pb isotopes of granitoids suggest devonian accretion of yangtze south china craton to north china craton feldspar separates of 30 granitoid intrusions ranging in age from neoproterozoic to mesozoic were analyzed for pb isotopic compositions together with associated precambrian basement whole rocks from the north and south qinling orogenic belts the two belts constitute the southern active margin of the north china craton and the northern passive margin of the yangtze craton respectively proterozoic basement rocks from the north and south qinling belts are clearly distinguished in terms of both present day pb isotopes and calculated initials at the time of granite magmatism with the former having considerably more radiogenic pb granitoids of the south qinling belt irrespective of age and specific granitoid rock type show a fairly homogeneous pb isotopic composition that is similar to that of the south qinling basement in contrast in the north qinling belt the pb isotopic composition of granitoids is correlated with their age neoproterozoic and early paleozoic granitoids have radiogenic pb isotopic compositions like those of the north qinling proterozoic basement rocks but late paleozoic and mesozoic granitoids show significantly less radiogenic pb isotopic compositions similar to those of the south qinling basement rocks the unusual change is interpreted to reflect underthrusting of the south qinling belt beneath the north qinling belt at ca 360 ma the process resulted in a change of the source for younger north qinling granitoids from the radiogenic north qinling to the less radiogenic south qinling basement rocks thus the yangtze craton accreted to the north china craton no later than 360 ma

volcanic tremor at volcan de colima mexico recorded during may 2002 and its interactions with the seismic signals produced by low energy explosive activity and rockfalls abstract the may 2002 eruption episode at volcan de colima mexico represented the transition period between two stages of effusive activity which were characterized by the formation of lava flows the short period seismic signals recorded during may 2002 at a distance of 1 6 km from the crater were represented by volcanic tremor and the signals produced by low energy explosions and rockfalls two types of volcanic tremor were recognized harmonic with two fundamental spectral frequencies of 1 2 1 4 hz and 1 6 1 7 hz and non harmonic the existence of two fundamental frequencies of volcanic tremor may indicate a two vent magmatic conduit no clear relationship between the variations in the spectral content of tremor and occurrence of explosions was observed the waveforms of the signals produced by low energy explosions and rockfalls and recorded on the background of volcanic tremor were strongly modulated by the low frequency harmonic tremor signals forming in this manner pseudo long period events fourier analysis of the seismic signals associated with low energy explosions and rockfalls but recorded on the background of regular seismic noise indicated their high frequency sources characterized by dominant frequencies within 2 3 hz and 3 4 5 hz respectively

observations and analysis of b type earthquakes explosions and volcanic tremor at pavlof volcano alaska an eight station network of short period seismometers has been operated near pavlof volcano 55 25 n 161 54 w alaska peninsula since 1976 high quality analog to digital and direct digital data were recorded during eruptions in 1980 through 1983 data are analyzed from explosions with distinct air phases b type volcanic earthquakes shallow low frequency events lacking clear s phases and volcanic tremor to determine source and propagation effects between zero and several hundred b type events and explosions per day are recorded with higher numbers during eruptions magnitudes range between 0 5 and 1 3 and b values range between 1 9 0 1 and 2 6 0 1 with no systematic relation to eruptive activity six results are most important 1 data from a recently installed three component station reveal that the highest amplitude waves of the b type events show retrograde elliptical particle motion and normal dispersion and are hence probably rayleigh waves 2 stacking of the events enhances the p wave which has a velocity of 3 1 0 1 km sec 1 3 the explosions and b type events have similar hypocenters as evidenced by signal characteristics and wave arrival times 4 the b type events contain virtually no high frequency energy even when allowing for attenuation effects in particular we estimate the anelastic attenuation coefficient q to have a value of 45 20 for rayleigh waves in the shallow part of the volcano 5 volcanic tremor spectra exhibit evenly spaced narrow peaks which we model as eigenvalues of organ pipe resonance in the magma conduit we estimate the length of the conduit to be a maximum of 1 6 km 6 the volcano shows evidence of extreme lateral variation of velocity and attenuation in its shallow structure

theory of the airborne sound field generated in a resonant magma conduit abstract explosive sources triggered inside a magma conduit may excite the conduit into acoustic resonance the acoustic field in the conduit can propagate into the atmosphere through an open vent and ensonify the overlying atmosphere the character of the airborne sound field is determined by a combination of propagation and source effects the resonance of the magmatic conduit and the diffraction of the sound field at the volcanic vent are acoustic propagation effects whereas the explosion pressure signature and the firing rate of the explosions define the source characteristics for wavelengths larger than the conduit radius only the longitudinal resonances of the magmatic conduit are relevant and the open vent radiates like a piston surrounded by an infinite baffle in this case the fluid particle velocities are directed along the axis of the conduit and the sound field may propagate into the surrounding bedrock through the conduit wall displacement induced by the fluid overpressure this coupling may produce seismic signals with banded spectra such as volcanic tremor and long period events the airborne pressure field retains the modal structure of the sound field in the magmatic conduit which contains information on the conduit geometry and geo acoustic properties of the magma the seismic wavefield is driven by the acoustic field in the magma and also contains this information although it may be filtered by propagation effects in the bedrock the theoretical sound field in the magma conduit is used to interpret seismic tremor signals recorded at mt spurr volcano alaska rapid variations in the acoustic impedance of the magma conduit terminations can create systematic changes in the tremor spectra which can be used to monitor changes in the magmatic system the results of the modelling illustrate the difference between source effects and conduit resonance as well as the value of seismoacoustic measurements in volcanic environments

period doubling and other nonlinear phenomena in volcanic earthquakes and tremor abstract evidence of subharmonic period doubling cascades has recently been recognized in seismograms of volcanic tremor from several volcanoes this phenomenon occurs only in nonlinear systems and is the commonest route by which such systems change from periodic to chaotic behavior it is predicted to occur in a model of volcanic tremor excitation by flow induced vibration and it might well also occur in other volcano seismic source process if the possibility of period doubling is not taken into account in interpreting spectra of tremor and long period earthquakes then low frequency sub harmonic oscillations may be mis identified as normal modes of a linear acoustic resonator leading to errors of an order of magnitude or more in inferred magma body dimensions this example illustrates the importance of nonlinear phenomena in attempts to understand volcano seismic phenomena physically linear systems are fundamentally incapable of causing earthquakes or exciting tremor so nonlinearity is essential to any theory of volcano seismic phenomena nonlinear processes are in many respects qualitatively different from linear ones a few of their characteristics that might be relevant in volcanoes include the possibility 1 that damping might increase rather than decrease oscillation frequencies and 2 that these frequencies might be functions of the amplitude of oscillation so that temporal variations in spectral peak frequencies might not be manifestations of changes of conditions within the magmatic system

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

timing of collision of the sino korean and yangtse cratons u pb zircon dating of coesite bearing eclogites the suture zone between the sino korean and yangtse cratons in central china is marked by a series of fault bounded belts composed of crustal protoliths in the dabie mountains some of these blocks contain coesite and diamond indicating subduction to minimum depths of 120 km as a result of continental collision the blocks range from the structurally lowest ultrahigh pressure metamorphic belt and decrease in metamorphic grade upsection to the structurally highest low greenschist facies belt furthermore the faults mark large contrasts in metamorphic grade these features form a structure that is similar to metamorphic core complexes indicating extension as part of the exhumation process timing of the continental collision has previously been inferred as late triassic from regional geologic relations or caledonian from 40 ar 39 ar dating of the adjacent and possibly related qinling metamorphic belt u pb dating of zircon from ultra high pressure eclogites yields a metamorphic age of 209 2 ma this age coincides with later stages of collision and is therefore a minimum estimate of the time of collision

observations of volcanic tremor during the january february 2005 eruption of mt veniaminof alaska mt veniaminof alaska peninsula is a stratovolcano with a summit ice filled caldera containing a small intracaldera cone and active vent from january 2 to february 21 2005 mt veniaminof erupted the eruption was characterized by numerous small ash emissions vei 0 to 1 and accompanied by low frequency earthquake activity and volcanic tremor we have performed spectral analyses of the seismic signals in order to characterize them and to constrain their source continuous tremor has durations of minutes to hours with dominant energy in the band 0 5 4 0 hz and spectra characterized by narrow peaks either irregularly non harmonic tremor or regularly spaced harmonic tremor the spectra of non harmonic tremor resemble those of low frequency events recorded simultaneously with surface ash explosions suggesting that the source mechanisms might be similar or related we propose that non harmonic tremor at mt veniaminof results from the coalescence of gas bubbles while low frequency events are related to the disruption of large gas pockets within the conduit harmonic tremor characterized by regular and quasi sinusoidal waveforms has duration of hours spectra containing up to five harmonics suggest the presence of a resonating source volume that vibrates in a longitudinal acoustic mode an interesting feature of harmonic tremor is that frequency is observed to change over time spectral lines move towards higher or lower values while the harmonic nature of the spectra is maintained factors controlling the variable characteristics of harmonic tremor include changes in acoustic velocity at the source and variations of the effective size of the resonator

seismicity associated with eruptive activity at langila volcano papua new guinea abstract during periods of eruptive activity at langila volcano various combinations of low frequency earthquakes and high frequency air waves have been recorded ranging from earthquakes alone to air waves alone it is shown that these different types of events are part of a continuous range of events which are all interpreted to be explosions at or near the summit continuous tremor is also often recorded for durations of several minutes to hours and is classified into two types harmonic and non harmonic spectral analysis shows that the non harmonic tremor resembles a string of low frequency events in contrast the spectra of harmonic tremor show simple modal characteristics which indicate some type of resonating source this source is thought to include a gas filled cavity above the magma body within the volcano

deep volcanic tremor and magma ascent mechanism under kilauea hawaii deep harmonic tremor originating at depths around 40 km under kilauea was studied using records accumulated since 1962 at the hawaii volcano observatory of the u s geological survey the deep source of the tremor was determined by onset times and confirmed by the relative amplitude across the island wide network of seismometers the period of tremor was conclusively shown to be determined by the source effect and not by the path or station site effect because the period would change considerably in time but maintained uniformity across the seismic net during the tremor episode the tremor appeared to be primarily composed of p waves we interpret the observed period and amplitude in terms of the stationary crack model of aki et al 1977 and find that the seismic moment rates for deep tremors are considerably larger than those for shallow tremors suggesting more vigorous transport for the former we propose a kinematic source model which may be more appropriate for deep tremor according to this model a measurable quantity called reduced displacement is directly proportional to the rate of magma flow a systematic search for deep tremor episodes was made for the period from 1962 through 1979 and the amplitude period and duration of the tremor were tabulated we then constructed a cumulative reduced displacement plot over the 18 year period the result shows a generally steady process which does not seem to be significantly affected by major eruptions and large earthquakes near the surface the total magma flow estimated from the reduced displacement is however one order of magnitude smaller than that estimated by swanson 1972 it may be that most channels transport magma aseismically and only those with strong barriers generate tremor

modeling of volcanic tremor as explosive point sources in a single layered elastic half space i investigate path effects on the waveform of a volcanic tremor using a model that consist of an impulsive dilatational point source embedded in a single layered elastic half space such a source may arise during a variety of volcanic conditions such as a sequence of rapid explosions at a volcanic vent as well as gas piston activity observed in basaltic lava lakes using acoustic signals recorded during the 1975 tolbachik eruption the 1983 klyuchevskoy eruption and the 1989 tokachi dake eruption i propose a general impulsive time function for the tremor source consisting either of a single impulse or a sequence of identical impulses computed seismograms illustrate the influence of a low velocity surface layer on the shape and spectra of the waveforms for the same layered model a single impulse produces a dispersive wave while a sequence of identical impulses produces a wave of multiple harmonics for a single impulse the peak in the seismograms shifts to higher frequencies when the surface layer is very thin for multiple impulses spectral peaks shift to higher frequencies as the time between successive impulses increases indicating an increasing importance of higher order harmonics

comparison of short term seismic precursors and explosion parameters during the 2016 2017 bogoslof eruption in december 2016 the unmonitored bogoslof volcano unexpectedly began erupting producing at least 70 explosions over the next 8 5 months roughly half of the explosions were preceded by observable short term precursory activity defined here as seismic activity ending within 30 min of the explosion onset or an earthquake swarm ending within a few hours before the explosion onset five different types of precursors were noted during the bogoslof eruption non swarm earthquakes earthquake swarms rapid rate events tremor and chromatic tremor most of the precursors that were detectable by the nearby seismic networks 45 km away occurred during the first 3 months of the eruption with nearly all precursory earthquake swarms occurring during this period a hydrophone deployed 7 km northeast of the summit for the last 3 months of the eruption detected weaker activity that was not recorded by the more distant seismic networks we describe the observed precursors and discuss their inter relations overall the precursors seem indicative of processes occurring throughout the volcanic system and suggest possible changes in the system during the eruption we then compare the short term precursors with explosion parameters such as plume height duration and occurrence of lightning to look for relations that may provide more insight into the eruption dynamics and subsurface processes and help to further improve forecasting we find no obvious relations between any of the precursor or explosion parameters suggesting that their use in forecasting eruption characteristics at bogoslof is limited

a palaeoproterozoic basement beneath the rangnim massif revealed by the in situ u pb ages and hf isotopes of xenocrystic zircons from triassic kimberlites of north korea in situ u pb and hf analyses were used for crustal zircon xenocrysts from triassic kimberlites exposed in the rangnim massif of north korea to identify components of the basement hidden in the deep crust of the rangnim massif and to clarify the crustal evolution of the massif the u pb age spectrum of the zircons has a prominent population at 1 9 1 8 ga and a lack of archaean ages the data indicate that the deep crust and basement beneath the rangnim massif are predominantly of palaeoproterozoic age consistent with the ages of widely exposed palaeoproterozoic granitic rocks in situ zircon hf isotope data show that most of the palaeoproterozoic zircon xenocrysts have negative hf t values 9 7 to 0 7 with an average hf model age of 2 86 0 02 ga 2 which suggests that the palaeoproterozoic basement was not juvenile but derived from the reworking of archaean rocks considering the existence of archaean remanent material in the rangnim massif and their juvenile features a strong crustal reworking event is indicated at 1 9 1 8 ga during which time the pre existing archaean basement was exhausted and replaced by a newly formed palaeoproterozoic basement these features suggest that the rangnim massif constitutes the eastern extension of the palaeoproterozoic liao ji belt of the north china craton instead of the archaean liaonan block as previously thought a huge palaeoproterozoic orogen may exist in the eastern margin of the sino korean craton

characteristics of the early cretaceous igneous activity in the korean peninsula and tectonic implications abstractthis study presents sensitive high resolution ion microprobe shrimp u pb zircon ages k ar ages and whole rock chemical and isotopic sr nd compositions of the early cretaceous igneous activity in western south korea the volcanics and plutons yield zircon u pb ages of ca 110 ma in the albian of the late early cretaceous k ar biotite and plagioclase ages are slightly younger ca 103 ma the geochemical signatures of the rocks are characterized by negative nb ta and ti anomalies relatively low nd t values between 15 91 and 9 36 and enrichment in light rare earth elements suggesting the effects of subduction related magmatism together with the sr and nd isotopic compositions of the intermediate to acid volcanics geochemical characteristics reflect a lower crustal magma source this albian event over the korean peninsula is related to early jurassic subduction and subsequent lithospheric delamination and or slab rollback after the early cretaceous amalgamation between the north c

analyses of unusual long period earthquakes with extended coda recorded at katmai national park alaska usa 1 a swarm of six long period lp events with slowly decaying coda wave amplitudes and durations up to 120 s was recorded by seismic stations located in the proximity of mt griggs a fumarolically active volcano in the katmai national park alaska during december 8 21 2004 spectral analyses reveal the quasi monochromatic character of the waveforms dominated by a 2 5 hz mode frequently accompanied by a weaker high frequency onset 6 0 9 0 hz particle motion azimuths and inclination angles show a dominant wnw ese direction of polarization for all the signals and suggest that seismic energy is radiated by a stable source at shallow depth damping coefficients between 0 0014 and 0 0063 are estimated by fitting an exponential decay model to the signal s coda corresponding quality factors range from 78 to 351 the source of the waveforms is modelled as a resonant cavity filled with a fluid gas mixture

nd isotopic study of upper cambrian conodonts from korea and implications for early paleozoic paleogeography abstract correlation of the korean peninsula with the neighboring south and north china blocks has been one of the most important and long debated issues in east asian tectonics the eastward extension of the chinese collisional belt between the south and north china blocks into the korean peninsula is still in dispute the lower paleozoic sedimentary rocks in south korea the joseon supergroup accumulated in the okcheon belt which has been proposed as the suture zone or the block boundary between the south and north china blocks in korea the joseon supergroup comprises five different lithostratigraphic units and has been proposed to represent two tectonostratigraphic blocks bounded by the honam shear zone hsz in the okcheon belt among them the yeongweol unit in the western part of the hsz is correlated with south china and the duwibong unit in the eastern part of the hsz with north china to test the above geodynamic interpretation this study analyzed the nd isotopic composition of upper cambrian conodonts from the duwibong and yeongweol units the difference of the nd t values between the upper cambrian duwibong and yeongweol units is about 3 units compared to a wide range of the nd 0 values in the modern oceanic basins this slight difference can be regarded as a variation in a same paleo watermass the nd t values of the two units are consistent with coeval values from north china and this suggests that the duwibong and yeongweol units shared the same oceanic watermass with the north china considering current early paleozoic paleogeographic reconstructions the nd isotopic signatures of north china duwibong and yeongweol units may be independent of laurentia and baltica and thus can be indicative of another unique oceanic watermass in contrast to the previous tectonic interpretations the same paleoceanographic signatures shown by the duwibong and yeongweol units and north china and recent developments suggest that the yeongweol unit in the early paleozoic joseon supergroup is not correlated with south china but correlated with north china and the korean peninsula and north china block may have been included in a larger continental block the sino korean block the collisional belt between the south and north china blocks may not extend into the korean peninsula

constraints on crust mantle transition zone with pn waveforms a case study of eastern china and southern korean peninsula abstract the seismic velocity structure of the crust mantle transition zone cmtz provides key constraints on crustal dynamics and can be studied with pn wave which propagates horizontally along the moho discontinuity in this study we first explore an effect of velocity gradient structures in the cmtz through synthetic pn waveforms and demonstrate that the shape of pn changes from step like to pulse like when the cmtz becomes from sharp to a gradient velocity structure respectively we then use pn waveforms of the regional earthquakes the july 2012 mw 4 8 earthquake in east china and the september 2016 mw 5 1 earthquake in south korea to examine the cmtz structures to the west and east of the yellow sea and thus to constrain tectonic affinity between the eastern china and southern korean peninsula the pn waveforms from the mw 4 8 event in east china show that the moho in southern yangtze craton is sharp whereas there may be a gradient structure in cmtz with a 6 10 km thickness in northern yangtze craton the pn waveforms from the mw 5 1 event in south korea show that the cmtz in south korea is also sharp similar to the southern yangtze craton observed difference in cmtz structures suggest that sulu orogenic belt may extend along the north of the gyeonggi massif in korea

on the volcanic waveguide an analytical solution for the sound field in a resonant magma conduit with depth dependent magma properties provides a versatile interpretative tool for the analysis of seismoacoustic signals generated by fluid processes in active volcanoes expressions are given for the acoustic field in the atmosphere and the seismic field in the ground radiated through the magma conduit vent and walls respectively a new source model allows the resonance in the conduit to be excited by the vertical fluid velocity at the bottom of the conduit this source model represents acoustic excitation induced by low frequency fluid oscillations or large volume fluctuations originating at depth the magma conduit is modeled as a three section duct with each section having a different density sound speed viscosity and dimension the modal structure of the coupled resonant system is retained as the sound field in the conduit propagates into the surrounding bedrock and the overlying atmosphere the source time function permits estimates of the total mass injected or removed from the magmatic system and the source spectrum acts as a band pass filter on the resonant modes of the conduit theoretical or empirical source functions can be used to drive the seismoacoustic wave field and the amplitude of the source velocity may be constrained by the ballistics of pyroclasts and the height of ash plumes the acoustic properties of the melt may be predicted from the temperature composition and flow conditions of the magma as a function of depth comparisons of synthetic waveforms and spectra with those of seismic and acoustic signals recorded on active volcanoes permit estimates of the conduit geometry density sound speed and attenuation properties of the melt and characterize the temporal and spectral features of the source function the ability to extract this information accurately and efficiently from seismic and acoustic data streams may permit near real time modeling of fluid driven processes in active volcanoes

seismoacoustic investigations of paroxysmal activity at mt etna volcano new insights into the 16 november 2006 eruption 1 on 16 november 2006 a 1 day long paroxysmal eruption occurred at the summit craters of mt etna volcano a multiparametric approach consisting of analyzing infrasonic seismic and video camera recordings was carried out to follow its evolution volcanological and geophysical observations identified three eruptive phases in the first phase infrasonic and seismic characteristics reflected the highly explosive nature of the activity waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of southeast crater sec during the second phase results highlighted the decoupling between seismic and infrasonic sources which was due to the decrease in explosive activity and the reactivation of effusive vents located south of bocca nuova and on the saddle between bocca nuova and sec the third phase was the most intense and was characterized by various volcanic phenomena pyroclastic flows jets of dark ash and white steam the very high radiated infrasonic energy together with infrasound event features led us to infer a gas enrichment of the shallow magma column preceding by a few minutes and likely related to the pyroclastic flows in the sec area after the eruption at sec variations in infrasound events related to the activity of northeast crater nec were found the observed spectral changes and the source mechanism modeling of the nec infrasound events suggest the existence of a link in the plumbing system feeding the two craters

a spherical source model for low frequency volcanic earthquakes a resonant magma chamber is modeled by a spherically symmetric whole space consisting of a small gas filled chamber surrounded by magma which is encased in country rock source boundary conditions are specified on the cavity boundary simulating a possible sudden gas expansion in the magma the simplicity of this model leads to an analytical closed form solution for the fourier transform of radial displacement which predicts a peaked spectrum and an oscillating decaying seismogram for physically reasonable values of the rock and magma elastic properties and dimensions of the model the dominant frequency of the signal is in the range of 1 to 5 hz near the values observed for low frequency volcanic earthquakes and volcanic tremor furthermore the seismograms and spectra bear resemblance to those observed for low frequency earthquakes the fundamental mode of oscillation is a pure radial breathing mode which has markedly different properties from single cavity solutions the fundamental frequency is insensitive to the magma chamber boundary radius when both the inner and outer radii are greater than specified values this may help to explain the apparent similarity of the dominant frequency of volcanic earthquakes over a wide range of physical situations the presence of an inner effective bubble of a certain minimum size is necessary for the existence of the dominant low fundamental frequency spectral peak although highly idealized we believe that this fundamental fluid solid cavity mode may provide an explanation for the observations of tremor and low frequency volcanic earthquakes

cl bearing fluorcalciobritholite in high ti basalts from apollo 11 and 17 implications for volatile histories of late stage lunar magmas

initial constraints on the timing of granitic magmatism in north korea using u pb zircon geochronology abstract the geology of north korea is very poorly known in this paper twenty seven granitic samples from the tumangang belt and the rangnim massif including diorite granodiorite and monzogranite were selected for in situ zircon u pb isotopic dating in the tumangang belt granites formed mainly in the jurassic with one sample giving a triassic age this is contrary to previous views that considered the granites to be permian to triassic in age in the rangnim massif precambrian granitic magmatism mainly took place at 2 1 and 1 9 1 8 ga no archean emplacement ages have been documented in this study although some inherited discordant zircon may be of this age mesozoic magmatism in this area can be divided into three stages with ages of 234 213 173 and 114 109 ma the triassic granites are mostly exposed in the north and the early cretaceous ones in the west the distribution of jurassic granites is less well documented and only one sample was identified in this study however previous data indicate they are more widely distributed in the area the 2 1 and 1 9 1 8 ga precambrian ages are comparable to paleoproterozoic magmatism in northeastern china indicating that the rangnim massif was most likely part of the north china craton during that time however the absence of 2 5 ga granites and the occurrence of 1 2 ga granites indicate that the rangnim massif was probably at the margin of the north china craton and affected by mesoproterozoic magmatism the similarity in age patterns of the mesozoic granites in north korea to surrounding areas of south korea and the liaodong peninsula of northeastern china indicate that they were controlled by subduction of the pacific ocean under eastern asia however roll back or retreat of the subduction zone resulted in a younging trend from northwest to southeast during the cretaceous

detrital zircon u pb ages of the jangsan formation in the northeastern okcheon belt korea and its implications for material source provenance and tectonic setting abstract the jangsan formation distributed in the taebaeksan basin central eastern korea is unfossiliferous and is composed of quartz arenite this formation is conventionally believed to be the lowermost stratigraphic unit of the lower paleozoic sequence deposited on the yeongnam massif in south korea corresponding to early cambrian in age u pb dating of detrital zircon grains using a laser ablation inductively coupled mass spectrometer yields ages ranging from archean to middle proterozoic 1738 67 ma to 3058 53 ma detrital zircons show no ages younger than 1 8 ga suggesting that the jangsan formation was deposited at some time after this age but much prior to ca 520 ma the depositional age of the immediately overlying myobong formation this interpretation is supported by the recent report on the presence of the unconformity between the jangsan and the myobong formations kim and lee 2006 zircon ages from jangsan sandstones define two major groups archean age grains with a maximum frequency at about 2 5 ga and paleoproterozoic age grains with maximum frequencies at about 2 1 and 1 8 ga the observed zircon age distribution in the jangsan sandstones may represent that of the yeongnam massif on which the jangsan formation was deposited such an age distribution of the yeongnam massif matches well with that the north china block suggestive of the yeongnam massif being a part of the sino korean craton during the precambrian

spectral analysis of harmonic tremor signals at mt semeru volcano indonesia a detailed spectral analysis of tremor signals recorded at mt semeru volcano indonesia in october 1992 by the german indonesian volcano expedition give 92 reveals clearly harmonic spectra containing up to 11 integer harmonics the spectral features can be explained by any rhythmically pulsating source producing a temporarily stable source signal as one realisation of this concept we model the source as a resonating gas volume generating seismic signals similar to the sound generated in a recorder

linking the sulu uhp belt to the korean peninsula evidence from eclogite precambrian basement and paleozoic sedimentary basins abstract considerable debate on whether and how the sulu orogenic belt extends eastward to the korean peninsula has remained over the past decade new results reported here include the following 1 an eclogite and retrograded eclogite bearing complex hongseong complex is discovered in south korea in which the eclogite occurs as lenses in circa 810 820 ma granitic gneiss shrimp zircon dating of the eclogite yields 230 ma for the metamorphic age and 880 ma for the protolith age 2 the basement of the rangnim gyeonggi and yeongnam massifs have affinities to the basement of the north china block ncb however the gyeonggi massif encloses a minor amount of large or small slabs of the hongseong complex that are similar to the rocks of the sulu belt 3 two main paleozoic basins within the rangnim and gyeonggi massifs have a similar paleozoic tectono stratigraphy to the ncb 4 the imjingang and ogcheon belts do not exhibit any metamorphic characteristics of collisional orogenic belts based on these facts we propose a crustal detachment and thrust model and suggest that the collision belt between the yangtze block yb and ncb sino korea craton is preserved along the western margin of the korean peninsula the lower part of the uhp metamorphosed lithosphere of the yb was subducted under the korean peninsula and not uplifted to the surface the lower crust of the yb the hongseong complex was detached from the subducted lithosphere and thrust over the korean peninsula and inserted into the basement rocks of the gyeonggi massif the upper crust of the yb possibly was detached from the lower crust and overthrusted along the honam and chugaryong shear zones the imjingang and ogcheon belts possibly represent the detached upper crust of yb and their present occurrences are controlled by a mesozoic strike slip shear structure all these detached lower and upper crustal slabs were strongly deformed during the late jurassic and early cretaceous tectonic event leading to their present geological distribution and characteristics

volcanic tremor and frequency gliding during dike intrusions at kilauea a tale of three eruptions to characterize syneruptive intrusive deviations from background volcanic tremor at kilauea hawai i we analyze the spatial and temporal properties of broadband tremor during dike intrusions into the east rift zone erz in 2007 and 2011 as well as during explosive eruptive activity at kilauea s summit in 2008 background tremor was similar for each event and the 2008 explosions did not affect its properties in contrast the intrusions were accompanied by departures from this background in the form of two phases of seismicity that were separated in space and time in both 2007 and 2011 phase i was characterized by a quick succession of discrete events which were most intense at the onset of intrusion near the presumed locations of the dikes intruding into the erz phase ii marked by continuous broadband tremor around the summit followed 10 14 h later in 2007 phase ii tremor was accompanied by a monotonic downward shift glide of spectral peaks between 0 6 and 1 5 hz over at least 15 h during phase ii in 2011 a gradual upward and subsequent symmetric downward glide between 0 6 and 6 6 hz occurred over 5 10 h respectively the spectra during both phases differed from the background and 2008 as well as from each other indicating different physical mechanisms phase i in 2007 and 2011 is probably related to the mechanics of dike intrusion phase ii tremor may be characteristic for evolving magma bubble dynamics related to the geometry of the plumbing system and the style of magma flow

nd isotopic study of precambrian basement of south korea evidence for early archean crust we carried out a sm nd isotopic reconnaissance study of south korea eight river sediments gave crustal residence ages t dm between 1 7 and 2 7 ga implying that on average the crust of south korea was formed in early to middle proterozoic time twenty six precambrian basement rocks yielded t dm between 1 4 and 3 8 ga more than half of them exceed 2 5 ga indicating that south korea has a long history of crustal evolution four of the samples have t dm from 3 2 to 3 8 ga suggesting the possibility that there may be ancient continental crust in korea having ages comparable to those of the oldest cratons in the world however these samples also have preferentially higher sm nd so their old ages could be artifacts thus requiring confirmation the large variation in t dm of south korea is reminiscent of that for the south china block however the existence of early archean ages better matches that of the north china block because the basement of south china was thought to be mostly proterozoic in age the recent discovery of rare archean basement rocks in the south china block may favor models that attempt to correlate south korea with south china

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes

neoproterozoic 900 ma sariwon sills in north korea geochronology geochemistry and implications for the evolution of the south eastern margin of the north china craton article the sariwon sills are distributed in the pyongnam basin at the center of the korean peninsula eastern part of the north china craton these sills are up to 150 m in thickness and up to more than 10 km in length baddeleyite grains separated from a 50 m thick sill give a sims 206 pb 207 pb age of 899 7 ma mswd 0 34 n 14 which is interpreted to be the crystallization age of this sill zircon grains from the same sill gives a lower intercept u pb age of 400 ma which is likely a close estimation of the greenschist facies metamorphism of this sill the sariwon sills are dolerites and have tholeiitic compositions they show enrichment of light rare earth element concentrations la ybn 1 4 2 8 and are slightly depleted in high field strength elements e g nb zr and ti in comparison to neighboring elements on the primitive mantle normalized spidergram the whole rock endt t 900 ma values are around 2 whereas in situ ehft t 900 ma values from zircon grains vary from 25 to 8 they are similar to the coeval sills in other parts of the north china craton e g the chulan sills xu huai basin shandong peninsula and the dalian sills lv da basin liaodong peninsula these sills possibly originated from a depleted mantle source e g asthenosphere rather than from the ancient lithospheric mantle of the north china craton and have experienced significant assimilation of lithospheric materials the strata and sills in the xu huai lv da and pyongnam basins are comparable moreover the three basins are geographically correlatable based on neoproterozoic geographical reconstruction we therefore propose that there is a xu huai lv da pyongnam rift system along the south eastern edge of the north china craton during neoproterozoic 900 ma with the closure of the rift at 400 ma as a result of a continent margin process it is possible that this southeastern margin of the ncc did not face the inland in the configuration of the supercontinent rodinia

three distinct regimes of volcanic tremor associated with the eruption of shishaldin volcano alaska 1999 tremor signals associated with the eruption of shishaldin volcano on 19 and 23 april 1999 were the strongest recorded anywhere in the aleutian arc by the alaska volcano observatory avo in its 10 year history reduced displacements dr reached 23 cm2 on 19 april and 43 cm2 on 23 april during the activity dr and spectral data with a frequency resolution of 0 1 hz were computed and put on the world wide web every 10 min these data are analyzed here the general temporal patterns of seismicity of these eruption events were similar but the eruptions and their effects quite different the 19 april event is known to have culminated in a sub plinian phase which ejected ash to an altitude of 16 km despite higher amplitudes and the largest hotspot from satellite data the 23 april event produced little ash reaching only 6 km altitude for several hours prior to the sub plinian phase on 19 april tremor with a peak frequency of 1 3 hz intensified during the sub plinian phase the peak frequency increased to 4 8 hz however in 15 h after the eruption three episodes of stronger tremor occurred with a lower 1 0 hz peak alternating with weaker tremor with a 1 3 hz peak these transitions correspond to dr 8 cm2 although these strong tremor episodes produced higher dr levels than the sub plinian phase data from a pressure sensor show that only strong strombolian explosions occurred the suite of observations suggests three distinct tremor regimes that may correspond to slug flow bubbly flow and sustained strong eruptions or a cyclic change in source parameters e g geometry sound speed or ascent rate this behavior occurred at shishaldin only during the april 1999 sequence and we are not aware of similar behavior at other volcanoes