unexposed archean components and complex post archean accretion reworking processes beneath the southern yangtze block revealed by zircon xenocrysts from the paleozoic lamproites south china abstract integrated u pb dating and hf isotope analysis of zircon xenocrysts from the baifen lamproites of the zhenyuan area in the southeastern guizhou province offer a unique glimpse into the evolution of the deep continental crust beneath the southern part of the yangtze block south china a total of 148 zircons with 90 110 concordance yield u pb ages varying from 3458 9 ma to 252 2 ma they generally have high th u ratios 0 3 indicating a magmatic origin the two youngest magmatic zircons give a weighted mean 206pb 238u age of 253 0 2 8 ma which is interpreted as the emplacement age of the host baifen lamproites most zircons with pre eruption ages are xenocrysts derived from the deeper crust of the southern yangtze block they define two major paleoproterozoic age populations at 2 17 ga and 1 8 ga with similar hf model ages tcrust of 2 4 2 8 ga peak at 2 64 ga the oldest zircon has a 207pb 206pb age of 3458 9 ma with ehf t 1 47 and tcrust 3 7 ga this demonstrates the presence of archean crustal components or remnants as old as 3 7 ga beneath the southern yangtze block magmatic events involving significant addition of juvenile mantle derived materials mainly occurred at 2 2 2 1 ga and 2 0 1 8 ga but the latter event also involved reworking of the neoarchean crust and might represent the cratonization of the yangtze continent during the middle paleoproterozoic which could be correlated to the assembly of the columbia supercontinent this segment of the yangtze block became tectonically quiescent until 1 2 ga implying that the crustal stabilization lasted for ca 600 million years a few late mesoproterozoic zircon xenocrysts within the age range 1 3 1 0 ga suggest the occurrence of grenville aged events these neoproterozoic zircon xenocrysts 992 547 ma have a wide range of ehf t values 8 47 to 22 07 consistent with the zircon hf isotopic compositions of widespread coeval igneous rocks in the yangtze block the data show that the yangtze block has undergone important crustal growth and reworking during the neoproterozoic in response to the breakup of the rodinia supercontinent the early middle paleozoic zircon xenocrysts 513 357 ma have negative ehf t values 2 97 to 12 69 and tcrust hf model ages of 1 59 2 27 ga indicating reworking of the precambrian crustal basement without juvenile contributions during the caledonian orogeny the positive ehf t values 13 79 to 0 22 of twelve late paleozoic zircons 284 264 ma with a major age peak at ca 275 ma suggest that the precambrian basement beneath the southern yangtze block experienced an episode of strong rejuvenation during the permian we propose a possible linkage between the baifen lamproite magmatism 284 252 ma and the emeishan flood basalt volcanism

the progressive evolution of a continental climate in southeast central european lowlands during the middle pleistocene recorded in loess paleosol sequences 1 abstract little is known about the long term quaternary climate evolution of central and south east europe because suitable terrestrial paleoenvironmental records are scarce we present a multiproxy record of loess paleosol sequences in the middle and lower danube basins over the past 700 k y in these lowlands the continentality of interglacial climate progressively increased during the middle pleistocene corresponding trends are seen in other climate prox ies in the same region and in the lowlands of the northern black sea but not or less clearly in climate archives from outside these lowlands we conclude that a small scale increase in paleoelevation of central european mountain ranges the alps carpathians and dinarides during the middle pleistocene might be the cause of the progressive increase in climate conti nentality of southeast european lowlands

the shape of mars and the topographic signature of the hemispheric dichotomy reanalysis of occultation data from the mariner 9 and viking orbiter spacecraft to determine the shape of mars indicated that the hemispheric dichotomy is not a fundamental feature of the shape of the planet it is a consequence of an approximately 3 kilometer offset between mars9s center of mass and center of figure and the boundary along most of its length consists of broad gradual surface slopes over distances of thousands of kilometers this result was supported by analysis of high spatial resolution earth based radar topographic profiles any successful model for the origin of the dichotomy must explain a planet with an ellipsoidal shape and a long wavelength gradual topographic transition between the northern and southern hemispheres

the loess and loess like deposits along the sides of the western mediterranean sea genetic and palaeoclimatic significance abstract the loess and loess like deposits on the northern and southern sides of the western mediterranean generally dating to the upper pleistocene are derived from aeolian mobilization of dust from local sources and from their sedimentation where trapped in a dense steppe environment these aeolian deposits however differ from each other as regards the nature of the source material the sedimentary processes and the post depositional weathering loess deposits are more frequent on the north side of the mediterranean where deposited in attenuated periglacial conditions than in north africa where they accumulated in peridesert areas during pluvial periods

alpe arami a peridotite massif from depths of more than 300 kilometers the abundance of fetio 3 and chromite precipitates in olivine of the alpe arami peridotite massif switzerland requires a much higher solubility for highly charged cations than is found in mantle xenoliths from depths of 250 kilometers three previously unknown crystal structures of fetio 3 were identified that indicate that the originally exsolved phase was the high pressure perovskite polymorph of ilmenite implying a minimum depth of origin of 300 kilometers these observations coupled with the unique lattice preferred orientation of olivine further suggest that the original composition of olivine may reflect that of a precursor phase perhaps wadsleyite that is stable only at depths greater than 400 kilometers

u pb and hf isotope analysis of zircons in mafic xenoliths from fuxian kimberlites evolution of the lower crust beneath the north china craton mafic xenoliths from the paleozoic fuxian kimberlites in the north china craton include garnet granulite and minor pyroxene amphibolite metagabbro anorthosite and pyroxenite the formation conditions of the amphibolites are estimated at 745 820 c and 7 6 8 8 kb 25 30 km the granulites probably are derived from greater depths in the lower crust lam icpms u pb dating of zircons from four granulites reveals multiple age populations recording episodes of magmatic intrusion and metamorphic recrystallisation concordant ages and upper intercept ages interpreted as minimum estimates for the time of magmatic crystallisation range from 2 620 to 2 430 ma in three granulites two amphibolites and two metagabbros lower intercept ages represented by near concordant zircons are interpreted as reflecting metamorphic recrystallisation and range from 1 927 to 1 852 ma one granulite contains two metamorphic zircon populations dated at 1 927 55 ma and 600 700 ma separated minerals from one granulite and one amphibolite yield sm nd isochron ages of 1 619 48 ma 143nd 144nd i 0 51078 and 1 716 120 ma 143nd 144nd i 0 51006 respectively these ages are interpreted as recording cooling following metamorphic resetting model ages for both samples are in the range 2 40 2 66 ga lam mc icpms analyses of zircon show a range in 176hf 177hf from 0 28116 to 0 28214 corresponding to a range of ehf from 34 to 12 the relationships between 207pb 206pb age and ehf show that 1 the granulites amphibolites and metagabbro were derived from a depleted mantle source at 2 6 2 75 ga 2 zircons in most samples underwent recrystallisation and pb loss for 100 200 ma after magmatic crystallisation consistent with a residence in the lower crust 3 metamorphic zircons in several samples represent new zircon growth incorporating hf liberated from breakdown of silicates with high lu hf 4 in other samples metamorphic and magmatic zircons have identical 176hf 177hf and the younger ages reflect complete resetting of u pb systems in older zircons the fuxian mafic xenoliths are interpreted as the products of basaltic underplating derived from a depleted mantle source in neoarchean time an important period of continental growth in the north china craton paleoproterozoic metamorphic ages indicate an important tectonic thermal event in the lower crust at 1 8 1 9 ga corresponding to the timing of collision between the eastern and western blocks that led to the final assembly of the north china craton the growth of metamorphic zircon at 600 700 ma may record an asthenospheric upwelling in neoproterozoic time related to uplift and a regional disconformity in the north china craton

stratigraphy and spatial and temporal paleoclimatic trends in southeastern eastern european loess paleosol sequences abstract the loess paleosol sections batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine are presently located in areas of different types of steppe and are highly sensitive for recording climatic changes a stratigraphy for these three southeastern eastern european sections is presented based on pedostratigraphy and correlation of recently obtained susceptibility records with susceptibility data of other sections of the area koriten mostistea vyazivok of the chinese loess plateau and with the benthic 18o record of odp 677 six pedocomplexes were studied at the serbian and romanian sections and five at the ukrainian section the oldest are related to marine isotope stage mis 17 batajnica stari slankamen and mircea voda and mis 13 15 stary kaydaky some points concerning the existing loess chronostratigraphies of bulgaria ukraine and china are discussed comparative study of the profiles allows the tracing of paleoclimatic and paleoenvironmental changes in southeastern eastern europe in time and space reconstruction of paleoprecipitation based on susceptibility rainfall relationships and calculations of sedimentation rates are evaluated

moho vs crust mantle boundary evolution of an idea abstract the concept that the mohorovicic discontinuity moho does not necessarily coincide with the base of the continental crust as defined by rock type compositions was introduced in the early 1980s this had an important impact on understanding the nature of the crust mantle boundary using information from seismology and from deep seated samples brought to the surface as xenoliths in magmas or as tectonic terranes the use of empirically constrained p t estimates to plot the locus of temperature vs depth for xenoliths defined a variety of geotherms depending on tectonic environment the xenolith geotherms provided a framework for constructing lithological sections through the deep lithosphere and revealed that the crust mantle boundary in off craton regions commonly is transitional over a depth range of about 5 20 km early seismic reflection data showed common layering near the moho correlating with the petrological observation of multiple episodes of basaltic intrusion around the crust mantle boundary developments in seismology petrophysics and experimental petrology have refined interpretation of lithospheric domains the expansion of in situ geochronology especially zircon u pb ages and hf isotopes os isotopes of mantle sulfides has defined tectonic events that affected whole crust mantle sections and revealed that the crust mantle boundary can change in depth through time however the nature of the crust mantle boundary in cratonic regions remains enigmatic mainly due to lack of key xenoliths or exposed sections the observation that the moho may lie significantly deeper than the crust mantle boundary has important implications for modeling the volume of the crust mapping the crust using seismic techniques alone without consideration of the petrological problems may lead to an overestimation of crustal thickness by 15 30 this will propagate to large uncertainties in the calculation of elemental mass balances relevant to crust formation processes and the composition of the convecting mantle

quantification of magnetic coercivity components by the analysis of acquisition curves of isothermal remanent magnetisation abstract a new method of analysing isothermal remanent magnetisation irm acquisition curves based on cumulative log gaussian analysis robertson and france phys earth planet inter 82 1994 223 234 is proposed it is based on the curve fitting of the irm acquisition curve versus the logarithm of the applied field with i the acquisition curve on a linear scale ii the acquisition curve expressed as a gradient and iii the acquisition curve on a probability scale even when a sample is not saturated its magnetic properties can be defined although with less certainty the number of magnetic components required for an optimal fit to a measured irm acquisition curve is evaluated statistically the method discriminates on the basis of different mineral coercivity therefore additional rock magnetic tests are still required to separate minerals with similar coercivities

determining the origin of ultrahigh pressure lherzolites the occurrence of coesite and diamond in regional ultrahigh pressure metamorphic rocks requires that rocks formed at pressures of 3 to 4 gpa 100 to 120 km below the earth s surface have been transported back to the surface 1 1 l dobrzhinetskaya et al suggest that garnet lherzolite from

neoarchean 2 7 2 8 ga accretion beneath the north china craton u pb age trace elements and hf isotopes of zircons in diamondiferous kimberlites abstract zircon xenocrysts from the early paleozoic mengyin and fuxian diamondiferous kimberlites on opposite sides of the translithospheric tanlu fault in the north china craton have been used to probe the deep crust based on detailed studies of external forms and internal structures the zircons can be roughly divided into magmatic and metamorphic zircons there are no consistent differences in u th or th u between the two zircon populations the trace element affinities of the igneous zircons vary widely from mafic through intermediate to felsic rocks with minor populations similar to zircons from carbonatite and syenite in situ isotopic analysis for u pb and lu hf reveals that all zircons both from mengyin and fuxian kimberlites regardless of their chemical affinities have similar formation ages 2 5 2 7 ga and depleted mantle model ages t dm 2 7 2 8 ga these ages are also similar within error to those of zircons in mafic granulite xenoliths from the fuxian kimberlites implying that the lower crust was similar neoarchean cratonic basement beneath the mengyin and fuxian areas but the latter experienced stronger thermal modification in proterozoic time the magmatic zircons may be derived from late differentiates of underplated mafic magmas with some contamination by crustal components and the metamorphic populations developed during heating events linked to the ongoing underplating the addition of juvenile material up to 9 5 e hf at this time 2 7 2 8 ga corresponds to a known major episode of global crustal formation

pb and nd isotopic composition of the jigongshan granite constraints on crustal structure of tongbaishan in the middle part of the qinling tongbai dabie orogenic belt central china abstract the qinling dabie sulu belt is the world s largest ultrahigh pressure uhp metamorphic belt the uhp metamorphism is well dated at 220 245 ma in the dabie sulu belt but at 507 ma in the qinling belt the tongbaishan is located between the qinling orogenic belt to the west and the dabie sulu uhp metamorphic belt to the east it is the key area for studying the tectonic relation between the qinling and dabie sulu belts and the diachronous uhp metamorphism the jigongshan granitic pluton t 128 ma with a total area of 1200 km 2 composed of monzogranite was mostly emplaced into the tongbai complex an exposed basement in the tongbaishan the jigongshan granites have sio 2 69 85 72 35 k 2 o na 2 o 0 87 1 13 a cnk 0 91 1 03 rb sr 0 14 0 25 and th u 3 3 12 their ree compositions show strongly fractionated patterns with la yb n 14 58 and eu eu 0 79 1 05 the granites are characterized by low radiogenic pb isotopic composition the present day whole rock pb isotopic ratios are 20 6 pb 204 pb 16 707 17 055 207 pb 204 pb 15 239 15 326 and 208 pb 204 pb 37 587 37 853 which are similar to that of the continental lower crust their e nd t values range from 16 to 20 and depleted mantle nd model ages t dm from 1 8 to 2 2 ga the above evidence indicates that the magma of the jigongshan granites was derived from the partial melting of the continental crust the pb and nd isotopic compositions of the jigongshan granites resemble those of the dabie core complex in the dabieshan but are distinct from those of the tongbai complex in the tongbaishan thus the dabie core complex would be the magma source of the jigongshan granites the result implies that the dabie core complex is extended to the west and constitutes the unexposed basement underlaying the tongbai complex in the tongbaishan

distribution of igneous rocks in china revealed by aeromagnetic data abstract after several decades of aeromagnetic surveys the measured data now cover nearly the entire chinese continent and part of the china sea these data were first applied in this research and could provide important insights into the distribution of igneous rocks beneath the earth s surface because different types of igneous rocks have a magnetic difference and produce distinct aeromagnetic anomalies on aeromagnetic t image with reduction to the pole or other data calculating maps by analyzing more than 240 thousand magnetic susceptibility data points and aeromagnetic anomalies of known igneous rocks in the chinese continent it was determined that mafic ultramafic rocks commonly have a high magnetic susceptibility and cause linear and strong positive aeromagnetic anomalies intermediate felsic rocks have a stable and low magnetic susceptibility and show a flat gradient variation and regular shape volcanic rocks have large variability in regard to magnetic susceptibility and romance therefore the aeromagnetic anomalies are always random or show variation within a planar area and decrease rapidly when an upward continuation is applied following the aeromagnetic data and calculating the maps of the vertical first order derivative and the tilt derivative and combining this information with known outcrops of igneous rocks we renewed the boundaries of 82 known mafic ultramafic rocks 228 known intermediate felsic rocks and 131 known volcanic rocks in addition we newly mapped concealed igneous rocks of 203 mafic ultramafic rocks 2322 intermediate felsic rocks and 494 volcanic rocks the igneous rocks can be identified as nine ultra mafic belts 10 mafic belts or regions 27 intermediate felsic belts and eight volcanic blocks the results indicate that the mafic ultramafic rocks are mainly distributed in tibet erenhot of inner mongolia and northern qilian and the smaller zones in the western kunlun tianshan western junggar eastern tibet maqin in gansu and the ailao mountain mtn areas the mafic rocks are mostly outcropped in northern tibet southwestern sanjiang kangdian in sichuan baise and rongjiang in guangxi yinjiang in guizhou dabashan mtn southern dabie mtn bangbu in anhui qiemo in xinjiang the intermediate felsic rocks are mainly located in the orogenic system and rarely within the craton volcanic rocks are widely developed in eastern and western china such as the circumference of songliao basin erlian basin the southern yellow sea subei basin bohai bay basin eastern zhejiang the circumference of hainan island southern sichuan northern yunan central tibet the bachu area in tarim basin junggar basin and turpan hami basin

shrimp u pb zircon geochronology of the fuping complex implications for formation and assembly of the north china craton abstract the fuping complex located within the central zone of the north china craton is composed of amphibolite to granulite facies orthogneisses interleaved with minor supracrustal rocks at similar metamorphic grade the oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a shrimp u pb zircon age of 2708 8 ma we consider these enclaves to represent fragments of 2 7 ga continental materials incorporated in the biotite gneiss the biotite gneiss has a shrimp u pb zircon age of 2513 12 ma interpreted to be time of magmatic crystallisation of the igneous precursor based on the igneous characteristics of the zircons this indicates a major magmatic episode at 2 52 ga in the fuping complex identical to the age of felsic volcanism within the low grade wutai complex which crops out immediately to the west a gneissic granite that intrudes the biotite gneisses has a poorly defined 207pb 206pb age of 2045 64 ma this is within error of the age of 2097 46 ma obtained from a fine grained gneiss interlayered with amphibolite of the wanzi supracrustal suite wss interpreted to be volcanic in origin zircons from both these samples have strong oscillatory zoning and provide the first indication of a palaeoproterozoic magmatic event in the area again similar in age to magmatic events recently recognised in the adjacent wutai complex these data indicate a comparable history for the fuping and wutai complexes and support geochemical evidence that they had a common origin and formed part of a late archaean arc affected by later palaeoproterozoic re activation low uranium zircons without oscillatory zoning separated from a sample of biotite gneiss yield data clustered at 1817 26 ma which is interpreted to reflect a period of new zircon growth during a major metamorphic event these data support the recently proposed tectonic model that amalgamation of the north china craton occurred due to collision of the eastern and western blocks along the central zone at 1 8 ga ago

clinoenstatite in alpe arami peridotite additional evidence of very high pressure observations by transmission electron microscopy show that lamellae of clinoenstatite are present in diopside grains of the alpe arami garnet lherzolite of the swiss alps the simplest interpretation of the orientation crystallography and microstructures of the lamellae and the phase relationships in this system is that the lamellae originally exsolved as the high pressure c centered form of clinoenstatite these results imply that the rocks were exhumed from a minimum depth of 250 kilometers before or during continental collision

talc magnesite and ti clinohumite bearing ultrahigh pressure meta mafic and ultramafic complex in the dabie mountains china

cm5 a pre swarm comprehensive geomagnetic field model derived from over 12 yr of champ orsted sac c and observatory data a comprehensive magnetic field model named cm5 has been derived from champ rsted and sac c satellite and observatory hourly means data from 2000 august to 2013 january using the swarm level 2 comprehensive inversion ci algorithm swarm is a recently launched constellation of three satellites to map the earth s magnetic field the ci technique includes several interesting features such as the bias mitigation scheme known as selective infinite variance weighting sivw a new treatment for attitude error in satellite vector measurements and the inclusion of 3 d conductivity for ionospheric induction sivw has allowed for a much improved lithospheric field recovery over cm4 by exploiting champ along track difference data yielding resolution levels up to spherical harmonic degree 107 and has allowed for the successful extraction of the oceanic m2 tidal magnetic field from quiet nightside data the 3 d induction now captures anomalous solar quiet features in coastal observatory daily records cm5 provides a satisfactory continuous description of the major magnetic fields in the near earth region over this time span and its lithospheric ionospheric and oceanic m2 tidal constituents may be used as validation tools for future swarm level 2 products coming from the ci algorithm and other dedicated product algorithms

dynamic cause of marginal lithospheric thinning and implications for craton destruction a comparison of the north china superior and yilgarn cratons we present a comparative tectonic analysis of the north china craton ncc which has lost parts of its root with the yilgarn and superior cratons which preserve their roots we compare the geophysical structure and tectonic histories of these cratons to search for reasons why some cratons lose their roots while others retain them based on the comparison and analysis of geological geophysical and geochemical data it is clear that the lithospheric thinning beneath craton margins is a common phenomenon which may be caused by convergence between plates however craton destruction is not always accompanied by lithospheric thinning except for cratons that suffered subduction and collision from multiple sides the western block also known as the ordos block of the ncc yilgarn and superior cratons have not experienced craton destruction the common ground among them is that they are surrounded by weak zones e g mobile belts or orogens that sheltered the cratons from deformation which contribute

highly evolved archean basement beneath the western cathaysia block south china abstract how has the earth s continental crust evolved most of our knowledge comes from surface exposures but zircon xenocrysts in volcanic rocks can provide samples of deeper crustal levels the u pb and hf isotope systematics of xenocrystic zircons brought to the surface by the cenozoic 48 49 ma pingnan basaltic rocks and the mesozoic 166 ma pingle minettes in guangxi province south china suggest the presence of unexposed relict archean basement beneath the western cathaysia block where the oldest exposed rocks are neoproterozoic phanerozoic in age this basement has provided zircons with several distinct age populations 3 85 3 55 3 3 3 2 and mainly 2 9 2 5 ga these have hf depleted mantle model ages t dm of 2 5 to 3 9 ga the oldest t dm 3 9 ga shows the existence of paleo to eoarchean components in this area this relict basement experienced complex modification including the addition of juvenile mantle material with e hf up to 12 7 at ca 3 6 3 2 2 5 1 0 and 0 5 ga the zircons also record thermal events that reworked remelted the older crustal components of the block at ca 2 0 1 8 1 6 1 5 ga and 80 ma although these younger events have modified the archean nature of the basement it seems that they do not represent significant post archean crustal growth

silt 2 62 μm 9 4φ the particles in finer grained detrital sediments are usually composed of quartz they fall into two size grades sand 2 mm 62 m and silt 62 m 2 m these size gradings conceal important geological processes since there are geological controls on both the quartz sand and silt populations sand nature is largely controlled by geochemical reactions for example in cooling granite from which it is eventually released by weathering action the quartz is among the last part of the rock system to solidify and the eutectic like reaction which occurs ensures that the quartz exists as small crystalline units each suffering considerable cooling and recrystallisation stresses silt is broken quartz and has traditionally been considered to lack a specific geological control the situation is confused by the large range of materials that fall into the size category but there do seem to be distinguishable modes and possibly comminution limits within the 60 m span the controls operating in this size range are probably the critical concentration of moss defects in the quartz particles moss postulated the formation of specific crystal defects in the quartz formed in granites these affect sand formation and it is possible that they also control the mode size of silt particles within the silt range there may be several usefully definable populations as moss proposed for sand the quaternary appears to be a silt rich period due to tectonic and glacial activity but silt production is apparent throughout the sedimentary record very long term silt producing processes are required to produce silt in nature on a large scale very energetic processes are required many processes that are believed to generate silt particles have been listed however large scale production is essentially due to glacial grinding or to intense weathering processes in high cold tectonically active mountain regions the region of high asia of crustal overlap is a major generator of silt particles these form the productive alluvial soils of north india most of the nation of bangladesh the loess deposits along the syr darya and amu darya rivers in central asia and the great loess deposits of north china some claims have been made for silt production in hot deserts large amounts of very fine aerosolic dust are produced but in terms of loess sized particles this is a small scale process and leads to modest disputed deposits the loess deposits around the sahara usually have smaller mode sizes e g nigeria or larger mode sizes e g libya tunisia than the true chinese mode at 25 m this paper aims to introduce the distinguishing properties of sand and silt discuss in detail the possible processes of silt formation in relation to the evidence of what is produced describe the major silt populations and conclude on the most likely formation process es in particular three silt ranges are discussed in relation to the r size diagram c 2 5 m d1 20 30 m and d2 60 m these can represent canadian quickclay qq chinese loess and the ideal loughborough loess ll and north african loess nal it is intended that this paper will put into context the diverse work in the area and in so doing shed light on what is an often overlooked subject

downward rejuvenation of the continental lower crust beneath the southeastern north china craton abstract felsic to mafic granulite xenoliths and zircon xenocrysts from the cenozoic 1 ma nushan basalts were analyzed to construct a lower crustal column illustrating the fine structure and evolution of the deep crust beneath the southeastern north china craton felsic granulites sampled from the lowermost middle to the upper lower crust have a calculated vp of 6 32 km s relict magmatic zircons from them yield an upper intercept age of 2716 32 ma and depleted mantle hf model ages tdm of 3 1 2 9 ga metamorphic zircons with ages of ca 2100 ma have initial 176hf 177hf ratios similar to the magmatic ones implying in situ recrystallization of the older zircons the intermediate granulites with paleoproterozoic ages 2 1 1 9 ga whole rock nd tchur 3 4 ga and zircon hf tdm 3 1 2 8 ga huang et al 2004 zheng et al 2012 have a calculated vp of 6 53 km s being considered that they underlie the felsic granulites the lowermost crust is represented by mafic granulites vp 6 86 km s with the exception of three inherited zircons from the mafic granulites which yielded an upper intercept age of 2455 ma and tdm of ca 2 7 ga most zircons formed in the late mesozoic ca 115 ma zircon xenocrysts have concordant ages including the neoproterozoic early paleozoic late paleozoic early mesozoic and cenozoic our data integrated with published data suggest that the lower crust is younger at the bottom and dominantly composed of felsic intermediate and mafic granulites this trend reflects the vertical accretion of the crust including the addition of juvenile material during the mesoarchean and neoarchean and repeated reworking during the neoarchean paleoproterozoic and late mesozoic the neoproterozoic paleozoic and early mesozoic zircon xenocrysts may record the subduction events between the craton and the yangtze block which also affected the nature of the lower crust beneath the southeastern part of the craton

lithological and age structure of the lower crust beneath the northern edge of the north china craton xenolith evidence abstract deep seated xenoliths in volcanic rocks offer direct glimpses into the nature and evolution of the lower continental crust in this contribution new data on the u pb ages and hf isotopes of zircons in six felsic granulite xenoliths and one pyroxenite xenolith from the hannuoba cenozoic basalts combined with published data from mafic to felsic xenoliths are used to constrain the lithological and age structure of the lower crust beneath the northern edge of the north china craton two newly reported felsic granulites contain precambrian zircons with positive 7 5 10 6 and negative e hf values 10 1 to 3 7 corresponding to upper intercept ages of 2449 62 ma and 1880 54 ma respectively indicating crustal accretion in the late archean and reworking in paleoproterozoic time zircons in another four felsic xenoliths give phanerozoic ages from 142 ma to 73 ma and zircons from one pyroxenite xenolith give a concordant age of 158 ma the zircon e hf values of these four felsic xenoliths range between 23 3 and 19 1 reflecting re melting of the pre existing lower crust integration of geothermobarometric and geochronological data on the hannuoba xenoliths with seismic refraction studies shows that the lower crust beneath the northern edge of the north china craton is temporally and compositionally zoned the upper lower crust 24 33 km consists dominantly of archean 2 5 ga with minor 2 7 ga felsic granulites with subordinate felsic granulites that reworked at 140 120 ma both precambrian and late mesozoic mafic granulites are important constituents of the middle lower crust 33 38 km major late mesozoic 140 120 ma and less cenozoic 45 47 ma granulites and pyroxenites are presented in the lowermost crust 38 42 km the zoned architecture of the lower crust beneath hannuoba suggests a complex evolution beneath the northern margin of the craton including late neoarchean 2 5 ga accretion and subsequent episodic accretion and or reworking during paleoproterozoic 1 8 1 9 ga and phanerozoic 220 ma 120 140 ma 45 47 ma times with possible links to circum craton subduction collision events and the destruction of the north china craton

fluid rock interactions during ultra high pressure metamorphism dabie shan china oxygen isotope analyses of garnet separates and whole rock samples of gneiss and marble hosted eclogites from the ultra high pressure uhp dabie shan terrain fall in the range 6 76 to 10 76 comparison of the isotopic compositions of the eclogites with those of their host rocks leads to the following conclusions 1 the basaltic protolith of the eclogites had isotopic compositions in the range 2 15 to 4 99 it is proposed that this is the result of contamination of the parent basaltic magma with hydrothermally altered18o depleted source materials 2 18o enriched eclogite compositions resulted from local scale 3 m interaction between this basaltic eclogite protolith and fluids produced by decarbonation of impure marble lithologies during uhp metamorphism 3 18o depleted eclogite and gneiss compositions resulted from regional scale meteoric hydrothermal alteration of the basalts and their host rocks prior to uhp metamorphism epidote separates and whole rocks from the cores and rims of mineralogically zoned eclogite boudins within amphibolite grade biotite gneisses show no distinct isotopic differences this suggests that the preferential recrystallisation of the gneisses and the associated amphibolite grade overprint of the rims of eclogite bodies could not have resulted from regional scale infiltration of significant volumes of fluid during the exhumation of the dabie shan terrain

resolution of direction of oceanic magnetic lineations by the sixth generation lithospheric magnetic field model from champ satellite magnetic measurements the champ satellite continues to provide highly accurate magnetic field measurements from decreasing orbital altitudes 350 km at solar minimum conditions using the latest 4 years 2004 2007 of readings from the champ fluxgate magnetometer including an improved scalar data product we have estimated the lithospheric magnetic field to spherical harmonic degree 120 corresponding to 333 km wavelength resolution the data were found to be sensitive to crustal field variations up to degree 150 down to 266 km wavelength but a clean separation of the lithospheric signal from ionospheric and magnetospheric noise sources was achieved only to degree 120 this new mf6 model is the first satellite based magnetic model to resolve the direction of oceanic magnetic lineations revealing the age structure of oceanic crust

geophysical constraints on the link between cratonization and orogeny evidence from the tibetan plateau and the north china craton abstract understanding the geodynamic process of orogeny and cratonization and their transition is among the key topics of research in evaluating the link between plate tectonics and continental dynamics the tibetan plateau and the north china craton ncc two key areas in mainland china offer excellent laboratories to understand continental tectonics over a broad span of earth history particularly the deep structure of the lithosphere as imaged from geophysical data on the tibetan plateau and the ncc provide important clues in understanding orogeny and cratonization the tibetan plateau is the largest and highest plateau on earth in terms of mean altitude and is an important region for understanding the mechanisms of continent continent collision and cenozoic plateau uplift the ncc is an archean craton that underwent lithospheric disruption during the mesozoic here we reconstruct the main features of the structure of the crust and upper mantle from surface wave tomography and gravity modeling in tibet and its neighboring regions in order to understand the modality of the convergence and collision process between the indian and eurasian plates and the influence of this process on the uplift of the plateau in the ncc geological geochemical geophysical and tectonic investigations demonstrate that lithospheric destruction mainly occurred in the eastern block the crustal structure of the ncc is reconstructed from ambient noise surface wave tomography and the different possible disruption mechanisms are evaluated the vs shear wave velocity tomography results and the density structure of the crust and upper mantle to about 350 km depth demonstrate the lateral variation of the thickness of the metasomatic lid between the south and north of the bangong nujiang suture bns and the west and east of tibet which suggest that the leading edge of the subducting indian slab reaches the bns the subduction angle of indian plate indicates a transition from steep to shallow from the west to east tibet sections depicting the gravitational potential energy suggest that mantle flow contributes to the subduction of the indian plate as far as the bns and the transition from the asthenospheric layer to the metasomatic lid overlaps with the transition from north south shortening in south tibet to eastward tectonic escape in north tibet qiangtang and songpan ganzi blocks both vs and models suggest the following 1 north southward lower crust flow beneath the eastern ncc and interaction between the westward mantle flow and eastward escape flow beneath the central ncc in addition to the earlier proposed mechanisms of delamination and thermal erosion played important roles in the lithospheric disruption of the archean craton 2 mantle flow plays an important role in the continental tectonic transition between neighboring tectonic blocks and within the cycle between orogeny and cratonization

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

cold subduction and the formation of lawsonite eclogite constraints from prograde evolution of eclogitized pillow lava from corsica a new discovery of lawsonite eclogite is presented from the lancone glaucophanites within the schistes lustres nappe at defile du lancone in alpine corsica the fine grained eclogitized pillow lava and inter pillow matrix are extremely fresh showing very little evidence of retrograde alteration peak assemblages in both the massive pillows and weakly foliated inter pillow matrix consist of zoned idiomorphic mg poor 0 8 wt mgo garnet omphacite lawsonite chlorite titanite a local overprint by the lower grade assemblage glaucophane albite with partial resorption of omphacite and garnet is locally observed garnet porphyroblasts in the massive pillows are mn rich and show a regular prograde growth type zoning with a mn rich core in the inter pillow matrix garnet is less manganiferous and shows a mutual variation in ca and fe with fe enrichment toward the rim some garnet from this rock type shows complex zoning patterns indicating a coalescence of several smaller crystallites matrix omphacite in both rock types is zoned with a rimward increase in xjd locally with cores of relict augite numerous inclusions of clinopyroxene lawsonite chlorite and titanite are encapsulated within garnet in both rock types and albite quartz and hornblende are also found included in garnet from the inter pillow matrix inclusions of clinopyroxene commonly have augitic cores and omphacitic rims the inter pillow matrix contains cross cutting omphacite rich veinlets with zoned omphacite si rich phengite si 3 54 apfu ferroglaucophane actinolite and hematite these veinlets are seen fracturing idiomorphic garnet apparently without any secondary effects pseudosections of matrix compositions for the massive pillows the inter pillow matrix and the cross cutting veinlets indicate similar p t conditions with maximum pressures of 1 9 2 6 gpa at temperatures of 335 420 c the inclusion suite found in garnet from the inter pillow matrix apparently formed at pressures below 0 6 0 7 gpa retrogression during initial decompression of the studied rocks is only very local late veinlets of albite glaucophane without breakdown of lawsonite indicate that the rocks remained in a cold environment during exhumation resulting in a hairpin shaped p t path

very low temperature record of the subduction process a review of worldwide lawsonite eclogites abstract lawsonite eclogites preserve a record of very low temperature conditions in subduction zones all occur at active margin settings typically characterized by accretionary complexes lithologies and as tectonic blocks within serpentinite matrix melange peak lawsonite eclogite facies mineral assemblages garnet omphacite lawsonite rutile typically occur in prograde zoned garnet porphyroblasts their matrix is commonly overprinted by higher temperature epidote bearing assemblages greenschist or amphibolite facies conditions erase former lawsonite eclogite relics various pseudomorphs after lawsonite occur particularly in some blueschist eclogite transitional facies rocks coesite bearing lawsonite eclogite xenoliths in kimberlitic pipes and lawsonite pseudomorphs in some relatively low temperature ultrahigh pressure eclogites are known using inclusion assemblages in garnet lawsonite eclogites can be classified into two types l type such as those from guatemala and british columbia contain garnet porphyroblasts that grew only within the lawsonite stability field and e type such as from the dominican republic record maximum temperature in the epidote stability field formation and preservation of lawsonite eclogites requires cold subduction to mantle depths and rapid exhumation the earliest occurrences of lawsonite eclogite facies mineral assemblages are early paleozoic in spitsbergen and the new england fold belt of australia this suggests that since the phanerozoic secular cooling of earth and subduction zone thermal structures evolved the necessary high pressure temperature conditions buoyancy of serpentinite and oblique convergence with a major strike slip component may facilitate the exhumation of lawsonite eclogites from mantle depths

pleistocene environmental dynamics recorded in the loess of the middle and lower danube basin abstract the substantial loess deposits of the middle and lower danube basin in southeastern europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent yet are also the least well understood environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions which nevertheless reflect oscillations between relatively warm humid interglacial and cold dry glacial intervals this relative environmental stability may have proven important for hominins migrating into and through the region the loess stratigraphy comprises distinct loess paleosol sequences reflecting glacial interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry these phases are emphasised by variations in vegetation and malacofauna which respond to climatic change the loess deposits demonstrate broadly similar sedimentological characteristics across the basin danubian loess deposits initiated in response to the tectonic formation of the pannonian basin retreat of the large palaeolakes and increased sediment supply from the danube the period from 1 ma 500 ka mis 27 13 was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively in response to relatively humid forested conditions this period represents the opening of the danube corridor and provides the backdrop for initial hominin arrival into europe after 500 ka and particularly after mis 9 loess accumulation rates increased in response to relatively more steppic arid environments mis 9 and 13 15 were the most humid phases of the last 600 ky the mis 5 interglacial period was the warmest and relatively most humid period preceding the holocene and was followed by substantially increased loess accumulation during mis 4 which may be linked to north atlantic circulation the complexity of the mis 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time mis 3 corresponds with the first arrival of anatomically modern humans to europe the last glacial maximum and younger dryas of mis 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the north atlantic although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota as may also have been the case for most of the pleistocene glacial cycles the holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial

magnetite lamellae in olivine and clinohumite from dabie uhp ultramafic rocks central china ultrahigh pressure uhp minerals of the maowu mafic ultramafic complex in the dabieshan east central china exhibit many exsolution textures magnetite lamellae are common in olivines and ti clinohumites from harzburgite and garnet pyroxenite monazite ce lamellae occur in apatites from the garnet pyroxenite independent p t estimates suggest that these ultramafic rocks formed at p 5 gpa and t 700 50 c the lamellae bearing minerals are believed to preserve an earlier higher p t record prior to exsolution compositions and unit cell parameters of the magnetite and host olivine and intergrowth relations were determined using a newly developed x ray diffraction microprobe technique employing synchrotron radiation the host olivine and magnetite lamellae bear a topotaxial relation with 220 mag 200 ol 111 mag 3 3 1 ol 11 1 mag 331 ol 242 mag 2 2 0 ol the recalculated composition of primary olivine may contain up to 1 5 wt fe 2o3 four hypotheses may explain the observed intergrowths of oriented magnetite lamellae in olivine 1 oxidation of olivine 2 decomposition of fe 3 bearing olivine formed at 6 gpa 3 exsolution of a spinel wadsleyite solid solution fe 3o4 fe mg 2sio4 during decompression and 4 breakdown of phase a mg7si2 oh 6 enstatite the third hypothesis appears to be the most likely inasmuch as no additional silicate phase occurs as associated inclusions in the olivine host however the actual mechanism for exsolution of magnetite from olivine remains to be studied experimentally

palaeomagnetism of the loess palaeosol sequence in viatovo ne bulgaria in the danube basin abstract the results of a palaeomagnetic investigation of a 27 m thick loess palaeosol sequence in viatovo ne bulgaria are presented in this paper the sequence consists of topsoil s 0 seven loess horizons l 1 l 7 and six interbedded palaeosols s 1 s 6 overlying a red clay terra rossa complex magnetic viscosity experiments irm acquisition ams analysis and nrm stepwise alternating and thermal demagnetisation experiments of pilot samples were implemented for precise determination of the characteristic remanence and construction of a reliable magnetostratigraphical scheme analysis of irm acquisition curves using the expectation maximization algorithm of heslop et al heslop d dekkers m kruiver p van oorschot h 2002 analysis of isothermal remanent magnetization acquisition curves using the expectation maximization algorithm geophys j int 148 58 64 suggests that the best fitting is obtained by three coercivity components component 1 corresponds to sd maghemite magnetite while component 2 is probably related to the presence of oxidised detrital magnetites the third component shows varying coercivities depending on the degree of pedogenic alteration of the samples and probably reflects the presence of detrital magnetite grains oxidised at different degree the relevance of the viatovo section as a key representative sequence for the loess cover in the danube basin is confirmed by the presence of geomagnetic polarity changes in the lower part of the sequence the youngest one recorded in the seventh loess unit l 7 can be identified as corresponding to the matuyama brunhes palaeomagnetic polarity transition two normal magnetozones were found in the red clay complex probably corresponding to the jaramillo and olduvai subchronozones of the matuyama chron

the geomagnetic jerk of 2003 5 characterisation with regional observatory secular variation data abstract the 2003 5 geomagnetic jerk was identified in geomagnetic records from satellite data and a matching feature reported in variations in length of day lod but detailed study has been hampered by lack of geomagnetic observatory data where it appears strongest here we examine secular variation annual differences of monthly means based on a new resource of 43 chinese observatory records for 1998 until the present focusing on 10 series of particularly high quality and consistency to obtain a clean series we calculate the covariance matrix of residuals between measurements and a state of the art field model chaos 6 and use eigenvalue analysis to remove noisy contributions from the uncorrected data the magnitude of the most significant eigenvector correlates well with dcx corrected extended dst suggesting the noise originates from unmodelled external magnetic field removal of this noise eliminates much coherent misfit around 2003 2005 nevertheless the 2003 5 jerk is seen clearly in the first time derivative of the east component in chinese data and is also seen in the first time derivative of the vertical component in european data estimates of the jerk time are centred on 2003 5 but with some spatial variation this variation can be eliminated if we allow a discontinuity in the secular variation as well as its temporal gradient both regions also provide evidence for a jerk around 2014 although less clearly than 2003 5 we create a new field model based on new data and chaos 6 to further examine the regional signals the new model is close to chaos 6 but better fits chinese data although modelling also identifies some data features as unphysical

destruction of lithosphere within the north china craton inferred from surface wave tomography 1 the north china craton ncc is one of the oldest cratons in the world however the lithosphere of the craton was destructed during phanerozoic tectonism and then became tectonically and seismically active because the lithospheric structure of this complex craton has not been well studied the mechanism behind the thinning transformation and destruction of the lithosphere remains debated using an efficient and scalable 3 d surface wave tomography method we obtain a high resolution regional s wave velocity model that shows the three dimensional lithospheric structure of the ncc in addition we convert the s wave structure to an estimated thermal structure using accepted relationships between s wave velocity and temperature the model images a large upper mantle low velocity body beneath the eastern ncc especially beneath the seismically active zone from tangshan to xingtai this body is interpreted to represent hot material or volatiles escaping from the slab edge in the transition zone between the upper and lower mantle the low velocity body is a key piece of evidence in demonstrating thermochemical bottom up erosion transformation of the overlying cratonic lithosphere thereby leading to destruction of the lithosphere which may have occurred during the cenozoic this erosion mechanism appears to have had less influence in the western ncc ordos block however our results reveal a 130 km thick lithosphere beneath the present cratonic ordos block which is thinner than the 200 km thickness of the ncc lithosphere during the paleozoic as determined from analyses of xenoliths

journey beneath southern africa seismic analyses of the lithosphere undertaken as part of the kaapvaal project provide an unprecedented view of cratons the earliest parts of continental landmasses

shrimp u pb zircon geochronology of palaeoproterozoic metasedimentary rocks in the north china craton evidence for a major late palaeoproterozoic tectonothermal event abstract although metasedimentary successions are widely distributed across the north china craton those of palaeoproterozoic age are restricted to three orogenic belts namely the trans north china orogen the khondalite belt and the jiao liao ji belt prior to this work some of those successions were considered to be archaean in age the palaeoproterozoic metasedimentary rocks contain detrital igneous zircon grains with ages ranging from 3 0 to 2 1 ga with the majority recording an age between 2 3 and 2 0 ga this latter group define a series of magmatic events that occurred between formation of the archaean basement and deposition of the metasedimentary rock protoliths the metasedimentary rocks occur as two associations older volcano sedimentary units that formed between 2 37 and 2 0 ma and younger sedimentary units that formed mainly between 2 0 and 1 88 ga all these rock associations were then subjected to metamorphism during the late palaeoproterozoic 1 88 and 1 85 ga tectonothermal event named the luliang movement in early chinese literature which was a continent continent collision that led to the amalgamation of the north china craton

bedrock versus superficial deposits in the swiss jura mountains what is the legitimate soil parent material soils are generally considered to be the result of in situ weathered products of geological substrata nevertheless the earth s surface is mainly composed of superficial deposits made of sediments reworked during periods of climate instability glaciation aridification flooding etc but to what extent do these deposits influence present day soil development and or lessen the contribution of the geological substratum in the swiss jura mountains characterization and distribution of superficial deposits along a toposequence are used in order to decipher the polygenic sources of soil parent materials and question the importance of lithodependence in soil development the in situ weathering material and the allochtonous deposits are discriminated through analysis of mineralogical composition grain size distribution of the soil mineral fraction and multivariate statistical treatment as expected calcite is dominant in the autochonous mineral phase leading to high ph values in deep soil layers however the mineralogical composition of the surficial deposits is made of local mineral components mixed with allochtonous aeolian deposits this exogenous material is dominated by quartz and phyllosilicates and is reflected by low ph values in soil surficial horizons the grain size distribution curves of the insoluble residue from bedrocks are unimodal and dominated by fine loam and clays in contrast surficial deposits display polymodal curves demonstrating the contribution of various aeolian episodes and or sources analysis of the surface texture of quartz sand grains shows glacial marks intersected by aeolian shock marks indicating the posteriority of wind transportation loess material originates from alpine moraines of the swiss plateau and is mixed with deposits originating from more proximal jura moraines diluting the alpine signature consequently the soil development does not follow the expected and conventional decalcification process but is directly influenced by the origin of the primary sediments even when present only in small amounts and their evolution copyright 2012 john wiley sons ltd

geochronological and geochemical constraints on the subduction modified lithospheric origin of the early cretaceous volcanic rocks in the western north huaiyang belt of dabie orogen china geochronological elemental and sr nd hf isotopic data for intermediate acid volcanic sequences from the western north huaiyang belt of the dabie orogen china provide new constraints for the nature of the lithosphere and the potential involvement of subducted yangtze crust these rocks are calc alkaline andesite trachyandesite and dacite they yield ages of 129 127 ma and show a geochemical affinity to arc volcanic rocks 87sr 86sr i ratios and end t values range from 0 7065 to 0 7080 and 16 9 to 13 2 respectively zircon in situ ehf t values range from 29 4 to 20 2 and hf model ages from 3 03 to 2 46 ga these volcanic rocks were likely derived from a hybridized source involving enriched lithosphere of the north china craton ncc and deep recycled continental crust of yangtze block our data along with geological observations from early cretaceous igneous rocks suggest an east west extensional magmatic pulse at 130 120 ma along the entire north huaiyang belt the extent of involvement of the yangtze continental crust with the lithosphere of the ncc decreases from east to west this reflects along strike changes in triassic northward deep subduction and subsequent exhumation of the yangtze crust further lithospheric extension in the early cretaceous led to unrooting of the thickened lithosphere and generation of cretaceous volcanic rocks along the north huaiyang belt supplementary material microprobe data for all samples are available at https doi org 10 6084 m9 figshare c 4611911

danube loess stratigraphy towards a pan european loess stratigraphic model abstract the danube river drainage basin is the second largest river catchment in europe and contains a significant and extensive region of thick loess deposits that preserve a record of a wide variety of recent and past environments indeed the danube river and tributaries may themselves be responsible for the transportation of large volumes of silt that ultimately drive loess formation in the middle and lower reaches of this large catchment however this vast loess province lacks a unified stratigraphic scheme european loess research started in the late 17th century in the danube basin with the work of count luigi ferdinand marsigli since that time numerous investigations provided the basis for the pioneering stratigraphic framework proposed initially by kukla 1970 1977 in his correlations of loess with deep sea sediments loess palaeosol sequences in the middle and lower reaches of the danube river basin were a key part of this framework and contain some of the longest and most complete continental climate records in europe covering more than the last million years however the very size of the danube loess belt and the large number of countries it covers presents a major limiting factor in developing a unified approach that enables continental scale analysis of the deposits local loess palaeosol stratigraphic schemes have been defined separately in different countries and the difficulties in correlating such schemes which often change significantly with advances in age dating have limited the number of basin wide studies a unified basin wide stratigraphic model would greatly alleviate these difficulties and facilitate research into the wider significance of these loess records therefore we review the existing stratigraphic schemes and define a new danube basin wide loess stratigraphy based around a synthetic type section of the mosorin and stari slankamen sites in serbia we present a detailed comparison with the sedimentological and palaeoclimatic records preserved in sediments of the chinese loess plateau with the oxygen isotope records from deep sea sediments and with classic european pleistocene stratigraphic subdivisions the hierarchy of danubian stratigraphic units is determined by climatically controlled environmental shifts in a similar way to the chinese loess stratigraphic scheme a new unified danube loess stratigraphic model has a number of advantages including preventing confusion resulting from the use of multiple national schemes a more transparent basis and the potential to set pleistocene palaeoenvironmental changes recorded in the danube catchment area into a global context the use of a very simple labelling system based on the well established chinese loess scheme facilitates interpretation of palaeoenvironmental information reported from the danube basin loess sites in a wider more accessible context that can be readily correlated world wide this stratigraphic approach also provides for the first time an appropriate framework for the development of an integrated pan european and potentially pan eurasian loess stratigraphic scheme

recycling of subducted upper continental crust constraints on the extensive molybdenum mineralization in the qinling dabie orogen abstract the qinling dabie orogenic belt is the most important molybdenum ore belt in the world with a proven reserve of over 9 million tons metal mo more than 92 of the reserves come from porphyry skarn type deposits that are closely related to late mesozoic granite intrusions 158 101 ma occurring mainly along the southern margin of the north china craton where the majority of the continental crust was formed before 2 5 ga with crustal hf model ages of 2 8 to 3 2 ga the granite intrusions which consist mainly of granodiorite monzogranite and syenogranite intrude an archean to paleoproterozoic basement the granitic rocks are metaluminous to peraluminous with c cnk values mostly in range of 0 9 1 2 commonly alkaline rich with high k calc alkaline and shoshonitic features the linear trends of major and trace elements on harker diagrams suggest a common magma source for the granitic rocks abundant inherited zircons with neoproterozoic u pb ages and substantial younger crustal hf model ages averaging 2 4 ga and 2 0 ga for granitic rocks with u pb ages older and younger than 125 ma respectively demonstrate that these granitic rocks were probably derived from partial melting of the subducted northern yangtze continental crust with hf model age younger than 2 2 ga integrating the recent progresses in geological geochronological and geophysical investigations of the qinling dabie orogenic belt we propose that it is the conjunction of the decoupling of the subducted plate at the easternmost part and the slab rollback and subsequent breakoff at the westernmost part of the orogenic belt that resulted in the westward shallowing continental subduction along the manlue suture at the southern margin of the qinling dabie orogenic belt this subduction took place during westward propagating continental collision in the late triassic and the prolonged relative rotation of the north china craton and yangtze block that lasted until the middle jurassic the molybdenum source for the extensive mo mineralization in the qinling dabie orogenic belt was most likely derived from mo enriched components of subducted continental crust the decoupling of the subducted plate that occurred in the easternmost part of the orogenic belt where only less mo enriched components of the yangtze block have been subducted may account for the lack of economically significant mo mineralization there

the nature origin and accumulation of loess abstract loess can be defined simply as a terrestrial clastic sediment composed predominantly of silt size particles which is formed essentially by the accumulation of wind blown dust there are three fundamental requirements for its formation 1 a sustained source of dust 2 adequate wind energy to transport the dust and 3 a suitable accumulation site most loess has been modified to some degree by local reworking bioturbation and syn depositional weathering but a process of loessification is not necessary for a dust deposit to qualify as loess the terms primary loess and secondary loess have previously been used to described wind deposited loess and redeposited loess respectively but it is more accurate to describe material reworked and redeposited by non aeolian processes as loess derived colluvium or loess derived alluvium during the quaternary loess formed in three main situations 1 mid continental shield areas beyond the limits of ice sheets periglacial loess 2 on the margins of high mountain ranges perimontane loess and 3 on the semi arid margins of some lowland deserts peridesert loess peridesert loess is relatively poorly developed partly due to the limited efficiency of silt generating mechanisms in low land deserts compared with glaciation but also important is the tendency in arid areas for dust to be dispersed over a wide area and to be rapidly reworked after deposition particularly in areas which experience frequent climatic changes the remarkably thick loess of china and central asia results from an unusual combination of conditions which has persisted for much of the last 2 3 million years namely rapid uplift of the tibetan plateau and surrounding mountain ranges high rates of sediment production and supply to adjacent basins a strong northwesterly and westerly wind regime and the existence of effective dust traps downwind of the source regions

an ellipsoidal harmonic representation of earth s lithospheric magnetic field to degree and order 720 1 while high degree models of the earth s gravity potential have been inferred from measurements for more than a decade corresponding geomagnetic models are difficult to produce the primary challenge lies in the estimation of the magnetic potential which is not completely determined by available field intensity measurements and cannot be computed by direct integration described here is the methodology behind the third generation of the national geophysical data center s degree 720 magnetic model key issues are 1 the ellipsoidal harmonic representation of the magnetic potential 2 the reduction of ambiguities by a suitable penalty function and 3 the use of an iterative method to estimate the model coefficients the ngdc 720 model provides the lithospheric magnetic field vector at any desired location and altitude close to and above the earth s surface anticipated uses are in geological and tectonic studies of the lithosphere as a local correction for magnetic navigation and heading systems and the calibration of ground marine airborne and spaceborne magnetometers the ngdc 720 model is available at http geomag org models ngdc720 html and for long term archive at http earthref org cgi bin er cgi s erda cgi n 989

geochemical test for branching decay of 176lu abstract two different groups of values for the 176lu decay constant have been determined by recent high precision experiments the 176lu values of 1 86 1 87 10 11 a 1 were determined by age comparisons using terrestrial minerals of proterozoic and late archean age whereas values of 1 94 10 11 a 1 were determined in age comparison studies of meteorites a possible branched decay of 176lu could be the cause of this discrepancy the decay of 176lu to 176yb was detected in the early studies of radioactivity of 176lu with reported values of in the total 176lu ranging from less than 0 03 to 0 67 if the decay fraction is close to the upper limit of the reported values it can explain the 4 6 difference between the apparent 176lu values to get a reliable estimate for the decay of 176lu we have measured yb isotopic composition in 2 7 ga zircons with lu ybn chondrite normalized ratios of 1 40 and 1 45 in 1 0 ga xenotime with lu ybn 1 23 using yb from the 28 4 ma fish canyon tuff fct zircon and titanite as the modern reference value multiple analyses yielded the following weighted mean values 2 for the 176yb 174yb ratio 0 4022134 0 0000017 for the fct zircon and titanite 0 4022134 0 0000019 for the 1 0 ga xenotime and 0 4022124 0 0000033 for the 2 7 ga zircons these data yield 0 005 0 015 2 and establish an upper limit of 0 9 of total decays for the decay branch branching decay can therefore be eliminated as the cause of the discrepancy in 176lu decay constant estimates we discuss other possible causes of the 176lu terrestrial vs meteorite discrepancy

tectonic affinity of the west qinling terrane central china north china or yangtze 1 our ignorance about the tectonic affinity of the western qinling songpan ganzi tectonic region which is strategically located between the northeastern corner of the tibetan plateau the northwestern corner of the yangtze block and the southwestern corner of the north china block limits our understanding of the tectonic evolution of east asia basaltic volcanic rocks in the duofutun area within the west qinling terrane in qinghai province china the northernmost part of the songpan ganzi region contain coeval magmatic zircons that constrain the eruption age of the host basalts to 14 ma more significantly the basalts have entrained zircon xenocrysts from the deep crust that record the presence of unexposed neoarchean 2 7 2 5 ga basement u pb and hf isotope data from the xenocrysts reveal that this basement has undergone a complex evolution that includes the addition of new mantle derived material at 2 7 2 4 and 1 1 0 8 ga and crustal reworking events at 1 8 and 1 4 ga phanerozoic thermal events at 320 300 230 and 160 ma have also modified reworked the basement using these data we interpret at least the western part of the west qinling orogenic terrane as a microcontinental block that originally separated from the north china block closed with the northern yangtze block during the meso neoproterozoic and then redocked with the southern part of the north china block in the phanerozoic i e early paleozoic the west qinling terrane was then affected by the northward subduction and collision of the yangtze block in the paleozoic and early mesozoic and underwent lithospheric extension in jurassic time

continental collision and accretion recorded in the deep lithosphere of central china abstract basaltic andesitic volcaniclastic diatremes erupted in the mesozoic 160 ma in the xinyang area henan province of central china the locality lies on the western margin of the eastern block of the north china craton and the southern margin of this craton the diatremes carry a suite of xenoliths including lower crustal mafic to felsic granulites eclogites meta gabbros pyroxenites and mantle peridotites the petrological and geochemical data show that the crust in the area is temporally and compositionally zoned exposed rocks up to ca 2 85 ga old underlain by felsic granulites and rare pyroxenites with zircon ages of 3 6 3 4 ga to ca 30 km depth deeper ca 30 45 km parts of the lower crust consist of high pressure mafic to felsic granulites and meta gabbro which give paleoproterozoic 2 0 1 8 ga zircon ages our data show the significance of underplating vertical crustal growth in the paleoproterozoic which was related to the amalgamation of the eastern and western block of this craton and a global columbia supercontinent assembly hf isotope data indicate that both juvenile material and remelting of older 3 8 3 0 ga crustal rocks were involved in this important event paleozoic 440 260 ma and early mesozoic 228 219 ma zircons are also found in xenoliths from the deeper part of the lower crust and the uppermost mantle i e eclogite and peridotite they are interpreted as reflecting geodynamic processes related to the continental collision between this craton and the yangtze craton respectively the xenoliths from xinyang diatremes thus record the growth and modification of the old paleo mesoarchean continental lithosphere by magma underplating during several tectonic events assembly of the southern and northern parts of the eastern block in neoarchean time collision of the western and eastern blocks along the trans china orogen in the paleoproterozoic and subduction and collision of the yangtze craton with the north china craton in early paleozoic and triassic times respectively

geophysical evidence on segmentation of the tancheng lujiang fault and its implications on the lithosphere evolution in east china abstract the north south trending tancheng lujiang tanlu fault belt extends from northeast china to the dabie sulu orogenic belt for a length of more than 3000 km this fault belt probably has close links with the lithosphere evolution seismic activity and mineral resource concentration in east china surface geological mapping and studies on sedimentation and basin formation have indicated segmentation at the southern middle and northern domains of the fault here we employ geophysical constraints to evaluate these fault segments unlike previous geophysical studies focused on laterally varying crust mantle seismic velocity structure across the fault in this study we have integrated a variety of geophysical data sets such as crustal p wave velocity earthquake occurrence and released seismic energy seismogenic layer thickness surface heat flow and geothermal field to understand the deep structure and strength of the lithosphere along the tanlu segmented fault belt the results demonstrate remarkable crustal scale north to south segmentation this major fault the geophysical evidence and some geochemical constraints suggest that the tanlu fault belt probably served as a channel for melt and fluid percolation and exerted a significant control on the lithosphere evolution in east china

geochemical variations of the late mesozoic granitoids in the southern margin of north china craton a possible link to the tectonic transformation from compression to extension abstract the composition of the continental crust of the north china craton ncc is more felsic than that of the average bulk crust which is regarded to be the result of the delamination of the thickened lower crust during mesozoic however whether the thickened continental crust existed and when the delamination event happened along the southern margin of the ncc are still debated here we report geochronological geochemical and sr nd hf pb isotopic evidence that granitoids from the late jurassic wuzhangshan pluton and the early cretaceous huashani complex were derived by partial melting of the lower crust with different thickness our new data shows that the two lithofacies of the wuzhangshan pluton were mainly formed between ca 157 and 156 ma whereas the five lithofacies of the huashani complex were mainly emplaced between ca 132 and 125 ma the wuzhangshan pluton and the earlier four lithofacies granitoids of the huashani complex ca 160 125 ma both display adakitic geochemical features which are characterized by as high sio 2 63 26 72 71 wt al 2 o 3 13 97 16 89 wt and sr 413 1218 ppm contents and low y 6 30 14 98 ppm and yb n 1 55 4 43 and high sr y 33 112 and la yb n 11 53 29 72 ratios they also have high 87 sr 86 sr i 0 7066 0 7086 and low end t 9 9 to 18 8 and ehf t 11 to 26 values and two stage nd and hf model ages ranging from 2 4 to 1 7 ga and 2 7 to 1 7 ga respectively in contrast the late early cretaceous ca 125 110 ma granitoids have higher sio 2 71 30 76 78 wt and lower sr 64 333 ppm contents and lower sr y 17 29 and la yb n 13 25 18 36 ratios and similar end t 10 to 16 and relatively higher ehf t 10 to 14 values these geochemical variations suggest that the ca 160 125 ma granitoids were most probably produced by partial melting of thickened crust 45 km with eclogite garnet amphibolite or amphibolite residues whereas that the ca 125 110 ma granitoids were formed by partial melting of the thinner crust

early miocene european loess a new record of aridity in southern europe the intercalation of silty units and coarse grained units represented by conglomerates and breccia characterizes a lower miocene terrestrial sedimentary sequence in the north croatian basin a part of the southwestern pannonian basin system these sediments were previously interpreted as alluvial sediments where the silty units would reflect deposition on a floodplain however in this study we show new results that support a different interpretation of the genesis of the silty units the units which vary in thickness between 6 and 180 cm are mostly composed of structureless loose silt they are brownish yellow to yellowish brown in color and do not contain fossils scanning electron microscopy indicated that quartz grains show fracture faces conchoidal fractures v shaped percussion marks linear steps and conchoidal crushing features such microtextures together with the macroscopic characteristics of the silt units indicate that they were deposited by wind therefore this study reports the first occurrence of miocene loess outside of china silt sized particles were probably produced by salt weathering processes on salina type lake flats during long arid periods alluvial deposition was controlled by a more humid climate so the intercalation of eolian silty units with alluvial conglomerates and breccias reflects alternation of arid and more humid periods in the early miocene this agrees with regional paleoclimate studies that show cyclicity in the climate with a dry cycle and orbital scale climate variability controlling paleoenvironmental and sedimentary changes in the area during the early miocene

age of mammuthus trogontherii from kostolac serbia and the entry of megaherbivores into europe during the late matuyama climate revolution abstract at the drmno open pit coal mine near kostolac in serbia a nearly complete skeleton of mammuthus trogontherii nicknamed vika was discovered in a fluvial deposit overlain by a loess paleosol sequence where a second paleontological level named nosak with remains of m trogontherii was found we studied the magnetostratigraphy of the kostolac sedimentary sequence and found that the vika layer dates to 0 8 ma shortly before the brunhes matuyama boundary in addition according to our age model and previously reported optically stimulated luminescence and electron spin resonance dates the nosak fossils have an estimated age of 0 19 ma and lived during the earliest part of marine isotope stage 6 it appears therefore that at kostolac m trogontherii is preserved both at its earliest occurrence at 0 8 ma and close to its latest occurrence at 0 19 ma and may well have been present in between albeit not yet found we speculate that megaherbivores such as m trogontherii entered europe along a conjunct danube po river migration conduit connecting western asia levant with central southern europe where vast and exploitable ecosystems particularly suited for steppe or savanna adapted megaherbivores from asia and africa developed during the late early pleistocene climate revolution at around 0 8 ma

hadean continental crust in the southern north china craton evidence from the xinyang felsic granulite xenoliths abstract an increasing number of hadean detrital and xenocrystic zircon crystals have been discovered in china although its oldest crustal component remains enigmatic four xenoliths of garnet free felsic granulites entrained by the mesozoic xinyang volcanic rocks in the southern north china craton ncc were selected for u pb dating and lu hf isotopes of zircon as well as whole rock major and trace element analysis their petrography and geochemical composition reveal that the xenoliths are of igneous origin the magmatic zircons yield ages including 3 5 3 6 ga and ca 2 1 ga the 3 5 3 6 ga zircons have widely variable e hf t of 7 8 to 4 0 and model ages t crust of 3 51 4 12 ga the ca 2 1 ga zircon grains have very negative e hf t 29 0 to 26 2 and hadean model ages t crust 3 96 4 10 ga the metamorphic zircons from the studied xenoliths record several thermal episodes at ca 2 73 ga 2 13 2 35 ga and 1 77 1 86 ga these results suggest that hadean crustal components may exist in the deep crust of the southern ncc and probably suffered complex modification during paleoarchean paleoproterozoic time combined with published data the hf crustal model ages of zircons from the ncc peak at ca 3 94 ga are older than those from the south china craton peak at ca 3 77 ga this means that there is much more likelihood of finding more hadean continental crust in the ncc than in the south china craton by comparison with the ancient crustal components in the anshan and caozhuang areas of the northern ncc the xinyang area in the southern ncc may be more prospective for further occurrences of hadean zircons and or rocks

episodic widespread magma underplating beneath the north china craton in the phanerozoic implications for craton destruction abstract a comprehensive synthesis of u pb geochronology and hf isotopes of zircons from granulite pyroxenite xenoliths entrained in phanerozoic magmatic rocks and inherited xenocrysts from the associated lower crust rocks from various domains of the north china craton ncc provides new insights into understanding the phanerozoic evolution of the lower crust in this craton episodic widespread magma underplating into the ancient lower crust during phanerozoic has been identified throughout the ncc from early paleozoic to cenozoic broadly corresponding to the caledonian hercynian indosinian yanshanian and himalayan orogenies on the circum craton mobile belts the early paleozoic 410 490 ma ages come from xenoliths in the northern and southern margins as well as the central domain of the eastern block of the craton which mark the first phase of phanerozoic magma underplating since the final cratonization of the ncc in the paleoproterozoic the magmatism coincided with the northward subduction of the paleotethysian ocean in the south and the southward subduction of the paleoasian ocean in the north the subduction not only triggered magma underplating but also led to the emplacement of the diamondiferous kimberlites on the craton marking the initiation of decratonization the late paleozoic event as represented by the 315 ma garnet pyroxenite and or lherzolite xenoliths in hannuoba was restricted to the northern and southern margins of the craton correlating with the arc magmatism continuous associated with the subduction of the paleotethysian and paleoasian oceans and resulting in the interaction between the melts from subducted slabs and the lithospheric mantle lower crust the early mesozoic event also dominantly occurred in the northern and southern margins and was related with the final closure of the paleotethysian and paleoasian oceans as well as the collisional orogeny between the ncc and the yangtze craton the late mesozoic ca 120 ma was a major and widespread magmatic event which manifested throughout the ncc associated with the geothermal overturn due to the giant south pacific mantle plume the cenozoic magmatism identified only in the dark clinopyroxenite xenoliths in the hannuoba was probably induced by the himalayan movement in eastern asia and might also have been influenced by the subduction of the pacific ocean to some extent these widespread and episodic magma underplating or rejuvenation of the ancient lower crust beneath the ncc revealed by u pb and hf isotope data resulted from the corresponding addition of juvenile materials from mantle to lower crust with a mixing of the old crust with melts the process inevitably resulted in the compositional modification of the ancient lower crust similar to the compositional transformation from the refractory lithospheric mantle to a fertile one through the refractory peridotite infiltrated melt reaction as revealed in the lithospheric mantle beneath the craton

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

paleoproterozoic multistage evolution of the lower crust beneath the southern north china craton abstract it is generally recognized that the north china craton ncc resulted from the amalgamation of several micro blocks during the paleoproterozoic period however how the lower crust beneath the craton evolved during the amalgamation of these blocks is less well known four garnet bearing felsic granulite xenoliths entrained by the mesozoic xinyang volcanic rocks at the southwestern part of the eastern block of the craton were selected for analysis of whole rock major and trace elements and the u pb ages trace element patterns and lu hf isotopic composition of zircons these xenoliths are igneous in origin but with distinct sources the relict cores of magmatic zircon in the xenoliths give ages including ca 3 61 ga ca 2 22 ga and ca 2 05 ga and hadean neoarchean hf model ages tcrust 2 4 4 3 ga implying the existence of the hadean crustal components and a complex history in archean paleoproterozoic the metamorphic zircons from the xenoliths define three thermal episodes at ca 2 33 ga 1 86 1 91 ga and 1 72 1 77 ga and exhibit low but flat hree patterns and negative eu anomalies indicating that they formed in garnet bearing granulite facies rocks combined with the published data a vertical section of the lower crust can be built the upper part consists mainly of 3 4 3 6 ga garnet free felsic granulites and rare pyroxenites the middle part of 1 8 2 2 ga garnet bearing felsic granulites and meta gabbros and the lowermost part of 1 7 2 0 ga intermediate and mafic granulites and paleozoic eclogites these observations suggest that the lower crust beneath the area underwent multistage modification in the paleoproterozoic which was linked to the successive geological processes between the western and eastern blocks such as the subduction collision and rifting

sapphirine and ti clinohumite in ultra high pressure garnet pyroxenite and eclogite from dabie shan china sapphirine occurs as inclusions along with clinochlore enstatite talc corundum gedrite hornblende and phlogopite in millimetre size garnets from the orthopyroxenites in a 50 m thick mafic ultramafic lens in dabie shan in china the lens enclosed by felsic gneiss is made up of metre scale intercalation of garnet or thopyroxenite garnet clinopyroxenite eclogite and gneiss the equilibrium conditions of the matrix minerals as determined from the fe mg exchange equilibria between garnet and orthopyroxene and al solubility in orthopyroxene were 740 50 c temperature and over 40 kbar pressure pressures of over 28 kbar are also indicated by inclusions of quartz pseudomorphs after coesite in garnet from the eclogites phase relations among the inclusion minerals on the other hand indicate similar temperatures of 730 30 c but much lower pressures of 4 2 kbar the mafic ultramafic lens was therefore not a direct mantle fragment but was probably a low pressure cumulate in the upper crust the early granulite facies metamorphism was most likely part of a precambrian event genetically unrelated to the triassic ultra highpressure metamorphism ti clinohumite occurs in garnet orthopyroxenites as a matrix mineral and appears to have been stable during the ultra high pressure metamorphism its stability was controlled by the fluorine fugacity as documented by its reaction textures with olivine

age and tectonic setting of late archean greenstone gneiss terrain in henan province china as revealed by single grain zircon dating the authors report precise u pb zircon ages for single grains of a metarhyodacite from the late archean dengfeng greenstone belt in henan province china near the southern margin of the north china craton most grains belong to an igneous population whose u pb isotopic systematics define a straight line intersecting concordia at 2512 12 ma and this is interpreted as the time of crystallization of the original greenstone volcanics several grains are distinctly older between 2576 9 and 2945 44 ma and the authors interpret the older grains as xenocrysts of pre greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhyodacitic lava the xenocrysts suggest evolution of the dengfeng greenstone belt in a continental environment that may be represented by the taihua high grade gneisses bordering the dengfeng greenstones and for which the authors obtained ages of 2806 7 and 2841 6 ma the data add evidence to the now widely held concept that most archean greenstones developed on or near older continental crust and were therefore prone to crustal contamination in such cases conventional zircon dating may not always record the precise age of rock formation

the crust and upper mantle of the sulu uhpm belt abstract all results from integrated geophysical investigations in the sulu region are summarized in this paper trying to reconstruct the sulu uhpm processes new seismic s wave tomographic results suggest a velocity abnormal zone occurs beneath the sulu crust revealing detailed upper mantle structures that high velocity lumps within the abnormal zone are sequentially distributed beneath the bottom of the asthenosphere these high velocity lumps might represent delaminated eclogites or residuals of the subducted oceanic plate based on integrated interpretation of the geophysical data we propose a working model for tectonic reconstruction of the sulu uhpm processes which can explain the crust and upper mantle structures of the area the involved tectonic processes are related to north eastward escaping of the sulu terrane subduction and delamination cycles of the dabie sulu oceanic plate and post orogenic lithospheric thinning and magma underplating the uhpm rocks are believed to have syn subduction delaminated down to the bottom of the asthenosphere during 245 180 ma and the delamination process seemed smooth and nearly continuous without extensive violence

tracking deep crust by zircon xenocrysts within igneous rocks from the northern alxa china constraints on the southern boundary of the central asian orogenic belt abstract the southern boundary of the central segment of the central asian orogenic belt caob with the precambrian alxa block is not well constrained due to poor recognition of deep crust statistical analysis of zircon xenocrysts within igneous rocks from the northern alxa and its adjacent regions was applied to resolve this problem we compiled new and previously published geochronological zircon age data obtained by shrimp sims tims and la icp ms for 316 igneous rock samples of which 61 samples contain zircon xenocrysts new and previously published hf isotopic compositions of these zircon xenocrysts are combined with zircon ages in this study the zircon xenocrysts are mainly contained within permian rocks from the yabulai nurgong honggueryulin ynh zone and igneous rocks from the northwestern margin of the north china craton wncc a few xenocrysts were also found in permian igneous rocks from the zongnaishan shalazhashan zs zone neo proterozoic and paleo proterozoic intrusive rocks in the ynh zone as well as devonian to carboniferous granitoids and volcanic rocks from southern mongolia altogether we analyzed more than 270 zircon xenocrysts and considered only ages that are less than 10 discordant xenocryst ages within the permian igneous rocks from the zs zone are mainly around ca 350 ma ca 600 ma and ca 1400 ma the oldest age of zircon xenocrysts in this zone is similar to those of zircon xenocrysts from the caob 1 1 ga by contrast abundant zircon xenocrysts within permian igneous rocks from the ynh zone show highly variable age populations at ca 2 6 2 1 ga 1 8 1 6 ga 930 750 ma and 460 300 ma zircon xenocrysts from the zs zone have positive e hf t values of 6 3 to 13 9 whereas those from the ynh zone display highly variable e hf t values from 16 1 to 11 6 from the southern caob and the zs zone to the ynh zone the zircon xenocrysts show a significant shift from juvenile to crustal hf isotopic compositions suggesting that the area between the zs and the ynh zones constitutes the southern boundary of the caob in the deep crust within this region our study indicates that statistical analysis or isotopic mapping of zircon xenocrysts is an effective method to trace the nature of the deep continental crust and to separate between newly formed orogenic domain and ancient cratons

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

fifth generation lithospheric magnetic field model from champ satellite measurements 1 six years of low orbit champ satellite magnetic measurements have provided an exceptionally high quality data resource for lithospheric magnetic field modeling and interpretation here we describe the fifth generation satellite only magnetic field model mf5 the model extends to spherical harmonic degree 100 as a result of careful data selection extensive corrections filtering and line leveling the model has low noise levels even if evaluated at the earth s surface the model is particularly suited for inferring large scale structure and composition of the lithosphere it is also meant to serve as the long wavelength part of continental and global scale marine and aeromagnetic anomaly maps

zircon u pb and lu hf isotopic constraints on archean crustal evolution in the liaonan complex of northeast china abstract the changhai area is located in the southeastern part of the liaonan complex within the eastern block of the north china craton ncc in china early precambrian rocks in this area consist mainly of various types of gneisses and schists we present cathodoluminescence images u pb dates and trace element and hf isotope data for zircons from these rocks in order to constrain the formation and evolution of continental crust in the liaonan complex our results show that the magmatic precursors of the biotite monzonitic gneiss granitic gneiss garnet bearing monzogranitic gneiss and biotite granodioritic gneiss that is relatively sodium rich gneisses in the area were emplaced at ca 2543 ma muscovite bearing granitic gneiss monzogranitic gneiss and biotite granitic gneiss that is relatively potassium rich gneisses in the area were emplaced at ca 2516 ma whereas the sedimentary protolith s of the associated schists along the gneissose fabric of the gneisses were deposited after 2518 ma and metamorphosed at ca 1885 ma the latter age may represent the time of metamorphism of the south liaohe group in the jiao liao ji belt large numbers of inherited zircons with ages of 2596 2842 ma coupled with the results of previous studies suggest that multiple meso to neoarchean magmatic events took place in the liaonan complex at ca 2 84 2 75 2 67 2 61 2 54 and 2 51 ga lu hf isotopic results for magmatic zircon grains with ages of 2 61 2 84 ga have positive e hf values 2 4 to 11 3 and average continental crust model ages tc dm of 2 63 3 05 ga with a peak at 2 76 2 98 ga of the zircons with ages of ca 2 54 ga and 2 51 ga 94 have positive e hf values 0 13 to 8 57 average 3 1 and tc dm model ages of 2 53 3 06 ga similar to those of zircons with ages of ca 2 61 2 84 ga suggesting that both sets of zircons were derived from partial melting of juvenile crust however the remaining zircons 6 with ages of 2 54 2 51 ga and all metamorphic zircon grains with ages of ca 1885 ma have negative e hf values of 0 12 to 3 00 and 8 8 to 15 9 respectively and similar older tc dm model ages of 3 11 3 56 ga and 3 08 3 23 ga respectively these data combined with those from previous studies of the ncc indicate that the basement rocks of the liaonan complex underwent two significant juvenile crustal growth events at ca 2 71 2 99 ga and 2 54 2 51 ga a local reworking event at ca 2 51 ga and a major reworking event at 1 88 ga

magnetic anomaly map of the world merging satellite airborne marine and ground based magnetic data sets abstract we report here a simple but practical method to combine systematically the magnetic surveys of disparate specifications from marine ground aeromagnetic and satellite platforms that aims to be helpful in the framework of the world digital magnetic anomaly map project because the satellite coverage and data quality is more uniform than near surface surveys it is adopted as the base map for wavelengths larger than 400 km and up to spherical harmonic degree inclusive of 16 2500 km after checking that satellite models and large aeromagnetic wavelengths are not consistent we filter out wavelengths longer than 400 km in aeromagnetic compilations existing regional grids and when available individual surveys are merged to give a more uniform spatial variation of the magnetic anomalies the effects of merging the grids are examined by plotting profiles and difference maps of the overlapping regions a preliminary global map is obtained after combining the magnetic anomaly map with the downward continued champ satellite derived magnetic anomaly map forthcoming availability of new datasets as well as improvements in the procedure will help to produce increasingly reliable maps

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

sinking intrusion model for the emplacement of garnet bearing peridotites into continent collision orogens garnet and probably spinel bearing ultramafic rocks that form tectonic lenses within high metamorphic grade gneisses in mountain core zones may intrude by moving downward or laterally into deeply subducted continental crust from the overlying mantle wedge this model is most credible for garnet peridotites associated with ultrahigh pressure metamorphic terranes in mountains formed by continent continent collision the extremely high pressures implied by ultrahigh pressure metamorphism indicate that continental crust was subducted to mantle depths 100 120 km where the mantle is in the garnet peridotite facies exchange between mantle and crust seems likely particularly the transfer of mantle from the hanging wall into the crustal footwall the mantle wedge overlying the subducted crustal terrane creates a denser over lighter configuration that is gravitationally unstable if the interface becomes hot or wet enough so that peridotite can deform by ductile flow it would sink as mantle blobs into the underlying crustal rocks if not the exchange presumably occurs through a brittle mechanism the intruded bodies will be transported to the surface passively as the host crustal terrane is exhumed buoyantly toward the surface this mechanism is proposed in particular to explain the intrusion of garnetiferous peridotites in the ultrahigh pressure western gneiss region of the norwegian caledonides during the caledonian orogeny

into the forbidden zone very low temperatures at high pressures have long been believed to constitute a forbidden zone not realized in earth however recent studies of ultrahigh pressure uhp terranes indicate that these rocks have experienced such forbidden zone conditions liou et al discuss the implications of these observations for plate tectonics

crustal radial anisotropy beneath the dabie orogenic belt from ambient noise tomography summary in this study we continue our previous work of imaging isotropic shear velocity to study the crustal radial anisotropy beneath the dabie orogen and surrounding regions by jointly analysing rayleigh wave and love wave dispersion curves in addition to processing the vertical component data to retrieve rayleigh waves we collect horizontal component continuous ambient noise data and retrieve love waves from cross correlations of horizontal component noise data between station pairs then we measure love phase velocity dispersion curves at periods from 8 to 35 s using a spectral method and perform surface wave tomography to obtain high resolution phase velocity maps finally we determine crustal radial anisotropy by inverting the local phase velocity dispersion curves of rayleigh and love waves our model of crustal radial anisotropy reveals complex anisotropic patterns associated with the dynamic processes of continent continent collisions and post collision reworking between the north china craton and the yangtze craton in the huabei basin the radial anisotropy is positive throughout the entire crust corresponding to areas with extensional tectonics developed since the middle mesozoic in the jianghan basin strong positive radial anisotropy in the middle and lower crust is observed most likely resulting from subhorizontal alignment of seismic anisotropic materials under the crustal extensional deformation in the eastern dabie orogenic belt the radial anisotropy beneath northern dabie complex ndc appears positive in the upper and lower crust and negative in the middle crust the positive radial anisotropy in the upper crust is probably because of the presence of igneous rocks with anisotropic minerals aligned subhorizontally under the action of the extensional tectonics during igneous extrusion and emplacement whereas the positive radial anisotropy in the lower crust is probably because that subhorizontal alignment of anisotropic materials induced by magmatic underplating formed after the delamination of the orogeny in the middle crust finite strains associated with the vertical intrusion of deep magma might cause crystalline anisotropic minerals aligned vertically resulting in observed negative radial anisotropy in the western dabie orogenic belt positive radial anisotropy is present in the whole crust except beneath the hong an ultrahigh pressure uhp area where radial anisotropy is negative in the middle crust similar to ndc the hong an uhp probably experienced similar thermal geodynamic processes as the eastern dabie and the negative radial anisotropy might be also the result of vertical alignment of anisotropic minerals caused by the vertical intrusion of deep magma strong localized negative radial anisotropy in the middle crust beneath the xinyang area is imaged most likely caused by the vertical alignment of anisotropic minerals crystallized from the vertically intruding mafic magma originated from the upper mantle during the volcanism

magnetic properties of loess grain size fractions from the section at paks hungary abstract the approximately 50 m thick loess palaeosol sequence at paks brickyard hungary was deposited largely during the brunhes normal polarity chron and its magnetic properties resemble those of similar sections in europe central asia and china in order to get information on the grain size dependence of some of the magnetic parameters two loess and two palaeosol samples were separated into a number of grain size fractions the separation method employs consecutive sedimentation and centrifugation steps performed on bulk samples suspended in water and diluted with calgon ten grain size fractions were obtained ranging from 50 m down to 10 nm several magnetic parameters of the different grain size fractions have been measured at room temperature low field susceptibility hysteresis parameters and at low temperature susceptibility and thermoremanent magnetisation they show a strong grain size dependence for the ferromagnetic minerals low temperature measurements allow discrimination of the paramagnetic vs the ferromagnetic signal and give information on the grain size distribution of the very fine ferromagnetic minerals and on the mineral types carrying the magnetic signal strong relationships between weathering processes destruction of paramagnetic minerals and possibly iron hydroxides and enhancement of the ferromagnetic signal are observed

mafic crustal xenoliths and the origin of the lower continental crust abstract the la nb ratio 30 ppm at a mg number of 40 in oceanic plateau basalts and morb provide a useful index to distinguish them from arc basalts morb can generally be distinguished from plateau basalts by their lower nb contents

an early brunhes 0 78 ma age for the lower paleolithic tool bearing kozarnika cave sediments bulgaria abstract we present a new sedimentological profile and a magnetostratigraphy of the tool bearing kozarnika cave sediments from bulgaria modal analysis of cave infilling sedimentary texture indicates that the tool bearing layers contain a sizable fraction of sediment interpreted as loess we also find evidence for a relatively thick and well defined normal magnetic polarity in the upper middle part of the section interpreted as a record of the brunhes chron followed down section by reverse polarity directions interpreted as a record of the matuyama chron the lowermost levels with lower paleolithic tools layers 13a c lie in the early brunhes at a nominal maximum age of 0 75 ma while the brunhes matuyama boundary 0 78 ma falls in layer 13 lower immediately below this finding represents a conspicuous revision of previous age estimates for the same tool bearing layers

extending comprehensive models of the earth s magnetic field with orsted and champ data summary a new model of the quiet time near earth magnetic field has been derived using a comprehensive approach which includes not only pogo and magsat satellite data but also data from the orsted and champ satellites the resulting model shows great improvement over its predecessors in terms of completeness of sources time span and noise reduction in parameters with its well separated fields and extended time domain of 1960 to mid 2002 the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997 because all sources are coestimated in a comprehensive approach intriguing north south features typically filtered out with other methods are being discovered in the lithospheric representation of the model such as the s atlantic spreading ridge and andean subduction zone lineations in addition this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection the f region currents through which the satellites pass are now treated as lying within meridional planes as opposed to being purely radial results are consistent with those found previously for magsat but an analysis at orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite besides the model a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset this has proven very useful in diagnosing the cause of peculiar artefacts in the magsat vector data which seem to suggest the presence of a small misalignment bias in the vector magnetometer

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

seismic consequences of warm versus cool subduction metamorphism examples from southwest and northeast japan warm and cool subduction zones exhibit differences in seismicity seismic structure and arc magmatism which reflect differences in metamorphic reactions occurring in subducting oceanic crust in southwest japan arc volcanism is sparse and intraslab earthquakes extend to 65 kilometers depth in northeast japan arc volcanism is more common and intraslab earthquakes reach 200 kilometers depth thermal petrologic models predict that oceanic crust subducting beneath southwest japan is 300 to 500 c warmer than beneath northeast japan resulting in shallower eclogite transformation and slab dehydration reactions and possible slab melting