provenance of jurassic sediments in the hefei basin east central china and the contribution of high pressure and ultrahigh pressure metamorphic rocks from the dabie shan abstract the provenance of the jurassic sediments in the hefei basin is constrained by compositions of the detrital k white micas and garnets and shrimp dating of the detrital zircons which can help to understand the evolution and to reconstruct the paleogeographic distribution of hp uhp rocks in the jurassic dabie shan 1 for the oldest mesozoic sediments at the bottom of the fanghushan formation j 1 the predominance of the early paleozoic and luliang 1700 1900 ma zircons indicates a major source from the north china block however neoproterozoic zircons as the major component in other jurassic sediments indicate that the source rocks were mainly derived from the exhumed yangtze block in the dabie shan 2 the co occurrence of high si phengites and triassic zircons provides stratigraphic evidence that the first exposure of the uhp rocks at the earth s surface in the dabie shan occurred in the early jurassic during deposition of the fanghushan formation 3 from the east to the west of the hefei basin there is a spatial variation in the compositions for detrital micas and garnets and in the u pb ages of detrital zircons evidently hp uhp rocks were widely distributed at outcrop in the eastern dabie shan in contrast they were less important in the western dabie shan during the jurassic

ultrahigh pressure texture inheritance during retrogression evidence from magnetofabrics in eclogites and ultramafic rocks chinese continental scientific drilling project abstract in order to contribute to a better understanding of exhumation related retrogression processes ultrahigh pressure uhp mafic and ultramafic rocks from the chinese continental scientific drilling ccsd in the maobei eclogite body of the sulu ultrahigh pressure metamorphic belt in eastern china were studied for their magnetofabrics variably retrogressed eclogites and serpentinized ultramafic rocks were retrieved from the depth interval of 100 to 1000 m of the borehole a vein network of irregular shaped veins with a retrograde metamorphic assemblage cuts across the eclogite foliation at both low and high angles sem imaging of the eclogites documents that magnetite associated with retrograde pargasitic amphiboles developed around shape preferred garnet sem imaging of the serpentinized ultramafic rocks documents that magnetite rims grew around shape preferred garnet and that magnetite formed within a mesh texture related to serpentinization syn serpentinization magnetite growth increased bulk susceptibilities but reduced anisotropy maximum susceptibility axes from both eclogites and serpentinized garnet peridotites trend n s i e parallel with the stretching lineation as defined by olivine and omphacite grains this implies that the magnetic fabric mimics the uhp fabric and survived retrogression and that the fabric is inherited from the uhp stage as a consequence retrogression was not associated with substantial ductile deformation and the mafic ultramafic maobei body behaved as a rigid body within a ductile deforming quartzo feldspathic matrix during exhumation internal strain is restricted to brittle fracturing associated fluid circulation and vein formation facilitating retrograde reactions in the mafic ultramafic rocks

geometrical effects and low attenuation resonance of volcanic fluid inclusions for the source mechanism of long period earthquakes 1 we formulate the resonances of three simple geometrical inclusions a plane a cylinder and a sphere and find several clues to distinguishing the shape of volcanic fluid systems and their relevance to the observation of long period earthquakes the series of eigenfrequencies for a cylindrical and a spherical inclusion have shifts of 4 and 2 respectively in their higher modes from the eigenfrequencies of a planar inclusion the ratios between the higher and fundamental characteristic frequencies can be indicators of the geometry of volcanic fluid inclusions furthermore the eigenattenuation factor of a planar inclusion is a constant value that is determined uniquely by the impedance contrast between the fluid and the surrounding elastic medium and is independent of mode in marked contrast cylindrical and spherical inclusions have smaller or greater eigenattenuation factors particularly in lower modes under certain conditions of p wave velocity contrast and poisson s ratio of the surrounding elastic medium lower modes have less than 0 1 times the attenuation factor of higher modes we name these low attenuation modes lams lams are physically related to the conversion of volumetric changes to shear deformation of the surrounding elastic medium and the radiation of shear waves from the curved boundaries some monotonic waveforms of long period earthquakes can be interpreted by the excitation of these lams crack modes are also simply formulated by the resonance of a rectangular inclusion and also become lams whose attenuation factors are related to the aspect ratio of the crack

microstructure and magnetic susceptibility applied to emplacement kinematics of granites the example of the foix pluton french pyrenees abstract the variscan foix granite 40 km 2 central pyrenees was subjected to detailed microstructural magnetic susceptibility and anisotropy studies magnetic susceptibility is shown to be of dominant paramagnetic origin its magnitudes clearly define a zoning which compares with the petrographic zoning and reveals that the pluton is the southern remnant of a normally zoned pluton truncated during alpine tectonics magnetic susceptibility anisotropy characterizes the planar and linear preferred orientations of the main iron bearing silicates namely biotite and accessory amphibole it is argued that these fabrics also reflect the flow pattern of the granite microstructural observations aid in distinguishing the magmatic and late magmatic fabric signatures main body from the post magmatic solid state signature leucogranite in order to account for the consistently subhorizontal and ne sw directed magmatic lineations in the northern sector of the foix granite an oblique intrusion is proposed it may be coeval with the early variscan regional sw trending shearing event steepening of the structures in at least part of the southern sector may be coeval with the late development of upright folds and vertical cleavage in the country rocks the utility of combined microstructural and magnetic susceptibility studies is demonstrated as an aid in the structural interpretation of granite intrusions which act as kinematic markers of their host terranes

tornillos at vulcano clues to the dynamics of the hydrothermal system abstract the number of tornillo events has recently increased at the vulcano island italy while only 15 tornillos were recorded during 2004 2006 584 events occurred in 2007 2008 they were located just below la fossa crater at depths ranging between 0 1 and 1 km b s l during two intervals in 2007 2008 increases in the number of tornillos took place at the same time as temperature and geochemical anomalies were observed the spectral content of the tornillos generally characterized by one two dominant spectral peaks near 6 and 10 hz varied over time with changes also noted in the quality factors the simplest source mechanism proposed for tornillos is the free eigenvibration of a fluid volume within a crack or a conduit based on this model we propose a causal relationship between the temperature and geochemical anomalies and the increases in numbers of tornillos as the amount of hydrothermal fluids increases during the anomalies the upward flux of fluids grows the consequent changes in the pressure temperature and dynamics of the system of cracks and conduits result in the generation of tornillos based on the fluid filled crack conduit model the shallow depths of the sources and the values of the quality factors the fluid within the resonant crack conduit was inferred to be an ash gas or water droplet gas mixture moreover the observed variations in the wavefield can be caused by small changes in the location of the source in the source mechanism or in the medium in between the source and the seismic station finally another peculiar feature of tornillos is the amplitude modulation that can be explained as a result of a beating phenomenon

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

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project i petrology and geochemistry of the main hole 0 2 050 m the main hole mh of the chinese continental scientific drilling project ccsd in southern sulu has penetrated into an ultrahigh pressure uhp metamorphic rock slice which consists of orthogneiss paragneiss eclogite ultramafic rock and minor schist recovered eclogites have a uhp metamorphic mineral assemblage of garnet omphacite rutile phengite kyanite coesite epidote ultramafic rocks contain garnet olivine clinopyroxene orthopyroxene ti clinohumite phlogopite gneisses and schists contain an amphibolite facies paragenesis but their zircons have coesite garnet omphacite or jadeite and phengite inclusions indicating that eclogites and gneisses have been subjected to in situ uhp metamorphism using available geothermobarometers p t estimates of 3 1 4 4 gpa and 678 816 c for eclogites were obtained if surface outcrops and neighboring shallow drill holes are considered together we suggest that a huge supracrustal rock slab 50 km long 100 km wide 5 km deep was subducted to a depth 100 km and then exhumed to the surface the depth interval 0 2 050 m of the ccsd mh can be divided into six lithological units unit 1 consists of alternating layers of quartz rich and rutile rich eclogites with thin interlayers of gneiss and schist eclogites of unit 1 are characterized by nb ta sr and ti depletions low mg number and general lree enrichment unit 2 comprises rutile and ilmenite rich eclogite and minor normal eclogite and is characterized by high tio2 total fe v co and sr and very low sio2 alkali zr ba nb ta and total ree contents and lree depleted ree patterns with slightly positive eu anomalies unit 3 contains ultramafic rock and minor mgo rich eclogite protoliths of uhp rocks from units 1 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth units 4 and 6 consist of interlayered eclogite and paragneiss the eclogites are characterized by th u nb ta and ti depletion and k enrichment and lree enriched ree patterns paragneisses show nb ta sr and ti depletions and lree enriched ree patterns occasionally with slightly negative eu anomalies indicating that their protoliths represent metamorphic supracrustal series unit 5 consists mainly of orthogneisses showing distinct nb ta sr and ti depletions and lree enriched ree patterns with pronounced negative eu anomalies suggesting granitic protoliths in conclusion it is proposed that the southern sulu uhp belt consists of a series of meta supracrustal rocks a layered mafic ultramafic complex and granites

exhumation of the ultrahigh pressure continental crust in east central china cretaceous and cenozoic unroofing and the tan lu fault the orogenic architecture of the world s largest ultrahigh pressure exposure the hong an dabie mountains of the triassic qinling dabie orogenic belt is dominated by cretaceous and cenozoic structures that contributed to its exhumation from 30 km depth cretaceous magmatic crustal recycling 50 for the entire dabie and heating 250 to 700 c were most prominent in dabie and exhumation magmatism and cooling were all controlled by cretaceous transtension exhumation was accomplished principally by an asymmetric cordilleran type extensional complex in the northern dabie northern orthogneiss unit between 140 and 120 ma at rates as fast as 2 mm yr and average horizontal stretching rates of up to 6 mm yr cretaceous reactivation occurred within a regional transtensional strain field as a result of far field collisions and pacific subduction the onset of crustal extension was preceded and possibly facilitated by a reheating of the hong an dabie crust 140 ma coeval with the onset of voluminous magmatism in eastern china 145 ma which resulted from a change in pacific subduction from highly oblique to orthogonal the tan lu continental scale fault was a normal fault zone in the mid cretaceous 110 90 ma and underwent 5 4 km dip slip and 4 km throw in the cenozoic during the india asia collision the qinling dabie belt acted as the structural discontinuity between the strike slip dominated escape tectonics south of the qilian qinling dabie belt and the rifting dominated tectonism north of it the most prominent cretaceous and cenozoic structures of the hong an dabie the xiaotian mozitang and the jinzhai fault zones respectively reactivated major lithospheric structures of the triassic orogen i e the huwan detachment zone and the suture

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

magnetic fabrics in deformed metaperidotites of the outokumpu deep drill core finland implications for a major crustal shear zone abstract the outokumpu oku assemblage was studied in drill cores from the 2516 m deep oku deep drill hole finland and we observed that the strongest magnetic anomalies found in borehole measurements are related to three ferrimagnetic metaperidotite units with magnetic susceptibilities of up to 93 10 3 si separated by paramagnetic rock units the main ferrimagnetic minerals are magnetite and minor pyrrhotite magnetic fabric studies were done in order to examine deformation within the oku assemblage during the collisional deformation event 1 9 ga ago well defined magnetic axes kmax kmin and nearly horizontal magnetic foliation subparallel to the macroscopic foliation occur at the top and the bottom of the oku formation low and high field ams measurements showed that ferri and paramagnetic subfabrics are coaxial paramagnetic units intercalated between the ferrimagnetic units show mostly triaxial magnetic fabrics and low degrees of magnetic anisotropy values p 0 ferrimagnetic unit 2 shows the highest magnetic susceptibility and p up to 5 6 which is related to a high amount of magnetite and pyrrhotite mostly concentrated in huge aggregates and veins alignment of magnetic minerals parallel with the structural foliation and the high p values in the ferrimagnetic metaperidotite indicate that magnetic fabric was acquired in a high strain zone the magnetic fabrics represent shear zone sc fabrics which have been formed during early obduction related deformation of the svecofennian orogeny the stacked sequence of the ferri and paramagnetic metaperidotite bodies can be interpreted as a thrust system with an imbricate fan in which three individual listric thrust sheets occur this interpretation is in accordance with previous tectonic models of the outokumpu area

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project ii oxygen isotope and fluid inclusion distributions through vertical sections in order to reconstruct the formation and exhumation mechanisms of uhp metamorphic terrains the chinese continental scientific drilling program ccsd has been carried out in donghai of the dabie sulu ultrahigh pressure uhp metamorphic belt east china eclogite gneiss amphibolite retrograded from eclogite ultramafic rocks and minor schist and quartzite have been drilled aiming to reveal the fluid behaviour in a vertical sequence of an uhp slab we investigated fluid inclusion and oxygen isotope characteristics of selected drillcores from the main hole and the pilot holes pp2 and zk 703 of the ccsd more than 540 laser ablation oxygen isotope analyses on garnet omphacite quartz kyanite amphibole phengite rutile epidote amphibole plagioclase and biotite from various rocks in the depth range of 0 3 000 m mainly eclogite and gneiss show that the investigated rocks can be divided into two groups 18o depleted rocks as low as 18o 7 4 for garnet indicate interaction with cold climate meteoric waters whereas 18o normal rocks with bulk 18o 5 6 have preserved the o isotopic compositions of their protoliths meteoric water rock interaction has reached depths of at least 2 700 m oxygen isotope equilibrium has generally been achieved isotopic compositions of mineral phases are homogeneous on a mm to cm scale regardless of lithology but heterogeneous on the scale of a few metres oxygen isotope distributions in the vertical sections favour an in situ origin of the uhp metamorphic rocks the very negative 18o eclogites usually have higher hydroxyl mineral contents than the normal 18o rocks indicating higher water content during uhp metamorphism fluid inclusion data suggest that rocks with depleted 18o compositions have had different fluid histories compared to those with normal 18o values rocks with depleted 18o mainly have primary medium to high salinity inclusions in omphacite kyanite and quartz and abundant secondary low salinity or pure water inclusions in quartz indicating a high salinity brine dominated fluid system during peak uhp metamorphism no carbonic inclusions have been identified in these rocks by contrast primary very high density co2 inclusions are commonly found in the rocks with normal 18o values these observations suggest that fluid and oxygen isotope composition of minerals are related and reflect variable degrees of alterations of the dabie sulu uhp metamorphic rocks

a synthesis of the recent activity of galeras volcano colombia seven years of continuous surveillance 1989 1995 abstract the current period of re activation since 1988 at galeras volcano colombia has been characterized mainly by the following events 1 a semi continuous series of vulcanian eruptions during 5 9 may 1989 2 emplacement of an andesitic lava dome at the bottom of the main crater in october november 1991 3 six vulcanian eruptions during 1992 1993 the first of which destroyed most of the dome on 16 july 1992 and 4 three volcano tectonic seismic crises in april 1993 november december 1993 and march 1995 during much of this seven year period several small ash and gas emissions also have taken place the 4 9 may 1989 eruptions originated from the secondary crater el pinta and deposited ash lapilli and blocks in the crater area the 1992 1993 eruptions originated from the main crater and were associated with obstruction of the conduit by magma from dome emplacement in late 1991 causing overpressurization of the system for the 1992 1993 eruptions pre eruptive seismicity deformation and so2 flux all exhibited very low levels the eruptions were characterized by their sudden initiation low intensity vei 1 small eruption columns and small volumes of erupted material the source of the volcano tectonic seismic crises is located approximately 3 km north and northeast of the crater some of these events were felt in pasto and other towns located around the volcano on one occasion causing loss of life injuries and damage to buildings

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

magnetic properties of serpentinized garnet peridotites from the ccsd main hole in the sulu ultrahigh pressure metamorphic belt eastern china 1 magnetic properties of 14 serpentinized garnet peridotites from the interval of 603 20 683 53 m of the chinese continental scientific drilling ccsd hole in the sulu ultrahigh pressure uhp metamorphic belt eastern china were investigated and compared with those of ultramafic rocks from other tectonic settings to relate them to the uhp post metamorphic evolution serpentinized garnet peridotites are characterized by high susceptibility natural remanent magnetization nrm and q koenigsberger ratio nrm h where h is the intensity of the local geomagnetic field values the average nrm and q values are 299 65 10 7 m3 kg 1 19 15 10 3 am2 kg 1 and 16 59 respectively which are generally higher than those of other serpentinized peridotites in the world the serpentine concentration for most samples ranges from 40 to 60 suggesting that the peridotites are of obvious homogeneous serpentinization degree micro raman and x ray diffraction spectra of serpentine for representative samples indicate that lizardite is the only serpentine mineral opaque minerals in samples are mainly nonstoichiometric magnetite and cr spinel with or without minor ilmenite and fe sulfide magnetite occurs as rims around olivine and garnet as well as in clusters a chromian garnet further overgrew on the rims of the garnet the grain size of magnetite in rims is in the pseudo single domain region and favorable for development of high nrm high pressure uhp metamorphic processes possibly lead to enhanced concentrations of fe ti oxides in garnet peridotites and thus increase the magnetism of serpentinized garnet peridotites in the ccsd main hole integrated lizardite formation temperature 450 c and its relationships with the pressure temperature time evolution of the associated uhp rocks permit us to infer that serpentinization of garnet peridotites in the ccsd main hole occurred during late exhumation stages ca 200 215 ma ago under temperatures of 425 c however the exact relationship between magnetic properties of garnet peridotite and the uhp metamorphic process will require further studies

magnetic susceptibility zonation of the melilititic riedheim dyke hegau volcanic field germany evidence for multiple magma pulses the olivine melilitic riedheim dyke complex is related to the tertiary alkaline magmatism within the hegau volcanic field magnetic susceptibility measurements and the mineral composition of oxides together with petrographic observations imply two phases of magma intrusion for the emplacement of this dyke the first intrusion forms the eastern and western margins of the dyke section with high magnetic susceptibility values of up to 75 10 3 si which are related to ferrimagnetic mg al cr bearing titanomagnetites with a magnetite component between 0 59 and 0 75 mol a generally lower magnetic susceptibility of up to 45 10 3 si and a significantly lower and homogeneous magnetite component of the titanomagnetites xmt 0 38 mol are recorded for the second intrusion into the central part of the dyke furthermore a dependence of magnetic susceptibility on the amplitude of the ac field was measured which is more pronounced in the second intrusion hd 25 than in the first one 6 hd 10 confirming the magneto mineralogical data secondary pervasive alteration is more pronounced in the first intrusion phase characterised by a very fine grained and glassy matrix that is more receptive to hydrothermal overprint than the well crystallised matrix of the second intrusion localised thermally induced alteration at the intimately fractured contact between the first and second intrusion phase has oxidised the titanomagnetite of the first intrusion phase but did not significantly effect the second intrusion differences between the dyke sections are also documented by the anisotropy of magnetic susceptibility ams which reflects a magmatic flow fabric with long axis of the ams ellipsoids magnetic lineation parallel to the flow direction and short axis normal to the n s trending dyke boundary the orientation of the magnetic fabric for the individual magma pulses is different with a more moderate plunge of the magnetic lineation within both the western 177 57 and eastern parts 181 50 of the first dyke intrusion compared to a nearly vertical orientation in the second central dyke intrusion 180 78 we suggest that the primary crystallisation history of the two intrusion phases caused the magnetic susceptibility zonation in the riedheim dyke complex

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

curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods 1 the present study is aimed at improving the calibration of the compositional dependence of the curie temperature tc of titanomagnetite tmt on the basis of temperature dependent magnetic susceptibility c t curves measured on synthetic tmts in the fe ti o system in order to assess the possible influence of high temperature cation vacancies onto the tc values we have synthesized two types of assemblages in subsolidus conditions at 1 bar 1100c and 1300c under controlled oxygen fugacity conditions tmts synthesized in equilibrium with ilmenite hematitess ilmss are expected to have the highest vacancy concentrations those in equilibrium with wustite wus the lowest the composition and homogeneity of the synthetic tmts were carefully checked with a scanning electron microscope sem and an electron microprobe emp tc was determined from c t curves using a kappabridge and for comparison from ms t curves measured with a variable field translation balance our data set shows systematically higher tc values for tmt coexisting with ilmss than for tmt coexisting with wus most c t curves are nonreversible whereby the largest dtc 40 k concern tmt ilmss o f intermediate compositions synthesized at 1300c nonreversibility is interpreted as reflecting cation reordering in tmt during the high temperature c t measurements tc values obtained from ms t curves are higher than those obtained from the c t curves whereby the difference regularly increases up to 40 k with increasing ti content up to xusp 0 6 our new calibration curves are suitable to retrieve tmt compositions in basalts that were rapidly cooled and not oxidized by deuteric or hydrothermal fluids citation lattard d r engelmann a kontny and u sauerzapf 2006 curie temperatures of synthetic titanomagnetites in the fe ti o system effects of composition crystal chemistry and thermomagnetic methods j geophys res 111 b12s28

geochronology and isotopic character of ultrahigh pressure metamorphism with implications for collision of the sino korean and yangtze cratons central china the collision zone between the sino korean and yangtze cratons in central china is marked by subduction related metamorphic rocks composed of crustal protoliths these range in metamorphic grade from ultrahigh pressure eclogite to low greenschist facies the paragenesis of the ultrahigh pressure rocks coesite and diamond bearing indicates subduction to depths greater than 120 km as a result of continental collision despite extreme metamorphic conditions zircons have not undergone pb loss but rather illustrate two periods of growth crystallization between 700 and 800 ma and ultrahigh pressure metamorphism at 218 2 5 ma previous studies have predicted a time transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture u pb zircon ages of these ultrahigh pressure metamorphic rocks are 218 4 2 5 ma and 217 1 8 7 ma for the dabie mountains and shandong peninsula respectively the similar ages imply that the tan lu fault which offsets the ultrahigh pressure metamorphic rocks is a secondary feature not related to collision or subduction whole rock isotopic data show that both rb sr and u pb were open systems during metamorphism but that sm nd probably remained closed nd initial isotopes display crustal signatures indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth sm nd data in conjunction with u pb zircon dating indicate that the ultrahigh pressure rocks are not typical yangtze craton basement 2 9 ga but that they originally crystallized in a rift environment between 700 and 800 ma discrepancies between 40ar 39ar plateaus sm nd isochrons and u pb zircon ages render calculation of a p t t path unrealistic

high temperature geochronology constraints on the tectonic history and architecture of the ultrahigh pressure dabie sulu orogen 1 new u pb zircon and th pb monazite ages are presented from the giant sulu ultrahigh pressure uhp terrane combined with sm nd ages rb sr ages inclusion relationships and geologic relationships they help define the timing of peak recrystallization the timing of subsequent amphibolite facies metamorphism and the architecture of the dabie sulu suture zone between the collided sino korean and yangtze cratons the data indicate a 15 myr record of uhp recrystallization the first clearly documented for a giant uhp terrane this requires that continental subduction in the dabie sulu orogen involved multiple uhp tectonic or recrystallization events a 244 236 ma precursor uhp event seen only in the dabie shan was followed by a second 230 220 ma main uhp event which was itself terminated by a 220 205 ma amphibolite facies overprint older eclogite facies events seen in the qinling segment of this orogenic belt raise the possibility that these rocks have undergone u hp metamorphism three or four times but at present there is no geochronological evidence in the dabie sulu area to support this the subduction of the lower yangtze plate did not proceed in a simple fashion the ages of inherited zircon cores demonstrate that a ribbon continent of yangtze affinity escaped subduction and became wedged against the sino korean plate hanging wall

role of partial melting in the evolution of the sulu eastern china ultrahigh pressure terrane strongly deformed potassium feldspar rich dikes are widely distributed in the northern part of the sulu ultrahigh pressure uhp metamorphic terrane eastern china the fact that the crystallization ages of these dikes overlap with the age of peak uhp metamorphic conditions implies the presence of melt during metamorphism sr isotopic ratios of the dikes are compatible with their origin as partial melts of the dominant felsic sulu gneiss partial melting may be the key to solving several unusual features of the sulu and other uhp terranes such as the almost complete lack of mineralogical evidence for uhp conditions and the limited growth of zircon during uhp conditions in the dominant felsic gneiss in addition because partial melting will cause a drastic reduction in the strength of the uhp gneisses the most likely exhumation mechanism is diapiric rise of a low viscosity partially molten mass containing entrained blocks of eclogite and not a thin sheet as usually proposed

gas slug ascent through changes in conduit diameter laboratory insights into a volcano seismic source process in low viscosity magmas seismic signals generated during the flow and degassing of low viscosity magmas include long period lp and very long period vlp events whose sources are often attributed to dynamic fluid processes within the conduit we present the results of laboratory experiments designed to investigate whether the passage of a gas slug through regions of changing conduit diameter could act as a suitable source mechanism a vertical liquid filled glass tube featuring a concentric diameter change was used to provide canonical insights into potentially deep or shallow seismic sources as gas slugs ascend the tube we observe systematic pressure changes varying with slug size liquid depth tube diameter and liquid viscosity gas slugs undergoing an abrupt flow pattern change upon entering a section of significantly increased tube diameter induce a transient pressure decrease in and above the flare and an associated pressure increase below it which stimulates acoustic and inertial resonant oscillations when the liquid flow is not dominantly controlled by viscosity net vertical forces on the apparatus are also detected the net force is a function of the magnitude of the pressure transients generated and the tube geometry which dictates where and hence when the traveling pressure pulses can couple into the tube in contrast to interpretations of related volcano seismic data where a single downward force is assumed to result from an upward acceleration of the center of mass in the conduit our experiments suggest that significant downward forces can result from the rapid deceleration of relatively small volumes of downward moving liquid

seismic precursors of the february 10 1990 eruption of kelut volcano java abstract kelut volcano eastern java indonesia erupted on february 10 12 1990 seismic activity and an increase of temperature and acoustic noise in the crater lake appeared three months before the eruption and were the main precursory signs of this eruption during the pre eruptive stage the number of events was eight per day on average and the cumulative seismic energy released was 5 6 10 15 erg these low values are uncommon for an andesitic volcano seismic activity mainly consisted of swarms of very shallow volcano tectonic earthquakes many of which were part of seismic multiplets in the last three weeks before the eruption seismic activity remained at a very low level this quiescent period was followed 24 hours prior to the eruption initiation by an intense swarm of low energy events which progressively became continuous spasmodic tremor most of the data obtained during the pre eruptive stage are consistent with a process of fracturation of a shallow and low strength plug blocking the eruptive conduit before the eruption several observations suggest that water is an important element in the preeruptive and eruptive phenomena at kelut volcano in particular the monochromatic events observed at kelut are characterized by one narrow peak in their spectra the estimations of q value and impedance contrast for these events suggest that the fluid which fills the source resonator could be water

influence of detachment layer thickness on style of thin skinned shortening abstract there are several parameters which may determine whether detachment folds or thrust faults develop in thin skinned compressional systems a fundamental but little publicised parameter is apparent from consideration of detachment fold growth as a detachment fold amplifies its core must be filled by redistribution of ductile material if the mobile material were insufficient to supply the volume required by the fold core through redistribution fold growth would be inhibited and eventually faulting would occur the volume of a detachment fold core is compared here with the volume of available underlying mobile material for various amounts of shortening and sizes of fold the occurrence of detachment folds versus thrusts in several compressional belts is successfully predicted by this relationship

observations of volcanic tremor at mount st helens volcano digital recordings of ground motion during tremor episodes accompanying eruptions at mount st helens volcano in the state of washington on august 7 and october 16 18 1980 are studied the spectra of the vertical component waveforms contain at least two dominant peaks at 1 0 and 1 3 hz for all events recorded during both eruptions that were studied spectra of horizontal ground motion show peaks at 0 9 and 1 1 hz the relative amplitude of the two peaks changes between tremor episodes and during single tremor episodes and shows no consistent relation to amplitude of ground motion spectra of long period earthquakes are very similar to those of tremor events suggesting that tremor is composed of many long period earthquakes that occur over a period of time the unique waveform of tremor events observed at mount st helens must be due to a source effect since the relative amplitude of the two dominant peaks changes during tremor episodes the path effect on tremor waveforms is small since there are no peaks in the spectra of waveforms recorded during tectonic earthquakes occurring in the vicinity of mount st helens the consistency of the location of the spectral peaks for the wide range of tremor amplitudes means that there must be a physical length at the source that is constant independent of the amplitude of motion at the source variations in amplitude of motion generated during tremor events must be due to variations in the force driving the tremor amplitudes of ground motion varies between 0 11 and 4 7 m seismic moment rates during the two eruptions are calculated using the model of aki et al 1977 and found to vary between 6 1018 and 1 1020 dynes cm s 1 which are larger than values found by aki et al 1977 who studied amplitudes of shallow tremor events recorded during the october 1963 eruption of kilauea volcano in hawaii study of tremor amplitudes recorded at corvallis oregon leads to the conclusion that tremor accompanying the cataclysmic may 18 1980 eruption was at least one order of magnitude larger in amplitude than tremor during august and october

magnetic properties of ultrahigh pressure eclogites controlled by retrograde metamorphism a case study from the zk703 drillhole in donghai eastern china parallel studies on rock magnetic properties petrology and mineralogy were conducted on 16 eclogite samples from the zk703 hole and magnetic susceptibilities and densities of 41 eclogite samples with different degree of retrograde metamorphism from fresh eclogite to fully retrograded eclogite from the chinese continental scientific drilling ccsd near the zk703 hole located at donghai southern sulu ultrahigh pressure metamorphic belt eastern china results show 1 that the high field slopes obtained from the hysteresis loops the paramagnetic fraction para and density have a positive correlation with the volume concentration of garnet omphacite a typical mineral assemblage used to semi quantify the degree of retrograde metamorphism the low field slopes obtained from hysteresis loops the ferrimagnetic susceptibility fraction ferri saturation isothermal remanent magnetization mrs and saturation magnetization ms have a positive correlation with the volume concentration of symplectite a mineral related to retrograded metamorphism therefore they could be potential indicators for quickly semi quantifying the degree of retrograde metamorphism of the eclogite units 2 the dominant magnetic carriers in retrograded eclogites are magnetite particles in pseudo single domain grain size region 3 the p t conditions during the retrograde decompressional process could first increase the concentration of magnetite which can reach up to 3 for extensively retrograded eclogite and then was dissolved for fully retrograded eclogite therefore change in the magnetite contents during the retrograde process is the major factor controlling the magnetism of retrograde eclogites

the magnetic anisotropy of mantle peridotites example from the twin sisters dunite washington abstract the twin sisters dunite massif washington state provides unweathered peridotites for magnetic analysis these rocks have been chosen to test a new magnetic fabric based on measuring the anisotropy of magnetic susceptibility ams in high field with a vibrating sample magnetometer although the dunites are fresh they host small quantities of secondary magnetite formed along cracks under low field conditions magnetite masks the magnetic fabric of olivine and thus the magnetic fabric does not reflect mantle flow deformation above the magnetic saturation at a field of 1 t the ferrimagnetic component is removed and the high field slope represents the paramagnetic ams only this high field ams originates from the magnetocrystalline anisotropy of olivine the high field ams are compared with lattice preferred orientation lpo fabric data obtained by electron backscatter diffraction lpo point distributions are formed by high temperature plastic flow and match the high field measurements in contrast girdle lpos present notable departures from the high field ams axes

structural lithic units in external orogenic zones abstract changes in types of thrust fault structures are typical of external orogenic zones and are inferred here to be related to thickness and facies changes in stratigraphie sequences obvious deformation style changes occur from external to intermediate thrust sheets similar changes in style are observed and most easily interpreted along strike within individual thrust sheets to correlate stratigraphic and structural changes stratigraphic sections are divided into structural lithic units the subdivisions are based on the dominant deformation styles vertically in individual cross sections the major variables in determining deformation style are controlling stratigraphic members within individual stratigraphic structural units and the stacking sequence of lithologie types into different structural units in many areas the critical taper of one major dominant member regionally controls where structural style changes will occur areal change in either internal composition or in stacking sequence causes lateral change in deformation style lithological changes in structural units are coincident with changes in frontal thrust ramp positions connected by major lateral ramps and with changes in thrust zone geometries imbricate thrusts in one area versus a duplex zone along strike they are also associated with changes in thrust shapes from listric to stepped and changes from fault bend fold to fault propagation fold structures controlling members may be either strong or weak fold dominated regions and thrust faulted regions without major shales or evaporites are usually controlled by strong controlling members weak controlling members are major evaporite horizons or thick shales a thorough understanding of stratigraphic facies realms therefore may allow predictions of types and changes in structural styles it can also be very useful in the interpretation of less well exposed thrust terranes

anisotropy of magnetic susceptibility in natural olivine single crystals mantle flow dynamics can cause preferential alignment of olivine crystals that results in anisotropy of physical properties to interpret anisotropy in mantle rocks it is necessary to understand the anisotropy of olivine single crystals we determined anisotropy of magnetic susceptibility ams for natural olivine crystals high field ams allows for the isolation of the anisotropy due to olivine alone the orientations of the principal susceptibility axes are related to the olivine s crystallographic structure as soon as it contains 3 wt feo the maximum susceptibility is parallel to the c axis both at room temperature rt and at 77 k the orientation of the minimum axis at rt depends on iron content it is generally parallel to the a axis in crystals with 3 5 wt feo and along b in samples with 6 10 wt feo the ams ellipsoid is prolate and the standard deviatoric susceptibility k0 is on the order of 8 10210 m3 kg for the samples with 1wt feo and ranges from 3 1 1029 m3 kg to 5 7 1029 m3 kg for samples with 3 10 wt feo at 77 k the minimum susceptibility is along b independent of iron content the shape of the ams ellipsoid is prolate for samples with 5 wt feo but can be prolate or oblate for higher iron content the degree of anisotropy increases at 77 k with p0 7757 160 5 the results from this study will allow ams fabrics to be used as a proxy for olivine texture in ultramafic rocks with high olivine content

source mechanism of long period events at kusatsu shirane volcano japan inferred from waveform inversion of the effective excitation functions abstract we investigate the source mechanism of long period lp events observed at kusatsu shirane volcano japan based on waveform inversions of their effective excitation functions the effective excitation function which represents the apparent excitation observed at individual receivers is estimated by applying an autoregressive filter to the lp waveform assuming a point source we apply this method to seven lp events the waveforms of which are characterized by simple decaying and nearly monochromatic oscillations with frequency in the range 1 3 hz the results of the waveform inversions show dominant volumetric change components accompanied by single force components common to all the events analyzed and suggesting a repeated activation of a sub horizontal crack located 300 m beneath the summit crater lakes based on these results we propose a model of the source process of lp seismicity in which a gradual buildup of steam pressure in a hydrothermal crack in response to magmatic heat causes repeated discharges of steam from the crack the rapid discharge of fluid causes the collapse of the fluid filled crack and excites acoustic oscillations of the crack which produce the characteristic waveforms observed in the lp events the presence of a single force synchronous with the collapse of the crack is interpreted as the release of gravitational energy that occurs as the slug of steam ejected from the crack ascends toward the surface and is replaced by cooler water flowing downward in a fluid filled conduit linking the crack and the base of the crater lake

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

preservation of primary volcanic textures in the ultrahigh pressure terrain of dabie shan delicate primary volcanic features such as ash layers volcaniclastic breccias and pillow lavas with amygdaloidal rims have been identified in a terrigenous volcanosedimentary sequence forming part of the ultrahigh pressure unit of the dabie shan china the presence of coesite relics in crosscutting dikes confirms an ultrahigh pressure evolution for the entire sequence evaluation of the probable reaction history for zeolite compositions as supposed for the amygdaloidal rims reveals a scarcity of reactions at very high pressures such special conditions of low reactivity and fluid conserving reactions combined with a lack of directed stress have allowed the remarkable preservation of these primary volcanic features despite deep subduction

waveform inversion of oscillatory signatures in long period events beneath volcanoes 1 the source mechanism of long period lp events is examined using synthetic waveforms generated by the acoustic resonance of a fluid filled crack we perform a series of numerical tests in which the oscillatory signatures of synthetic lp waveforms are used to determine the source time functions of the six moment tensor components from waveform inversions assuming a point source the results indicate that the moment tensor representation is valid for the odd modes of crack resonance with wavelengths 2l n 2w n n 3 5 7 where l and w are the crack length and width respectively for the even modes with wavelengths 2l n 2w n n 2 4 6 a generalized source representation using higher order tensors is required although the efficiency of seismic waves radiated by the even modes is expected to be small we apply the moment tensor inversion to the oscillatory signatures of an lp event observed at kusatsu shirane volcano central japan our results point to the resonance of a subhorizontal crack located a few hundred meters beneath the summit crater lakes the present approach may be useful to quantify the source location geometry and force system of lp events and opens the way for moment tensor inversions of tremor

exhumation tectonics of the ultrahigh pressure metamorphic rocks in the qinling orogen in east china new petrological structural radiometric insights from the shandong peninsula 1 in eastern china the sulu area is recognized as the eastern extension of the qinling dabie belt which is famous for its ultrahigh pressure uhp metamorphism although numerous petrologic and geochemical works are available structural data are still rare this paper provides the first extensive study of bulk geometry and kinematic analysis of the shandong peninsula the study area is divided into three tectonic areas by cretaceous faults namely a southern uhp belt or sulu area a northern migmatite area and an eastern eclogite and migmatite area or weihai area conversely to the deeply entrenched idea that the later area belongs to the north china belt and the two others to the south china block scb we argue that all three areas are parts of the scb structural petrologic 40ar 39ar and u pb data comply with this new interpretation in the north shandong area mafic granulites enclosed as blocks within gneissic migmatites do not significantly differ from the sulu and weihai eclogites which also experienced a granulite facies overprint before migmatization the circa 210 200 ma age of the main ductile deformation is related to an extensional event during the triassic or indosinian orogeny this date corresponds to the temperature climax but the time of the pressure peak i e the real age of the uhp metamorphism is discussed

a model of vulcanian eruptions at galeras volcano colombia abstract a series of six vulcanian eruptions at galeras volcano colombia occurred during 1992 1993 these eruptions followed the emplacement of a lava dome in late 1991 which was accompanied by cooling crystallizing and partial solidification of the column of magma plugging the conduit five of the eruptions were preceded by episodes of monochromatic long period seismicity suggesting cyclic pressurization of the magma the quiescent intervals between eruptions generally decreased with each successive eruption we propose a model of gas release from magma into confined stationary pore spaces by 5 10 crystallization of anhydrous minerals causing repeated overpressurization of the magmatic system using initial lithostatic pressures of 20 100 mpa 800 3900 m depth gas buildup by crystallization indicates overpressures of 3 17 mpa which is the approximate fracture criterion for a magma chamber our galeras data suggest two models of pressurization 1 gas exsolution may have occurred at similar depths but with progressively smaller overpressures being developed before each successive eruption according to this model the comparatively long quiescent periods between the first eruptions resulted in relatively large amounts of gas exsolution from the magma and accumulation in pore spaces whereas the shorter quiescent periods for the later eruptions exsolved less gas the decrease in overpressure with time may have resulted from progressive fracturing of partly solidified magma during the eruptions which progressively decreased the tensile strength and increased the permeability of the magma 2 since overpressures are smaller at shallower depths for a given amount of crystallization the first eruptions of 1992 1993 were caused by gas exsolution at shallow depths while the last eruptions having shorter quiescent intervals resulted from a greater amount of gas exsolution at greater depths in this case the rate of gas exsolution varied as a function of depth the two scenarios for pressurization may be combined into a more general model involving edifice weakening and the development of a shallow hydrothermal system from continued degassing of the magma plug as weakening of the edifice formed an extensive system of fractures the shallow hydrothermal system deepened due to meteoric water input and magmatic degassing with time a greater number of fractures were filled and partly sealed by hydrothermal minerals at progressively deeper levels as a result the source of the overpressure also deepened with time

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

time space variation of volcano seismic events at la fossa vulcano aeolian islands italy new insights into seismic sources in a hydrothermal system we investigated the relationship between volcano seismic events recorded at la fossa crater of vulcano aeolian islands italy during 2004 2006 and the dynamics of the hydrothermal system during the period of study three episodes of increasing numbers of volcano seismic events took place at the same time as geothermal and geochemical anomalies were observed these geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids three classes of seismic events long period high frequency and monochromatic events characterised by different spectral content and various similarity of the waveforms have been recognised these events clustered mainly below la fossa crater area at depths of 0 5 1 1 km b s l were space distributed according to the classes based on their features we can infer that such events at vulcano are related to two different source mechanisms 1 fracturing processes of rocks and 2 resonance of cracks or conduits filled with hydrothermal fluid in the light of these source mechanisms the increase in the number of events at the same time as geochemical and geothermal anomalies were observed was interpreted as the result of an increasing magmatic component of the hydrothermal fluids implying an increase of their flux indeed such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids increased pore pressures gave rise to fracturing processes while the increased fluid flux favoured resonance and vibration processes in cracks and conduits finally a gradual temporal variation of the waveform of the hybrid events one of the subclasses of long period events was observed likely caused by heating and drying of the hydrothermal system

unusual low frequency volcanic seismic events with slowly decaying coda waves observed at galeras and other volcanoes abstract events with slowly decaying coda waves are observed in active andesitic volcanoes associated mainly with vulcanian type eruptions or large gas emissions however these signals are also recorded in some quiescent volcanoes these unusual signals are considered to be related to magmatic activity and generally occur beneath the active crater the signals have been observed to be a short term precursor galeras volcano colombia 1992 1993 asama yama volcano japan 1983 after eruption tokachi dake volcano japan 1989 during seismic swarms meakan dake volcano japan 1982 and during quiescence puracevolcano colombia 1994 1995 tarumai volcano japan 1970 1971 1975 spectral analysis reveals common characteristics for this type of signal the spectrum is characterized by one or several sharp frequency peaks fundamental frequencies are not affected by epicentral distance azimuth or travel time indicating a source effect the damping coefficient for coda waves ranges from 0 002 to 0 02 and is related to large values of the quality factor q c ranging from 250 to 25 respectively these parameters may be the result of large amounts of gas bubbles in the magma body

tornillos modeled as self oscillations of fluid filling a cavity application to the 1992 1993 activity at galeras volcano colombia abstract tornillos are quasi monochromatic seismic signals with a slowly decaying coda that are observed near active volcanoes and geothermal areas worldwide in this work a lumped parameter model describing the tornillo source process as the self oscillations of fluid filling a cavity is investigated a nonlinear ordinary differential equation is derived that governs the behavior of the model taking into account viscous and nonlinear damping as well as the reaction force of the fluid inside the cavity this equation is numerically integrated both for different cavity sizes and different fluids of volcanological interest such as gas h2o co2 h2o so2 and gas particle mixtures ash so2 water droplets h2o this cavity model predicts that when the filling fluid is a mixture of ash and so2 the signal duration will increase until the mixture becomes enriched in ash and then the duration exhibits a decrease additionally the damping coefficients 1 2q of the synthetic signals are estimated in the range between 0 002 and 0 014 both results agree well with the temporal variation of tornillos duration and the estimated q quality factors damping coefficients observed at galeras volcano in the context of the cavity model tornillo frequency variations from 4 hz to 1 hz observed prior to eruptions can be interpreted as the result of fluid composition changes as more ash particles are added this is in agreement with the observation that gas accumulation at galeras was a steady rather than an episodic process and that tornillos were most likely triggered after a fluid pressure threshold had been exceeded

correlations between so2 flux and long period seismicity at galeras volcano the 14 january 1993 eruption of galeras volcano in colombia which killed six scientists and three tourists1 was followed by a larger eruption on 23 march 19932 both eruptions were preceded by episodes of long period seismicity the source of long period seismic events has been modelled extensively3 8 as the resonance within a fluid filled crack induced by pressure transients in the fluid5 7 here we use the so2 flux from galeras volcano measured remotely to infer the degassing history during the episode of long period events preceding the 23 march eruption so2 flux and long period seismicity have been monitored separately elsewhere to forecast volcanic activity9 13 our results show how the combination and correlation of the two methods can be used to interpret the movement of gases from the magma body to the surface and to monitor the pressure buildup leading to an eruption at explosive volcanoes

tornillo type seismic signals at galeras volcano colombia 1992 1993 abstract unusual low frequency seismic events called tornillos screws at the observatorio vulcanologico y sismologico de pasto ovsp have been observed at galeras volcano during 1992 1993 of six eruptions that occurred between july 1992 and june 1993 five were preceded by episodes of tornillo signals these signals are characterized by 1 a waveform having a homogeneous distribution of frequencies 2 a long coda lasting up to several minutes 3 a small amplitude compared to the duration and 4 a slow decay of the coda the tornillo signals have been grouped into thirteen principal forms the 1992 1993 tornillos showed four main periods of occurrence each of which was followed by an eruption episode i occurred from 11 to 16 july 1992 and consisted of nine events episode ii lasted from 23 december 1992 to 14 january 1993 with twenty events episode iii was observed from 13 february to 23 march 1993 with 74 events episode iv lasted from 10 april to 7 june 1993 with 109 events the seismic activity at galeras in april may 1993 was characterized mainly by the occurrence of tornillo signals the behavior of these signals was similar to that before previous episodes ending with eruptions these observations permitted us to forecast the 7 june 1993 eruption several days to weeks beforehand the occurrence of tornillos is the most important criterion for determining the probability of an eruption at galeras in the current period of reactivation the maximum daily number of tornillos and the longest duration of individual events occur near the end of each episode within an individual episode the durations of single events increase progressively near to the point of eruption a positive correlation is observed between the total number of pre eruptive tornillo signals during an episode and the volume of material ejected by the eruption these observations may suggest that the presence of tornillos is an indication of variations in the physical conditions between the fluid and the surrounding solid material within the volcano and they constitute an important tool for forecasting future eruptions at galeras

response of a hydrothermal system to magmatic heat inferred from temporal variations in the complex frequencies of long period events at kusatsu shirane volcano japan we investigate temporal variations in the complex frequencies frequency and quality factor q of long period lp events that occurred at kusatsu shirane volcano central japan we analyze lp waveforms observed at this volcano in the period between 1988 and 1995 which covers a seismically active period between 1989 and 1993 systematic temporal variations in the complex frequencies are observed in october november 1989 july october 1991 and september 1992 january 1993 we use acoustic properties of a crack filled with hydrothermal fluids to interpret the observed temporal variations in the complex frequencies the temporal variations in october november 1989 can be divided into two periods which are explained by a gradual decrease and increase of a gas volume fraction in a water steam mixture in a crack respectively the temporal variations in july october 1991 can be also divided into two periods these variations in the first and second periods are similar to those observed in november 1989 and in september november 1992 respectively and are interpreted as drying of a water steam mixture and misty gas in a crack respectively the repeated nature of the temporal variations observed in similar seasons between july and november suggests the existence of seasonality in the occurrence of lp events this may be caused by a seasonally variable meteoritic water supply to a hydrothermal system which may have been heated by the flux of volcanic gases from magma beneath this volcano

parameterization of multichromatic tornillo signals observed at galeras volcano colombia in the past decade several of the ash eruptions at galeras volcano colombia have been preceded by tornillos these unusual tremor wavelets have quasi sinusoidal waveforms with screw like envelope profiles and can last up to several minutes a swarm of tornillos occurred at galeras volcano between 8 december 1999 and 12 february 2000 these tornillos appear to be more complex than those previously recorded with the broadband instruments or with the short period network of the observatorio vulcanologico y sismologico in pasto they are multichromatic with a varying number of narrow spectral peaks between 1 and 20 hz we describe a procedure for parameterizing the tornillo signals in the time and frequency domains to determine signal parameters in addition to wavelets like the tornillos the procedure can be applied to random signals such as volcanic tremor we derive distribution and correlation functions for the signal parameters determined from the swarm these provide along with the signal signature constraints for modelling variations of the source process from these observations we derive qualitative conclusions about the characteristics of differential equations which describe the underlying processes and excitation mechanisms as forced or self excited oscillators

basement cover sequences within the uhp unit of the dabie shan field data define two lithologically distinct basement cover sequences within the ultrahigh pressure metamorphic uhpm unit of the dabie shan eastern china one of the cover units the changpu unit comprises calc arenitic metasediments in stratigraphic contact with a basement consisting of gneisses of the yangtze craton the second cover unit the ganghe unit consists of felsic intermediate metavolcanics and clastic metasediments basement exposure of the ganghe unit is not known fold axes in the ganghe unit are oblique to those of the changpu unit which are parallel to those of the yangtze gneisses preservation of primary textures in some volcanic rocks and tectonic separation from the yangtze gneisses by a greenschist facies mylonite support an interpretation of the ganghe unit as a low strain domain protolith associations in the ganghe and changpu units are compatible with deposition in a rift setting and along a passive continental margin respectively a u pb single zircon age of 761 33 ma for volcanoclastic rocks of the ganghe unit demonstrates a neoproterozoic deposition age concordant with inferred rifting at that time eclogite facies parageneses in the gneisses and both cover units along with p t data demonstrate regional uhpm in the dabie shan

mineral oxygen isotope and hydroxyl content changes in ultrahigh pressure eclogite gneiss contacts from chinese continental scientific drilling project cores a combined study of mineral o isotopes and hydroxyl contents was carried out for the contacts between ultrahigh pressure eclogite and gneiss from main hole of the chinese continental scientific drilling project in the sulu orogen while there is a large d 18 o variation from 8 3 to 7 3 for all minerals different styles of mineral pair fractionation occur at the boundaries of different lithologies both equilibrium and disequilibrium o isotope fractionations are observed between quartz and the other minerals with reversed fractionations between omphacite and garnet in some samples of eclogite this suggests that both eclogite and gneiss acquired their negative d 18 o values by meteoric hydrothermal alteration of their protoliths at high temperatures before subduction and that fluid assisted o isotope exchange did take place across the boundary of different lithologies at local scales during amphibolite facies retrogression fourier transform infrared spectroscopy analysis yielded h2o concentrations of 50 to 1144 p p m by weight for garnet and 139 to 751 p p m for omphacite the state of equilibrium or disequilibrium o isotope fractionations between omphacite and garnet are correlated with variations in their water content at local scales indicating that the internally derived fluid plays a critical role in retrograde metamorphism during exhumation the retrograde metamorphism results in mineral reactions and o isotope disequilibria between some of the minerals but the fluid for retrogression was derived from the decompression exsolution of structural hydroxyl and thus internally buffered in the o isotope composition a quantitative estimate suggests that a hand specimen 3 6 9 cm of eclogite composed of 70 garnet and 30 omphacite can release 0 316 g water by the decompression exsolution of structural hydroxyl which can form 14 4 g amphibole during exhumation this provides sufficient amounts of water for the amphibolite facies retrogression

petrofabrics and seismic properties of garnet peridotite from the uhp sulu terrane china implications for olivine deformation mechanism in a cold and dry subducting continental slab abstract lattice preferred orientations lpo of olivine diopside enstatite and garnet from the zhimafang garnet peridotite body in the sulu ultrahigh pressure uhp metamorphic terrane china were measured using the electron backscatter diffraction ebsd technique the peridotite was captured from a mantle wedge immediately adjacent the subducted yangtze slab and then experienced the uhp metamorphism at 750 950 c and 4 7 gpa the olivine lpo is characterized by the 001 axis close to the stretching lineation and the 100 plane subparallel to the foliation indicating the prevailing of 100 001 slip enstatite lpo displays the dominance of 100 001 slip diopside developed complex lpo patterns that are difficult to explain using a single slip system of 100 001 garnet is almost randomly oriented due to its low volume fractions cubic symmetry and the presence of numerous slip systems calculated seismic properties of the peridotite yield a maximum p wave velocity normal to the foliation and a minimum along the foliation with anisotropy up to 8 in strongly sheared samples the s wave velocity pattern is complex but the fast polarization plane generally normal to the foliation the inferred shear sense from the olivine lpo is top to se in contrary to exhumation induced top to nw thrusting recorded in the quartz lpo implying that the olivine lpo formed at early uhp metamorphic conditions the olivine crystals have relatively low water contents 141 475 h 106 si indicating a fluid deficient environment for the lpo formation the present study suggests that a combination of low temperature and uhp plays a much more important role than the water content to promote the activation of 100 001 slip in olivine

temporal evolution of a hydrothermal system in kusatsu shirane volcano japan inferred from the complex frequencies of long period events 1 we present a detailed description of temporal variations in the complex frequencies of long period lp events observed at kusatsu shirane volcano using the sompi method we analyze 35 lp events that occurred during the period from august 1992 through january 1993 the observed temporal variations in the complex frequencies can be divided into three periods during the first period the dominant frequency rapidly decreases from 5 to 1 hz and q of the dominant spectral peak remains roughly constant with an average value near 100 during the second period the dominant frequency gradually increases up to 3 hz and q gradually decreases from 160 to 30 during the third period the dominant frequency increases more rapidly from 3 to 5 hz and q shows an abrupt increase at the beginning of this period and then remains roughly constant with an average value near 100 such temporal variations can be consistently explained by the dynamic response of a hydrothermal crack to a magmatic heat pulse during the first period crack growth occurs in response to the overall pressure increase in the hydrothermal system caused by the heat pulse once crack formation is complete heat gradually changes the fluid in the crack from a wet misty gas to a dry gas during the second period as heating of the hydrothermal system gradually subsides the overall pressure in this system starts to decrease causing the collapse of the crack during the third period

tornillos beneath tongariro volcano new zealand abstract unusual low frequency seismic events have recently begun to occur beneath tongariro volcano new zealand because the seismic waveforms appear similar to waveforms called tornillos which have been recorded at galeras volcano in colombia and have been found to precede small to medium sized ash eruptions there by several weeks to months we are monitoring them closely at tongariro these events are characterised by small amplitude monochromatic or multichromatic waveforms that decay slowly with time features that suggest a source involving magmatic or hydrothermal fluids within a zone surrounded by hard rock the frequency content of monochromatic events is typically between 1 and 3 hz and is often found to be peaked at f 1 2 hz event durations range from about 10 to 80 s the appearance of the shorter duration events is identical to so called lp or long period events the lps and tornillos appear to be co located so that the only difference between lps and tornillos is the extended duration of the latter these events have been identified in the seismograms of the permanent monitoring station kavz since at least january 2001 occurring at a rate of about one per month during june august 2001 the rate of occurrence gradually increased peaking in september 2001 at several events per day we deployed two broadband and several short period seismometers at close distances to the expected source location the resulting seismograms show a complex mixture of seismic waves originating from shallow depth beneath the area of the te maari craters located approximately 0 5 km from the nearest station the close range broadband records reveal some interesting details about the tornillo source the tornillo waveform is found to consist of two parts a low frequency f 1 2 hz part and a higher frequency f 3 hz part the high frequency energy travels at body wave speeds c 3 0 km s while the low frequency energy travels at the speed of shear or surface waves in the shallow crust c 1 km s interestingly for some events the low frequency waves arrive before the high frequency body waves at the closest station this and comparison with several lp events suggests a spatial separation of the high and low frequency sources with the low frequency energy originating at shallow depth and acting as a trigger for the release of tectonic stress at greater depth in the form of high frequency body waves

excitation of a buried magmatic pipe a seismic source model for volcanic tremor recent observations of seismic events at various volcanoes suggest that harmonic tremor results from the sustained occurrence of so called long period or low frequency events accordingly we can view the long period volcanic event as the elementary process of tremor and interpret it as the impulse response of the tremor generating system we present a seismic model in which the source of tremor is the acoustic resonance of a fluid filled volcanic pipe triggered by excess gas pressure the model consists of three elements namely a triggering mechanism a resonator and a radiator for simplicity we assume a hemispherical trigger cylindrial resonator and circular radiator set in a vertical configuration with the trigger capping the top of the pipe and the disk shaped radiator shutting off its bottom considering the simple case of a source buried in a homogeneous half space we then apply the discrete wave number method to obtain a complete representation of the ground motion response at near and intermediate distances the results demonstrate that the displacement attributed to the pipe dominates the near field motion while that due to the disk is representative of the intermediate and far fields the trigger itself has a smaller contribution mainly limited to the field in the proximity of the source the characteristics displayed by the free surface response evolve from a strong impulsive signature in the immediate vicinity of the epicenter to a well developed harmonic wave train dominated by rayleigh waves at larger distances no clear shear arrival can be detected in the synthetic seismograms the displacement spectrum reflects the organ pipe modes of the conduit and the bandwidth associated with the dominant spectral peak of motion is controlled by the combined losses due to viscous attenuation in the fluid and elastic radiation into the solid in the case of the cylindrical magma column considered the radiation loss is proportional to the square of the pipe radius while the loss related to viscous damping is inversely proportional to the same factor indicating that the relative importance of the two loss mechanisms is critically dependent on the geometry of the magma reservoir the relative importance of the pipe and disk elements likewise is a function of the conduit cross section this suggests the possibility of determining the geometry of the source as well as the radiation loss and in situ magma viscosity from a comparison of near and far field observations

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

resonances of a volcanic conduit triggered by repetitive injections of an ash laden gas 1 a swarm of long period lp seismic events was recorded in december 2001 before heightened eruptive activity of tungurahua volcano an andesitic stratovolcano in ecuador the lp events showed simple decaying harmonic oscillations with frequencies ranging from 2 to 3 5 hz and quality factors q significantly larger than 100 our spectral analysis of the lp events identified systematic temporal variations in both frequency and q of the lp events assuming a crack resonator at the source of lp events the temporal variations can be consistently explained by increasing the ash content within the resonator which may be caused by repetitive injections of an ash laden gas into a pre existing crack in the conduit as a preparatory process for eruptions

emplacement of an archean gneiss dome northern ontario canada inflation inferred from magnetic fabrics 1 previous field structural studies of the ash bay gneiss dome revealed an upward convex foliation with an integral east west lineation defined by a quartzo felspathic matrix unfortunately the amphibolite facies gneisses lack traditional indicators of microfabric evolution such as kinematic indicators so that it is difficult to relate the foliation s orientation distribution to an emplacement mechanism for the dome fortunately anisotropy of magnetic susceptibility isolates a distinct microfabric because of the preferred orientation of high susceptibility accessory magnetite the magnetite subfabric developed late in the metamorphic crystallization history and its magnetic foliation and magnetic lineation are similarly oriented to the s l fabric of the quartz feldspar matrix however the magnetite foliation dips less steeply and forms a less convex domal surface than the field schistosity the metamorphic schistosity and the magnetite foliation thus isolate the domal deflection at different stages confirming the inflation and upward motion of the ash bay diapir during the closing stages of amphibolite facies metamorphism

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

a method for the separation of paramagnetic ferrimagnetic and haematite magnetic subfabrics using high field torque magnetometry summary in this study the contribution of the paramagnetic ferrimagnetic and haematite components to the magnetic anisotropy is separated by means of high field torque magnetometry torque measurements at different fields which are high enough to saturate the ferrimagnetic minerals however still low enough that the torque resulting from the haematite is linear with field allow for the separation of the three magnetic anisotropy components the method has been applied to haematite single crystals in which no paramagnetic or ferrimagnetic components have been found contribute to the torque signal the mean direction of the poles to the crystallographic basal plane in the haematite single crystals is subparallel to the minimum susceptibility direction measured in low field the separation analysis has also been applied to highly deformed red beds from the lower glarus nappe complex switzerland no ferrimagnetic phases are present in the rocks and therefore they cannot contribute to the anisotropy of magnetic susceptibility the magnetic fabric arises from a paramagnetic subfabric carried by the phyllosilicate minerals and haematite in which the basal planes of both phases are in the cleavage plane the measured magnetic lineation seen in low field anisotropy of magnetic susceptibility appears to be an apparent lineation that arises from a weak girdling of haematite and the paramagnetic minerals conforming the rock

magnetic petrology of high fe ti eclogites from the ccsd main hole implications for subduction zone magnetism 1 the high fe ti eclogites with exsolved lamellar in 530 600 m depths from the chinese continental scientific drilling ccsd main hole in the sulu ultra high pressure uhp metamorphic belt eastern china record an anomalously high susceptibility natural remanent magnetization nrm and koenigsberger ratio q nrm ji ji is induced magnetization this provides us with a good opportunity to study the effects of magnetic minerals and exsolution lamellae on the magnetic properties of deep rocks in this paper we have measured systematically magnetic properties and mineral assemblage and structure for three special samples no 83 no 86 and no 89 results show that these fe ti rich eclogites are the result of the fine grained titano magnetite exsolution in pyroxene and lamellar structure consisting of finely interlayered ilmenite and hematite in exsolved hemo ilmenite we found that the dominant fe bearing oxide minerals in samples studied are ilmenite hematite hem ilm up to 25 little titano magnetite and pyrite the ferromagnetic susceptibility is mainly controlled by fine grained titano magnetite and nrm is closely related to the exsolved lamellar structure we hence propose that the anomalous magnetism of these eclogites observed in our samples is the result of exsolution from homogenous pyroxene and ilmeno hematite during cooling and decompression processes these fe ti rich eclogites might be one of the sources of high magnetic anomalies observed in the sulu subduction zone eastern china

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata

the anisotropy of magnetic susceptibility of lava flows an experimental approach measurements of the anisotropy of magnetic susceptibility ams of natural lavas have shown that ams varies with depth within a lava flow we have investigated the reasons for such variation by studying the effects of temperature and strain rate on the ams of recent lava in the laboratory samples of lava from kilauea were melted and subjected to a range of strain rate and cooling histories the results show that the degree of anisotropy is a function of both the thermal and shearing history of a sample high degrees of anisotropy were found only in samples that were deformed at temperatures close to those encountered during eruption and then rapidly quenched lavas subjected to similar shear stresses at high temperatures had low degrees of anisotropy if allowed to cool down slowly without further deformation additionally lava subjected to complex shearing yield a lower degree of anisotropy even when high strain rates were imposed on it these results lead to the conclusion that only the last phase of deformation is detectable using ams and that high strain rates will not result in high degrees of anisotropy if either deformation ends while lava is still fluid or if the orientation of the maximum shear stress varies with time the relation between the orientation of the principal susceptibilities and that of shear is less sensitive to variation on shear with time consequently flow directions can be inferred confidently with this type of measurements

petrology of ultrahigh pressure rocks from the southern su lu region eastern china abstract in the su lu ultrahigh p terrane eastern china many coesite bearing eclogite pods and layers within biotite gneiss occur together with interlayered metasediments now represented by garnet quartz jadeite rock and kyanite quartzite in addition to garnet omphacite rutile coesite other peak stage minerals in some eclogites include kyanite phengite epidote zoisite talc nyboite and high al titanite the garnet quartz jadeite rock and kyanite quartzite contain jadeite quartz garnet rutile zoisite apatite and quartz kyanite garnet epidote phengite rutile omphacite assemblages respectively coesite and quartz pseudomorphs after coesite occur as inclusions in garnet omphacite jadeite kyanite and epidote from both eclogites and metasediments study of major elements indicates that the protolith of the garnet quartz jadeite rock and the kyanite quartzite was supracrustal sediments most eclogites have basaltic composition some have experienced variable crustal contamination or metasomatism and others may have had a basaltic tuff or pyroclastic rock protolith the su lu ultrahigh p rocks have been subjected to multi stage recrystallization and exhibit a clockwise p t path inclusion assemblages within garnet record a pre eclogite epidote amphibolite facies metamorphic event ultrahigh p peak metamorphism took place at 700 890 c and p 28 kbar at c 210 230 ma the symplectitic assemblage plagioclase hornblende epidote biotite titanite implies amphibolite facies retrogressive metamorphism during exhumation at c 180 200 ma metasedimentary and metamafic lithologies have similar p t paths several lines of evidence indicate that the supracrustal rocks were subducted to mantle depths and experienced in situ ultrahigh p metamorphism during the triassic collision between the sino korean and yangtze cratons