evolution of the archean and paleoproterozoic lower crust beneath the trans north china orogen and the western block of the north china craton abstract we report u pb ages and hf isotopes of zircons in granulites from two continental suture zones in the north china craton ncc from granulite xenoliths entrained in the cenozoic hannuoba basalts within the trans north china orogen tnco that amalgamates the western and eastern blocks and from a mafic granulite associated with ultrahigh temperature uht granulites within the inner mongolia suture zone imsz that welds the yinshan and ordos blocks the zircons in these rocks together with the inherited zircons from mesozoic subalkalic intrusives of these regions show several distinct u pb age populations and provide constraints on the evolution of the lower crust beneath the ncc parts of the older zircons from the tnco yield discordant data that project to ages of about 2 5 to 2 7 ga these old zircons show hf tdm model ages of 2 6 2 9 ga suggesting the existence of archean lower crust beneath the tnco which is coupled with the neoarchean metamorphic basement and greenstone belt a major zircon population grew at 1 75 2 0 ga consistent with the timing of the paleoproterozoic collision between the various crustal blocks within the ncc suggesting that this event had a significant effect on the archean lower crust the older inherited zircons from the western block also yield discordant data that project to younger ages of about 1 8 to 1 9 ga this age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the uht rocks in the khondalite belt within the imsz these older zircons yield hf tdm model ages of 2 0 2 5 ga suggesting that the lower crust beneath the western block in the ncc to be dominantly paleoproterozoic and decoupled with the archean metamorphic basement of the region yet another population of zircons from the hannuoba banded granulite xenoliths garnet bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of phanerozoic concordant ages ranging from 470 ma to 40 ma with peaks at 315 ma 220 230 ma 120 ma and 46 ma the late paleozoic zircons predominantly occur in the garnet bearing pyroxenite xenoliths and yield variable ehf t values of 24 to 18 triassic cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable ehf t values ranging from 48 to 16 the tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted ehf t with a dominant range from 0 to 18 these data suggest episodic magmatic underplating in the ancient lower crust of the ncc lasting continuously throughout phanerozoic producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust our data clearly demonstrate the important events of phanerozoic magmatic underplating beneath the neoarchean paleoproterozoic crust of the ncc

extension of tube wave detection for quality evaluation of pile foundation abstract based on the theory of tube wave propagation in a fluid filled borehole this paper proposes a new method for detecting the integrity of pile foundation and overcomes some limitations of the existing pile integrity tests the basic principle of detecting the pile integrity by the tube wave testing equipment and concrete quality evaluation of piles are introduced the feasibility of the tube wave detection for geological exploration of a bridge pile in a karst development area is verified by field tests through some test cases of prestressed high strength concrete pipe piles cast in place piles and rock socketed piles with defects the accuracy of the tube wave detection and other methods is compared then some issues of the application of the tube wave for detecting pile defects are discussed finally the content of this paper is summarized and some suggestions on further research are put forward

the interaction of tube waves with borehole fractures part ii analytical models we solve numerically the equations of elastodynamics that govern the propagation of waves in a fluid filled borehole intersected by one or more fluid filled fractures thus extending earlier work on formations presumed to be rigid the model is axis symmetric and it allows for arbitrary radial and vertical variations in the elastic properties of the formation we have developed a novel gridding scheme that takes advantage of the assumed thinness of the fracture compared to any relevant wavelength this technique obviates the necessity for a mesh within the fracture itself and thereby saves computational time and memory we illustrate our technique by means of examples with single and double fractures with or without washouts as well as examples with variable width fractures we compute the frequency dependent reflection and transmission coefficients of tube waves by fractures from the time waveforms generated by the present method major conclusions of this work are 1 reflections of tube waves by fr

a modelling study of open hole single well seismic imaging single well or uni well imaging uses an acoustic source and an array of receivers located in the same borehole to image local geological structure due to the intrinsic attenuation of the formation it is likely that a source emitting frequencies in the typical cross well range would be necessary to illuminate structure at distances above 100 m from the borehole at these frequencies a significant proportion of the source energy is converted into tube waves from which are for the purpose of these surveys noise this paper reports the results of a modeling study designed to assess the feasibility of using existing cross well hardware i e a piezo electric source and hydrophone array modified to run in a single borehole to perform single well surveys in particular the authors study the case of an open borehole in a gas filled low permeability sandstone reservoir the results suggest that the amplitudes of the tube wave reverberations generated by calliper variations are such that reflections of interest arriving in the time window after the first tube wave arrival will not be visible however reflections may be visible in the time window preceding the first tube wave arrival provided tube waves from previous shots are not still present and the long source receiver offsets requiredmore to make observations in this window can be incorporated into the tool design less

monitoring the width of hydraulic fractures with acoustic waves during scaled hydraulic fracturing experiments in our laboratory the fracture growth process is monitored in a time lapse experiment with ultrasonic waves we observe dispersion of compressional waves that have propagated across the hydraulic fracture this dispersion appears to be related to the width of the hydraulic fracture this means that we can apply the dispersion measurements to monitor the width of the hydraulic fracture in an indirect manner for a direct determination of the width the resolution of the signal is required to distinguish the reflections that are related with two distinct fluid solid interfaces delimiting the hydraulic fracture from its solid embedding to make this distinction the solid fluid interfaces must be separated at least one eighth of a wavelength and represent sufficient impedance contrast the applicability of the indirect dispersion measurement method however extends to a fracture width that is in the order of 1 of the incident wavelength the time lapse ultraso

hydraulic fracture diagnostics from krauklis wave resonance and tube wave reflections abstractfluid filled fractures support guided waves known as krauklis waves the resonance of krauklis waves within fractures occurs at specific frequencies these frequencies and the associated attenuation of the resonant modes can be used to constrain the fracture geometry we use numerical simulations of wave propagation along fluid filled fractures to quantify fracture resonance the simulations involve solution of an approximation to the compressible navier stokes equation for the viscous fluid in the fracture coupled to the elastic wave equation in the surrounding solid variable fracture aperture narrow viscous boundary layers near the fracture walls and additional attenuation from seismic radiation are accounted for in the simulations we then determine how tube waves within a wellbore can be used to excite krauklis waves within fractures that are hydraulically connected to the wellbore the simulations provide the frequency dependent hydraulic impedance of the fracture which can then be used

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

idealized dry quasi 2 d mesoscale simulations of cold air outbreaks over the marginal sea ice zone with fine and coarse resolution a nonhydrostatic model nh3d is used for idealized dry quasi 2 d simulations of arctic cold air outbreaks using horizontal grid spacings between 1 25 and 60 km despite the idealized setup the model results agree well with observations over fram strait it is shown that an important characteristic of the flow regime during cold air outbreaks is an ice breeze jet ibj with a maximum wind speed exceeding often the large scale geostrophic wind speed according to the present simulations which agree very well with those of another nonhydrostatic mesoscale model metras the occurrence strength and horizontal extent l of this jet depend strongly on the external forcing and especially on the direction of the large scale geostrophic wind relative to the orientation of the ice edge the latter dependency is explained by the effects of the thermally induced geostrophic wind over open water and coriolis force it is found that coarse resolution runs underestimate the strength of the jet this underestimation has important consequences to the surface fluxes of heat and momentum which are also underestimated by about 10 15 on average over the region between the ice edge and 120 180 km downstream our results suggest that a grid spacing of about l 7 is required about 10 30 km to simulate the ibj strength with an accuracy of at least 10 thus the results of large scale models as well might contain uncertainties with regard to the simulated ibj strength which would influence the energy budget in a large region along the marginal sea ice zones

finite difference and frequency wavenumber modeling of seismic monopole sources and receivers in fluid filled boreholes in borehole seismic experiments the presence of the borehole has a significant effect on observations unfortunately including boreholes explicitly in modeling schemes excludes the use of some methods e g frequency wavenumber and adds prohibitively to the cost of others e g finite difference to overcome this problem we use the concept of an effective source receiver array to replace the explicit representation of the borehole by a distributed seismic source receiver this method mimics the presence of the borehole at seismic frequencies under a wide variety of conditions without adding a significant computational cost it includes the effects of dispersive and attenuative tube wave propagation the generation of secondary sources at interfaces and caliper changes and the generation of conical waves in low velocity layers comparison with a finite difference scheme with an explicit borehole representation validates the approach the modeling method applied to a continuity logging geometry demon

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

a dynamic model for fluid flow in open borehole fractures the attenuation of stoneley waves by an open borehole fracture is closely related to fluid flow in the fracture we consider the dynamic response of a viscous fluid in a borehole fracture to the oscillating pressure excitation of stoneley waves at the fracture opening a dynamic model has been developed to describe the fluid motion in the fracture this model relates both viscous shear effects at the fracture surface and the acoustic wave propagation in the fracture fluid the dynamic conductivity is derived to characterize the fluid conduction through the fracture this model is applied to study stoneley wave attenuation across a horizontal and along a vertical borehole fracture in the horizontal fracture case the theory is found to agree with laboratory fracture modeling data after minimizing scattering effects due to the fracture in the vertical fracture case where the scattering effects are minimal the theory is in excellent agreement with the laboratory data

fracture evaluation using reflected stoneley wave arrivals we use the low frequency reflected stoneley wave mode to locate permeable fractures intersecting a borehole and to estimate their effective apertures assuming a model in which the average aperture of the fracture is roughly constant theoretical work relates the magnitude of the stoneley wave reflectivity to an effective fracture width we treat both the case of a horizontal fracture and the case of a fracture crossing the borehole at an angle laboratory experiments verify the analytic solution for the case of a horizontal fracture full waveform array sonic data were also acquired in a wellbore with a long recording time 25 5 ms in order to capture the late stoneley wave arrivals the data processing involves computation of the stoneley wave reflectivity response using the measured direct and reflected stoneley wave arrivals a least squares fit to the arrival time of the reflected wave arrivals is used to estimate the locations of permeable fractures and the effective width of the fractures is esti

propagation of tube waves generated by an external source in layered permeable rocks summary tube wave characteristics generated in a fluid filled borehole may be used to determine enclosing media parameters and in particular to localize petroliferous strata if any and estimate their permeabilities as a rule tube waves are generated by an external seismic source of explosive type located some distance away from a borehole embedded in a layered medium the modelling of tube wave excitation and propagation is a complicated problem whose solution is necessary for solving the inverse problem in the present study an efficient numerical algorithm is presented to compute the tube waves propagation caused by external explosive perturbations in a fluid filled borehole located in a layered enclosing medium fluid flow between the borehole interior and the enclosing saturated porous rocks can easily be taken into account within the framework of the algorithm the solution is obtained by sommerfeldintegral representation of external field potentials on the borehole axis and subsequent analytical integration of the external field along the borehole intervals of homogeneity the resultant tridiagonal amplitude matrix is solved numerically the method was tested in detail numerical results for simple medium configurations surrounding a fluid filled borehole have been obtained the modelling of tube waves caused by the incident p reflected pp ps and the rayleigh wave in a fluid filled borehole of finite length located in an elastic half space adequately describes the main features of tube wave propagation tube wave modelling that includes the presence of a layer with hydraulic conductivity shows a high efficiency of tube wave generation at the layer boundaries and significant amplitude attenuation inside it it follows from the results of testing that the algorithm developed can be used for adequate modelling of vsp data

fracture compliance estimation using borehole tube waves abstractwe tested two models one for tube wave generation and the other for tube wave attenuation at a fracture intersecting a borehole that can be used to estimate fracture compliance fracture aperture and lateral extent in the tube wave generation model we consider tube wave excitation in the borehole when a p wave is incident on the fracture the amplitude ratio of the pressure due to the tube wave to that of the incident p wave is a function of fracture compliance aperture and length similarly the attenuation of a tube wave in the borehole as it crosses a fracture intersecting the borehole is also a function of fracture properties numerically solving the dispersion relation in the fracture we study tube wave generation and the attenuation coefficient as a function of frequency we observed that measuring amplitude ratios or attenuation near a transition frequency can help constrain the fracture properties the transition frequency corresponds to the regime in which the viscous skin depth in

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

investigation of permeable fracture zones by tube wave analysis summary in vertical seismic profiling tube waves are generally classified as noise they have however useful applications tube waves can be generated by compressional waves at fluid filled cracks crossing the wall of the borehole in this case the permeability of the fracture zone can be estimated from the amplitude ratio of the incident p wave and the generated tube wave in the present study an improved model for tube wave amplitude interpretation is presented while former models assumed isolated cracks now the consideration of fracture zones of a certain porosity permeability and width is allowed master curves are used to check the sensitivity of the amplitude ratio of tube and p waves with respect to the formal parameters of computation it is shown moreover that mainly those parts of a fracture contribute to the tube wave generation which are within a radius of about 1 m of the borehole the problem of localization and characterization of fracture zones by tube waves was investigated with several complementary field experiments in shallow boreholes in crystalline rocks as vertical seismic profiling vsp with three component borehole geophones and hydrophones televiewer measurements well tests and temperature measurements it turned out that fracture zones were met at all depths where tube waves were generated however not all of them were found to be hydraulically activated during well tests and temperature measurements this means that fractures detected by tube wave vsp are not necessarily of hydrological importance transmissivity values based on tube wave analysis are therefore an upper limit for the well under consideration on the other hand the transmissivity values derived from the well tests agreed quite well with those of the tube wave analysis if only the open fracture zones were considered a fact which seems to confirm our theoretical model

the equivalent force system of a monopole source in a fluid filled open borehole one of the major contributors to the complexity of boundary value problems pertaining to theoretical modeling of exploration elastodynamics is the presence of both vertical and horizontal discontinuities it has been known for a long time that it is sometimes possible to replace certain boundaries by a system of images provided the extra stresses and displacements induced by these images could indeed mimic the discontinuities caused by the said boundaries e g ben menahem and singh 1981 in this vein we show that part of the field created by a monopole source acting on the axis of a fluid filled open borehole surrounded by a homogeneous and isotropic formation can be reconstructed with the aid of an equivalent force system efs that mimics the geometrodynamic effects of the borehole the advantages of the efs are twofold in the first place it simplifies the physical setup and brings many seemingly different problems into a common denominator in a sense that they are reduced to fields of known basic force systems second and this is not less important much computer time is saved and numerical complexities are avoided

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

krauklis wave initiation in fluid filled fractures by seismic body waves abstractkrauklis waves are a special wave mode that is bound to and propagates along fluid filled fractures they can repeatedly propagate back and forth along a fracture and eventually fall into resonance emitting a seismic signal with a dominant characteristic frequency they are of great interest because this resonant behavior can lead to strongly frequency dependent propagation effects for seismic body waves and may explain seismic tremor generation in volcanic areas or affect microseismic signals in fractured fluid reservoirs it has been demonstrated that krauklis waves can be initiated by a seismic source inside the fracture for example by hydrofracturing here the aim is to study krauklis wave initiation by an incident plane p or s wave in numerical simulations both seismic body waves are reflected and scattered at the fracture but also two krauklis waves are initiated with significant amplitude one at each fracture tip i e at the diffraction points of the fracture generally the incid

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

experimental verification of spatially varying fracture compliance estimates obtained from amplitude variation with offset inversion coupled with linear slip theory abstractthe elastic compliance of a fracture can be spatially varying reflecting the variation of microscale properties of the fracture e g aperture contact asperities and fracture infill characterizing the spatial heterogeneity of a fracture is crucial in explaining the apparent frequency dependence of fracture compliance and in addressing the spatially varying mechanical and hydraulic properties of the fractured medium apparent frequency dependence of the estimated fracture compliance is caused when the used seismic wavelength is very large compared to the scale of heterogeneity we perform ultrasonic laboratory experiments and characterize the spatially varying compliance along a fluid filled fracture we simulate a horizontal fracture and introduce heterogeneous fluid distribution along the fracture we perform amplitude variation with offset avo inversion of the p p reflections in which we obtain the theoretical angle dependent reflection responses by considering the linear slip model t

guangtoushan granites and their enclaves implications for triassic mantle upwelling in the northern margin of the north china craton abstract mineral electron microprobe bulk rock major trace elements and nd isotopes and zircon u pb and hf isotopic data are reported for granites and dioritic enclaves from the guangtoushan granitic complex in the northern margin of the north china craton the zircon u pb dating identifies two stages of magmatism the early stage enclave and host granite have identical ages 250 2 ma and similar bulk rock nd isotopes end t 11 5 to 12 2 as well as similar zircon hf isotopes ehf t 13 3 to 17 4 however although the late stage enclave 206 2 ma host granite 208 1 ma and leucogranite 207 3 ma display comparable ages but exhibit distinct isotopic features the granite displays moderate bulk rock nd isotopic value end t 8 3 and zircon ehf t from 2 6 to 10 4 the enclave shows least negative bulk rock end t of 3 9 and zircon ehf t from 0 to 5 4 and the leucogranite possesses more pronounced negative bulk rock nd end t 17 2 and zircon hf isotopic compositions ehf t 6 2 to 19 0 an integration of field observations geochronology geochemistry and zircon hf isotopic data points to a complex petrogenetic history where the early stage enclave granite pair is a product of the early crystallization of felsic magmas that evolved from a mafic magma whereas the late stage enclave and granite were derived by magma mixing the late stage leucogranite is considered as a product of remelting of phanerozoic igneous rocks within this region the guangtoushan granitic complex offers robust evidence for a gradual mantle upwelling during triassic in the northern margin of the north china craton

mafic inclusions from the glenbog and blue gum granite suites southeastern australia mafic inclusions from the i type granites of the glenbog and blue gum suites of the lachlan fold belt of southeastern australia are less than 1 m and mostly less than 10 cm in size and are generally in sharp contact with the surrounding host granites unless otherwise stated the term granite is used in this paper in the general sense to include granite senso stricto adamellite granodiorite tonalite etc although some inclusions are irregular in shape the majority have an elliptical or circular outline when viewed on exposed surfaces rounded and subrounded individuals outnumber those with an angular appearance abundances of inclusions in seven plutons of the glenbog and blue gum suites range from about 6 to less than 0 1 their abundance is negatively correlated with the sio2 content of the host rock mafic inclusions contain the same mineral species as the host granite but plagioclase and hornblende are more abundant and quartz and k feldspar are less abundant in inclusions mafic inclusions all contain more than 54 sio2 and are mostly intermediate in composition the abundances of many elements in the mafic inclusions follow those of that element in the host granites sr and nd isotopic compositions in both the granites and the inclusions are similar and relatively evolved various models for the origin of the inclusions are considered it is concluded that of those considered the only model capable of explaining all data is that the inclusions represent fragments of more refractory source material that were carried up with the magma it is suggested that this more refractory character resulted from a lesser degree of hydration of the source rocks of the magmas prior to partial melting

crust mantle interaction in the central north china craton during the mesozoic evidence from zircon u pb chronology hf isotope and geochemistry of syenitic monzonitic intrusions from shanxi province abstract in situ zircon u pb ages hf isotopic compositions and whole rock geochemical and sr nd isotopic compositions are presented for three mesozoic syenitic monzonitic intrusions from shanxi province central north china craton zircons from these intrusions all show core rim structures in that the oscillatory rims recorded their intrusive ages whereas the cores are interpreted as xenocrysts the u pb age data reveal that the northernmost dishuiyan monzonite was emplaced at 241 ma while the huyanshan and erfengshan syenitic monzonitic complexes were emplaced at 130 ma and 128 134 ma respectively the dishuiyan monzonite is petrologically and geochemically uniform it shows lree enrichment and hfse depletion and exhibits enriched sr and nd isotopic compositions with 87 sr 86 sr i 0 7065 and end t 8 3 7 9 the zircon rims in the dishuiyan monzonite show highly varied hf isotopic compositions with ehf t 27 8 6 4 the varied hf isotopic compositions and enriched sr nd isotopic compositions together with the ubiquitous xenocrystic zircon cores suggest the dishuiyan monzonite was produced by the mixing of melts from enriched lithospheric mantle and lower crust the monzonite and syenite from the huyanshan complexes exhibit different geochemical features the end t values of syenite which are higher than those of monzonite resemble the enriched lithospheric mantle and together with the absence of zircon in the syenite we propose that it was originated by partial melting of enriched lithospheric mantle monzonites from huyanshan and erfengshan share similar petrological and geochemical characteristics being enriched in lree and depleted in hfse and they show low end t values between 18 2 and 13 9 similar to zircon rims in the dishuiyan monzonite those in the huyanshan and erfengshan monzonites also exhibit highly varied hf isotopic compositions the consistent ages between the xenocrystic zircons in monzonites and the lower crustal basement rocks of the ncc reveal a significant contribution from the lower crust in the formation of the monzonites we propose that the monzonites from huyanshan and erfengshan were formed through hybridization of enriched lithospheric mantle derived and lower crust derived magmas the mesozoic syenitic monzonitic intrusions in shanxi province were produced under extensional environments which linked to different geodynamic settings the triassic dishuiyan monzonite is a product of post collisional lithospheric extension related to the subduction of the paleo asian oceanic plate under the ncc and subsequent slab break off in the north while the cretaceous huyanshan and erfengshan syenite monzonite was produced under a back arc extensional regime linked to the subduction of the paleo pacific slab beneath east asia

laboratory evidence for krauklis wave resonance in fractures and implications for seismic coda wave analysis abstractkrauklis waves are of major interest because they can lead to resonance effects in fluid filled fractures this resonance is marked by seismic signals with a dominant signature frequency which may reveal fracture related rock properties in our laboratory study we used homogeneous plexiglas samples containing a single well defined i e manufactured fracture we recorded the signals obtained from propagating ultrasonic p and s waves source frequency 0 6 1 and 2 25 mhz along a sample without a fracture and samples with a fracture with different inclination angles of 30 45 and 60 with respect to the short axis the experimental results obtained from an incident s wave confirmed that the presence of the fracture led to resonance effects at frequencies lower than the dominant source frequency which slowly decayed over time in the recorded seismic coda after the first arrival the resonance frequency was independent of the fracture orientation and the source frequency we have interpret

borehole stoneley wave propagation across permeable structures this study investigates the propagation of borehole stoneley waves across permeable structures by modeling the structure as a zone intersecting the borehole a simple 1d theory is formulated to treat the interaction of the stoneley wave with the structure this is possible because the stoneley wave is a guided wave with no geometric spreading as it propagates along the borehole the interaction occurs because the zone and the surrounding formation possess different stoneley wavenumbers given appropriate representations of the wavenumber the theory can be applied to treat a variety of structures including a fluid filled fracture of special interest are the cases of permeable porous zones and fracture zones the results show that while stoneley wave reflections are generated strong stoneley wave attenuation is produced across a very permeable zone this result is particularly important in explaining the observed strong stoneley wave attenuation at major fractures where it has been difficult to explain the attenuation in terms of the single planar fracture theory in addition by using a simple and sufficiently accurate theory to model the effects of the permeable zone a fast and efficient method is developed to characterize the fluid transport properties of a permeable fracture zone

stoneley wave generation by an incident p wave propagating in the surrounding formation across a horizontal fluid filled fracture abstract this study investigates the generation of the low frequency borehole stoneley wave tube wave by a plane p wave propagating through the surrounding elastic formation which is intersected by a fluid filled fracture a model is constructed taking into account the dynamic fluid coupling between the borehole interior and the fluid filled fracture of infinite extent with parallel walls the basic mechanism of such coupling is due to the contraction of the fracture walls by the incident p wave leading to seismic radiation into the fracture the dynamic fluid flux from the fracture into the borehole interior and vice versa is the source of the low frequency stoneley wave an expression for the monopole pressure source exciting the tube wave is obtained the tube wave equation in the long wave approximation is derived in the presence of a fluid filled fracture of infinite extent amplitudes and waveforms of stoneley waves are analysed in the seismic wavelength range for p wave pulses of various shapes it is shown that the amplitude and waveform of the stoneley wave depends significantly on the two dimensionless parameters of the problem 1 the ratio of the borehole radius to the dominant wavelength of the incident pulse 2 the ratio of the fracture width to the borehole radius it is found that the amplitude of the generated stoneley wave can be of the order of the p wave amplitude in the borehole fluid stoneley waveforms are found to be completely different from those of the incident pulse

late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block constraints on the composition and evolution of the lithospheric mantle abstract the late paleozoic to early mesozoic mafic ultramafic complexes from the northern north china block ncb are used to constrain the isotopic composition and evolution of mantle reservoirs during different tectonic stages prior to the initiation of lithosphere destruction in the late mesozoic zircon u pb ages show that emplacement of the mafic ultramafic complexes occurred in at least three stages middle devonian ca 395 ma late carboniferous early permian 308 276 ma and triassic 250 220 ma most of the middle devonian complexes display low initial 87sr 86sr ratios of 0 70467 0 70492 weak to moderate negative end t values from 6 3 to 1 5 and weakly negative to weakly positive zircon ehf t values from 11 5 to 5 5 indicating that the parent magma was derived from slightly enriched lithospheric mantle the late carboniferous early permian complexes are characterized by low initial 87sr 86sr ratios of 0 70521 0 70604 significant negative end t values from 14 1 to 9 3 and zircon ehf t values from 17 0 to 10 5 and were probably derived from metasomatized lithospheric mantle the early triassic complexes exhibit initial 87sr 86sr ratios of 0 70656 0 70825 and significant negative end t values from 17 1 to 8 2 indicating their derivation from enriched lithospheric mantle however the late triassic mafic ultramafic complexes display weakly negative to weakly positive end t values of 4 4 to 0 5 and zircon ehf t values from 2 9 to 1 7 indicating that magma sources likely resulted from mixing of depleted asthenospheric mantle and enriched lithospheric mantle zircon ages geochemistry and sr nd hf isotopic studies suggest that the lithospheric mantle beneath the northern ncb had a slightly enriched signature during the middle devonian but it became significantly enriched during the late carboniferous to early permian due to metasomatism of lithospheric mantle during the southward subduction of the paleo asian oceanic plate after final closure of the paleo asian ocean and amalgamation of the mongolian arc terranes with the northern ncb in the latest permian to earliest triassic enriched lithospheric mantle still existed beneath the northern ncb during the early triassic however in the late triassic involvement of asthenospheric mantle became significant owing to strong upwelling of asthenospheric mantle and post collisional lithospheric delamination in the early late triassic these results suggest that the cratonic lithospheric mantle beneath the northern ncb underwent multiple stages of modification prior to its destruction and thinning initiation of lithospheric destruction and thinning in the northern ncb likely occurred during the early late triassic which is much earlier than in other parts of the ncb where it occurred in the late mesozoic it appears likely that lithospheric destruction and thinning of the ncb initially started at the northern and eastern margins of the craton as a result of post collisional lithospheric delamination and then spread to the interior of the craton

geophysical and geological tests of tectonic models of the north china craton abstract the geometry and timing of amalgamation of the north china craton have been controversial with three main models offering significantly different interpretations of regional structure geochronology and geological relationships one model suggests that the eastern and western blocks of the ncc formed separately in the archean and an active margin was developed on the eastern block between 2 5 and 1 85 ga when the two blocks collided above an east dipping subduction zone a second presumes the eastern block rifted from an unknown larger continent at circa 2 7 ga and experienced a collision with an arc perhaps attached to the western block above a west dipping subduction zone at 2 5 ga and the 1 85 ga metamorphism is related to a collision along the northern margin of the craton when the ncc joined the columbia supercontinent a third model suggests two collisions in the central orogenic belt at 2 1 and 1 88 ga but recognizes an early undated deformation event recent seismic results reveal details of the deep crustal and lithospheric structure that support both the second and third models showing that subduction beneath the central orogenic belt was west directed and that there is a second west dipping paleosubduction zone located to the east of the cob dipping beneath the western block ordos craton the boundaries identified through geophysics do not correlate with the boundaries of the trans north china orogen suggested in the first model and the subduction polarity is opposite that predicted by that model high pressure granulite facies metamorphism at 1 85 ga is not restricted to the tnco as suggested by the first model but is documented across the ncc as predicted by the second model suggesting a major continent continent collision along the north margin of the craton at 1 85 ga further it has recently been shown that in the southern tnco there is no record of metamorphism at circa 1 85 ga but only at 2 7 2 5 ga showing that the tnco as defined as a circa 1 85 ga orogen does not exist this is further confirmed by recent re os isotopic studies which show that the subcontinental lithospheric mantle beneath the southern cob is late archean in age and that a province in the northern ncc is circa 1 8 ga correlating with the proposed collision belt of the ncc with the columbia supercontinent across the entire ncc the cob is an archean convergent belt re worked in the paleoproterozoic and the paleoproterozoic tectonism is widespread across the ncc as predicted by the model whereby the previously amalgamated eastern and western blocks experienced a continental collision with columbia at circa 1 85 ga but uplift exhumation rates are slow necessitating a re evaluation of the tectonic models of the ncc

early permian plutons from the northern north china block constraints on continental arc evolution and convergent margin magmatism related to the central asian orogenic belt recent zircon dating identified several late carboniferous to early permian hornblende gabbro diorite quartz diorite granodiorite tonalite granite plutons in lithological assemblages at the northern margin of the north china block ncb that were previously regarded as archaean to palaeoproterozoic our geochronological results indicate that emplacement of these plutons was a continuous process during the late carboniferous to early permian from 324 6 to 274 6 ma and lasted for at least 50 ma in this paper the early permian components with compositions from gabbro to granite within the intrusive complex were studied the early permian plutons exhibit calc alkaline or high k calc alkaline metaluminous geochemical features and highly variable sio2 contents they have no significant eu anomaly in their ree patterns and in primitive mantle normalized spidergrams they display depletion in th u nb ta p and ti and enrichment in ba k pb and sr the granitoid bodies within these plutons display i type and adakitic geochemical signatures the early permian rocks exhibit low whole rock initial 87sr 86sr ratios from 0 70520 to 0 70615 and have negative whole rock e nd t values ranging from 17 4 to 9 3 and zircon e hf t values of 23 2 to 10 5 the gabbros exhibit higher e nd t values from 11 1 to 9 3 and e hf t values from 16 5 to 10 5 and one granodiorite exhibits an even lower e nd t value of 17 4 and zircon e hf t values of 23 2 to 15 1 geochemical sr nd and in situ zircon hf isotopic compositions suggest that the hornblende gabbros were derived from a metasomatized lithospheric mantle and the diorite and quartz diorite were generated from a gabbroic magma by fractional crystallization coupled with differential assimilation of ancient lower crustal material the granodiorite was likely derived from partial melting of ancient lower crust with involvement of some mantle components involvement of both lithospheric mantle and ancient lower crust in the generation of the early permian plutons indicates strong crust mantle interaction in the northern ncb petrological associations as well as geochemical and sr nd hf isotopic results show that the early permian plutons were emplaced along an andean type active continental margin during southward subduction of the palaeo asian oceanic plate beneath the ncb integration of our results with previously published data for late carboniferous and late permian to middle triassic intrusions suggests that the continental arc on the northern margin of the ncb existed for at least 50 ma during the late palaeozoic and final amalgamation of the mongolian arc terranes with the northern ncb likely occurred during a period from 270 to 250 ma i e in the late permian to earliest triassic

hydraulic properties of closely spaced dipping open fractures intersecting a fluid filled borehole derived from tube wave generation and scattering fluid filled fractures and fissures often determine the pathways and volume of fluid movement they are critically important in crustal seismology and in the exploration of geothermal and hydrocarbon reservoirs we introduce a model for tube wave scattering and generation at dipping parallel wall fractures intersecting a fluid filled borehole a new equation reveals the interaction of tube wavefield with multiple closely spaced fractures showing that the fracture dip significantly affects the tube waves numerical modeling demonstrates the possibility of imaging these fractures using a focusing analysis the focused traces correspond well with the known fracture density aperture and dip angles testing the method on a vsp data set obtained at a fault damaged zone in the median tectonic line japan presents evidences of tube waves being generated and scattered at open fractures and thin cataclasite layers this finding leads to a new possibility for imaging characterizing and monitoring in situ hydraulic properties of dipping fractures using the tube wavefield

dubious case for slab melting in the northern volcanic zone of the andes it was first suggested by r w kay that adakites may represent melts of subducted slab since then the term adakite has become synonymous with slab melts based on their unusual geochemical signature this contribution using the northern volcanic zone of the andes as an example aims 1 to expose the weakness in simply associating a geochemical signature with a genetic mechanism and 2 to underline the importance of using several integrated lines of evidence in assessing the viability of slab melting we conclude that although slab melting probably occurs in some arcs regional geochemical trends in the northern volcanic zone and their relationship to the subduction zone architecture are not indicative of slab melting and can be accounted for by normal arc magmatic processes acting on wedge derived basaltic magmas

detection of open fractures with vertical seismic profiling in vertical seismic profiling surveys tube waves are generated by compressional waves impinging on subsurface fractures or permeable zones the problem of generation of these waves by a nonnormal incident p wave for an inclined borehole intersecting a tilted parallel wall fracture is formulated theoretically the amplitude of tube waves depends on the permeability the length of the fracture and the frequency the relative effects of these parameters are studied individually the problem is also formulated for a thin oblate ellipsoidal penny shaped fracture the results for the two fracture models are compared and contrasted field data from tyngsboro massachusetts are shown for open fractures in granite from tube wave amplitudes normalized to p wave amplitudes calculated permeabilities are of the order of 100 mdarcy