petrogenesis and tectonic implications of early paleozoic granitic magmatism in the jiamusi massif ne china geochronological geochemical and hf isotopic evidence abstract this paper reports geochronological whole rock geochemical and zircon hf isotopic data for the early paleozoic granitic rocks in the jiamusi massif in the eastern segment of the central asian orogenic belt caob in order to investigate their precise geochronological framework petrogenesis sources and tectonic setting la icp ms zircon u pb age data indicate that the syenogranite monzogranite and granodiorite were emplaced during the period of 530 484 ma geochemically these granitoids have high sio2 64 66 79 17 and k2o 3 08 7 33 low mgo 0 14 2 63 and cao 0 37 3 87 with a cnk and eu values of 0 89 1 10 and 0 16 1 77 respectively these rocks are characterized by enrichment in rb and nd and depletion in nb ta p and ti in addition in situ hf isotopic analyses of zircons from the granitic rocks reveal that they have ehf t 5 8 to 2 3 with two stage hf model ages tdm2 varying from 1 3 ga to 2 4 ga indicating that they probably originated from the partial melting of a dominantly old paleo mesoproterozoic crustal source additionally these granites have variable major and trace element concentrations magmatic zircons from these rocks record consistent homogeneous u pb ages but have heterogeneous ehf t values reflecting that they resulted from fractional crystallization and crustal assimilation based on these geochemical data combined with regional geological investigations we propose that the early paleozoic granitic magmatism in the study area occurred in a post collisional extensional setting which was probably related to the collapse of a thickened crust

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

new shrimp u pb zircon ages from the heilongjiang high pressure belt constraints on the mesozoic evolution of ne china the heilongjiang complex is a high pressure accretionary belt composed mainly of serpentinite glaucophane bearing metabasalt epidote glaucophane albite schist greenschist marble two mica schist muscovite albite schist quartz schist and quartzite chert located along the suture zone separating the jiamusi and songliao blocks in ne china shrimp u pb zircon analyses of two samples of granitic gneiss from yilan that are interleaved with the heilongjiang complex record diverse protolith ages that are consistent with derivation from regional permian granitoids 263 7 ma and the adjacent mashan complex 492 6 ma indicating tectonic incorporation of older granitic components into the accretionary complex the age of the basaltic protolith of two samples of glaucophane albite schist from yilan is 245 ma and is slightly younger than the protolith age of two samples of amphibole schist from mudanjiang located about 200 km south of yilan that define weighted mean 206pb 238u ages of 257 4 and 257 5 ma all four samples contain a few older inherited zircon grains and also show the effects of an isotopic disturbance at 200 to 190 ma most likely related to the subsequent high pressure metamorphism the timing of which has been determined in previous studies the basaltic rocks record rifting and ocean development from 260 to 210 ma based on previous studies in which both e morb and oib protolith signatures were identified detrital zircons in two samples of mica schist from mudanjiang show distinct populations at 700 ma 500 to 450 ma 350 to 213 ma peak at 255 ma 290 to 200 ma and 200 ma all except the youngest ages can be matched with rocks from the older components of the jiamusi block and with other areas in the central asia orogenic belt caob supporting the view that the jiamusi block was most likely the eastern segment of the caob prior to rifting the youngest concordant magmatic detrital grain with an age of 207 3 ma defines the maximum age of sedimentation this also limits the timing of high pressure metamorphism in the heilongjiang complex to post late triassic consistent with argon data obtained in previous studies final closure between the jiamusi and songliao blocks took place in the latest triassic early jurassic with the two blocks accreted as a result of pacific ocean subduction this suggests that the heilongjiang complex records the time when north south closure of the caob in china gave way to westward movement related to the pacific ocean subduction which has dominated the tectonics of ne china and far east russia since that time

intrusive mechanisms at mt etna forerunning the july august 2001 eruption from seismic and ground deformation data in this work we present seismological and ground deformation evidence for the phase preparing the july 18 to august 9 2001 flank eruption at etna the analysis performed through data from the permanent seismic and ground deformation networks highlighted a strong relationship between seismic strain release at depth and surface deformation this joint analysis provided strong constraints on the magma rising mechanisms we show that in the last ten years after the 1991 1993 eruption an overall accumulation of tension has affected the volcano then we investigate the months preceding the 2001 eruption in particular we analyse the strong seismic swarm on april 20 24 2001 comprising more than 200 events mmax 3 6 with prevalent dextral shear fault mechanisms in the western flank the swarm showed a ca ne sw earthquake alignment which in agreement with previous cases can be interpreted as the response of the medium to an intrusive process along the approximately nnw sse volcano genetic trend these mechanisms leading to the july 18 to august 9 2001 flank eruption are analogous to ones observed some months before the 1991 1993 flank eruption and more recently in january 1998 before the february november 1999 summit eruption

reassessment of continental growth during the accretionary history of the central asian orogenic belt we argue that the production of mantle derived or juvenile continental crust during the accretionary history of the central asian orogenic belt caob has been grossly overestimated this is because previous assessments only considered the palaeozoic evolution of the belt whereas its accretionary history already began in the latest mesoproterozoic furthermore much of the juvenile growth in central asia occurred in late permian and mesozoic times after completion of caob evolution and perhaps related to major plume activity we demonstrate from zircon ages and nd hf isotopic systematics from selected terranes within the caob that many neoproterozoic to palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous precambrian crust or through mixing of old continental crust with juvenile or short lived material most likely in continental arc settings at the same time juvenile growth in the caob occurred during the latest neoproterozoic to palaeozoic in oceanic island arc settings and during accretion of oceanic island arc and precambrian terranes however taking together our data do not support unusually high crust production rates during evolution of the caob significant variations in zircon ehf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources we reiterate that the chemical characteristics of crustally derived granitoids are inherited from their source s and cannot be used to reconstruct tectonic settings and thus many tectonic models solely based on chemical data may need re evaluation crustal evolution in the caob involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history and we see many similarities with the evolution of the sw pacific and the tasmanides of eastern australia

crystal size distributions of plagioclase in lavas from the july august 2001 mount etna eruption during the 2001 eruption of mount etna two independent vent systems simultaneously erupted two different lavas the upper vents system uv opened between 3100 and 2650 m a s l emitted products that are markedly porphyritic and rich in plagioclase while the lower vents system lv opened at 2100 and 2550 m a s l emitted products that are sparsely porphyritic with scarce plagioclase in this study the crystal size distributions csds of plagioclase were measured for a series of 14 samples collected from all the main flows of the 2001 eruption the coefficient of r 2 determination was used to evaluate the goodness of fit of linear models to the csds and the results are represented as a grid of r 2 values by using a numerical code developed ad hoc r 2 diagrams suggest that the 2001 products can be separated into two main groups with slightly different characteristics plagioclase csds from the uvs can be modeled by three straight lines with different slopes while the plagioclase csds from the lvs are largely concave we have interpreted the csds of the uvs as representing three different populations of plagioclases i the large phenocrysts type i which started to crystallize at lower cooling rate in a deep reservoir from 13 to 8 months before eruption onset ii the phenocrysts type ii which crystallized largely during continuous degassing in a shallow reservoir and iii the microlites which crystallized during magma ascent immediately prior to the eruption the plagioclase csd curves for the lvs lava are interpreted to reflect strong and rapid changes in undercooling induced by strong and sudden degassing

detrital zircon reference for the north china block abstract u pb analyses of 250 single detrital zircons from upper proterozoic to ordovician strata collected from the zhuozi shan in north central china provide a detrital zircon reference for the north china block a major crustal entity in the asian tectonic collage the results which range in age from 1 72 to 2 97 ga shed new light on the age of the crystalline basement in north china much of which is covered by younger sedimentary units in addition this detrital zircon reference can be used to help determine the provenance of clastic sedimentary units and for assessing validity of paleogeographic and regional tectonic models that include the complex history of asian continental amalgamation terrane accretion and subsequent translation that is ongoing today

3d crystal size distributions a case study on quantifying olivine populations in kimberlites abstract new advances in textural analysis and imaging allow the possibility for the true distribution of mineral phases in a rock to be quantified to high resolution also we are able to explore the relations between 2d to 3d datasets more rigorously in this study the application of 2d and 3d textural analysis to the quantification of olivine populations in kimberlites is investigated crystal size distribution studies csd are carried out on two kimberlite samples 1 one from the venetia k2 kimberlite pipe south africa and 2 one from the dutoitspan kimberlite pipe kimberley south africa a 3d x ray ct study is undertaken to investigate the application of this developing technique in kimberlite research and to test the 2d and 3d data sets csd profiles show markedly curved upwards profiles synonymous with fragmented csds supporting an initial crystal population which is modified by fragmentation of crystals on ascent raw plots of 2d area size frequency provide a powerful first estimate of the population 3d statistics in terms of volume size frequency allowing a quick analysis of olivine phases during exploration which can be quality controlled using more detailed 3d studies where necessary the 3d data set provides accurate analysis over a range of 6 0 5 mm below which the separation of grains becomes very difficult additionally the 3d data provides valuable information on crystal shape which can further be used to distinguish different olivine populations both 2d and 3d textural studies using state of the art textural analysis techniques have been successfully tested on complex kimberite textures and will prove useful techniques in the routine quantification of key indicator phases in kimberlite analysis

a crystal size distribution study of the kiglapait layered mafic intrusion labrador canada evidence for textural coarsening crystal size distributions csd of plagioclase olivine and clinopyroxene from the kiglapait intrusion labrador were measured for a series of 13 samples spanning most of the exposed intrusion all csds lack small crystals and are slightly curved to the right concave up all csds of a mineral sweep out a fan as expected where there is relatively little variation in phase proportion csd dispersion can be replicated using the communicating neighbours model of textural coarsening ostwald ripening most of the textural variation in the intrusion is the result of variable degrees of coarsening it is proposed that coarsening occurred in the outer part of the crystallisation boundary layer where release of latent heat and changes in the intercumulus liquid composition resulted in a reduction in undercooling suppression of nucleation and coarsening particularly coarse grained areas reflect focusing of circulating magmatic fluids during coarsening the effects of crystal settling were not observed in the csds even within single well developed layers they were probably concealed by the pervasive textural coarsening csds do not suggest that mechanical compaction has played an important role in the formation of texture although it is very likely to have occurred however samples from the lower part of the intrusion show textural evidence of pressure solution compaction

a review of seismic geophysical testing in iran for building near surface velocity models abstract it has long been understood that the near surface structure of the earth affects several aspects of civil engineering practice particularly in seismic applications therefore the implementation of a competent subsurface exploration program not only addresses the need for comprehensive site characterization but also reduces the devastating consequences of seismic activities typical geotechnical practice for subsurface exploration has often relied on a combination of drilling in situ testing such as standard penetration testing and cone penetration testing and laboratory testing of field samples however geophysical techniques have been developed over the years to evaluate near surface velocity models as a proxy for subsurface stiffness in seismic applications in this regard seismic geophysical methods such as refraction reflection downhole and crosshole testing spectral analysis of surface waves sasw and multichannel analysis of surface waves masw have continued to receive increase

characterization and quality control of stone columns using surface wave testing seismic surface waves are well suited for the study of the elastic profile of soils this study evaluates the application of surface waves in characterizing the properties of laterally heterogeneou

early paleozoic metamorphic rocks of the erguna block in the great xing an range ne china evidence for the timing of magmatic and metamorphic events and their tectonic implications abstract the erguna block is a crustal unit located along the eastern margin of the central asian orogenic belt caob in the far north of china it contains a variety of khondalitic rocks that include sillimanite and garnet bearing gneiss biotite plagioclase gneiss and carbonate in association with hornblende plagioclase gneiss and a variety of granitic orthogneisses these rocks are collectively referred to as the mohe complex and make up the basement rocks in this poorly exposed terrane four samples were analyzed for this study including two samples of biotite plagioclase gneiss one sample of garnet sillimanite gneiss and a sample of hornblende plagioclase gneiss all samples provide evidence of metamorphism in the form of discrete zircon grains or metamorphic rims around detrital cores and they record remarkably consistent 206 pb 238 u ages between 495 2 ma and 497 6 ma detrital zircon cores with oscillatory zoning from the two biotite plagioclase gneiss samples yield magmatic ages that range from 608 8 ma to 1015 12 ma whereas those in the garnet sillimanite gneiss range from 678 8 to 1373 17 ma these results establish that a range of meso to neoproterozoic magmatic rocks were present in the source area and contributed to the sedimentary protoliths the youngest zircon core with an age of 608 8 ma limits the maximum possible age of deposition indicating that the rocks of the mohe complex cannot be late archean to early proterozoic as previously considered the 500 ma age for the granulite facies metamorphic event in the mohe complex is identical to that recorded in the mashan complex of the jiamusi block and the hutou complex of the khanka block 1000 km to the south southeast implying that an extensive early paleozoic khondalite belt extended across much of the eastern caob rocks of similar age and metamorphic grade have also been recorded from the sayang baikal orogen along the southern margin of the siberia craton 1000 km to the west it is unclear at present whether these two belts are directly related but whatever the relationship it is evident that extensive tracts of khondalitic rocks were present in the eastern caob they were subsequently affected by high grade metamorphism in the early paleozoic forming collisional accretionary terranes that were accreted during the late pan african global event

present trends and the future of zircon in geochronology laser ablation icpms in situ u th pb geochronology was born some two decades ago with the introduction and development of high resolution secondary ion mass spectrometry sims or shrimp sensitive high mass resolution ion microprobe compston et al 1984 williams 1998 compston 1999 davis et al this volume ireland and williams this volume this technique clearly demonstrated the existence of age heterogeneities within the single crystals of zircon and other accessory phases and therefore the need for high spatial resolution tens to hundreds of cubic micrometers geochronological data in situ dating by ion probe is capable of achieving an analytical precision that is only an order of magnitude worse than the conventional isotope dilution thermal ionization mass spectrometry id tims dating technique it has the advantage however of more readily identifying concordant portions of grains does not require chemical treatment of samples prior to the analysis is essentially nondestructive and can achieve greater sample throughputs a major obstacle to the wider use of ion probe dating has always been the high cost of instrumentation and hence relative scarcity of suitably equipped geologic laboratories laser ablation inductively coupled plasma mass spectrometry la icpms emerged in 1985 and rapidly became an important analytical tool for trace element determinations in geological samples jackson et al 1992 it was soon realized that the large variations in radiogenic pb and pb u isotopic ratios found in nature could be resolved by icpms techniques and when coupled to a laser icpms could be used as a dating tool similar to the ion probe the pioneering work of feng et al 1993 fryer et al 1993 hirata and nesbitt 1995 and jackson et al 1996 illustrated the potential usefulness of laser sampling for in situ dating by icpms particularly well however these studies and others that followed also revealed the major

opening and closure history of the mudanjiang ocean in the eastern central asian orogenic belt geochronological and geochemical constraints from early mesozoic intrusive rocks abstract the tectonic evolution of the ancient mudanjiang ocean within the central asian orogenic belt caob is strongly debated the ocean played an important role in the amalgamation of the songnen and jiamusi massifs however the timings of its opening and closure have remained ambiguous until now in this study we analyzed early mesozoic intrusive rocks from the eastern songnen and western jiamusi massifs in the eastern caob the new zircon u pb ages hf isotope data and whole rock major and trace element data are used to reconstruct the tectonic evolution of the mudanjiang ocean zircon u pb dating indicates that early mesozoic magmatism in the eastern songnen massif occurred in three stages early to middle triassic ca 250 ma late triassic ca 211 ma and early jurassic ca 190 ma the triassic intrusive rocks typically consist of bimodal rock suites which include gabbros hornblende gabbros and granitoids the compositional information indicates an extensional environment that was probably related to the final closure of the paleo asian ocean we integrated the results with observations from triassic a type granitoids and coeval sedimentary formations in the eastern songnen massif as well as depositional ages of metasedimentary rocks from heilongjiang complex we conclude that the opening of the mudanjiang ocean took place in the early to middle triassic the early jurassic intrusive rocks are bimodal and include olivine gabbros hornblendites hornblende gabbros gabbro diorites and granitoids the bimodal rock suite indicates a back arc style extensional environment this setting formed in relation to westward subduction of the paleo pacific plate beneath the eurasia during the early jurassic following subduction the closure of the mudanjiang ocean and subsequent amalgamation of the songnen and jiamusi massifs happened during the late early jurassic to middle jurassic this sequence of events is further supported by ages of metamorphism and deformation acquired from the heilongjiang complex based on these observations we conclude that the mudanjiang ocean existed between the middle triassic and early jurassic making it rather short lived

pge mineralization in andesite explosive breccias associated with the poperechny iron manganese deposit lesser khingan far east russia whole rock geochemical 190pt 4he isotopic and mineralogical evidence abstract we report in this paper an unusual occurrence of platinum group minerals in evolved explosive breccia associated with the poperechny iron manganese deposit lesser khingan range far east russia pgms in andesite breccia are represented by fe pt solid solutions 85 and pgm mostly os ir ru solid solutions sulfides and sulfarsenides 15 textural and compositional variations in pgm assemblages suggest that pt fe and os ir ru solid solutions as well as erlichmanite laurite series sulfides were formed during high temperature fractionation of mantle derived mafic parental melt similar to alaskan type complexes and were entrained in the evolved andesitic melt during its emplacement in the crust pd pt plumbostannide and copper gold solid solutions reflect late magmatic re crystallization and metasomatism early cretaceous 125 ma age of ferroplatinum in the explosive breccia suggests that pgm bearing ultramafic material could have been sampled during regional slab window tectonics related to the late mesozoic subduction of izanagi plate along southern margin of the north asian continent

source study of local coalfield events using the modal synthesis of shear and surface waves summary coalfield events account for a large fraction of the short period seismic recordings made on the british geological survey s uk network these data provide an ideal opportunity to investigate the source of such seismic disturbances in more detail this is achieved by analysing vertical component seismograms generated by local coal mining tremors in the midlothian coalfield in scotland using a waveform matching technique the basis for this technique is the modal summation method for constructing synthetic seismograms this computation of synthetic seismograms facilitates a full comparison between the effects of different earth structures source depths source orientation and types of event the results of these analyses are applied to the s and surface wave portion of the seismogram for two stations the p waves also to yield well resolved details of the depth to within 100 m and nature of the seismic source the final solutions constrain the range of physical mechanisms which could have caused the tremors and hence the degree to which the events resemble natural earthquakes

u pb dating on single detrital zircon grains from the triassic songpan ganze flysch central china provenance and tectonic correlations the songpan ganze flysch belt central china covers a huge triangular area of more than 200 000 km and is bounded by the continental blocks of south china north china and the tibetan plateau detrital zircons extracted from three flysch samples collected in the central part of the belt were analyzed grain by grain using the u pb method two samples of middle triassic sandstones collected at different locations in the belt provide identical results which suggests similar source regions the detrital zircons yield a wide range of ages and indicate their principal derivation from mid proterozoic 1 8 2 0 ga source rocks with minor contribution from late archean ca 2 5 2 6 ga material the discordance and pb loss patterns from low u zircons indicate disturbances during a subsequent event which may be of caledonian age as suggested by concordant zircon grains at ca 420 and 450 ma one sample collected within the palang shan pass zone provides concordant zircon grains at around 230 ma 231 1 ma and 233 1 ma these triassic ages are synchronous to flysch deposition and suggest intense geological activity calc alkaline volcanism at that time in the area close to the basin the data support an origin of the clastic material mainly from a northeastern landmass corresponding to the southern margin of the sino korean craton to a lesser degree inputs from the yangtze craton and possibly from the northern margin of the basin kunlun arc are also detected the age spectrum from the upper triassic sandstone is significantly different and shows predominance of sinian ca 760 ma grains probably derived from the yangtze craton this change in the source region is interpreted as reflecting the tectonic evolution of this area and in particular as being linked to the late triassic collision between south china and north china in the middle triassic while subduction of the songpan sea northward beneath the north china plate was still taking place continental subduction of south china in the dabie region was responsible for uplift of the overriding plate i e the sino korean craton which supplied large volumes of sediments during the late triassic clockwise rotation of the south china block uplifted the indo sinian part of the qinling belt and closed the basin as the accretionary wedge was thickening along the southern margin of north china detritus derived from this source region were unable to reach the flysch basin the age spectrum presented by detrital zircons indicates

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

delineation of a collapse feature in a noisy environment using a multichannel surface wave technique a collapse developed at calvert cliffs nuclear power plant maryland in early 2001 the location of the collapse was over a groundwater drainage system pipe buried at an elevation of 0 9 m reference is to chesapeake bay level the cause of the collapse was a subsurface drain pipe that collapsed because of saltwater corrosion of the corrugated metal pipe the inflow outflow of sea water and groundwater flow caused soil to be removed from the area where the pipe collapsed to prevent damage to nearby structures the collapse was quickly filled with uncompacted sand and gravel 36 000 kg however the plant had an immediate need to determine whether more underground voids existed a high frequency multichannel surface wave survey technique was conducted to define the zone affected by the collapse although the surface wave survey at calvert cliffs nuclear power plant was conducted at a noise level 50 100 times higher than the normal environment for a shallow seismic survey the shear s wave velocity

three magmatic components in the 1973 eruption of eldfell volcano iceland evidence from plagioclase crystal size distribution csd and geochemistry abstract the 1973 eruption of eldfell volcano iceland appears to have been a short simple event but textural and geochemical evidence suggest that it may have had three different magmatic components the first erupted fissure magmas were chemically evolved rich in plagioclase 18 and had shallow straight crystal size distribution csd curves the early lavas were less evolved chemically had lower plagioclase contents 13 and steeper slightly concave up csds the late lavas were chemically similar to the early lavas but even richer in plagioclase than the initial magmas 24 and had the steepest csds there was no chemical evidence for plagioclase fractionation but compositional diversity could be produced by clinopyroxene fractionation which must have occurred at depth we propose that the eruption started with old coarsened ostwald ripened magma left over from a previous eruption possibly that which produced surtsey island ten years earlier the early flows may be mixtures of small amounts of this old magma with a new low crystallinity uncoarsened magma or a completely new magma the late flows are another new magma from depth chemically similar to the early flows but which has grown plagioclase under increasing saturation undercooling perhaps during its ascent all three magmatic components may have originated from the same parent but had varying degrees of clinopyroxene fractionation plagioclase nucleation and growth and coarsening

application of surface wave tomography to mineral exploration a case study from siilinjarvi finland abstract in order to assess the feasibility and validity of surface wave tomography as a tool for mineral exploration we present an active seismic three dimensional case study from the siilinjarvi mine in eastern finland the aim of the survey is to identify the formation carrying the mineralization in an area south of the main pit which will be mined in the future before acquiring the data we performed an accurate survey design to maximize data coverage and minimize the time for deployment and recollection of the equipment we extract path averaged rayleigh wave phase velocity dispersion curves by means of a two station method we invert them using a computationally efficient tomographic code which does not require the computation of phase velocity maps and inverts directly for one dimensional s wave velocity models the retrieved velocities are in good agreement with the data from a borehole in the vicinity and the pseudo three dimensional s wave velocity volume allows us to identify the geological contact between the formation hosting most of the mineralization and the surrounding rock we conclude that the proposed method is a valid tool given the small amount of equipment used and the acceptable amount of time required to process the data

pb u and th diffusion in natural zircon zircon zrsio4 is one of the most widely used minerals for determining the age origin and thermal history of rocks by u th pb geochronology but the parameters describing the solid state volume diffusion rates of these elements in natural zircon which are themselves important for establishing the limits on the applicability of zircon for geochronological studies have remained poorly quantified1 this is because of the measurement difficulties associated with the low p p m concentrations and low diffusion rates of these elements in natural zircon and the chemical and physical heterogeneity present in most crystals here we present direct measurements of the uranium thorium and lead loss from a thermally treated gem quality natural zircon and show that lead diffuses much faster than uranium or thorium we find that the u th pb isotopic system in natural zircon will typically have a closure temperature greater than 900 c which explains why zircon is apparently such a robust geochrometer and is capable of remaining isotopically closed through extended periods of high grade metamorphism and partial melting of the host rock

late triassic intrusive complex in the jidong region jiamusi khanka block ne china geochemistry zircon u pb ages lu hf isotopes and implications for magma mingling and mixing abstract whole rock major and trace element geochemistry together with zircon u pb ages and lu hf isotope compositions are reported for a late triassic intrusive complex in the jidong region jiamusi khanka block ne china zircon u pb dating yields ages between 211 and 208 ma for enclaves of microgranular diorite and quartz diorite and between 211 and 209 ma for the host granitoids these ages correlate with a previously established intensive late triassic magmatic event along the eastern asian margin field observations together with petrographic features geochemistry and zircon hf isotope data preclude simple crystal fractionation or restite unmixing as a genetic link for the various rock types within the intrusive complex the syenogranite suite has high sio 2 75 5 76 3 wt and low mgo 0 15 0 19 wt and yields enriched lile and lree patterns most of the zircons in the syenogranites have two stage model ages of 766 and 1461 ma together with positive e hf t values of 0 6 to 9 1 these results indicate that the granitoid magmas were generated by partial melting of meso to neoproterozoic lower crust the gabbro suite has a restricted range of sio 2 46 1 51 9 wt together with high mg values 49 70 and high concentrations of ni co and cr zircons from two diorite samples have single stage hf model ages of 557 787 ma and e hf t values of 1 9 to 8 3 that are consistent with the coeval gabbros previously studied in the jidong region these features together with the observation that all the gabbros are enriched in lree and lile suggest that the mafic magmas were derived from melting of depleted neoproterozoic lithospheric mantle that had been metasomatized by slab derived fluids it is concluded that the dominant igneous suites within the late triassic intrusive complex formed by mingling mixing of felsic and mafic magmas the geochemical data combined with regional geological investigations indicate that the late triassic intrusive complex formed during lithospheric extension caused by slab break off of the yuejinshan oceanic plate that was subducting westward beneath the jiamusi khanka block

physical modelling of a surface wave survey over a laterally varying granular medium with property contrasts and velocity gradients laboratory experiments using laser based ultrasonic techniques can be used to simulate seismic surveys on highly controlled small scale physical models of the subsurface most of the time such models consist in assemblies of homogeneous and consolidated materials to enable the physical modelling of unconsolidated heterogeneous and porous media the use of granular materials is suggested here we describe a simple technique to build a two layer physical model characterized by lateral variations strong property contrasts and velocity gradients we use this model to address the efficiency of an innovative surface wave processing technique developed to retrieve 2 d structures from a limited number of receivers a step by step inversion procedure of the extracted dispersion curves yields accurate results so that the 2 d structure of the physical model is satisfactorily reconstructed the velocity gradients within each layer are accurately retrieved as well confirming current theoretical and experimental studies regarding guided surface acoustic modes in unconsolidated granular media

small strain stiffness of natural granitic saprolite in hong kong nonlinear stress strain characteristics and shear stiffness shear strain relationships of sedimentary soils and recompacted sands at small strains have been reported by many researchers however research work on the behavior of granitic soils at small strains has not attracted much attention despite the fact that many countries around the world are underlain by granitic saprolites in the study reported in this paper shear stiffness of a natural granitic saprolite from hong kong has been investigated in the field using the self boring pressuremeter and geophysical techniques such as the suspension p wave and s wave logging method and in the laboratory using a triaxial apparatus equipped with internal displacement measuring devices the observed stiffness strain relationships of the natural granitic saprolite are highly nonlinear at small strains shear stiffness decreases significantly as shear strain increases at very small shear strains in the order of 0 001 the elastic shear moduli deduced f

constrained 1d joint inversion of seismic surface waves and p refraction traveltimes we present a joint inversion scheme that couples p wave refraction and seismic surface wave data for a layered subsurface an algorithm is implemented with a damped least squares approach the estimated parameters are s and p wave velocities and layer thicknesses while densities are assumed constant during inversion the coupling is both geometric and physical layer thicknesses are the same for sand p wave velocity profiles and p wave velocities enter in both forward algorithms sensitivity analysis performed on synthetic data reveals that surface wave dispersion curves can be sensitive also to p wave velocity of some layers especially for poisson s ratio values smaller than about 0 35 allowing synergic resolution of this parameter applications on both synthetic and field data show that the proposed approach mitigates the hidden layer problem of seismic refraction and leads to more accurate results than individual inversions also for surface waves additional constraints on the objective function on a priori poisson s ratio values allow unrealistic and not admissible vp and vs values to be avoided such constraints were applied in one field case considering the a priori information available about water table depth it is also shown that estimation of porosity can help the selection of the proper constraint on a priori poisson s ratio

scattering of high frequency surface waves in scotland high frequency 5 hz coda waves for velocities of arrival less than 3 km s recorded on vertical component instruments and generated from a local earthquake in scotland are analyzed to ascertain their cause the adaption of existing velocity models and scattering from near surface irregularities in scotland such as mountains and lochs are considered as possible causes of the observed behavior the former mechanism is not feasible as it implies a significant alteration of the velocities in the upper 2 km crust contradicting previous seismic surveys in the area an analysis of the effects of scattering is performed using a formalism derived from the born approximation the scattered wave field is computed for interactions between first six rayleigh and love modes the general character of the synthetic seismograms for these scattered waves agrees with the observations on a qualitative basis the apparent absence of the fundamental mode energy from the records is also explained by the synthetic seismograms the calculations imply that scatterers with a scale length of less than 300 m are applicable to these data from the northernmost stations but around 2 km for the more southern areas it is thought that the scale length relates to the size of a region on the slopes of the mountains or lochs where there is a sharp gradient this study emphasises the effectiveness of linear scattering theory in accounting on a qualitative basis for many of the observed features of the apparently complex coda waves

pan african metamorphic and magmatic rocks of the khanka massif ne china further evidence regarding their affinity the khanka massif is a crustal block located along the eastern margin of the central asian orogenic belt caob and bordered to the east by late jurassic early cretaceous circum pacific accretionary complexes of the eastern asian continental margin it consists of graphite sillimanite and cordierite bearing gneisses carbonates and felsic paragneisses in association with various orthogneisses metamorphic zircons from a sillimanite gneiss from the hutou complex yield a weighted mean 206 pb 238 u age of 490 4 ma whereas detrital zircons from the same sample give ages from 934 610 ma magmatic zircon cores in two garnet bearing granite gneiss samples also collected from the hutou complex yield weighted mean 206 pb 238 u ages of 522 5 ma and 515 8 ma whereas their metamorphic rims record 206 pb 238 u ages of 510 500 ma these data indicate that the hutou complex in the khanka massif records early palaeozoic magmatic and metamorphic events identical in age to those in the mashan complex of the jiamusi massif to the west the older zircon populations in the sillimanite gneiss indicate derivation from neoproterozoic sources as do similar rocks in the jiamusi massif these data confirm that the khanka massif has a close affinity with other major components of the caob to the west of the dun mi fault based on these results and previously published data the khanka massif is therefore confirmed as having formed a single crustal entity with the jiamusi and possibly the bureya massif since neoproterozoic time

effects of magma storage and ascent on the kinetics of crystal growth the size distributions of crystals of olivine plagioclase and oxides of the 1991 93 eruption at mt etna italy are analyzed the simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas three distinct episodes are detectable a storage of the magma in a deep reservoir characterized by nearly constant and low nucleation and growth rates near to equilibrium an ascent phase with an ever increasing nucleation rate related to volatile exsolution and finally a quenching phase in addition to geochemical and geophysical evidence the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of etnean lavas are due to mixing of different populations this strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates

a triassic jurassic westward scissor like subduction history of the mudanjiang ocean and amalgamation of the jiamusi block in ne china constraints from whole rock geochemistry and zircon u pb and lu hf isotopes of the lesser xing an zhangguangcai range granitoids abstract ne china recorded the key tectonic evolution history of the eurasian plate from the paleozoic mesozoic collisional formation of the central asian orogenic belt to the mesozoic subduction of the paleo pacific ocean to better understand this tectonic transition it is crucial to constrain the time and pattern of the initial subduction of the paleo pacific ocean recently some researchers proposed that the mudanjiang ocean existed between the songnen and jiamusi blocks was part of the paleo pacific ocean here through geochemical and geochronological studies on the widespread granitoids in the lesser xing an zhangguangcai range in the eastern songnen block we verify that these magmatic rocks show volcanic arc affinity with increased mantle contribution from east to the west of the range likely related to a flattening subduction of the mudanjiang ocean in addition a universal westward younging trend for over 70 myr can be observed for the granitoids throughout the lesser xing an zhangguangcai range indicating a long lasting subduction of the mudanjiang ocean more interestingly the oldest ages of the granitoids in the east display a northward younging trend from 275 ma to 218 ma suggesting that the subduction of the mudanjiang ocean had been initiated at latest by 275 ma in the south and then progressively expanded to the north based on these observations we proposed a new tectonic evolution model for the mudanjiang ocean i e a triassic jurassic westward scissor like subduction and closure to contribute to the understanding of the early subduction of the paleo pacific ocean

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

zircon u pb ages and geochemistry of newly discovered neoproterozoic orthogneisses in the mishan region ne china constraints on the high grade metamorphism and tectonic affinity of the jiamusi khanka block abstract the jiamusi khanka block located in the easternmost segment of the central asian orogenic belt caob is one of the least understood blocks in northeastern china the age of its basement the timing of the high grade metamorphism and the tectonic affinity of this block have all been subjects of controversy here we describe newly discovered neoproterozoic orthogneisses from the mishan region in the central jiamusi khanka block sims and la icp ms u pb dating of the magmatic cores of zircons from three of these high grade orthogneisses yielded weighted mean ages that range from 898 4 to 891 13 ma indicating that early neoproterozoic magmatism did occur in the jiamusi khanka block twenty two analyses of metamorphic zircons rims as well as some grains gave two groups of concordant ages one at ca 563 ma interpreted as the timing of the high grade metamorphism and the other around 518 496 ma interpreted as representing a subsequent retrograde metamorphism the orthogneisses represent metamorphosed peraluminous syn collisional syenogranites with sio2 71 29 78 08 wt a cnk 1 06 1 99 and na2o k2o 0 03 1 49 and they belong chemically to the high potassium calc alkaline series they have low sr 32 134 ppm contents and sr y ratios 1 6 16 9 and display strongly fractionated to nearly flat ree patterns with negative eu anomalies eu 0 22 0 95 and depletions in nb ta these geochemical characteristics suggest that the syenogranitic rocks were derived under low pressures from a crustal source with a high proportion of sedimentary rocks perhaps in a subduction related setting that was undergoing transition from compression to extension in the context of the reconstruction of gondwana the ca 898 891 ma magmatic activity and the ca 563 ma high grade metamorphism in the mishan region provide constraints on the possible linkages between the jiamusi khanka block and east gondwana during the neoproterozoic to early paleozoic

experimental quantification of plagioclase crystal size distribution during cooling of a basaltic liquid an experimental study has been conducted to constrain how thermal history controls crystal size distribution csd of plagioclase in cooling basalts data from all experiments are dominated by a log linear segment of decreasing number density with increasing crystal size consistent with observations in many natural rocks the slope of the csd is found to be a function of cooling rate faster cooling leading to greater slopes at constant cooling rate the csds flatten as temperature decreases and are sometimes kinked characteristics consistent with independent textural observations that crystal agglomeration contributes significantly to crystal growth a downturn is observed toward small size which suggests ostwald ripening furthermore we find that thermal history above the liquidus has a major influence on csds and on the temperatures of phase appearance we conclude that near the liquidus heterogeneous nucleation typically dominates

the crustal accretion history and tectonic evolution of the ne china segment of the central asian orogenic belt abstract the basement rocks in parts of ne china constitute a khondalitic sequence of sillimanite and garnet bearing gneisses hornblende plagioclase gneiss and various felsic paragneisses zircon u pb dating of garnet sillimanite gneiss samples from the erguna xing an jiamusi and khanka blocks indicates that high grade metamorphism occurred at 500 ma evidence from detrital zircons in paleozoic sediments from the songliao block also indicates the former presence of a 500 ma component this uniformity of u pb ages across all crustal blocks in ne china establishes a 1300 km long late pan african khondalite belt which we have named the ne china khondalite belt this indicates the blocks of ne china were amalgamated prior to 500 ma contrary to current belief one scenario is that this amalgamated terrane had a tectonic affinity to the siberia craton once forming part of the late pan african 500 ma sayang baikal orogenic belt extensively developed around the southern margin of the siberia craton this belt was the result of collision between currently unidentified terranes with the southeastern angara anabar province at about 500 ma where the rocks were deformed and metamorphosed to granulite facies it appears likely that at sometime after 450 ma the combined ne china blocks rifted away from siberia and moved southward to form what is now ne china the combined block collided with the north china craton along the solonker xar moron changchun suture zone at 230 ma rather than in the end permian as previously thought local rifting at the eastern extremity of the developing central asian orogenic belt caob resulted in the splitting away of the jiamusi khanka bureya blocks however this was only transient and sometime between 210 and 180 ma these were re united with the caob by the onset of pacific plate subduction which has dominated the tectonic evolution of the region since that time

pb diffusion in zircon abstract chemical diffusion of ti under anhydrous conditions at 1 atm and under fluid present elevated pressure 1 1 1 2 gpa conditions has been measured in natural zircon the source of diffusant for 1 atm experiments was a zro2 tio2 zircon mixture with experiments run in crimped pt capsules diffusion experiments done in the presence of h2o co2 fluid were run in a piston cylinder apparatus using a source of ground tio2 zrsio4 and sio2 with oxalic acid added to produce h2o co2 vapor and partially melt the solid source material yielding an assemblage of rutile zircon melt vapor nuclear reaction analysis nra with the resonant nuclear reaction 48ti p 49v was used to measure diffusion profiles for both sets of experiments the following arrhenius parameters were obtained for ti diffusion normal to cover the temperature range 1350 1550 c at 1 atm d ti 3 33 10 2 exp 754 56 kj mol 1 r t m 2 s 1 ti diffusivities were found to be similar for experiments run under fluid present conditions a fit to all of the data yields the arrhenius relation d 1 34 102 exp 741 46 kj mol 1 rt m2 s 1 these data suggest that zircon should be extremely retentive of ti chemical signatures indicating that the recently developed ti in zircon crystallization geothermometer watson e b harrison t m 2005 zircon thermometer reveals minimum melting conditions on earliest earth science 308 841 844 will be quite robust in preserving temperatures of zircon crystallization titanium diffuses somewhat faster in zircon than larger tetravalent cations u th and hf but considerably more slowly than pb the ree and oxygen hence ti crystallization temperatures may be retained under circumstances when radiometric ages or other types of geochemical information are lost

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

the cascadia megathrust earthquake of 1700 may have rejuvenated an isolated basalt volcano in western canada age and petrographic evidence the basaltic tseax flow is the product of one of only two eruptions in western canada during the last thousand years reinterpretations of 14c and paleomagnetic data indicate that tseax volcano last erupted between 1668 and 1714 ce this date straddles that of the cascadia megathrust earthquake of 26 january 1700 whose rupture lay 450 km to the south hence the largest recent earthquake in northwest north america may have rejuvenated an existing magmatic system and produced this isolated flow although the flow is chemically uniform there are significant textural differences between the early and late parts of the flow it is proposed that both magmatic components were contained within a steep conduit gas produced by degassing of magma in the lower part of the conduit ascended heated magma in the upper part coarsening plagioclase and then continued to the surface along fissures this stable configuration was disrupted by the cascadia earthquake dilatation widened the conduit and enabled both magmas to rise to the surface along existing fissures

precambrian geology of china preface abstract the north china south china and tarim cratons compose the tectonic framework of china in the last decade extensive structural metamorphic geochemical geochronological and geophysical investigations have been carried out on these cratonic blocks producing an abundant amount of new data and competing interpretations which have resulted in refinement of and in some cases significant reinterpretations of the precambrian crustal formation and evolution of china this forms a justification for organizing this special issue in which we invited representative experts working in the north china south china and tarim cratons to present overviews or detailed studies on the formation and tectonic evolution of major precambrian blocks in china twenty four contributions collected in this special issue provide current knowledge of the components and tectonic evolution of major precambrian blocks in china and discuss some key issues based on new data and interpretations which will provide important insights into understanding the precambrian geology of china

shear wave measurements of the elasticity of the ground shear waves provide a direct way of determining the dynamic shear modulus of the ground that is independent of poisson s ratio two shear wave methods have been applied to determine in situ properties as a function of depth on three clay sites the first method was that of shear wave refraction using a strong shear wave source and an enhancement seismograph the second method measured the velocity of rayleigh or surface waves generated by vibrators on the surface of the ground in addition compression wave velocities were measured enabling the dynamic poisson s ratio to be calculated on all three sites the moduli were found to increase with depth they were compared with semi static values from plate tests and pressuremeter measurements the comparisons were made by means of a generalized viscoelastic model based on published values of damping for clays as a function of strain les ondes de cisaillement permettent de determiner directement le module de cisaillement dynamique du sol qui est independant du

petrologic evidence of a complex plumbing system feeding the july august 2001 eruption of mt etna sicily italy after the major 1991 1993 eruption mt etna resumed flank activity in july 2001 through a complex system of eruptive fissures cutting the ne and the s flanks of the volcano and feeding effusive activity fire fountains strombolian and minor phreatomagmatic explosions throughout the eruption magmas with different petrography and composition were erupted the vents higher than 2 600 m a s l hereafter upper vents uv erupted porphyritic plagioclase rich trachybasalt typical of present day summit and flank activity differently the vents located at 2 550 and 2 100 m a s l hereafter lower vents lv produced slightly more primitive trachybasalt dominated by large clinopyroxene olivine and uncommon minerals for etna such as amphibole apatite and orthopyroxene and containing siliceous and cognate xenoliths petrologic investigations carried out on samples collected throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity namely the coeval occurrence of distinct magmas we interpret this evidence as the result of a complex plumbing system it consists in two separate magma storage systems a shallow one feeding the activity of the uv and a deeper and more complex storage related to the activity of lv in this deep storage zone which is thermally and compositionally zoned the favourable conditions allow the crystallization of amphibole and the occurrence of cognate xenoliths representing wall cumulates throughout 2001 eruption uv and lv magmas remain clearly distinct and ascended following different paths ruling out the occurrence of mixing processes between them furthermore integrating the 2001 eruption in the framework of summit activity occurring since 1995 we propose that the 2001 magma feeding the vents lower than 2 600 m a s l is a precursor of a refilling event which reached its peak during the 2002 2003 etna flank eruption

textural effects of steady state behaviour of the stromboli feeding system abstract the exceptionally persistent activity of stromboli volcano has lasted for at least 1400 years the normal strombolian activity is periodically interrupted by more energetic explosions 1 2 per year and by sporadic effusive episodes every 10 20 years normal activity and effusive episodes are characterized by crystal rich high k to shoshonitic basalts issuing from a volatile poor shallow system crystal poor pumice are emitted only during more violent explosions and are thought to derive from deep pulses of volatile rich magma shallow level degassing induces massive crystallization of deep pulses of feeding magma that continuously mixing with the resident one produces the crystal rich shoshonite of the persistent activity we examined the crystallization history of the crystal rich shallow reservoir using plagioclase crystal size distribution csd analysis of scoriae and lavas emitted in the past twenty years csds show a linear dependence from crystal size in the size interval 0 06 1 2 mm number density of larger crystals is biased by right hand truncation effects csds slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view the linear crystal size distribution are reached by the system through episodes of growth and resorption respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system plagioclase net growth rate 2 10 11 cm s results from a balance of growth 10 10 cm s and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 m csds of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics the evaluation of pyroxene and olivine csd on the whole data set however confirms the conclusions acquired from plagioclase csds

geochronology and geochemistry of middle permian middle triassic intrusive rocks from central eastern jilin province ne china constraints on the tectonic evolution of the eastern segment of the paleo asian ocean abstract to constrain the permian early mesozoic tectonic evolution of the eastern segment of the paleo asian ocean we conducted zircon u pb dating and whole rock geochemical analyses on six middle permian middle triassic intrusive plutons in central eastern jilin province ne china zircons from the six plutons display distinct oscillatory zoning and striped absorption in cathodoluminescence cl images and th u ratios of 0 11 1 41 indicating a magmatic origin zircon u pb dating indicates that the intrusive rocks formed in the middle permian ca 260 ma to middle triassic ca 245 ma in central eastern jilin province the middle permian and middle triassic plutons are composed mainly of strongly deformed monzogranites with affinities to adakitic rocks which are formed from partial melting of thickened mafic lower crust in contrast the late permian the early triassic plutons in central eastern jilin province consist of a bimodal association including gabbros and granitoids and deformed monzonites which typically form in extensional settings these observations along with the results of previous studies on early middle permian granitoids in western jilin province indicate that the eastern segment of the paleo asian ocean underwent the initial closure in central western jilin province during the middle permian and the final closure in eastern jilin province in the middle triassic

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

geochronology and geochemistry of late pan african intrusive rocks in the jiamusi khanka block ne china petrogenesis and geodynamic implications abstract to constrain the early paleozoic tectonic evolution of the jiamusi khanka block and its relationship to the late pan african event in gondwana we undertook zircon u pb dating and geochemical analyses major and trace elements and hf isotopic compositions of early paleozoic intrusive rocks in the jiamusi khanka block ne china la icp ms zircon u pb age data demonstrate that these intrusive rocks were emplaced at three stages during the late pan african event represented by 540 ma syenogranite 515 ma quartz syenite and 500 ma monzogranite and gabbro geochemically the 500 ma gabbros in the jiamusi khanka block have low sio 2 50 26 51 21 wt relatively high mgo 4 08 5 67 wt ni 13 1 14 1 ppm and cr 28 4 56 0 ppm and are slightly enriched in liles e g ba k and lrees and depleted in zr hf nb ta and p the e hf t values of zircons in the gabbro range from 2 6 to 6 4 all these geochemical features indicate that the gabbros were likely produced by the partial melting of a depleted mantle that had been metasomatized by fluids derived from a subducted slab in contrast the ca 540 500 ma granites and quartz syenites contain high sio 2 64 49 72 20 wt and low mgo 0 40 0 75 wt cr 1 69 6 88 ppm and ni 1 26 3 26 ppm they have relatively low 176 hf 177 hf ratios of 0 282247 0 282599 with hf two stage model ages of 1173 2280 ma and most of the magmatic zircons have positive e hf t values varying from 0 2 4 8 indicating that these granites and quartz syenites were probably derived from a dominantly paleo mesoproterozoic old crustal source with possible different degrees of addition of juvenile materials according to the geochemical data and global geological investigations we propose that the 541 498 ma intrusive rocks in the jiamusi khanka block formed in a post collisional or post orogenic extensional setting linked to the collapse of a late pan african orogen associated within the gondwana

cooling kinetics experiments on different stromboli lavas effects on crystal morphologies and phases composition abstract controlled cooling experiments at atmospheric pressure and fo2 of the nno buffer were performed on three stromboli lavas of calcalkaline ca high k calcalkaline hkca and shoshonitic sho affinities the experiments were conducted at cooling rates of 900 c h fast cooling rate fcr and 1 c h slow cooling rate scr respectively to investigate the kinetic factors governing textural and compositional features such as phase growth morphology phase relations and phase compositions the experiments produced different types of textures as both the cooling rate and the quenching temperatures were varied in general fcr experiments show a decrease of crystal size as well as a change in crystal shape from euhedral to granular to skeletal up to dendritic morphology with decreasing temperatures scr experiments produce less variable crystal size and crystal morphology measurements of plagioclases indicate that the crystal size and calculated crystal growth are functions of cooling rate crystal growth rates are about two orders of magnitude higher in fcr experiments than scr ones such textural responses are in agreement with the empirical calibration based on the plagioclase size dependence on cooling rate developed by cashman 1993 experimental phase relations display three main features of the crystallization process 1 the delay in the crystallization of the liquidus phase in the fcr experiments with respect to the scr ones 2 crystallization controlled by the multiphase cotectic relations plagioclase pyroxenes olivine is more enhanced for fcr experiments compared to that of scr ones at the lowest experimental temperature 1100 c 3 crystallization of augite and pigeonite is sensitive to cooling rate and system compositions pigeonite not found in the natural rocks crystallizes in the ca sample across scr and fcr runs and in the hkca sample just in the scr experiments fcr and scr experiments produce similar liquid lines of descent for both ca and hkca starting materials suggesting that the processes of nucleation and growth play reciprocal roles through mass balance as cooling rate varies this is not true for the sho composition where the trends of melt composition appear to be especially influenced by the different amounts of olivine crystallization at the different cooling rates data on mineral compositions show that plagioclase and clinopyroxene are the phases more strongly affected by the cooling gradients crystals from scr experiments and to a lesser extent from fcr experiments show zoning patterns mainly at the lowest experimental temperature

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

spatial temporal relationships of mesozoic volcanic rocks in ne china constraints on tectonic overprinting and transformations between multiple tectonic regimes abstract la icp ms zircon u pb ages and geochemical data are presented for the mesozoic volcanic rocks in northeast china with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the paleo asian ocean mongol okhotsk and circum pacific tectonic regimes the new ages together with other available age data from the literature indicate that mesozoic volcanism in ne china can be subdivided into six episodes late triassic 228 201 ma early middle jurassic 190 173 ma middle late jurassic 166 155 ma early early cretaceous 145 138 ma late early cretaceous 133 106 ma and late cretaceous 97 88 ma the late triassic volcanic rocks occur in the lesser xing an zhangguangcai ranges where the volcanic rocks are bimodal and in the eastern heilongjiang jilin provinces where the volcanics are a type rhyolites implying that they formed in an extensional environment after the final closure of the paleo asian ocean the early middle jurassic 190 173 ma volcanic rocks both in the erguna massif and the eastern heilongjiang jilin provinces belong chemically to the calc alkaline series implying an active continental margin setting the volcanics in the erguna massif are related to the subduction of the mongol okhotsk oceanic plate beneath the massif and those in the eastern jilin heilongjiang provinces are related to the subduction of the paleo pacific plate beneath the eurasian continent the coeval bimodal volcanic rocks in the lesser xing an zhangguangcai ranges were probably formed under an extensional environment similar to a backarc setting of double direction subduction volcanic rocks of middle late jurassic 155 166 ma and early early cretaceous 145 138 ma age only occur in the great xing an range and the northern hebei and western liaoning provinces limited to the west of the songliao basin and they belong chemically to high k calc alkaline series and a type rhyolites respectively combined with the regional unconformity and thrust structures in the northern hebei and western liaoning provinces we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the mongol okhotsk suture belt the late early cretaceous volcanic rocks widely distributed in ne china belong chemically to a low to medium k calc alkaline series in the eastern heilongjiang jilin provinces i e the eurasian continental margin and to a bimodal volcanic rock association within both the songliao basin and the great xing an range the volcanics in the eastern heilongjiang jilin provinces formed in an active continental margin setting related to the subduction of the paleo pacific plate beneath the eurasian continent and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust or both late cretaceous volcanics limited to the eastern heilongjiang jilin provinces and the eastern north china craton ncc consist of calc alkaline rocks in the eastern heilongjiang jilin provinces and alkaline basalts in the eastern ncc suggesting that the former originated during subduction of the paleo pacific plate beneath the eurasian continent whereas the latter formed in an extensional environment similar to a backarc setting taking all this into account we conclude that 1 the transformation from the paleo asian ocean regime to the circum pacific tectonic regime happened during the late triassic to early jurassic 2 the effect of the mongol okhotsk suture belt on ne china was mainly in the early jurassic middle late jurassic and early early cretaceous and 3 the late early cretaceous and late cretaceous volcanics can be attributed to the subduction of the paleo pacific plate beneath the eurasian continent

ordovician 40ar 39ar phengite ages from the blueschist facies ondor sum subduction accretion complex inner mongolia and implications for the early paleozoic history of continental blocks in china and adjacent areas we obtained 453 21 8 ma and 449 41 8 ma 2 laser step heating 40 ar 39 ar plateau ages for phengite from quartzite mylonites from the blueschist facies ondor sum subduction accretion complex in inner mongolia northern china these ages are within error of the inverse isochron ages calculated using the plateau steps and the weighted mean ages of total fusion of single grains the compositional change from glaucophane in the cores to crossite in the rims of blue amphiboles as revealed by electron microprobe analysis points to decompression probably caused by progressive exhumation of the subducted material the late ordovician ages were not affected by excess argon incorporation because in all likelihood the oceanic sediments were wet on arrival at the trench and free of older detrital mica the ca 450 ma ages are hence interpreted as the time of crystallization during mylonitization under high fluid activity at fairly low temperatures this means that accretion of the quartzite mylonite unit occured about 200 ma before final closure of the paleo asian ocean amalgamation of the siberian tarim and north china cratons and formation of the end permian solonker suture zone we argue that the early paleozoic evolution of the ondor sum complex occurred along the northeastern cimmerian margin of gondwana which was composed of micro continents fringed by subduction accretion complexes and island arcs the later evolution took place during the building of the eurasian continent following middle devonian and younger rifting along the east gondwanan margin and northward drift of the detached north china craton an extensive review shows that this type of two stage scenario probably also applies to the geodynamic evolution of other micro continents like south china tarim a number of kazakh terranes alashan qaidam and kunlun as well as south kitakami and correlatives in japan and probably indochina like the north china craton these were bordered by early paleozoic subduction accretion complexes island arcs or contained calc alkaline volcanic mar gins like for example the central tienshan north qinling north qaidam altun north qilian and kunlun belts in china as well as the oeyama and miyamori ophiolites and matsugadaira motai blueschist belt of japan and the dismembered sergeevka ophiolite of the southern part of the russian far east this implies that a vast orogenic system comprising an archipelago of micro continents seems to have existed along the cimmerian margin of east gondwana in early paleozoic time in which the ultrahigh pressure metamorphism that characterizes the early evolution of many of the asian micro continents occurred introduction and aim

kinetics of crystal evolution as a probe to magmatism at stromboli aeolian archipelago italy abstract the kinetics of hydrated basaltic melts erupted during the present activity at stromboli have been studied to estimate the growth and dissolution rate of plagioclase specifically a high k basalt composition pst 9 has been studied to investigate magma and eruption dynamics at stromboli volcano by combining crystallization kinetics of plagioclase and csd measurements on natural samples from literature armienti et al 2007 fornaciai et al 2009 a series of water saturated decompression experiments over a range of final water pressure pf 75 5 mpa at constant temperature 1075 c show that plagioclase is systematically present from 50 to 5 mpa at water saturated conditions moreover these experiments show that anorthite an content decreases with decreasing p h 2 o reaching the same composition as the natural plagioclase in stromboli scoria at pressure below 20 mpa and that the plagioclase crystal fraction increases as the experimental conditions tend to lower final pressure plagioclase growth rate gl is observed to increase with undercooling for the pf investigated during decompression experiments except for the 75 mpa pf serie that only has two samples with the presence of plagioclase crystals the values of gl vary from 10 7 to 10 8 cm s for pf from 75 to 25 mpa while at pf from 10 to 5 mpa growth rates are approximately of 10 6 cm s a series of dissolution experiments at atmospheric pressure and over a range of temperature has been done for plagioclase t range of 1220 1240 c dissolution rate g for plagioclase 10 7 cm s tends to be slightly higher at higher temperature in the range of 1220 1240 c and appears to be time independent for the experimental durations investigated 10 30 h these trends could be related to development of a diffusion limited boundary layer adjacent to the dissolving crystal by comparison of the experimental data on plagioclase composition growth rates and dissolution in stromboli basalt it is possible to place the reservoir of the crystal rich magma in the upper part from 400 m to the surface of the volcanic conduit kinetic data of the plagioclase the most important phase of the shallow magmatic system of stromboli show that the magmatic processes are quite dynamic and in a relatively short time hours or several days the system can change considerably furthermore the results from this work combined with observations on natural samples help to improve our knowledge of the magma plumbing system of interactions between resident magma and new magmas the dynamics of volcanic activity of stromboli and the time scales of magmatic processes that change in a few hours to 1 month

lidar strip adjustment application to volcanic areas dems derived from lidar data are nowadays largely used for quantitative analyses and modelling in geology and geomorphology high quality dems are required for the accurate morphometric and volumetric measurement of land features we propose a rigorous automatic algorithm for correcting systematic errors in lidar data in order to assess sub metric variations in surface morphology over wide areas such as those associated with landslide slump and volcanic deposits our procedure does not require a priori knowledge of the surface such as the presence of known ground control points systematic errors are detected on the basis of distortions in the areas of overlap among different strips discrepancies between overlapping strips are assessed at a number of chosen computational tie points at each tie point a local surface is constructed for each strip containing the point displacements between different strips are then calculated at each tie point and minimization of these discrepancies allows the identification of major systematic errors these errors are identified as a function of the variables that describe the data acquisition system significant errors mainly caused by a non constant misestimation of the roll angle are highlighted and corrected comparison of dems constructed using first uncorrected and then corrected lidar data from different mt etna surveys shows a meaningful improvement in quality most of the systematic errors are removed and the accuracy of morphometric and volumetric measurements of volcanic features increases these corrections are particularly important for the following studies of mt etna calculation of lava flow volume calculation of erosion and deposition volume of pyroclastic cones mapping of areas newly covered by volcanic ash and morphological evolution of a portion of an active lava field over a short time span

provenance age and tectonic implications of neoproterozoic strata in the jiamusi massif evidence from u pb ages and hf isotope compositions of detrital and magmatic zircons abstract the jiamusi massif forms part of the eastern central asian orogenic belt caob and the pacific oceanic tectonic domain but its tectonic affinity is highly controversial here we present u pb ages and hf isotope compositions of detrital zircons from five metasedimentary rocks and one monzogranite within the jiamusi massif and our aim was to constrain the depositional ages and provenance of the strata as well as the tectonic affinity of the massif two specimens of two mica schist from the upper and lower kimkanskaya groups russian far east yielded zircon age populations at 572 826 891 958 and 1776 ma and 682 752 835 and 925 ma respectively a sericite schist and muscovite schist from the majiajie group ne china yielded zircon age populations at 951 1232 1419 1643 and 2687 ma and 1151 1276 1444 1623 1805 and 2652 ma respectively and a two mica schist from the ximashan formation of the mashan group ne china yielded zircon age populations at 994 1281 1439 1647 and 1805 ma taking into account the general geological relationships in the area zircon age populations and hf isotopic compositions combined with an age of 492 ma for a monzogranite that intrudes the ximashan formation we conclude that the lower kimkanskaya group formed in the neoproterozoic and was sourced mainly from a neoproterozoic terrane whereas the majiajie group and ximashan formation formed in the neoproterozoic but were sourced dominantly from a mesoproterozoic terrane taking into account previous paleomagnetic data our dating results and comparisons with zircon age populations in precambrian rocks from northeastern gondwana and the southern siberia north china and tarim cratons suggest that the jiamusi massif has an affinity with the tarim craton

the most ancient ophiolite of the central asian fold belt u pb and pb pb zircon ages for the dunzhugur complex eastern sayan siberia and geodynamic implications abstract ophiolitic rocks with a zircon age of 1020 ma occur in the dunzhugur complex of east sayan siberia and are part of a neoproterozoic to early palaeozoic segment of the central asian fold belt the most spectacular suite is exposed along the oka and bokson rivers where a complete ophiolite sequence with mantle tectonites a layered sequence composed of dunite wehrlite and pyroxenite a gabbro section a sheeted diabase dyke complex and basaltic pillow lavas are exposed petrologic and geochemical data suggest that all members of the ophiolite originally belonged to the same cogenetic mafic ultramafic crustal section and support a supra subduction zone setting in a fore arc rifting environment for its origin two multigrain zircon size fractions from a plagiogranite are both slightly discordant but yielded a combined mean 207pb 206pb age of 1020 10 ma evaporation of three additional fractions of three to four grains each from the same sample produced a mean 207pb 207pb age of 1019 9 0 7 ma that we consider to most closely reflect the time of igneous crystallization of the plagiogranite this is the oldest ophiolite so far dated from the central asian fold belt the southern margin of the siberian craton and the palaeo asian ocean were established at the end of the mesoproterozoic at least 1000 ma ago during the time interval 1000 570 ma one or several large ocean basins existed between baltica siberia kazakhstan tarim and northern china and these blocks are therefore unlikely to have been part of the supercontinent rodinia rifting initiation of subduction and marginal basin formation began prior to 1000 ma and continued through 570 ma the dunzhugur ophiolite of eastern sayan provides evidence for the early opening of the palaeo asian ocean not later than 1000 ma ago

a syn eruptive ground deformation episode measured by gps during the 2001 eruption on the upper southern flank of mt etna ground deformation occurring on the southern flank of mt etna volcano during the july august 2001 eruption was monitored by gps measurements along an e w profile crossing the fissure system this profile was measured eight times during the eruption using the stop and go semi kinematic technique horizontal and vertical displacements between gps surveys are reported for each station the most significant event is a deformation episode occurring during the first week of the eruption between 25 27 july displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture data inversions for measured displacements were performed using the okada model the model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east dipping fault parallel to the 1989 fracture

understanding crystal populations and their significance through the magma plumbing system crystals are rarely composed of a single crystal population that have grown solely from the batch of magma in which they are resident on emplacement either by eruption or shallow intrusion close investigation of the majority of crystal populations reveal that they comprise up to four main components phenocrysts crystals co genetic with their magmatic host xenocrysts crystals wholly or in part foreign to the magmatic host and magma system antecrysts crystals which are recycled one or several times before inclusion in the host magma but have an origin within the magmatic system and microlites which represent small co genetic crystals which nucleate and grow rapidly on decompression and eruption textural analysis techniques are employed to quantify key aspects of the crystal population including crystal shape crystal size distributions spatial distribution patterns and textural modification using dihedral angles santorini provides a case study of an active volcanic system where a combined textural analysis study has been developed highlighting how the crystal population is being continuously modified by a series of replenishment and mixing events developing textural and microgeochemical techniques provides the next stage in the interrogation of crystal populations linking textures to isotopic heterogeneities and providing fingerprints of where crystals are sourced and re cycled