reply to comment by qi and wang on similar crust beneath disrupted and intact cratons arguments against lower crust delamination as a decratonization trigger

late neogene deep sea benthic foraminifera at odp site 762b eastern indian ocean diversity trends and palaeoceanography abstract in the present investigation the late neogene deep sea benthic foraminiferal diversity at odp site 762b has been measured by using hurlbert s diversity index s m this index measures the expected number of species to a common sample size m here m is put equal to 100 this method is relatively more advantageous than other commonly used diversity indices because it eliminates differences in sample size the late neogene section at site 762b is characterised by marked variations in species diversity s 100 of the deep sea benthic foraminiferal assemblages species diversity broadly exhibits an inverse relationship with the values of uvigerina proboscidea abundance and percentage of infaunal taxa in the examined section of the site this suggests that temporal variations in primary productivity of the overlying surface waters are reflected in the late neogene deep sea benthic foraminiferal diversity trends the species diversity pattern explains that the trophic level of the bottom water changed at the beginning of the late pliocene 3 5 ma due to an increased surface water productivity the higher values of species diversity during the early pliocene was due to a stable deep sea environment with low trophic resource levels however the late pliocene and pleistocene interval is largely characterised by low diversity reflecting an unstable deep sea environment with higher surface water productivity a distinct increase in the values of species diversity along with low percentages of u proboscidea and infaunal taxa during the latest pliocene 2 3 1 9 ma suggests low organic carbon influx in the bottom waters due to a decrease in the surface water productivity

crustal p wave velocity structure beneath the se margin of the tibetan plateau from deep seismic sounding results abstract the crust and uppermost mantle beneath the southeastern se margin of tibetan plateau record the lateral expansion of tibet and far field effects from the ongoing continental collision and convergence in order to obtain constraints on the deep structure and the eastward expansion of the plateau we synthesized deep seismic sounding dss results in this region and constructed the p wave velocity models for each terrane the principal characteristics of the crustal velocity model and tectonic significance are 1 crustal thickness decreases from 53 km beneath the songpan ganzi terrane sgt to 34 km in the south direction beneath simao terrane smt and 42 km in the east direction beneath chengdu area the crust is dominantly felsic in upper crust with a small percentage of mafic composition in the lower crust 2 the crustal structure is very heterogeneous in this region the indochina block is characterized by low seismic velocities in the upper crust while the west yangtze terrane wyzt and sgt show higher velocities in the upper crust the lower crust beneath wyzt is relatively thicker than other terranes 3 we deduce that the high velocity in the upper crust and relatively thick lower crust beneath the sgt and wyzt can be associated with magmatic processes that generated the emeishan flood basalts which may have been triggered by rifting or mantle plume the lateral variations of the crustal thickness in se tibet may be due to lower crustal flow from the tibetan plateau to the se direction after blocked by the cold and rigid yangtze craton in the east direction

late quaternary benthic foraminifera and deep water paleoceanography in the south china sea abstract recent and late quaternary deep sea benthic foraminifera in the south china sea scs have been quantitatively studied in order to approach some disputable questions about the glacial deep circulation of the pacific from the paleoceanographic records of a marginal sea for example whether or not there existed the north pacific deep water npdw during glacials based on the quantitative data of deep sea benthic foraminiferal faunas from sixty six surface sediment samples of the scs a q mode factor analysis indicates that the globocassidulina subglobosa assemblage the astrononion novozealandicum and bulimina aculeata assemblages and the eggerella bradyi assemblage are associated with the intermediate water mass iwm deep water mass dwm and the deep water below ccd in the scs respectively the factor assemblages resulted from surface sample data were then applied to the quantitative analysis of late quaternary deep sea benthic foraminifera in eight cores from the scs and western pacific the results show a generally increased contribution of the dwm assemblage relative to that of the iwm assemblage during glacials which implies that the influence of the dwm increased and that of the iwm decreased in the scs and western pacific however there were two major deep water paleoceanographic changes during the late quaternary 1 the deep sea carbonate dissolution of the scs and western pacific was intensified during 18 0 stages 4 5 evidenced by the higher arenaceous calcareous ratios of benthic foraminifera and relative abundance of eggerella bradyi 2 the influence of the pacific dwm above 2500 m greatly increased during the last glacial maximum lgm inferred from the increased abundances of the pacific dwm benthic foraminiferal assemblage as compared to those of the pacific iwm and pacific bottom water mass assemblages in the western pacific particularly the water in which favocassidulina favus was distributed could not enter the scs since the lgm meanwhile the great changes had taken place in the dwm of the scs during the lgm reflected in the occurrence of a clearly cooled and ventilated dwm and the replacement of a novozealandicum and b aculeata assemblages by b aculeata melonis barleeanum assemblage at water depths of 1000 2500 m these significant changes during the lgm may be related to the formation of the npdw

the progressive intensification of northern hemisphere glaciation as seen from the north pacific ocean drilling project odp site 882 50 22 n 167 36 e provides the first high resolution grape density magnetic susceptibility carbonate opal and foraminifera planktonic and benthic stable isotopes records between 3 2 and 2 4 ma in the northwest pacific we observed a dramatic increase in ice rafting debris at site 882 at 2 75 ma which is coeval with that found in the norwegian sea suggesting that the eurasian arctic and northeast asia were significantly glaciated from 2 75 ma onwards prior to 2 75 ma planktonic foraminifera 18o records indicate a warming or freshening trend of 4 c or 2 over 80 ka if this is interpreted as a warm pre glacial pliocene north pacific it may have provided the additional moisture required to initially build up the northern hemisphere continental ice sheet the dramatic drop in sea surface temperatures sst 7 5 c at 2 75 ma ended this suggested period of enhanced sst and thus the proposed moisture pump moreover at 2 79 and 2 73 ma opal mass accumulation rates mar decrease in two steps by five fold and is accompanied by a more gradual long term decrease in caco3 mars evidence from the southern ocean odp site 704 indicates that just prior to 2 6 ma there is a massive increase in opal mars the opposite to what is found in the north pacific this indicates that the intensification of northern hemisphere glaciation was accompanied by a major reorganisation of global oceanic chemical budget possibly caused by changes in deep ocean circulation the initiation of northern hemisphere glaciation occurred in the late miocene with a significant build up of ice on southern greenland however the progressive intensification did not occur until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia glaciated at 2 75 ma approximately 100 ka before the glaciation of alaska 2 65 ma and 200 ka before the glaciation of the north east american continent 2 54 ma

crustal structure across the ne tibetan plateau and ordos block from the joint inversion of receiver functions and rayleigh wave dispersions abstract we investigated the crustal structure at 34 stations using the h stacking method and jointly inverting receiver functions with rayleigh wave phase and group velocities these seismic stations are distributed along a profile extending across the songpan ganzi terrane qinling qilian terranes and southwestern ordos basin our results reveal the variation in crustal thickness across this profile we found thick crust beneath the songpan ganzi terrane 47 59 km that decreases to 45 47 km in the west qinling and qilian terranes and reaches its local minimum beneath the southwestern ordos block 43 51 km at an average crustal thickness of 46 7 2 5 km a low velocity zone in the upper crust was found beneath most of the stations in ne tibet which may be indicative of partial melt or a weak detachment layer our observations of low to moderate vp vs 1 67 1 79 represent a felsic to intermediate crustal composition the shear velocity models estimated from joint inversions also reveal substantial lateral variations in velocity beneath the profile which is mainly reflected in the lower crustal velocities for the ordos block the average shear wave velocities below 20 km are 3 8 km s indicating an intermediate to felsic lower crust the thick ne tibet crust is characterized by slow shear wave velocities 3 3 3 6 km s below 20 km and lacks high velocity material vs 4 0 km s in the lower crust which may be attributed to mafic lower crustal delamination or and the thickening of the upper and middle crust

deep shallow coupling response of the cenozoic bohai bay basin to plate interactions around the eurasian plate abstract the bohai bay basin bbb is a meso cenozoic intracontinental petroliferous basin where four pre existing continental scale fault zones intersect in east china the bbb has experienced complex deformational and evolutionary history that records significant information about how the lithosphere there has responded to the coeval plate interactions around the eurasian plate and or their resulting deep crust mantle processes in the cenozoic now both deep and shallow deformational and evolutionary processes of the bbb have been well studied but many geodynamic mechanisms previously proposed for those processes are too general to explain them well based on various data and principles we first summarized both deep and shallow responses and processes of the bbb in the cenozoic and then matched reasonable geodynamic mechanisms for each of them the results show as follows the cenozoic differential reactivation of pre existing continental scale weak zones controlled the coeval deep shallow differential coupling evolution of the bbb the paleogene extension in the bbb was mainly caused by crust mantle processes triggered by the stagnant izanagi slab the cenozoic strike slip faulting was influenced by various plate interactions in which the oblique subduction and anticlockwise rotation of young pacific plate resulted in the complex pre oligocene strike slip history of the tan lu fault zone to the south of the zhang peng fault zone while the india eurasia collision has caused the intense and synchronous strike slip faulting of various faults there since 35 ma which was then weakened by the oblique subduction and clockwise rotation of young philippine sea plate in the neogene the compression resulting from both the india eurasia collision and the philippine sea plate s subduction contributed to the latest paleogene tectonic inversion in the bbb the arrival of mantle flow triggered by both the india eurasia collision and the stagnant slab of the pacific plate resulted in the tectonic reactivation there in the late neogene

a thinned lithospheric image of the tanlu fault zone eastern china constructed from wave equation based receiver function migration 1 we apply the newly proposed wave equation based receiver function poststack migration method to the northern china interior structure project broadband data to image the lithospheric structure of the tanlu fault zone area in eastern china our migration result reveals a 60 to 80 km thick present day lithosphere beneath the study region significantly thinned from the paleozoic lithosphere of 180 km the lithosphere asthenosphere boundary lab is coherently imaged along the 300 km east west profile displaying an arc like shape with its apex roughly coincident with the transverse location of the tanlu fault zone on the surface an obvious uplift from 36 km to 32 km of the moho is also clearly detected right below this fault zone the coincidence of the imaged moho uplift and the lab apex with the surface location of the tanlu fault zone provides seismological evidence for the steep geometry and deep penetration of the fault system and indicates that the tanlu fault zone might have acted as a major channel for anthenosphere upwelling during the mesozoic cenozoic continental extension and lithospheric thinning in eastern china frequency analysis and synthetic modeling suggest that both the moho and the lab are sharp and strong the latter in particular is constrained to have a 3 7 drop in s wave velocity over a depth range of 10 km or less such a rapid velocity change at the base of the lithosphere in the study region cannot be solely explained by thermal variation but likely reflects the presence of volatiles or melt in the asthenosphere or is partially attributed to the compositional contrast between the preserved depleted and dehydrated cratonic lithospheric veneer and the uplifted hydrated and fertile asthenospheric materials

late quaternary paleoproductivity and deep water circulation in the eastern south atlantic ocean evidence from benthic foraminifera abstract two late quaternary sediment cores from the northern cape basin in the eastern south atlantic ocean were analyzed for their benthic foraminiferal content and benthic stable carbon isotope composition the locations of the cores were selected such that both of them presently are bathed by north atlantic deep water nadw and past changes in deep water circulation should be recorded simultaneously at both locations however the areas are different in terms of primary production one core was recovered from the nutrient depleted walvis ridge area whereas the other one is from the continental slope just below the coastal upwelling mixing area where present day organic matter fluxes are shown to be moderately high recent data served as the basis for the interpretation of the late quaternary faunal fluctuations and the paleoceanographic reconstruction during the last 450 000 years nadw flux into the eastern south atlantic ocean has been restricted to interglacial periods with the strongest dominance of a nadw driven deep water circulation during interglacial stages 1 9 and 11 at the continental margin high productivity faunas and very low epibenthic 13c values indicate enhanced fluxes of organic matter during glacial periods this can be attributed to a glacial increase and lateral extension of coastal upwelling the long term glacial interglacial paleoproductivity cycles are superimposed by high frequency variations with a period of about 23 000 yr enhanced productivity in surface waters above the walvis ridge far from the coast is indicated during glacial stages 8 10 and 12 during these periods cold nutrient rich filaments from the mixing area were probably driven as far as to the southeastern flank of the walvis ridge

2d model of the crust and uppermost mantle along rift profile siberian craton abstract a two dimensional model of the crust and uppermost mantle for the western siberian craton and the adjoining areas of the pur gedan basin to the north and baikal rift zone to the south is determined from travel time data from recordings of 30 chemical explosions and three nuclear explosions along the rift deep seismic sounding profile this velocity model shows strong lateral variations in the crust and sub moho structure both within the craton and between the craton and the surrounding region the pur gedan basin has a 15 km thick low velocity sediment layer overlying a 25 km thick high velocity crystalline crustal layer a paleo rift zone with a graben like structure in the basement and a high velocity crustal intrusion or mantle upward exists beneath the southern part of the pur gedan basin the sedimentary layer is thin or non existent and there is a velocity reversal in the upper crust beneath the yenisey zone the siberian craton has nearly uniform crustal thickness of 40 43 km but the average velocity in the lower crust in the north is higher 6 8 6 9 km s than in the south 6 6 km s the crust beneath the baikal rift zone is 35 km thick and has an average crustal velocity similar to that observed beneath the southern part of craton the uppermost mantle velocity varies from 8 0 to 8 1 km s beneath the young west siberian platform and baikal rift zone to 8 1 8 5 km s beneath the siberian craton anomalous high pn velocities 8 4 8 5 km s are observed beneath the western tunguss basin in the northern part of the craton and beneath the southern part of the siberian craton but lower pn velocities 8 1 km s are observed beneath the low angara basin in the central part of the craton at about 100 km depth beneath the craton there is a velocity inversion with a strong reflecting interface at its base some reflectors are also distinguished within the upper mantle at depth between 230 and 350 km

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

detecting remotely triggered microseismicity around changbaishan volcano following nuclear explosions in north korea and large distant earthquakes around the world we conduct a systematic survey on locally triggered earthquakes by large distant earthquakes in changbaishan volcano an active intraplate volcano on the border between china and north korea we examine waveforms of distant earthquakes recorded at broadband station changbaishan cbs near the volcano with estimated dynamic stresses over 5 kpa between 2000 and 2016 out of 26 selected distant earthquakes three of them show positive evidence of triggering during large amplitude surface waves the earthquakes that had positive or possible evidences of triggering generated larger long period surface waves indicating that they are more efficient in triggering microseismicity in addition since 2006 north korea has conducted five underground nuclear explosion une tests only 140 km away from changbaishan volcano by systematically examining waveforms of these unes recorded at station cbs we find that none of them have triggered microearthquakes in changbaishan volcano

pliocene pleistocene stable isotope and paleoceanographic changes in the northern south china sea abstract based on the stable isotopic analysis of planktonic and benthic foraminifers from ocean drilling program core 1148 of the northern south china sea scs pliocene pleistocene isotope stratigraphy and events have been reconstructed the benthic foraminiferal 18o record shows that the pacific intermediate water had a greater influence upon the scs or the pacific deep water above 2600 m was warmer before 3 2 ma than at present after that the benthic 18o conspicuously increased during the 3 2 2 5 ma period in correspondence to the formation of the northern hemisphere ice sheet whereas the planktonic 18o signal suggests a stepwise overall decrease of sea surface temperature during the 2 2 0 9 ma period compared to the equatorial pacific records the decrease in planktonic globigerinoides ruber 13c during the 3 2 2 2 ma period is particularly striking suggesting that fertility of surface water increased noticeably according to the modern 13c distribution of g ruber in the northern scs it is inferred that the east asian winter monsoon strengthened during this interval afterwards there were several conspicuous decreases of g ruber 13c at 1 7 1 3 0 9 0 45 and 0 15 ma bp that is about every 0 4 ma suggesting that the east asian winter monsoon became episodically stronger this is confirmed by changes in relative abundance of planktonic foraminifer species neogloboquadrina dutertrei a typical east asian winter monsoon proxy the deep water 13c of the scs is close to that of the pacific but lighter than that of the atlantic implying that the pattern of deep water originating mainly from the atlantic and through the pacific entering the scs existed at least since the early pliocene after 1 4 ma the benthic 13c signal decreased conspicuously but with a periodicity of 100 ka suggesting that the deep water ventilation of the scs was reduced probably corresponding to a decrease of the north atlantic deep water and or further isolation of the scs deep basin from the pacific during glaciations

post critical sspmp and its applications to virtual deep seismic sounding vdss 3 back projection imaging of the crust mantle boundary in a heterogeneous lithosphere theory and application

crustal structure of the eastern alps and their foreland seismic model beneath the cel10 alp04 profile and tectonic implications summary the subject of this paper concerns the seismic modelling of the crustal structure in the transition zone from the bohemian massif across the molasse basin and the eastern alps to the southern alps mainly on the territory of austria the cel10 alp04 profile crosses the triple point of the european plate adriatic microplate and the recently identified pannonian fragment the seismic data along the presented profile originate from two large experiments celebration 2000 and alp 2002 the wavefield observed in the eastern alps is more complex than in the bohemian massif strong first arrivals pg are distinct up to 60 90 km offset and are characterized by large variations in apparent velocity and amplitude the contact between the molasse basin and the eastern alps represents a barrier for seismic waves midcrustal reflections pc are usually recorded at short distance intervals 20 50 km and are also characterized by variations in apparent velocity and amplitude the moho reflections are usually strong and well correlated while pn arrivals are only fragmentarily recorded detailed 2 d forward modelling of all refracted post critical and reflected phases identified in the correlation process was undertaken using a ray tracing technique the p wave velocity in the crystalline upper crust of the bohemian massif and molasse basin is about 6 15 km s 1 which is slightly higher than in the alpine area about 6 0 km s 1 below the northern accretionary wedge of the eastern alps low velocity sediments penetrate towards the southwest sw down to about 10 km depth in the middle crust of the alpine part a reflective zone was modelled by a lamellae structure with alternating high and low velocities and thicknesses of about 2 3 km the lower crust in this part of the model is more homogeneous with a velocity of about 6 9 km s 1 in the bohemian massif a high velocity hv body vp 7k m s 1 o f af ew kilometres thickness was delineated in the depth interval 18 23 km the crustal thickness along the cel10 alp04 profile changes from about 42 44 km in the sw alpine part to around 40 km in the central part of the profile molasse basin and 38 40 km in the ne bohemian massif the velocity in the uppermost mantle determined from pn wave traveltimes is about 8k m s 1 along the whole profile the interpretation of the seismic wavefield is supplemented by an existing 3 d p wave velocity model of the area main features derived by 2 d modelling low velocities beneath the accretionary wedge high velocities in the lower crust of the bohemian massif moho topography well correlate with the 3 d model furthermore the 3 d model allows assessing the lateral extent of significant features alongside the cel10 alp04 profile this area is affected by both collision and escape tectonics the high reflectivity zone

the north china basin an example of a cenozoic rifted intraplate basin the north china basin was a stable continental region that has undergone several distinct phases of rifting and subsidence during the mesozoic and cenozoic eras the last major phase featuring block faulting rapid subsidence and widespread calc alkaline basaltic volcanism began during early tertiary time this intraplate rifting appears to be the result of an approximately 30 extension and thinning of the lithosphere beneath the northeastern china by the late tertiary period active rifting had slowed and postrift thermal subsidence had begun this regional extension and subsidence resulted in the present day north china basin a large saucer shaped oil producing basin with thinner crust and lower upper mantle p and s wave velocities than the surrounding regions during the quaternary period however the subsidence rate increased in the north china basin the frequent occurrence of destructive earthquakes and observations of relatively high heat flow suggest that the quaternary tectonic activity differs from the late tertiary simple thermal subsidence pattern and may indicate a new phase of rifting

magnetostratigraphic record of the late miocene onset of the east asian monsoon and pliocene uplift of northern tibet abstract widespread eolian red clay underlying the plio pleistocene loess palaeosol succession in northern china has been dated magnetostratigraphically back to 8 35 ma indicating that the east asian monsoon started at about the same time as the indian monsoon an initial sedimentation rate of 11 m myr increased gradually to 17 5 m myr by 6 ma and then decreased to 6 m myr between 5 ma and 3 5 ma a marked increase in sedimentation rate and grain size beginning between 3 5 ma and 3 1 ma indicates that the east asian winter monsoon strengthened at this time and intensified further after 2 6 ma the temporal coincidence of the stronger winter monsoon and the pliocene uplift of northwestern tibet just before the onset of the northern hemisphere glaciation indicate that the three events could be causally linked

neogene and quaternary paleoceanographic changes in the southern south china sea site 1143 the benthic foraminiferal record deep sea benthic foraminiferal assemblages from ocean drilling program odp site 1143 located in the southern south china sea scs were investigated to evaluate the relationship between faunal composition patterns and paleoceatiographic changes during the last 6 million years late miocene to holocene we used multivariate statistics correspondence analysis to analyze carbon flux related changes in assemblage composition of benthic foraminifers additional proxies for carbon flux and deep water ventilation include delta 13 c records of epifaunal cibicidoides wuellerstoifi and infaunal uvgefina peregrina var dirupta and melonis pompilioides benthic foraminiferal accumulation rates bfarss diversity indices and relative abundances of indicator species we observe three significant benthic faunal changes in the southern south china sea during the last 6 million years strong fluctuations in bfar and relative abundance of productivity indicator species between glacial and inter glacial stages after the mid pleistocene revolution mpr at approximately 0 9 ma indicating stronger seasonal carbon flux fluctuations are accompanied by the extinction of such species as stilostomella spp increases in carbon flux indicator species are coupled with an overall deer ease in benthic foraminifer diversity around 3 0 ma in the late pliocene this may indicate increasing carbon flux in a period of productivity maximum caused by enhanced offshore upwelling from intensified winter monsoon wind strength c 2004 elsevier b v all rights reserved

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

seismic crustal structure of the north china craton and surrounding area synthesis and analysis we present a new digital model nccrust of the seismic crustal structure of the neoarchean north china craton ncc and its surrounding paleozoic mesozoic orogenic belts 30 45 n 100 130 e all available seismic profiles complemented by receiver function interpretations of crustal thickness are used to constrain a new comprehensive crustal model nccrust the model presented on a 0 25 0 25 grid includes the moho depth and the internal structure thickness and velocity of the crust specified for four layers the sedimentary cover upper middle and lower crust and the pn velocity in the uppermost mantle the crust is thin 30 32 km in the east while the moho depth in the western part of the ncc is 38 44 km the moho depth of the sulu dabie qinling qilian orogenic belt ranges from 31 km to 51 km with a general westward increase in crustal thickness the sedimentary cover is 2 5 km thick in most of the region and typical thicknesses of the upper crust middle crust and lower crust are 16 24 km 6 24 km and 0 6 km respectively we document a general trend of westward increase in the thickness of all crustal layers of the crystalline basement and as a consequence the depth of the moho there is no systematic regional pattern in the average crustal vp velocity and the pn velocity we examine correlation between the moho depth and topography for seven tectonic provinces in the north china craton and speculate on mechanisms of isostatic compensation

spatial variations of current tectonic stress field and its relationship to the structure and rheology of lithosphere around the bohai sea north china abstract the tectonic stress field in the middle upper crust is closely related to the structure and rheology of the lithosphere to determine the stress field in the deep crust we inversed the focal mechanism solutions fmss of 62 earthquakes that occurred between 2009 and 2015 in the bohai sea and its surrounding areas using broadband seismic waveforms collected from 140 stations we then derived the tectonic stress field using the software satsi spatial and temporal stress inversion based on the damped linear inversion method the inversion results show that both the maximum 1 and minimum 3 principle stress axes throughout the entire region are nearly horizontal except in the tangshan and haicheng areas suggesting that the study area is predominantly under a strike slip faulting stress regime the 1 and 3 axes are found to be oriented in the nee sww or nearly e w and nnw sse or nearly s n directions respectively these results indicate that the stress field in the north china craton is controlled by the combined effects of the pacific plate westward subduction and the india eurasia plate collision however localized normal faulting stress regimes where the vertical stress v 1 are observed in the tangshan and haicheng areas where low viscosity bodies lvbs were identified using geophysical data based on the analysis of focal mechanism solutions active faults and lithosphere rheology characteristics in the tangshan and haicheng areas we speculate that the anomalous stress regime is caused by the local extension resulting from the movement of strike slip faults under the action of the regional stress field the existence of lvb may indicate weakness in the crust that favors the accumulation of tectonic stress and triggers large earthquakes

late quaternary upwelling intensity and east asian monsoon forcing in the south china sea foraminifera from two cores off eastern vietnam and the northwestern philippines where modern summer and winter monsoon driven upwelling occurs in the south china sea respectively were analyzed to evaluate the changes in paleoproductivity and upper water structure over the last 220 000 yr we observed enhanced organic carbon flux and a shoaled thermocline when upwelling intensified off eastern vietnam during interglacial ages and off the northwestern philippines during glacial ages this indicates that the east asian summer monsoon increased while the winter monsoon decreased during interglacial ages particularly the upwelling reached a maximum off eastern vietnam during late marine isotopic stage mis 5 and off the northwestern philippines during mis 2 implying that the summer monsoon decreased gradually since mis 5 while the winter monsoon displayed an opposite trend the variations in upwelling proxies exhibit a distinct cyclicity with frequencies near 41 000 yr and 23 000 yr off eastern vietnam in contrast to a strong frequency peak near 100 000 yr off the northwestern philippines we suggest that the east asian summer monsoon has been forced by changes in solar insolation associated with precession and obliquity while ice volume forcing is probably a primary factor in determining the strength and timing of the east asian winter monsoon but with less important insolation forcing

the cenozoic tectonic evolution of the great north china two types of rifting and crustal necking in the great north china and their tectonic implications abstract the great north china underwent widespread continental rifting during cenozoic time that caused extension and necking of the crust in this area and formed four major rift systems in this paper we provide geological and geophysical evidence that rifting and extension in the western part of the great north china differs from that in its eastern part in age and nature the space time relationships show that the origins of the western rift group of the great north china are probably related to the tibet plateau tectonics whereas those of the eastern rift group are related to the subduction events in the western margin of the pacific plate furthermore the quaternary tectonic regime in the eastern part of the great north china differs from the neogene tectonic pattern and shows relations with western rifts we speculate that during the quaternary the processes that caused rifting in the west have spread further east and now affect the eastern part of the great north china

three large shifts in east asian monsoon circulation indicated by loess paleosol sequences in china and late cenozoic deposits in japan abstract correlations between loess paleosol sequences in china and late cenozoic deposits in japan suggest that the east asian monsoon circulation experienced three large shifts during the late cenozoic about 2 5 ma ago the onset of loess accumulation in north central china accompanied by a dramatic increase in eolian dust flux to the sea of japan marked a pronounced development of the east asian winter monsoon winds since ca 1 2 to 1 1 ma ago the obvious alternation of loess and paleosols in the chinese loess sequence with increased coarse grain size fraction in the loess units and higher than average magnetic susceptibility values in the paleosols and the repeated occurrence of interstratified marine clay layers in the osaka group of central japan indicate that the east asian monsoon circulation strengthened and the contrast between the summer and winter monsoons increased the paleosols of the chinese loess sequence were more strongly developed from ca 550 ka ago and loess started to accumulate in areas of the mid lower reaches of the yangtze river and in lake biwa of central japan from ca 450 ka ago reflecting more vigorous summer and winter monsoon circulations since ca 550 to 450 ka ago these large changes in east asian monsoon circulation were not only related to the changing solar radiation global glacial interglacial cycles and the changing configuration of land and sea but were also directly controlled by the uplift of the tibetan plateau

the contribution of orbital forcing to the progressive intensification of northern hemisphere glaciation in this study we reconstruct the timing of the onset of northern hemisphere glaciation this began in the late miocene with a significant build up of ice on southern greenland however progressive intensification of glaciation did not begin until 3 5 3 ma when the greenland ice sheet expanded to include northern greenland following this stage we suggest that the eurasian arctic and northeast asia were glaciated at approximately 2 74 ma 40 ka before the glaciation of alaska 2 70 ma and about 200 ka before significant glaciation of the north east american continent 2 54 ma we also review the suggested causes of northern hemisphere glaciation tectonic changes such as the uplift of the himalayan and tibetan plateau the deepening of the bering strait and the emergence of the panama isthmus are too gradual to account entirely for the speed of northern hemisphere glaciation we therefore postulate that tectonic changes may have brought global climate to a critical threshold but the relatively rapid variations in the earth s orbital parameters and thus insolation triggered the intensification of northern hemisphere glaciation this theory is supported by computer simulations which despite the relative simplicity of the model and the approximation of some factors e g using a linear carbon dioxide scenario neglecting the geographical difference between the pliocene and the present suggest that it is possible to build up northern hemisphere ice sheets between 2 75 and 2 55 ma by varying only the insolation controlled by the orbital parameters c 1998 elsevier science ltd all rights reserved

global deep sea extinctions during the pleistocene ice ages the dark near freezing environment of the deep oceans is regarded as one of the most stable habitats on earth and this stability is generally reflected in the slow turnover rates extinctions and appearances of the organisms that live there by far the best fossil record of deep sea organisms is provided by the shells of benthic foraminifera protista a little known global extinction of deep sea benthic foraminifera occurred during the pleistocene ice ages in the southwest pacific it caused the disappearance of at least two families 15 genera and 48 species 15 25 of the fauna of dominantly uniserial elongate foraminifera with distinctive apertural modifications these forms progressively died back and became extinct during glacial periods in the late pliocene to middle pleistocene ca 2 5 0 6 ma most extinctions occurred between 1 0 and 0 6 ma at the time of the middle pleistocene climatic revolution this first high resolution study of this extinction event indicates that it was far more significant for deep sea diversity loss than previously reported 10 species the middle pleistocene extinction was the most dramatic last phase of a worldwide decline in the abundance of these elongate forms a phase that began during cooling near the eocene oligocene boundary and continued during the middle miocene clearly these taxa declined when the world cooled but the reason is yet to be resolved

the seasonal variation of the intrusion of the philippine sea water into the south china sea the seasonal variation of the intrusion of the philippine sea water into the south china sea was studied by analyzing the historical hydrographic station data in the northern south china sea and the philippine sea water masses at 150 200 and 250 m were classified by discriminant analysis according to their temperature salinity characteristics at each depth most water in the study region was classified into two groups representing the philippine sea water and the south china sea water respectively the geographic distribution of water masses in the south china sea shows that the philippine sea water was present along the continental margin south of china between october and january a westward current in the northern south china sea in winter was inferred from the distribution of the intrusion water

foraminiferal responses to major pleistocene paleoceanographic changes in the southern south china sea a detailed age model for core 17957 2 of the southern south china sea was developed based on delta 18 o coarse fraction magnetostratigraphy and biostratigraphy for the last 1500 kyr the delta 18 o record has clear similar to 100 kyr cycles after the mid pleistocene revolution mpr at the entrance of marine isotopic stage mis 22 planktonic foraminifera responded to the mpr immediately showing the increased sea surface temperature sst and dissolution after the mpr benthic foraminifera did not respond to it until the brunhes matuyama boundary since the mpr the depth of thermocline gradually became shallower until miss 6 5 this major change within miss 6 5 was also reflected in the decreased ssts and increased productivity and deep water mass thus two major pleistocene paleoceanographic changes were found one was around the mpr the other occurred within miss 6 5 which speculatively might be ascribed to the reorganization of surface and deep circulation possibly induced by tectonic forces

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

growth of the lower continental crust via the relamination of arc magma abstract how does continental crust transition from basaltic mantle derived magmas into an andesitic composition the relamination hypothesis has been presented as an alternative dynamical mechanism to classical delamination theory to explain new crust generation and has been supported by petrological and geochemical studies as well as by thermomechanical numerical modeling however direct evidence of this process from detailed seismic velocity structures is lacking here we imaged the three dimensional 3d velocity structures of the crust and uppermost mantle beneath the geologically stable ordos terrane of the north china craton ncc we identify a region of continental crust that exhibits extreme growth using teleseismic data and an imaging technique that models the common conversion point ccp stacking profiles our results show an approximately 400 400 km2 wide growth zone that underlies the primitive crust at depths of 30 50 km and exhibits a gradual increase of velocity with depth the upper layer of the growth zone has a shear wave velocity of 3 6 3 9 km s vp 6 2 6 8 km s indicating felsic material and the lower layer has a shear wave velocity of 4 1 4 3 km s vp 7 2 7 5 km s which corresponds to mafic material we suggest that this vertical evolution of the layered structure could be created by relamination and that the keel structure formed by relamination may be the root of the supernormal stability of the ancient ordos terrane

late pliocene variations in the carbon isotope values of north atlantic benthic foraminifera biotic control of the isotopic record abstract analyses of benthic foraminifera carbon isotope values were made in 172 samples from the late pliocene at dsdp site 548 which is located in the northeast atlantic on the continental slope southwest of ireland 1253 m water depth the carbon isotope record is quite stable from about 3 4 to 2 5 ma and contrasts with the record at site 552a in the north atlantic 2311 m water depth which is much more variable for this time period the carbon record at site 548 is also consistently more negative than that of site 552a after 2 5 ma the benthic carbon isotope record of uvigerina at site 548 becomes extremely variable with large negative deviations these isotopic variations might be associated with paleoceanic circulation changes caused by glaciation between 2 5 and 2 ma however paired analyses of uvigerina and cibicidoides species for 38 samples within the glacial interval yield carbon isotopic records which are quite different from one another the uvigerina record contains larger negative deviations than does the cibicidoides record also the isotopic difference between uvigerina and cibicidoides increases during glaciations and in a long term trend from 2 5 to 2 0 ma the lack of covariance between the uvigerina and cibicidoides carbon isotope records indicates that after 2 5 ma at site 548 biotic factors influenced the benthic isotopic record

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

complex evolution of the lower crust beneath the southeastern north china craton the junan xenoliths and xenocrysts abstract in our paper we suggested that the junan granulite xenoliths and xenocrysts record evolution of the precambrian lower crust beneath the southeastern north china craton ncc yuan and xia 2015 disagree with us however they have not fully considered the evolutional histories of the ncc lithosphere and geochemical and isotopic compositions of the junan xenoliths we also contend that they have misinterpreted the available geophysical data synthesizing the geochronological characteristics of the ncc lower crust nature of the junan granulite xenoliths and reinterpretation of the resistivity profile we again emphasize that the junan granulite xenoliths are tectonically affiliated to the ncc lower crust and the junan zircon data could reflect the complex evolution of the lower crust beneath the southeastern ncc

crustal structure of the middle segment of the qilian fold belt and the coupling mechanism of its associated basin and range system abstract we present an analysis of the p wave seismic velocity structure of the qilian fold belt based on a 750 km long seismic wide angle reflection refraction profile the results show that the internal portion of the alxa block has a crustal thickness of approximately 45 48 km with an average velocity of 6 19 km s although the alxa crust is thick it is lateral homogeneous and relatively stable the hexi corridor which is located on the southern margin of the alxa block has been affected by the collision and extrusion of the northern margin of the tibetan plateau the hexi corridor has a crustal thickness of 48 59 km with substantial thickening southward and an average seismic velocity of 6 10 6 13 km s indicating strong crustal deformation located on the northeastern margin of the tibetan plateau the qinling fold belt qfb gonghe basin and elashan mountains all have a crustal thickness is 51 56 km with a low average seismic velocity of 5 86 6 10 km s indicating significant reconstruction via shortening that has resulted in thickening of the northeastern tibetan plateau crust the tectonic coupling between the qilian fold belt and the neighboring blocks in the south and north form a crustal scale depression combining the regional geology gravity and gps measurements and strong earthquake focal mechanism solutions we constrain the crustal deformation processes of the northeastern of tibet plateau

crustal structure across the tesz along polonaise 97 seismic profile p2 in nw poland abstract the polonaise 97 po lish l ithospheric on set a n i nternational s eismic e xperiment 1997 seismic experiment in poland targeted the deep structure of the trans european suture zone tesz and the complex series of upper crustal features around the polish basin one of the seismic profiles was the 300 km long profile p2 in northwestern poland across the tesz results of 2d modelling show that the crustal thickness varies considerably along the profile 29 km below the palaeozoic platform 35 47 km at the crustal keel at the teisseyre tornquist zone ttz slightly displaced to the northeast of the geologic inversion zone and 42 km below the precambrian craton in the polish basin and further to the south the depth down to the consolidated basement is 6 14 km as characterised by a velocity of 5 8 5 9 km s the low basement velocities less than 6 0 km s extend to a depth of 16 22 km in the middle crust with a thickness of ca 4 14 km the velocity changes from 6 2 km s in the southwestern to 6 8 km s in the northeastern parts of the profile the lower crust also differs between the southwestern and northeastern parts of the profile from 8 km thickness with a velocity of 6 8 7 0 km s at a depth of 22 km to ca 12 km thickness with a velocity of 7 0 7 2 km s at a depth of 30 km in the lowermost crust a body with a velocity of 7 20 7 25 km s was found above moho at a depth of 33 45 km in the central part of the profile sub moho velocities are 8 2 8 3 km s beneath the palaeozoic platform and ttz and about 8 1 km s beneath the precambrian platform seismic reflectors in the upper mantle were interpreted at 45 km depth beneath the palaeozoic platform and 55 km depth beneath the ttz the polish basin is an up to 14 km thick asymmetric graben feature the basement beneath the palaeozoic platform in the southwest is similar to other areas that were subject to caledonian deformation avalonia such that the variscan basement has only been imaged at a shallow depth along the profile at northeastern end of the profile the velocity structure is comparable to the crustal structure found in other portions of the east european craton eec the crustal keel may be related to the geologic inversion processes or to magmatic underplating during the carboniferous permian extension and volcanic activity

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

an integrated mineral system model for the gold deposits of the giant jiaodong province eastern china abstract the giant jiaodong gold province with more than 5000 t of proven gold resources is unique in that its mesozoic gold deposits are hosted in a precambrian basement block there has long been debate on the source of gold the mechanism for its extreme enrichment and a holistic genetic model for these spectacular deposits in order to improve understanding of these factors a mineral system model is proposed for the jiaodong gold deposits for the first time it is based on a detailed review of the architecture and composition of the underlying mantle lithosphere the geodynamic setting at the time of gold mineralization the geological and geochemical features of the deposits themselves and mechanisms of their preservation regional geodynamic reconstructions combined with the nature of mesozoic magmatic systems show that late mesozoic breakoff of the subduction slab and rollback of the paleo pacific plate caused asthenosphere upwelling and lithosphere extension and thinning robust geochronological studies demonstrate that the jiaodong gold deposits formed at ca 120 ma during a change of subduction direction of the paleo pacific plate and the synchronous transition of tectonic regime from regional compression to transpression or transtension prior to peak extension caused by thinning of the lithosphere geophysical exploration data and hf nd isotope mapping of the jiaodong peninsula reveal a relatively simple ancient crustal structure cut by near vertical shear or fault zones including the lithosphere scale tan lu and wulian yantai faults that provided the first order architecture for emplacement of mantle magmas and sub crustal fluids in terms of fertility the significant older pre mineralization crustal metamorphism combined with sulfur lead and strontium isotope ratios indicate a dominant sub crustal source for the ore components for the jiaodong gold deposits consistent with evidence for volatile and gold fertilized metasomatized mantle lithosphere beneath the north china block helium ar and c o isotope ratios implicate mantle sources of ore fluids with contamination by crustal components en route to crustal depositional sites in terms of crustal architecture combined geophysical structural mineralogical fluid inclusion and geochemical studies show that the deeply sourced ore fluids and metals advected upwards through lithosphere scale faults to deposit gold via sulfidation and phase separation in crustal scale nne ne trending fault systems at mid to upper crustal levels preservation of disseminated to stockwork style deposits and auriferous quartz pyrite vein deposits was enhanced by deep crustal formation combined with limited uplift and exhumation of the province the jiaodong gold deposits although commonly hosted in granite intrusions clearly post date them on the basis of robust and reliable geochronology the spatial but non temporal relationships of gold deposits with granites their strong structural control and their other characteristics clearly place them in the orogenic gold group it is suggested because of their uniqueness that they be termed jiaodong type orogenic gold deposits

deep sea benthic foraminiferal assemblage response to a surface ocean productivity gradient a test a transect of samples from the eastern equatorial pacific where surface ocean productivity is the only changing environmental variable was used to test the response of benthic foraminiferal assemblages to an open ocean productivity gradient the transect runs along the east pacific rise from the highly productive waters near the equator to the oligotrophic south pacific subtropical gyre surface sediment benthic assemblages show progressive change along the transect with strong compositional shifts corresponding to the rapid productivity gradient near the equator and to the position of the southern convergence near 18 19 s the relationship of the assemblages to surface ocean productivity was tested by statistical regression of quantitative estimates of productivity on the assemblage principal component scores calculated for each sampling location the regression yielded an r squared of 0 87 demonstrating a clear relationship between surface ocean productivity and deep sea benthic foraminiferal assemblage composition the species most important to this relationship display a consistent response to oceanic productivity for long stretches of geologic time this conservative behavior and the results of the regression analysis indicate that benthic foraminiferal assemblages can be used to estimate surface ocean productivity for the geologic past

changes in arctic ocean paleoproductivity and hydrography during the last 145 kyr the benthic foraminiferal record the benthic foraminiferal record of two sediment cores at 900 and 2500 m water depth in the marginal arctic ocean reflects fluctuations in paleoproductivity ice sheet extent and atlantic water inflow highest paleoproductivity is observed in interglacial periods and at the termination of interstadials to stadials within oxygen isotope substages ois 6 3 5 3 5 1 3 1 and termination ia stable and high paleoproductivity at the ice edge during terminations is indicated by the melonis zaandami benthic foraminiferal association periods of glacial ice sheet advance or retreat from the core site are dominated by benthic foraminiferal associations related to seasonal organic carbon flux temperate saline atlantic water entered the arctic ocean within ois 6 3 5 5 and the holocene coincident paleoproductivity maxima are related to extended seasonal ice retreat during glacial periods of stagnating atlantic water advection unusual low paleoproductivity values are observed in the arctic ocean indicating increasing ice coverage deep water was poorly ventilated during these periods and the deeper site became exposed to corrosive bottom waters

is the ordos basin floored by a trapped oceanic plateau abstract the ordos basin in china has about 10 km of neoarchean to quaternary sediments covering an enigmatic basement of uncertain origin the basement is tectonically stable has a thick mantle root low heat flow few earthquakes and has been slowly subsiding for billions of years the basement has geophysical signatures that indicate it is dominantly intermediate to mafic in composition and is similar to some other cratons world wide and also to several major oceanic plateaus it was accreted to the amalgamated eastern block and central orogenic belt of the north china craton ncc in the paleoproterozoic then involved in several proterozoic tectonic events including being over thrust by an accretionary orogen and intruded by andean arc related magmas and then involved in a continent continent collision during amalgamation with the columbia supercontinent thus the basement rocks are deformed metamorphosed to granulite facies and determining their initial origin is difficult we suggest that the data is consistent with an origin as an oceanic plateau that accreted to the ncc and later experienced different episodes of differentiation associated with later subduction and collisions formation of cratonic lithosphere by accretion of oceanic plateaus may be one mechanism to create stable cratons other cratons that apparently formed by partial melting of underplated and imbricated oceanic slabs are stable in some cases but also re activated and de cratonized in some cases in asia where they have been affected by younger subduction hydration slab roll back and melt peridotite reactions this suggests that the initial mode of craton formation may be a factor in the preservation of stable cratons and de cratonization is not only influenced by younger tectonic activity

moho depth variations from receiver function imaging in the northeastern north china craton and its tectonic implications a detailed knowledge of the crustal thickness in the northeastern north china craton ncc is important for understanding the unusual phanerozoic destruction of the craton we achieve this goal by employing a 2 d wave equation based migration method to p receiver functions from 198 broadband seismic stations using ps conversions and surface reflected multiples by combining receiver function images along 19 profiles we constructed a high resolution moho depth model for the northeastern ncc the results present dominant e w moho depth variations similar to previous observations and new regional n s variations beneath both sides of the north south gravity lineament to the west while a deeper moho approximate to 42km appears in the interior of the trans north china orogen a relatively shallow moho approximate to 38km exists in the northern margin of the trans north china orogen to western ncc to the east the crust beneath the yan mountains in the marginal area is thicker approximate to 32 40km than that approximate to 26 32km beneath the bohai bay basin in the craton interior and the moho further shallows from ne approximate to 32km to sw approximate to 26km within the basin along with other observations we conclude that the dominant e w difference may have been associated with the paleo pacific plate subduction under eastern asia since the mesozoic the newly observed complex n s variations may have reflected the structural heterogeneity of the cratonic lithosphere inherited since the formation of the ncc in the paleoproterozoic or spatially uneven effects on the cratonic lithosphere of subsequent thermotectonic events during the long term evolution of the craton or both

significance of crustal extension and magmatism to gold deposits beneath jiaodong peninsula eastern north china craton seismic evidence from receiver function imaging with a dense array abstract the jiaodong peninsula located in the eastern north china craton ncc is a key region to study the genetic linkage between large scale gold mineralization and craton destruction we construct a fine crustal structural image across the jiaodong peninsula using teleseismic p wave receiver function data recorded by a dense linear array of 340 short period seismic stations the results reveal significant similarities and differences between the eastern and the western jiaodong peninsula the presence of an intracrustal low velocity zone and the north dipping interfaces beneath the jiaolai basin imply widespread crustal extension in the whole region in the northwest jiaodong metallogenic belt the identified detachment faults small vertical velocity gradients in the upper part of the lower crust and the thick crust mantle transition zone provide evidences for intense crustal extension in this area probably coeval with the peak of lithospheric thinning and destruction of the eastern ncc in the late mesozoic in the muru metallogenic belt distinct differences are found on the opposite sides of the wulian yantai fault zone wyfz in the depth and structure of the moho intracrustal low velocity zone upper crustal vp vs ratios and bouguer gravity anomalies indicating that the wyfz may be a steep transcrustal fault we propose that the coupled effects of intense crustal extension voluminous magmatism and water released from the subducting paleo pacific slab may have been responsible for the concentrated gold deposits in the northwest jiaodong during the peak of the ncc destruction while limited gold deposits in the muru metallogenic belt may have been attributed to relatively weak crustal extension and steep faults

modeling wide angle seismic data for crustal structure southeastern grenville province a modeling methodology for obtaining two dimensional 2 d crustal structure from wide angle seismic data is applied to data from the southeastern grenville province pre modeling steps include 1 assignment of arrival pick uncertainties for appropriate data fitting and weighting using an empirical relationship based on signal to noise ratio 2 using a modified form of travel time reciprocity to avoid unreasonable levels of model heterogeneity and 3 identifying data unsuitable for 2 d modeling the goal of the travel time inversion amplitude modeling approach is to obtain a minimum structure and minimum parameter model that takes into account both horizontal and vertical variations in the resolution of typical wide angle data each step of a layer stripping procedure involves a series of inversions in which a one dimensional or simple starting model is improved with additional velocity and or interface nodes until a satisfactory trade off between travel time fit parameter resolution and complete ray coverage of all source receiver pairs is achieved using zero vertical velocity gradient layers and head waves during preliminary first arrival inversion can 1 decrease the number of intermediate models 2 allow greater lateral heterogeneity to be imaged and 3 simplify incorporation of amplitude modeling constraints into the final model using amplitude distance curves allows quantitative modeling of the relative amplitude and offset variations of phases discrepancies between observed and calculated reflection amplitudes are used to infer fundamental non step like velocity changes at layer boundaries later arrivals due to unresolved velocity anomalies are modeled using reflecting segments that float within the model without an associated velocity structure these reflectors provide a spatial image like that obtained from vertical incidence reflection data as opposed to a velocity image the model of grenville crustal structure is more detailed than a model obtained from a previous interpretation of the data and includes elements analogous to those imaged in nearby deep reflection data a crustal scale zone of wide angle reflectors with an average easterly apparent dip of 13 defines a major grenvillian terrane boundary

the bending mechanism of anping ground fissure in the hebei plain north china the anping fissure is one typical and particular ground fissure in the north china plain this study was carried out in anping area with geological means such as surveying mapping trenching and drilling the geological structure and disasters were analyzed by both qualitative and quantitative methods the main conclusions are as follows 1 anping ground fissure is the local manifestation of regional tectonic stress field and is basically folding directional hidden and intermittent 2 under the control of shen rao fault anping ground fissure was exposed and expanded by water related human activities and then was cracked by small and medium sized earthquakes 3 the forming process followed the bending cracking rules the uplifting force from deep in the earth bent the entire overlying strata the tangential stress below the ground surface counterbalanced the horizontal stress of soils even breaking through their tensile strength and inducing cracks the fissure was periodic and wavery because the cracking force was proportional to the uplifting force but inversely proportional to the stratigraphic depth

crustal structure of the trans european suture zone region along polonaise 97 seismic profile p4 1 the large scale polonaise 97 seismic experiment investigated the velocity structure of the crust and upper mantle in the trans european suture zone tesz region between the precambrian east european craton eec and paleozoic platform that comprises terranes added during the caledonian and variscan orogenies 530 370 and 370 225 ma respectively this experiment included 64 shots recorded by 613 seismic stations during two deployments very good quality data were recorded along five profiles and the longest and most important one p4 is the focus of this paper clear first arrivals and later phases of waves reflected refracted in the crust and moho were interpreted using two dimensional 2 d tomographic inversion and ray tracing techniques the crustal thickness along the profile varies from 30 35 km in the paleozoic platform area to 40 km below and due northeast of the tesz to 43 km in the polish part of the eec and to 50 km in lithuania the paleozoic platform and eec are divided by the polish basin so the upper crustal structure varies considerably in the area of the polish basin the p wave velocity is very low vp 6 1 km s down to depths of 15 20 km indicating that a very thick sedimentary sequence is present we suggest two possible tectonic interpretations of the velocity models 1 baltica indented avalonia obducting its upper crust and underthrusting its lower crust in a tectonic flake structure and 2 a rifted margin of baltica underlies the polish basin this model is similar to other interpretations of seismic profiles recorded in the baltic sea the second model implies that the paleozoic platform solely consists of avalonian lithosphere and the eec of baltica lithosphere it offers a simple explanation of the difference in crustal thickness of the two platforms it also implies that the caledonian and variscan orogenies in this area were relatively soft collisions that left this continental margin largely intact

crustal structure and tectonic study of north china craton from a long deep seismic sounding profile abstract in this paper we present the results of modeling refracted and reflected waves employing 2d ray tracing for a 1600 km long refraction reflection profile that extends e w across the entire north china craton ncc the resulting p wave velocity models reveal substantial structural variations among different geological units of the ncc the taihangshan mountains are the geographical and geological demarcation lines of the ncc in the eastern part of the ncc bohai bay basin the craton appears to be destructed as evidenced from the widespread of crust thinning 30 km development of large sedimentary basins and weaken of crust mantle boundary coupling these features indicated that cenozoic tectonic reactivation succeeded mesozoic destruction in the eastern part of ncc in the western part of ncc the craton remains high crustal p wave velocity stable cold and strongly crust mantle boundary coupling crust the tanlu faults and the taihangshan faults are the tectonic boundaries in the ncc and play important roles in the process of cratonic destruction the structural feature of the east secondary tectonic differential settlement in the process of basin extension is that the most faults in bohai bay basin are the boundaries between the depression basin and uplift area comprehensive study found an apparent difference between the north and south part in eastern ncc destruction in that the large scale cenozoic stretching mainly occurred in the bohai bay basin and the weakly existed only in the local area and in hehuai basin we discussed the crust and upper mantle tectonic evolution of ncc under the action of the convergence of regional tectonic stress field in different geological periods since the mesozoic era the plate movement around ncc affects the lithospheric and crustal modification of the eastern north china and controls the deep structural background of seismicity and metallogenesis

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas