water masses and the ambient temperature range at each site seasonal paleotemperature ranges are estimated from the 18 o profiles of the fossils by comparison with those of the modern specimens a simple model is developed to correct the paleotemperature ranges for the influence of differences in seawater 18 o between water masses and seasonal variations caused by freshwater discharge paleotemperatures calculated for the skull cliff site alaskan arctic coastal plain are close to but slightly cooler than those of modern specimens from peard bay and icy cape the isotopic composition of a pelukian specimen collected near wainwright shows the obvious influence of locally reduced salinities with a correction for lower seawater 18 o this profile yields a summer temperature of 13 c which is 3 c warmer than that from the modern icy cape specimen the isotope records of two specimens from the nome coastal plain suggest salinities that were 3 5 psu lower than the modern eastern bering shelf the paleotemperature range of 0 15 c is consistent with modern conditions in norton sound the character of the isotope profiles of the pelukian specimens from st lawrence island is very different than that of modern specimens near the island but matches the 18 o values of shells from deeper sites in anadyr water this suggests that the fossil mollusks were living in anadyr strait and were transported by a glacial advance from the chukotka peninsula the last interglacial specimens from the val katlen suite have isotope profiles with large seasonal 18 o ranges and the clear influence of a reduced salinity coastal water mass calculated paleotemperatures from the val katlen specimens range from 0 to 13 c differences in the 13 c of shell carbonate between sites appears to reflect the regional distribution of the 13 c of sedimentary organic matter som which is a mixture between terrestrial organic matter mean 13 c of 24 and marine phytoplankton 21 partitioning of 13 c between shallow and deep waters by phytoplankton productivity and remineralization may also affect the regional distribution differences in shell 13 c between taxa may relate to feeding mode and the type and isotopic composition of ingested particles the filter feeders mya and astarte typically have 13 c values 1 2 more positive than the deposit feeders macoma and serripes this effect is attributed to a 13 c difference between marine phytoplankton and som with a component of terrestrial organic carbon

timing of metamorphism in the paleoproterozoic jiao liao ji belt new shrimp u pb zircon dating of granulites gneisses and marbles of the jiaobei massif in the north china craton abstract the paleoproterozoic jiao liao ji belt lies in the eastern block of the north china craton with its southern segment extending across the bohai sea into the jiaobei massif high pressure pelitic and mafic granulites have been recently recognized in the paleoproterozoic jingshan group jiaobei massif new shrimp u th pb geochronology combined with cathodoluminescence cl imaging of zircon has been applied to the determination of the timing of the metamorphism of the high temperature and high pressure granulites and associated gneisses and marbles metamorphic zircons in these high pressure granulites gneisses and marbles occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores metamorphic zircons are all characterized by nebulous zoning or being structureless with high luminescence and relatively low th u values metamorphic zircons from two high pressure mafic granulites yielded 207pb 206pb ages of 1956 41 ma and 1884 24 ma one metamorphic zircon from a garnet sillimanite gneiss also gave an apparent 207pb 206pb age of 1939 15 ma these results are consistent with interval of ages of c 1 93 1 90 ga already obtained by previous studies for the north and south liaohe groups and the laoling group in the northern segment of the jiao liao ji belt metamorphic zircons from a high pressure pelitic granulite and two pelitic gneisses yielded weighted mean 207pb 206pb ages of 1837 8 ma 1821 8 ma and 1836 8 ma respectively two diopside olivine phlogopite marbles yielded weighted mean 207pb 206pb ages of 1817 9 ma and 1790 6 ma these paleoproterozoic metamorphic ages are largely in accordance with metamorphic ages of c 1 85 ga produced from the ji an group in the northern segment of the jiao liao ji belt and c 1 86 1 80 ga obtained for the high pressure pelitic granulites from the jingshan group in the southern segment as this metamorphic event was coeval with the emplacement of a type granites in the jiao liao ji belt and its adjacent areas it is interpreted as having resulted from a post orogenic or anorogenic extensional event

ecological and paleoenvironmental information using stable isotope profiles from living and fossil molluscs stable oxygen and carbon isotopic profiles from recent specimens of spisula solidissima and placopecten magellanicus collected off the virginia coast are used to calibrate annual temperature controlled cycles in the 18o profile and shell growth characteristics the amplitude of the annual 18o cycles decreases with increasing water depth and may be used as a relative depth indicator the isotopic of profiles of two fossil specimens of pleistocene spisula are very similar in amplitude and character to modern analogues and verify the formation of annual growth increments in these fossil specimens offsets between the 18o profiles of the fossil and modern specimens are related to known temperature and ice volume effects during the late pleistocene and support the utility of mollusc isotope records as a stratigraphic tool carbon isotopic profiles from all specimens show light values in the spring and or fall associated with seasonal phytoplankton productivity offsets in the carbon isotopic composition between infaunal and epifaunal species may be related to sediment porewater geochemistry and oxidation of organic matter trends toward lighter 13c values through ontogeny suggest the effects of metabolic changes from a fast growing juvenile into a slower growing sexually mature adult anomalies in both the oxygen and carbon isotopic profiles identify the formation of minor shell growth increments as corresponding to hydrographic perturbations and to winter cold temperatures

epma u th pb monazite and shrimp u pb zircon geochronology of high pressure pelitic granulites in the jiaobei massif of the north china craton the jiaobei massif constitutes the southern segment of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton and contains high pressure hp mafic and pelitic granulites the hp pelitic granulites contain four distinct mineral assemblages garnet kyanite biotite muscovite rutile m1 garnet kyanite ternary feldspar biotite muscovite rutile m2 garnet sillimanite biotite perthite anti perthite m3 and biotite muscovite sillimanite plagioclase m4 of which m2 is a typical hp pelitic assemblage the origin of these hp granulites is important for understanding the tectonic evolution of the jiao liao ji belt but the timing of the hp event still remains unknown this study applied the epma u th pb monazite and shrimp u pb zircon dating techniques to determine the metamorphic ages of the hp pelitic granulites in the jiaobei massif cl images and th u ratios show that all monazite and zircon grains in the analyzed samples are of metamorphic origin eighty two epma analyses on 16 monazite grains from two samples yielded three age groups at 1895 to 1882 ma 1814 to 1813 ma and 1706 to 1692 ma and the ages of 16 shrimp analyses on 14 zircon grains from one sample range from 1864 to 1803 ma the oldest ages of 1895 to 1882 ma were yielded from high y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite and thus interpreted as the time of the hp m2 granulite facies metamorphism the epma monazite ages of 1814 to 1813 ma and shrimp zircon ages of 1864 to 1803 ma are interpreted as the approximate ages of the post hp granulite facies metamorphism m3 most probably resulting from the exhumation of the hp granulites to the medium pressure granulite facies levels the youngest age group of 1706 to 1692 ma obtained from low y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism m4 that occurred when the hp pelitic granulites were exhumed to the upper crust the presence of paleoproterozoic hp mafic and pelitic granulites in the southern segment of the jiao liao ji belt suggests that the evolution of the jiao liao ji belt in the eastern block of the north china craton must have been involved in subduction or collision related tectonic processes

influence of the upwelling events on the δ13c and δ18o of the benthic bivalve shells of the south western continental margin of india in this study the influence of the spatial and temporal variability of upwelling intensity and the associated biological productivity observed during different phases of summer monsoon along the southwestern continental margin of india swcmi on the 13c and 18o of the inorganic biogenic carbonate shells was investigated multispecies benthic bivalve shells 1 5 mm separated from ten surface sediment samples of swcmi off 12 n 10 n and 9 n collected during the onset osm and peak psm phase of the summer monsoon of 2009 were analysed for 13c and 18o sea surface temperature along the study region indicates prominent upwelling in psm than in osm a comparison of analytical and predicted values for 18o in the bivalve shells confirmed their in situ origin during both the sampling periods during psm the 13c values in the benthic bivalve shells were more depleted in 13c than during osm which recorded lower values of 13c in dissolved inorganic carbon of bottom waters expected in the study region in psm due to the upwelled waters high surface productivity and the associated high degradation of the organic matter in the subsurface and bottom waters however this depletion of 13c was not observed in benthic bivalve shells obtained from 10 n since it is influenced by high export fluxes of carbon from the cochin estuary since early monsoon months

computer simulation of crosswell seismic propagation and determination of elastic parameters the potential usefulness of crosswell seismic measurement in determining the dynamic elastic parameters of subsurface material is demonstrated it is shown that tomographic inversion of seismic wave travel time for a combined borehole to borehole and borehole to surface configuration provides the characteristics of shape size and orientation of anomalies the travel time for each source and receiver paths are computed and are inverted to determine the elastic parameters the procedure described in this paper can prove to be economic and less time consuming in mapping anomalous regions such as soft pockets tunnels and buried pipes that are quite often encountered by civil engineers during site selection for large construction projects key words crosshole measurement tomographic inversion dynamic parameters site investigation seismic investigation

a study of methods for tomographic velocity estimation in the presence of low velocity zones this paper deals with the problem of seismic velocity estimation from first arrival traveltimes in a two dimensional 2 d cross hole geometry where explosions are detonated in one borehole while recordings are made in another borehole and on the surface standard tomographic procedures are based on decomposition of the cross hole area into a number of cells and a simplifying assumption of straight raypaths in the presence of significant low velocity zones the resulting images may be contaminated different ways of performing tomographic inversion are tested on a number of synthetic examples images obtained by direct unrestricted least squares inversion are often seriously distorted however methods using more cells and some kind of damping often give more satisfactory results because the risk of distorted images is always present in inversion procedures comparison with synthetic data forward modeling is a valuable tool in the interpretation process with a reasonably good initial solution impro

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

metallogeny of the north china craton link with secular changes in the evolving earth abstract the north china craton ncc has experienced a complex geological evolution since the early precambrian and carries important records of secular changes in tectonics and metallogeny here we synthesize the salient geological and tectonic features of the evolution and destruction of the ncc vis a vis major metallogenic events and the formation of potential ore deposits we identify a close relationship between the major geological events in the ncc and those reported elsewhere on the globe we trace the records of a regular change in the pattern of metallogeny mineral deposit character spatial distribution and genetic mechanisms which closely match the timing and styles of the major geological and tectonic events in this craton the ncc went through five major tectonic cycles 1 neoarchean crustal growth and stabilization 2 paleoproterozoic rifting subduction accretion collision with imprints of the great oxidation event goe 3 late paleoproterozoic neoproterozoic multi stage rifting 4 paleozoic orogenesis at the margins of the craton and 5 mesozoic extensional tectonics associated with lithospheric thinning and decratonization coinciding with these major geological events are five major metallogenic systems identified as follows 1 an archean bif system 2 paleoproterozoic cu pb zn and mg b systems 3 a mesoproterozoic ree fe pb zn system 4 a paleozoic orogenic cu mo system and 5 mesozoic intracontinental au and ag pb zn and mo systems the ore deposit types in each of these metallogenic systems show distinct characteristics and tectonic affinities from early precambrian through late precambrian to paleozoic and mesozoic the ncc records a transition from primitive to modern style plate tectonics evidence for imbricated oceanic plate stratigraphy in a subduction accretion setting and collisional orogenesis along at least three major zones of ocean closure are documented major transitions in tectonic style and surface environmental changes recorded in other parts of the world are also reflected in the geological history and metallogenic events in the ncc large scale gold deposits formed through intraplate tectonics during the mesozoic provide important insights into mantle dynamics and crust mantle interaction associated with lithospheric thinning and craton destruction the ncc provides one of the best examples for documenting secular changes in the geological history and metallogenic epochs of an evolving earth

distribution of crustal fluids in northeast japan as inferred from resistivity surveys abstract we carried out magnetotelluric mt surveys in central northeastern japan two dimensional resistivity profiles along three survey lines show similar features each other by comparing the resistivity distribution to the distribution of seismic velocities we inferred the distribution and flow of crustal fluids three fluid flow paths were detected based on the distribution of regions of low resistivity the first path ascends from the top of the upper mantle passes through the lower crust and reaches the surface forming a fluid chamber within the lower or middle crust this path is related to the volcanic activity in the backbone range the second path rises from the first fluid chamber and has produced small fluid reservoirs on both sides of the backbone range these small reservoirs are considered to be related to the seismicity of the region the third path is located to the east of the volcanic front and represents another fluid flow path from the uppermost mantle to the lower crust that may have formed a small fluid reservoir to the east of the volcanic front

geochronology and geochemistry of the paleoproterozoic meta basalts from the jiao liao ji belt north china craton implications for petrogenesis and tectonic setting abstract geochronology geochemical and isotopic studies were carried out on the paleoproterozoic meta basalts and related rocks from the jiao liao ji belt north china craton to understand the mantle source characteristics and the geodynamic setting u pb isotopic dating using the la icpms method on zircons from the metamorphosed volcanic rocks reveals that they formed at ca 2204 2158 ma and were metamorphosed at ca 1895 1919 ma respectively the meta basalts are of calc alkali affinity and have arc like geochemical compositions they are enriched in lrees la yb n 3 5 5 1 and liles sr ba rb depleted in hfses nb ta zr hf ti and show variable high nd t values 2 4 to 4 5 the basaltic rocks experienced significant fractional crystallization and minor crustal contamination during magma evolution modeling suggests that the parent magma of the meta basalts was derived from 20 partial melting of spinel garnet lherzolites that were previously metasomatized by subduction zone fluids melts in the late archean petrological geochronological and geochemical data suggest that the paleoproterozoic volcanic rocks formed in an active continental margin setting and were subsequently deformed and metamorphosed to amphibolite facies due to the arc continental collision at ca 1 9 ga rather than in a continental rifting setting as previously thought by most workers

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

zircon u pb and lu hf isotopic and whole rock geochemical constraints on the protolith and tectonic history of the changhai metamorphic supracrustal sequence in the jiao liao ji belt southeast liaoning province northeast china abstract the changhai metamorphic supracrustal rocks located in the eastern central part of the jiao li ji belt in the north china craton ncc are composed mainly of various garnet mica schists along with minor quartzites and marbles this study presents whole rock major and trace element data zircon u pb dates and hf isotope data for these rocks in order to constrain their protolith age and provenance and discuss the tectonic implications geochemical results indicate that the source rocks were mainly granitoids with a possible minor contribution from clastic sediments with an active continental margin signature detrital zircons have u pb age peaks at approximately 1887 2174 2552 2765 and 3212 ma hf values of 11 1 to 13 0 and three major time windows of average continent crustal model ages t dm c of 2 04 2 33 2 48 2 56 and 2 72 2 93 ga besides these units also contain significant numbers of concordant metamorphic zircons that yielded a peak age of ca 248 ma indicating that the region was modified by an early triassic tectono thermal event these results suggest that sediments of the changhai metamorphic supracrustal rocks were mainly sourced from nearby basement granitoid rocks and to a lesser extent from paleoproterozoic metamorphosed strata such as the north and south liaohe groups furthermore the source rocks of the magmatic zircons analyzed in this study appear to have originated from interaction between old continental crust and juvenile material the youngest concordant zircon age peak at 1879 ma coincides with the timing of formation of regionally widespread granitoids mafic igneous rocks and metamorphism of the south liaohe and ji an groups in the jiao liao ji belt and suggest that the sedimentary protoliths of the changhai metamorphic supracrustal rocks were deposited after this time the results indicate that the archean liaobei jinan complex in the north and the liaonan nangrim complex in the south were already a single continental block by 1887 ma and that the changhai metamorphic supracrustal rocks were deposited at an active continental margin

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

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

source and petrogenesis of paleoproterozoic meta mafic rocks intruding into the north liaohe group implications for back arc extension prior to the formation of the jiao liao ji belt north china craton abstract meta mafic rocks as sills dykes and veins are widely distributed within the north liaohe group liaodong peninsula which consist mainly of meta diabase gabbro and garnet amphibolite with minor felsic clastic rocks as enclaves although a long standing debate existed about the petrogenesis for the meta mafic rocks it is a critical judgement for using geochemistry and geochronology of these rocks to reveal the complicated tectonic evolution of the paleoproterozoic jiao liao ji belt jljb in this paper a combined study of zircon u pb isotopic data whole rock geochemistry and sm nd isotope analyses are reported for these rocks to investigate their sources petrogenesis and tectonic settings abundant zircon u pb la icp ms age data reveal that the meta mafic rocks have a magmatic emplacement age of ca 2130 ma with a metamorphic age of ca 1878 ma these meta mafic rocks have characteristic geochemical compositions with moderate sio2 46 68 53 90 wt low tio2 0 56 2 33 wt and variable total fe2o3 9 65 17 58 wt mgo 2 77 11 49 wt cr 1 44 1580 ppm and ni 6 4 168 ppm similar to evolved tholeiitic basalt they exhibit enriched mid ocean ridge basalt e morb like geochemical features e g trace element patterns with highly variable end t values from 1 5 to 3 1 relative enrichment of light rare earth elements lrees and depletion of high field strength elements hfses e g nb ta zr hf and ti the geochemical trends of major and trace elements and nd isotopes suggest that the primary magma for these meta mafic rocks were probably derived from partial melting of a depleted asthenospheric mantle in the spinel stability field with extensive fractional crystallization of a three phase assemblage of olivine clinopyroxene and plagioclase crustal assimilation e g continental detritus and limited metasomatism from subduction related fluids and or melts in view of the widespread distribution of paleoproterozoic magmatism including the liaoji granites and the voluminous sedimentary rocks in the liaodong peninsula a newly tectonic model has been proposed that a ca 2 1 ga oceanic plate subduction event induced a back arc basin opening which closed to form the jljb in the period of ca 1 9 ga

a model for interpreting continental shelf hydrographic processes from the stable isotope and cadmium calcium profiles of scallop shells abstract stable oxygen and carbon isotope and cadmium calcium profiles from the shells of scallops collected from the outer continental shelf of the south atlantic bight and the virginia bight appear to trace the hydrographic processes of the two regions a model is developed to distinguish two principal modes of nutrient and trace metal input to the outer shelf from the biogeochemical profiles of the shell the oxygen isotope profiles record bottom water temperature changes caused by seasonal temperature cycles and water mass movements nutrient input and subsequent phytoplankton blooms are recorded in the carbon isotope and cd ca profiles the shell profiles from the south atlantic bight record the dominant effect of upwelling caused by gulf stream meandering the shell profiles from the virginia bight show the influence of spring river runoff and summer water column stratification biogeochemical profiles in mollusk shells are potentially important tools for studying the dynamics of both modern and ancient continental shelf upwelling systems

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