the modi taung nankwe gold district slate belt central myanmar mesothermal veins in a mesozoic orogen abstract the recently discovered quartz gold veins comprising the modi taung nankwe gold district in central myanmar are largely hosted by mudstones of the late palaeozoic slate belt mesozoic rocks of the paunglaung mawchi zone separate the slate belt from the shan scarp and shan plateau to the east at modi taung 5 km of exploration adits indicate that the veins within steeply dipping oblique reverse slip shear zones are displaced by movements along the shears intruded by late jurassic calc alkaline dykes and offset on conjugate cross faults drill intercepts show that mineralization extends vertically for more than 500 m coarse visible gold book and ribbon texture and stylolitic laminations and trace metal values are consistent with mineralization at mesothermal depths of several kilometres in the brittle ductile regime our field observations suggest that mineralization took place in the early jurassic following collision of myanmar on the passive western margin of a greater shan thai continental block with an oceanic arc on the overriding plate to the west collision generated intra continental thrusting in and east of the paunglaung mawchi zone metamorphism of plateau rocks thrust west beneath the slate belt to form the mogok metamorphics and ascent of mineralizing fluids expelled from dehydrating underthrust rocks reversal in orogenic polarity initiated late jurassic eastward subduction of oceanic crust beneath myanmar and generation of a magmatic arc with dykes cutting the quartz gold veins renewed east directed thrusting translated the slate belt over arc clastics and probably resulted in exhumation of the mogok metamorphics and offsets of the veins on conjugate faults young k ar rb 87 sr 86 and ar 40 ar 39 ages on the mogok metamorphic belt imply renewed tertiary uplift and possibly intrusion of mid tertiary or palaeogene granites

the western ailaoshan volcanic belts and their se asia connection a new tectonic model for the eastern indochina block the western ailaoshan wal volcanic belts mark the western boundary of the south china indochina suture zone along the ailaoshan fold belt geochronological and geochemical evidence suggests that the wal volcanic belts vary in ages and origins and includes 1 l carboniferous earliest m permian ca 300 270 ma incipient backarc basin magmatism 2 m permian ca 265 ma island arc mature backarc basin magmatism 3 early l permian ca 260 255 ma wal indochina arc continent collision and the associated syn collisional granitic magmatism as well as subsequent 4 e triassic ca 250 245 ma post collisional magmatism regional geological comparison indicates that the post l carboniferous wal tectonic evolution was closely related to the eastern indochina block we present a new g plate geodynamic evolution model for the ailaoshan fold belt and its surrounding south china indochina region based on new and published u pb zircon ages together with whole rock and pb isotope geochemical data

time dependent spatial amplitude patterns of harmonic tremor at arenal volcano costa rica seismic wave interferences seismograms recorded at the receivers of a small aperture seismic array usually display very similar waveforms and amplitudes as a consequence of their close proximity during the analysis of the volcanic tremor wave field at arenal volcano costa rica we detected significant differences in the amplitudes of harmonic tremor recorded at the stations of a small aperture 210 m seismic array the amplitude distributions are geometrically complex and characterized by strong gradients they occur just for harmonic tremors any other type of seismic event produces nearly uniform amplitudes across the array this suggests some relation with harmonic frequency content moreover the spatial amplitude patterns change with time some of these observations could be explained by an extreme combination of source path and site effects but they also could be produced by interference of different components of the seismic wave field we use numerical calculations to investigate the amplitude pattern generated by two interfering plane waves and are able to reproduce the main features of the observed amplitude patterns we propose mechanisms that might generate seismic wave fields with multiple components and conclude that interference can explain the complexity and variability of the harmonic tremor wave field at arenal volcano online material wave field animation

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

u pb zircon dating of granitoid plutons from the west coast province of peninsular malaysia u pb zircon dating of granitoid plutons from the west coast province of peninsular malaysia yields precise and unambiguous ages of 198 220 ma late triassic these ages are considerably older than previously reported k ar mica ages which have been largely reset but agree with or are younger than rb sr whole rock apparent ages the u pb zircon ages are considered to represent the best estimate of the intrusive ages of the plutons some of the problems associated with the interpretations of the pre triassic rb sr whole rock apparent ages are discussed here and alternative ways to explain these ages in the light of recent work are considered reversely discordant patterns displayed by zircon populations from a number of plutons yield consistent upper intersection ages of 1500 1700 ma that approximately date source derived inherited zircon components the precambrian ages of these inherited zircon components suggest that the west coast province s type granitoids are derived from sedimentary sources recycled at least in part from mid proterozoic crystalline basement sources

magma rates in feeding conduits of different volcanic centres abstract a quasi stationary magma flow rate in asthenospheric and crustal conduits of central type volcanoes and volcanic centres was studied analytically under the following conditions magma rises through cylindrical channels in which the magma temperature does not change with time but the wall rocks are gradually heated the magma rates were calculated for basaltic andesitic and dacitic volcanoes using the continental and oceanic geotherms it follows from these calculations that the magma supply rate may determine the kind of activity of a volcanic centre being constant for large and very active volcanoes intermittent for usual volcanic centres of island arcs or sporadic for volcamic fields clusters of cinder cones and areal volcanism theoretical conclusions are consistent with observational data

genesis and tectonic setting of the malaysian waterfall granites and tin deposit constraints from la icp mc ms zircon u pb and cassiterite dating and sr nd hf isotopes abstract the waterfall tin deposit located in the south peninsular malaysia is one of the earliest exploited tin deposit of the giant southeast asian tin belt satb which is a world class tin metallogenic belt and holds the largest tin resource and reserves in the world it is a skarn type deposit genetically associated with the waterfall granites samples from the waterfall biotite granites were analyzed using the la mc icpms zircon u pb dating techniques and the results show that these ages range from 241 2 2 5 ma mswd 1 3 to 239 0 3 4 ma mswd 1 2 in addition these ages are consistent with weighted average age of 238 5 1 7 ma mswd 0 23 using the la icpms cassiterite u pb dating techniques indicating a coeval granitic magmatism and tin mineralization event these granites are characterized by high contents of sio2 al2o3 na2o and k2o low contents of p2o5 enrichment in th u nb zr and hf and depletion in ba nb sr p and ti indicating that they likely belong to i type granites with high k calc alkaline and metaluminous to peraluminous signatures the sr nd isotopes show that the waterfall granites are characterized by relatively low initial 87sr 86sr ratios of 0 706131 0 707291 slightly negative end t values of 5 63 to 5 30 and old two stages nd model ages of 1 28 1 26 ga the zircon ehf t values of the zircon grains from the waterfall biotite granites vary from 2 4 to 0 5 with average crustal hf model ages of 1 42 1 24 ga based on the elemental and sr nd isotopic compositions of the meta igneous rocks in the kontum massif indochina block a model using the amphibolite and gneiss as two endmembers indicates that the magma for the waterfall granites were possibly originated from the partial melting of the meta igneous rocks of the kontum massif the waterfall granites were likely emplaced in a syn collision setting triggered by the subduction of the paleo tethys ocean floor beneath the indochina block these granitic rocks enriched in tin are in favor of the tin mineralization resulting in the giant tin mineralization in the satb

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

triassic radiolarian faunas from the mae sariang area northern thailand and their paleogeographic significane abstract early to late triassic spathian to carnian radiolarians were obtained from the bedded chert sequence of the mae sariang group distributed in northern thailand based on the similarity of radiolarian fauna and petrographical characteristics it is inferred that the fine grained siliceous and calcareous sediments of the mae sariang group are equivalent to those belonging to the eastern marginal facies of the sibumasu block moreover the occurrence of an early carnian radiolarian assemblage from bedded chert shows that the closure of the paleotethys ocean between the sibumasu and indochina blocks in northern thailand occurred after the early carnian

gold distribution and source of the j4 gold bearing breccia pipe in the qiyugou district north china craton constraints from ore mineralogy and in situ analysis of trace elements and s pb isotopes abstract the qiyugou district is one of the most important gold deposit distribution areas in the xiong ershan region north china craton these deposits are hosted in archean taihua supergroup rocks as gold bearing breccia pipes here we report a detailed in situ analysis of trace elements and s pb isotopes in sulfides from different ore stages in combination with electron probe microanalysis of ore minerals from the gold bearing j4 breccia pipe in the qiyugou district to unravel the gold distribution and their textural relationships to pyrite the metal sources and s pb isotopic composition variations during the ore forming processes the qiyugou breccia pipes hosted gold ore over 70 t au average grade of 2 5 g t that formed in four mineralization stages i e an early k feldspar biotite magnetite quartz pyrite py 1 stage i that can be further divided into two substages namely the ia k feldspar biotite magnetite stage and the ib quartz pyrite stage a gold pyrite py 2 quartz stage ii a gold quartz polymetallic sulfide py 3 stage iii and a late quartz carbonate stage iv the visible native gold and electrum grains occur as small inclusions and disseminations in the fractures within py 2 and py 3 tellurides and bi pb minerals are widespread in the stage ii stockworks and veins as is intergrowth with visible native gold and py 2 in situ la icp ms trace element analysis reveals the presence of invisible gold hosted in three types of pyrite with extremely low au content py 1 0 05 ppm py 2 0 03 ppm py 3 0 02 ppm concentrations of te bi and pb in pyrite are high and correlate well with au concentrations but as content is low therefore the te bi and pb played a significant role in gold mineralization in as deficient ore fluids in the j4 gold bearing breccia pipe from the qiyugou district high precision in situ laser ablation multiple collector inductively coupled mass spectrometry la mc icp ms lead isotope analyses indicate that the sulfides have 206pb 204pb 207pb 204pb and 208pb 204pb ratios from 17 250 to 17 629 from 15 401 to 15 621 and from 37 649 to 38 290 respectively which are similar to the granite porphyry in the district and indicative of their similar lead sources high precision in situ la mc icp ms sulfur isotope analyses of pyrite show a large 34s variation e g from 18 1 to 11 1 per mil for py 1 from 12 2 to 6 6 per mil for py 2 and from 4 9 to 1 6 per mil for py 3 with a remarkable increasing trend from stage i stage iito stage iii this trend may record a decreasing oxygen fugacity of the ore forming fluids during mineralization

near coastal satellite altimetry sea surface height variability in the north sea baltic sea area 1 the radiometer wet tropospheric correction is a limiting factor of the application of near coastal altimetry observations in the north sea baltic sea area using an ecmwf model based correction instead we increase the return rate from 70 to 95 with observations as close as 10 km from the coast the altimetry and 39 coastal tide gauges are referenced to the same state of the art regional geoid the two data sets are highly correlated and reveal a consistent mean dynamic topography and two distinct correlation regimes separated by the danish islands the combination of the two data sets in a simple statistical model is shown to estimate the sea surface height with the same error level as state of the art operational models indicating the potential for near coastal applications of satellite altimetry observations

eruptions at lone star geyser yellowstone national park usa 1 energetics and eruption dynamics 1 geysers provide a natural laboratory to study multiphase eruptive processes we present results from a 4 day experiment at lone star geyser in yellowstone national park usa we simultaneously measured water discharge acoustic emissions infrared intensity and visible and infrared video to quantify the energetics and dynamics of eruptions occurring approximately every 3 h we define four phases in the eruption cycle 1 a 28 3 min phase with liquid and steam fountaining with maximum jet velocities of 16 28 m s 1 steam mass fraction of less than 0 01 intermittently choked flow and flow oscillations with periods increasing from 20 to 40 s are coincident with a decrease in jet velocity and an increase of steam fraction 2 a 26 8 min posteruption relaxation phase with no discharge from the vent infrared ir and acoustic power oscillations gliding between 30 and 40 s 3 a 59 13 min recharge period during which the geyser is quiescent and progressively refills and 4 a 69 14 min preplay period characterized by a series of 5 10 min long pulses of steam small volumes of liquid water discharge and 50

pb zn cu accumulation from seafloor sedimentation to metamorphism constraints from ore textures coupled with elemental and isotopic geochemistry of the tiemurt in chinese altay orogen nw china abstract the tiemurt pb zn cu deposit metal reserve 0 29 mt pb zn and 0 14 mt cu is hosted in the kangbutiebao formation volcanic sedimentary rocks in the chinese altay orogen nw china although some geological and geochemical characteristics of primary seafloor sedimentary mineralization are preserved major fault controlled pb zn cu orebodies are adjacent to the sarekbuobu orogenic gold deposit and therefore it is also interpreted to be closely related to regional deformational metamorphic processes the seafloor sedimentary mineralization is evidenced by the occurrence of the banded ores and marine sulfate originated sulfur isotopic compositions of the sulfides bimodal 34s values of 17 29 18 67 and 25 03 to 17 58 the lead isotope compositions accord with the evolution line of mantle implying that the pb were chiefly sourced from the mantle reservoir the later deformational and metamorphic overprinting are recorded by the fault controlled lodes with ore textures of epigenetic infilling and replacement besides well developed co2 rich fluid inclusions the d o isotopic data of the overprinting fluids fall into the area between metamorphic fluids and meteoric water line indicative of metamorphic fluids origin with meteoric water involvement to further trace the pb zn cu accumulation and remobilization processes systematic in situ trace elements in sulfides of different generations are analyzed using la icp ms ti mn cu pb zn bi concentrations in pyrite show a trend of progressive decrease from early to late generations similar decreasing trends of trace element concentrations are also present in sphalerite galena chalcopyrite and pyrrhotite although the combinations of trace element are slightly different this indicates that the ore forming metals esp cu pb and zn were initially locked up in the crystal lattice of the vms sulfides especially pyrite deformational and metamorphic processes of the primary ores during the permian triassic collisional orogeny have likely led to trace element remobilization and sulfides purification which redistributed the metals and upgraded the ores combined with previous studies we proposed that the pb zn cu of tiemurt had been accumulated from seafloor sedimentation ca 400 ma to deformation metamorphism processes ca 240 ma

the origin of harmonic tremor at old faithful geyser volcanic tremor the seismic signal which is often associated with eruptions is among the least understood phenomena in seismology large variations in the physical properties of volcanic rocks and fluids along with the complex geological structure make it difficult to obtain reliable source models old faithful geyser yellowstone national park was chosen as a laboratory for studying fluid flow induced seismicity the geyser s cyclic behavior on an hourly time scale and its accessibility make it suitable for a detailed study of seismic behavior between eruptions simultaneously with underwater pressure measurements inside the geyser we observe that sharp pressure pulses inside the water column attributed to steam bubble collapse are followed by distinct seismic events with a sharp onset and a harmonic horizontal motion whose frequency varies spatially but not temporally a superposition of these events creates the appearance of continuous harmonic tremor since the pressure in the water column exhibits no sign of resonance the harmonic motion must be caused by elastic waves reverberating in the solid medium a near surface soft layer is demonstrated to be a possible elastic model the harmonic tremor observed at old faithful seems analogous to some examples of shallow volcanic tremor

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

genesis of the late ordovician kukaazi pb zn deposit in the western kunlun orogen nw china new insights from in situ trace elemental compositions of base metal sulfides abstract the kukaazi pb zn deposit was recently discovered in the western kunlun orogen wko nw china this deposit consists of three ore blocks ki to kiii hosted in mesoproterozoic metamorphosed rocks ores are mainly composed of sphalerite galena chalcopyrite and scheelite here we present in situ la icp ms trace elemental compositions of sphalerite and galena of sulfide ores from ore blocks ki and kii to shed light on the ore formation and its regional tectono metallogenic implications sphalerite from ore block ki contains higher contents of fe mn co cu bi sn and sb than sphalerite from ore block kii nonetheless sphalerite from the two ore blocks has compositions similar to the sphalerite from typical skarn deposits galena from ore block ki is compositionally different from galena from ore block kii and has relatively high ag cd and tl contents and low sb content such differences are probably due to different ore forming temperatures in these two ore blocks based on the cd partition coefficient between the co existing sphalerite galena pairs sulfide ores in ore block ki may have formed under higher temperatures 265 387 c than those in ore block kii 229 251 c combined with previous studies we propose that the pb zn mineralization at kukaazi was distal skarn related and formed in a continental arc setting discovery of this deposit implies that wko is a promising area for future porphyry skarn related pb zn cu w mineral exploration in northwestern china

geological geophysical and geochemical characteristics of the ban kiouchep cu pb ag deposit and its exploration significance in northern laos abstract the simao indochina basin is located between the loei luang prabang dien bien phu fold belt and the jinghong nan uttaradit suture zone composed of mesozoic and cenozoic red beds it overlies the marine clastic rocks and volcanic sedimentary rocks of a paleozoic back arc foreland sequence the late triassic indosinian orogeny and subsequent superimposition and intracontinental shearing and structural superimposition may have facilitated the formation of various deposits in this basin including hydrothermal skarn and porphyry types of mineralization the ban kiouchep cu pb ag deposit is a medium low temperature hydrothermal deposit that is largely controlled by faults and is hosted in carbonate rocks and volcanic sedimentary rocks the formation of this deposit includes a series of geological and metallogenic processes i neritic littoral facies volcanic sedimentation in a late paleozoic to late triassic back arc foreland setting ii indosinian orogenic transformation iii mesozoic cenozoic tectonic hydrothermal overprinting and iv epigenetic oxidized leaching the ore minerals are primarily malachite azurite and galena followed by sphalerite chalcocite and chalcopyrite with associated silver minerals using induced polarization ip geophysical surveys and soil geochemical surveys large scale and highly overlapping coincident anomalies and a mineralized zone at a scale of 100 110 m size ore body i was discovered in the area two anomalies p1 c1 and p5 c4 with the best metallogenic conditions and the deepest extensions of the known ore bodies were further selected as engineering verification targets the two following verifying drill holes revealed pb zn ag mineralization in the fault zone however no mineralized ore bodies consistent with the anomalies were found the high background value of the fe cu pb zn ag elements strong fracturing and hydrothermal alteration as well as later oxidized leaching with lateritization resulted in in situ dispersion and local secondary enrichment of the metallogenic elements these may be the primary causes of the overlapping anomaly distribution along the strata and faults therein lateritic ag mineralization has been also found in the area the geological geophysical and geochemical characteristics and the prospecting are of great importance for further research and prospecting for other related deposits for example the vhms sedex hydrothermal cu polymetallic deposits and porphyry skarn epithermal sediment hosted orogenic au deposits with lateritic ag au deposits in the simao indochina basin of northern laos

strain offsets with monotonous damped oscillations during the 1986 izu oshima volcano eruption the sequential process of the 1986 izu oshima volcano eruption japan was recorded by a volumetric strain meter near the erupted summit the records show occasional strain offsets accompanying long period damped oscillations which we interpret as responses of the volcanic system to perturbations in magmatic pressure the polarities of strain offsets were contractive for all events before the enormous ground deformation of november 21 due presumably to the intensive dike intrusion on the contrary all events after that had expansive polarities the characteristic frequencies of oscillations were 42 6 mhz for the events before changing abruptly to half that after the ground deformation in our model which is a one dimensional magma filled conduit the boundary condition at the top of the conduit changed from a closed to an open end upon a void formation at the top of the magma head due to its descent immediately after the dike intrusion before the magma escape from the reservoir as a dike magma was episodically supplied from the reservoir to the conduit and thus contraction events were generated after the magma escape magma left in the conduit was episodically drained back to the reservoir to generate expansion events this episodic magma supply or drainage was modeled by a prescribed pressure change at the bottom of the conduit we solved the free oscillation problem of the conduit pipe with an elastic sidewall to calculate the resultant volumetric strain outside the pipe physical properties of the magma and the excitation mechanism are inferred from the application of our formulation to the observation the conduit length and fluid acoustic velocity are estimated to be 10 km and 430 m s respectively suggesting that the fluid is composed of a gas liquid mixture if the conduit radius is taken to be 40 m and if the damping of oscillation occurred by viscous dissipation the fluid viscosity is 108 109 pa s a reasonable estimate for the basaltic magma the applied pressure changes at the bottom of the conduit are in a range from 105 to 106 pa with risetimes of the order of 4 to 100 s

tectonic evolution of the malay peninsula abstract the malay peninsula is characterised by three north south belts the western central and eastern belts based on distinct differences in stratigraphy structure magmatism geophysical signatures and geological evolution the western belt forms part of the sibumasu terrane derived from the nw australian gondwana margin in the late early permian the central and eastern belts represent the sukhothai arc constructed in the late carboniferous early permian on the margin of the indochina block derived from the gondwana margin in the early devonian this arc was then separated from indochina by back arc spreading in the permian the bentong raub suture zone forms the boundary between the sibumasu terrane western belt and sukhothai arc central and eastern belts and preserves remnants of the devonian permian main palaeo tethys ocean basin destroyed by subduction beneath the indochina block sukhothai arc which produced the permian triassic andesitic volcanism and i type granitoids observed in the central and eastern belts of the malay peninsula the collision between sibumasu and the sukhothai arc began in early triassic times and was completed by the late triassic triassic cherts turbidites and conglomerates of the semanggol formation were deposited in a fore deep basin constructed on the leading edge of sibumasu and the uplifted accretionary complex collisional crustal thickening coupled with slab break off and rising hot asthenosphere produced the main range late triassic earliest jurassic s type granitoids that intrude the western belt and bentong raub suture zone the sukhothai back arc basin opened in the early permian and collapsed and closed in the middle late triassic marine sedimentation ceased in the late triassic in the malay peninsula due to tectonic and isostatic uplift and jurassic cretaceous continental red beds form a cover sequence a significant late cretaceous tectono thermal event affected the peninsula with major faulting granitoid intrusion and re setting of palaeomagnetic signatures

subsurface cyclic magma sill expansions in the 2000 miyakejima volcano eruption possibility of two phase flow oscillation 1 step like tilt changes were observed at intervals of dozens of hours during the caldera formation stage occurred during the 2000 miyakejima volcano eruption our analysis suggests that these tilt steps were caused by the cyclic expansion of a subsurface sill like magma plumbing system trending from se to nw of the volcano in the same period a caldera gradually grew at the summit area to a very large 1 6 km in diameter and 450 m in depth the source mechanism of these tilt steps is fairly well explained by a two phase flow instability called a pressure drop oscillation this model indicates that the gas phase capacity in the upper part of the conduit acts as a pump that controls the flux of two phase magma in the sill like reservoir caldera formation as well as magma uplift and descent in the conduit may reflect temporal changes in the intervals between tilt steps which are themselves proportional to the volume of this gas capacity

nonlinear visco elastic volcanic model and its application to the recent eruption of mt unzen abstract a volcanic model is proposed the model consists of a magma reservoir which is a spherical hole in an elastic medium and is being replenished from below and a conduit which is a circular cylinder in a visco elastic medium the model is expressed by a system of two coupled nonlinear differential equations we solve the system as an initial value problem with a source term corresponding to the magma supply the supply rate is expressed by a bell shape function with a constant part this model works as follows supplied magma to the reservoir at a given rate increases pressure inside the reservoir the increased pressure expands the conduit through which the magma is discharged with the rate determined by poiseuille s flow law although the system eventually goes to a steady state in which the in and out flows are balanced the difference between response times of the reservoir and conduit causes the oscillation of the discharge rate this means that a volcanic activity oscillates for a pulse input expressed by a bell shape function the number of oscillations increases when the amount of inflow magma increases this model is applied to the recent volcanic activities of mt unzen the model well simulates the semi long term few years variation of the discharge rate of lava with a plausible replenishment rate of magma geometrical factors of the volcanic system the volume and radius of the reservoir the maximum and average radii of the conduit and some physical constants the maximum excess pressure viscosity of the country rock and mogi s coefficient are estimated under assumptions on the following quantities density difference between the country rock and magma rigidity of the country rock bulk modulus and viscosity of magma all quantities calculated except the viscosity agrees with corresponding values determined by independent methods within a factor of two or three we discussed physical background of these results together with the model itself

the geology and gold deposits of the victorian gold province abstract the palaeozoic succession of victoria represents a major world gold province with a total production of 2500 t of gold i e 78 million oz on a global scale central victoria represents one of the most gold mineralized areas outside the witwatersrand of south africa and remains the prime example of a slate belt gold province also known as turbidite hosted or shale greywacke gold province production came from quartz veins 1000 t modern placers 1200 t and palaeoplacers 300 t up to 7000 mines produced gold from quartz veins however the 168 mines of this type which produced over 1 t au contributed 68 of the primary gold production twelve goldfields have each produced 30 t au approximately one million ounces from all sources with bendigo 697 t ballarat 408 t and castlemaine 173 t being the largest these twelve goldfields have contributed 71 of the combined primary and secondary production gold mining commenced in 1851 declined dramatically around 1914 and has not increased significantly since the palaeozoic succession of victoria is part of an extensive fold belt along much of eastern australia i e the tasman orogenic belt in victoria the succession is dominated by cambrian to early devonian clastic metasedimentary rocks that have undergone major upright deformation and low grade metamorphism culminating in the middle devonian tabberabberan orogeny north south inliers of cambrian metavolcanic and metasedimentary rocks associated with regional fault zones divide the province into several geologically distinct zones in central victoria there are particularly well developed acid volcanic complexes of late devonian age and synchronous peraluminous granites which represent high temperature crustal melting tertiary to quaternary basalts have covered some of the palaeozoic gold deposits and have also covered several rich gold placer deposits of cainozoic age larger goldfields including bendigo and ballarat occur in ordovician slate and greywacke sequences but a wide range of metamorphosed sedimentary and igneous rock types are host to goldfields most if not all primary deposits demonstrate structural control although the controlling structural features differ between deposits wallrock alteration is strongly influenced by host rock in metasedimentary rocks it is limited and subtle but it is more pervasive in mafic and felsic igneous rocks carbonates muscovite and pyrite are the most widespread alteration minerals in these rocks representing co 2 k and s addition enrichment of as within gold deposits is common with sb important in some small deposits whereas base metals are only abundant locally and bi w mo and te show strong spatial association with granites and are rarely associated with economic gold deposits granites are an important component of the palaeozoic succession in victoria no large deposits are within granites but a few goldfields including maldon 65 t au are within contact aureoles of either s or i type granites of differing degrees of fractionation and silica content a single stage but protracted and possibly diachronous period of gold introduction near the time of the middle devonian tabberabberan deformation can explain geological relationships at many gold deposits the possibility that this event was slightly older i e silurian or early devonian in the west of the state cannot be precluded from the available evidence the mineralizing event appears linked to the same thermal event as diorite lamprophyre dykes and graite intrusions acidic and basaltic volcanism deformation and regional metamorphism the limited amount of fluid chemistry data from victorian gold deposits suggests low salinity fluids which contained co 2 and variable methane with homogenization temperatures from 150 to 300 c the sulphur isotopic compositions of pyrite are mostly 1 to 5 with some values slightly above 10 mineralizing temperatures are inferred to be near 300 c and pressure around 1 2 kbar sulphide rich gold deposits in the east of victoria many of which contain significant base metals contrast with the rest of the province which contains mostly gold deposits with lower sulphide content and this eastern area should possibly be viewed as separate from the victorian gold province per se the benefits to victorian gold mining coming from the 1980 s global gold boom have been insignificant compared to the historical importance of the victorian gold province there seems little justification for assuming that all the large deposits have been discovered and there is reason to believe new deposit styles may emerge to complement the limited current exploration activity which is focussed on the search for extensions and repeats of known deposit types a major advance in scientific understanding of these oft neglected deposits could kindle a major exploration and production revival

observed characteristics of tide surge interaction along the east coast of india and the head of bay of bengal hourly tide gauge data at chennai visakhapatnam and paradip along the east coast of india and at hiron point at the head of bay of bengal were analysed statistically for tide surge interaction dependency of surge maxima on magnitude and phase of the tide were examined separately and interaction was quantified for each site along the east coast of india interaction is found to be less but significant the degree of interaction is highest at hiron point where surges peak more frequently about 4 hours before the high tide application of a simple model shows the observed surge peak distribution at hiron point can be explained in terms of phase alteration of tide due to surge and surge modulation by tide the degree of interaction tends to increase northward as the tidal range and surge height increases

variations in tilt rate and harmonic tremor amplitude during the january august 1983 east rift eruptions of kilauea volcano hawaii abstract during january august 1983 a network of telemetered tiltmeters and seismometers recorded detailed temporal changes associated with seven major eruptive phases along the east rift of kilauea volcano hawaii each eruptive phase was accompanied by subsidence of the summit region and followed by reinflation of the summit to approximately the same level before renewal of eruptive activity the cyclic summit tilt pattern and the absence of measurable tilt changes near the eruptive site suggest that conditions in the summit region controlled the timing of the last six eruptive phases the rate of summit subsidence progressively increased from one eruptive phase to the next during the last six phases the amplitude of harmonic tremor increased during the last four phases the increases in subsidence rate and in tremor amplitude suggest that frequent periods of magma movement have reduced the flow resistance of the conduit system between the summit and the rift zone

ground deformation associated with volcanic tremor at izu oshima volcano izu oshima volcano had summit and fissure eruptions in november 1986 after 12 years of dormancy and three small eruptions followed these events within one year episodic and continuous volcanic tremors were observed for the period containing these eruptions it is a remarkable discovery that the episodic volcanic tremor was accompanied by a small but sharp ground deformation the polarity of which was variable the distribution of tilt vectors reveals that the source of ground deformation was always located beneath the northwestern flank of the volcano where a magma reservoir was predicted by other studies on the other hand the seismologically detected tremor source was determined to be at a shallow depth below the central pit crater a few kilometers away from the predicted magma reservoir it is thus inferred that the tremor source near the crater generated pressure increases or decreases that were simultaneously transmitted through the vent to the magma reservoir and lead to its expansion or contraction

geology geochemistry and metallogenesis of the selinsing gold deposit central malaysia malaysia is endowed with a number of major sediment hosted orogenic gold deposits that lie parallel to but east of the bentong raub suture zone which runs approximately n s in central malaysia the selinsing gold deposit is one of the major economic deposits in central malaysia and is hosted by meta sedimentary units the deposit is affected by later deformation and metamorphism during the triassic due to the collision of the sibumasu terrane with the sukhothai arc laser ablation icp ms u pb zircon dating of the host rocks indicates a carboniferous ca 331 300 ma maximum depositional age ore minerals include pyrite arsenopyrite galena sphalerite chalcopyrite pyrrhotite and gold detailed textural and geochemical studies revealed five distinctive pyrite types sub rounded framboidal pyrite pyrite 1 rounded recrystallized pyrite pyrite 2 anhedral inclusion rich pyrite pyrite 3 anhedral to subhedral clean pyrite pyrite 4 and coarse euhedral clean pyrite pyrite 5 laser ablation icp ms trace element analysis of the framboidal pyrite indicates enrichment in v as mo ni se te ag and zn relative to the other pyrite types pyrite sulfur isotope composition 1 2 9 2 suggests a likely mixture of magmatic and local sedimentary source for the sulfur pyrite pb isotope results pb206 pb204 18 94 19 10 pb207 pb204 15 72 15 73 suggest a high u source rock for the lead fluid inclusions are co2 rich 95 100 mol and yielded homogenization temperatures from 194 to 348 c and salinities between 1 23 and 9 98 wt nacl equiv suggesting involvement of metamorphic fluids during ore formation based on these results we suggest a two stage model for the formation of the gold deposit at selinsing stage 1 consists of early enrichment of the elements au v as mo se te ni ag and zn in framboidal pyrite in the sediments whereas stage 2 is characterized by multiple post diagenetic deformation and metamorphic processes favoring the development of fluid pathways and au remobilization into later pyrites regionally the selinsing gold deposit shares geological similarities in term of host rocks ore mineralogy and geochemistry with many other sediment hosted orogenic gold deposits in mainland se asia such as the sepon gold deposit laos langu gold deposit thailand modi taung and meyon gold deposits myanmar and phuoc son gold deposit central vietnam we suggest that our two stage model may have important implications to mineral exploration for future research on sediment hosted orogenic gold deposits in se asia

observing storm surges in the bay of bengal from satellite altimetry abstract in the present study we examined 15 years 1993 2007 of satellite altimeter and coastal tide gauge records in the bay of bengal and demonstrate that satellite altimetry can be a useful complementary dataset for the study of storm surges we first examined the performance of x track processed altimeter data during the period of study 1993 2007 30 19 21 09 09 07 and 07 01 storm surge events were identified from tide gauges altimetry at hiron point paradip visakhapatnam and chennai respectively the magnitudes of surges observed by altimeters are comparable to those recorded in tide gauges though observing storm surges by altimeters rely purely on a chance the presence of multiple satellite tracks in a region considerably enhances the chances of capturing the signals of an extreme event moreover information on cross shelf variations of storm surges is useful for model validation

multistage sedimentary and metamorphic origin of pyrite and gold in the giant sukhoi log deposit lena gold province russia gold mineralization at sukhoi log in eastern siberia is hosted in a deformed neoproterozoic organic bearing and pyritic black shale and siltstone sequence that is folded into a tight overturned anticline the deposit contains about 30 million ounces of gold at an average grade of 2 0 g t au and is one of the largest known undeveloped gold resources the high grade gold zone forms a gently dipping tabular body in the core of the anticline the best gold grades occur in narrow bedding parallel pyrite quartz veinlets that have been folded during the main deformation event lower grade gold is associated with disseminated pyrite developed in and around the high grade core of the deposit detailed paragenetic studies of the mineralization and host rocks have defined six stages of pyrite development in the carbonaceous sediments the two earliest forms of pyrite termed py1 and py2 are commonly developed in stratiform layers of micron sized crystals framboids and fine euhedra which are interpreted as synsedimentary to early diagenetic in origin coarser grained bedding parallel aggregates of inclusion rich pyrite termed py3 contain inclusions of arsenopyrite native gold and gold tellurides and are interpreted to form during late diagenesis and earliest deformation coarse euhedral pyrite py4 overgrows the earlier pyrite py1 py2 and py3 and the slaty cleavage developed in the host rocks indicating a syndeformation timing late stage inclusion free pyrite py5 overgrows and replaces earlier sulfides and is considered to be syn to late deformation laser ablation inductively coupled plasma mass spectrometry la icpms analyses of the various pyrite types indicate that the synsedimentary py1 contains the highest levels of invisible gold varying from 0 4 to 12 1 ppm with a mean of 3 22 ppm au and 1 900 ppm as py1 is also enriched in a suite of trace elements mo sb ni co se te ag cu pb zn mn ba cr u v which are similar to those concentrated by organic processes in euxinic sedimentary environments later generations of pyrite from py2 to py5 including pyrite in bedding parallel pyrite quartz veinlets contain progressively lower contents of invisible gold and most other trace elements however this metamorphic and postmetamorphic pyrite contains microinclusions of free gold arsenopyrite pyrrhotite sphalerite and chalcopyrite the paragenetic textural and chemical relationships at sukhoi log suggest that gold was clearly initially introduced prior to cleavage development accompanying sedimentation of the organic rich shales and fixed during diagenesis within the structure of diagenetic arsenian pyrite subsequently accompanying deformation gold was liberated from recrystallized diagenetic pyrite to become concentrated as free gold and gold tellurides within metamorphic pyrite and folded bedding parallel pyrite quartz veinlets two key processes are considered vital to the formation of the sukhoi log deposit original synsedimentary and early diagenetic concentration of gold dissolved within arsenian pyrite in organic rich black shales and metamorphic processes that liberated gold from the early forms of arsenian pyrite to be concentrated as free gold and gold tellurides within late diagenetic and metamorphic pyrite and associated pyrite quartz veinlets in the core of an overturned anticline these ore forming processes are unlikely to be unique to sukhoi log other black shale and turbidite hosted deposits that occur in rifted continental margin environments which have undergone collision and basin inversion may form by similar processes

geology and fluid characteristics of the ulu sokor gold deposit kelantan malaysia implications for ore genesis and classification of the deposit abstract the ulu sokor gold deposit is one of the most famous and largest gold deposits in malaysia and is located in the central gold belt this deposit consists of three major orebodies that are related to ns and ne striking fractures within fault zones in permian triassic meta sedimentary and volcanic rocks of the east malaya block the faulting events represent different episodes that are related to each orebody and are correlated well with the mineralogy and paragenesis the gold mineralization consists of quartz dominant vein systems with sulfides and carbonates the hydrothermal alteration and mineralization occurred during three stages that were characterized by i silicification and brecciation ii carbonatization sericitization and chloritization and iii quartz carbonate veins fluid inclusions in the hydrothermal quartz and calcite of the three stages were studied the primary co 2 ch 4 h 2 o nacl fluid inclusions in stage i are mostly related to gold mineralization and display homogenization temperatures of 269 389 c salinities of 2 77 11 89 wt nacl equivalent variable co 2 contents typically 5 29 mol and up to 15 mol ch 4 in stage ii gold was deposited at 235 398 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 0 83 9 28 wt nacl equivalent variable co 2 contents typically 5 63 mol and up to 4 mol ch 4 the 18 o h 2 o and d values of the ore forming fluids from the stage ii quartz veins are 4 5 to 4 8 and 44 to 42 respectively and indicate a metamorphic hydrothermal origin oxygen fugacities calculated for the entire range of t p x co 2 conditions yielded log f o 2 values between 28 95 and 36 73 for stage i and between 28 32 and 39 18 for stage ii these values indicate reduced conditions for these fluids which are consistent with the mineral paragenesis fluid inclusion compositions and isotope values the presence of daughter mineral bearing aqueous inclusions is interpreted to be a magmatic signature of stage iiia combined with the oxygen and hydrogen isotopic compositions 18 o h 2 o 6 8 to 11 9 d 77 to 62 these inclusions indicate that the initial fluid was likely derived from a magmatic source in stage iiib the gold was deposited at 263 to 347 c from a co 2 ch 4 h 2 o nacl fluid with a salinity of 5 33 to 11 05 wt nacl equivalent variable co 2 contents typically 9 15 mol and little ch 4 the oxygen and hydrogen isotopic compositions of this fluid 18 o h 2 o 8 1 to 8 8 d 44 to 32 indicate that it was mainly derived from a metamorphic hydrothermal source the co 2 h 2 o ch 4 nacl fluids that were responsible for gold deposition in the stage iiic veins had a wide range of temperatures 214 483 c salinities of 1 02 to 21 34 wt nacl equivalent variable co 2 contents typically 4 53 mol and up to 7 mol ch 4 the oxygen and hydrogen isotopic compositions 18 o h 2 o 8 5 to 9 8 d 70 to 58 were probably acquired at the site of deposition by mixing of the metamorphic hydrothermal fluid with deep seated magmatic water and then evolved by degassing at the site of deposition during mineralization the log f o 2 values from 28 26 to 35 51 also indicate reduced conditions for this fluid in stage iiic moreover this fluid had a near neutral ph and 34 s values of h 2 s of 2 32 to 0 83 which may reflect the derivation of sulfur from the subducted oceanic lithospheric materials the three orebodies represent different gold transportation and precipitation models and the conditions of ore formation are related to distinct events of hydrothermal alteration and gold mineralization the gold mineralization of the ulu sokor deposit occurred in response to complex and concurrent processes involving fluid immiscibility fluid rock reactions and fluid mixing however fluid immiscibility was the most important mechanism for gold deposition and occurred in these orebodies which have corresponding fluid properties structural controls geologic characteristics tectonic settings and origins of the ore forming matter these characteristics of the ulu sokor deposit are consistent with its classification as an orogenic gold deposit while some of the veins are genetically related to intrusions

the bentong raub suture zone abstract it is proposed that the bentong raub suture zone represents a segment of the main devonian to middle triassic palaeo tethys ocean and forms the boundary between the gondwana derived sibumasu and indochina terranes palaeo tethyan oceanic ribbon bedded cherts preserved in the suture zone range in age from middle devonian to middle permian and melange includes chert and limestone clasts that range in age from lower carboniferous to lower permian this indicates that the palaeo tethys opened in the devonian when indochina and other chinese blocks separated from gondwana and closed in the late triassic peninsular malaysia segment the suture zone is the result of northwards subduction of the palaeo tethys ocean beneath indochina in the late palaeozoic and the triassic collision of the sibumasu terrane with and the underthrusting of indochina tectonostratigraphic palaeobiogeographic and palaeomagnetic data indicate that the sibumasu terrane separated from gondwana in the late sakmarian and then drifted rapidly northwards during the permian triassic during the permian subduction phase the east malaya volcano plutonic arc with i type granitoids and intermediate to acidic volcanism was developed on the margin of indochina the main structural discontinuity in peninsular malaysia occurs between palaeozoic and triassic rocks and orogenic deformation appears to have been initiated in the upper permian to lower triassic when sibumasu began to collide with indochina during the early to middle triassic a type subduction and crustal thickening generated the main range syn to post orogenic granites which were emplaced in the late triassic early jurassic a foredeep basin developed on the depressed margin of sibumasu in front of the uplifted accretionary complex in which the semanggol formation rocks accumulated the suture zone is covered by a latest triassic jurassic and cretaceous mainly continental red bed overlap sequence

volcanic tremor induced by gas liquid two phase flow implications of density wave oscillation 1 we model the source mechanism of volcanic tremor at shallow depths of a volcano by hydrothermal dynamics steam water two phase flow in the pipe is formulated and its instability known as density wave oscillation can produce monotonic characteristics similar to those of a volcanic tremor the oscillation is closely related to the heat supplied to the system and we quantitatively obtain the upper and lower limits of the heating quantity to realize this monotonic oscillation this source mechanism can be realized only when the effect of gravity is small i e horizontal flow since the effect of depressurization due to upwelling is significant for bubble growth with vertical flow including gravity and heating and vaporization are less important

numerical simulation of the steam water flow instability as a mechanism of long period ground vibrations at geothermal areas summary we present a model for the excitation of continuous ground vibration at geothermal areas and active volcanoes which is based on the instability of water steam two phase flow through a series of numerical experiments we evaluate the amplitude and period of ground vibrations excited by density wave oscillation called dwo one of the flow instability phenomena which is known in the nuclear reactor engineering to occur under a wide variety of boundary conditions we consider a vertical cylindrical pipe buried underground and 1 d flows through it driven by the lithostatic pressure gradient water flows into the pipe from below and is evaporated by the heat supplied from outside when the heating rate is low after a perturbation such as a change in heating rate is given to the flow system a decaying oscillation of pressure flow velocity and void fraction occurs being followed by a stationary flow on the other hand when the heating rate exceeds a threshold the perturbation grows to a continuous oscillation with a fixed amplitude forming a limit cycle dwo we investigate how various parameters such as pipe length pressure and heating rate affect the stability of the two phase flow we then estimate the amplitudes of seismic waves excited by dwo assuming that the pipe is embedded in a elastic half space we find that a longer pipe can excite a dwo of longer period and of larger maximum amplitude for a pipe of length of 100 m with its bottom at the depth of 150 m the dwo period is nearly 10 s in this case the maximum pipe diameter for the excitation of limit cycle dwo for reasonable rates of stationary conductive heat supply from country rocks to the two phase mixture inside the pipe less than about 35 mw m 3 is 0 02 m the maximum amplitudes of ground displacement due to dwo are of the order of 7 10 8 m and 4 10 9 m at epicentral distances of 200 and 1000 m respectively typical geothermal areas and active volcanoes can supply heat and discharged water mass which are required to excite dwo larger than typical background noises therefore dwo due to a shallow water steam flow could excite ground motions with periods longer than 10 s which is large enough to be observed with suitably designed broadband seismic experiments at geothermal fields

cyclic fluid effusion accompanied by pressure change implication for volcanic eruptions and tremor magma effusion and tremor sometimes occur in quite regular intervals with periodic pressure changes as observed in volcanic eruptions at kilauea volcano lava dome growth at unzen volcano and tremor episodes at izu oshima volcano these events have more or less asymmetric pressure change of quasi sinusoidal to saw toothed shape with longer time elapsing in build up of the fluid pressure than in its relaxation such cyclic fluid effusion can be explained systematically by a simple model in which fluid is supplied at a constant rate accumulates in an elastic chamber and flows out in a cylindrical vent that may widen or narrow due to viscous deformation of the surrounding country rock

a carbonaceous sedimentary source rock model for carlin type and orogenic gold deposits this paper presents evidence and arguments that carbonaceous sedimentary rocks were a source for au and as in sediment hosted orogenic and carlin type gold deposits and develops a corresponding genetic model in this two stage basin scale model gold and arsenic are introduced early into black shale and turbidite basins during sedimentation and diagenesis stage 1 and concentrated to ore grades by later hydrothermal structural or magmatic processes stage 2 in reduced continental margin basin settings organic matter sedimented under anoxic to euxinic conditions immobilizes and concentrates gold arsenic and a range of trace elements particularly v ni se ag zn mo cu u present in marine bottom waters into fine grained black mudstone and siltstone of slope and basin facies during early diagenesis gold and certain other trace elements ni se te ag mo cu pge are preferentially partitioned into arsenian pyrite that grows in the muds these processes produce regionally extensive black shale and turbidite sequences enriched in syngenetic gold and arsenic commonly from 5 to 100 ppb au and 10 to 200 ppm as rare organic and sulfide rich metalliferous black shales may contain up to 1 to 2 ppm au and over 1 000 ppm as present as refractory gold in arsenian pyrite and nanoparticles of free gold during late diagenesis and early metamorphism stage 2 the diagenetic arsenian pyrite is recrystallized to form coarser grained pyrite generations and the organic matter is cooked to bitumen under higher grade metamorphism lower greenschist facies and above arsenian pyrite in carbonaceous shales is converted to pyrrhotite these processes release gold arsenic sulfur and other elements sb te cu zn mo bi tl and pb from the source rocks to become concentrated by hydrothermal processes locally to produce gold ores in structural sites such as fold hinge zones shear or breccia zones within or above the black shale sequence la icp ms analyses of diagenetic pyrite in carbonaceous sediments both associated and not associated with gold deposits suggests that invisible gold contents of greater than 250 ppb in diagenetic pyrite are indicative of carbonaceous shale source rocks with the potential to produce economic gold deposits application of this sedimentary source rock model enables a systematic exploration approach for sediment hosted gold deposits based on the distribution composition and structure of carbonaceous shale sequences and their contained diagenetic pyrite

pyrite geochemistry and metallogenic implications of gutaishan au deposit in jiangnan orogen south china abstract the gutaishan is an important intrusion related gold au deposit within the jiangnan orogen in south china it is characterized by the superposition of multistage alteration mineralization that occur as i pre ore barren quartz veining ii early ore quartz dolomite pyrite arsenopyrite mineralization iii late ore quartz dolomite native gold pyrite arsenopyrite stibnite mineralization and iv post ore quartz dolomite pyrite veining the main gold hosts of the gutaishan deposit are the stage ii to iv pyrites but these have different trace element compositions and occurrences for example from stages ii to iii there are variations in se co and bi that suggest increasing oxygen fugacity fo2 which then decreases slightly from stage iii to iv the stage ii fine grained pyrite has high as contents that may have resulted from rapid pyrite precipitation whereas the high as contents in the stage iv pyrite coupled with the absence of sericite in stage iv may be the result of neutralization of acidic ore fluids the gutaishan ore related pyrites have similar trace element compositions to those of typical hydrothermal pyrite such as se te 22 08 78 96 low co ni 0 03 0 95 and a wide ni range 0 195 892 ppm which implies a major sedimentary contribution this study integrates information on regional extensional setting published h o s pb data and an analysis of the close space time relationship between the gutaishan and baimashan granites the existence of a genetic link between gutaishan au mineralization and the emplacement of late triassic baimashan granite is proposed in addition to an amount of sedimentary input to the gutaishan these results reveal that the intrusion related gold deposits in the jiangnan orogen have considerable exploration potential

phanerozoic plate boundaries in mainland se asia the himalayas and tibet recently available geological data on tibet yunnan and burma facilitate recognition of phanerozoic subduction systems and two continental fragments of gondwanaland which extend through mainland se asia a cambrian subduction system and 5 mesozoic early caenozoic collision belts are identified in the region indochina eastern thailand and central tibet accreted to china in the early triassic western se asia and s tibet separated from gondwanaland in the permian or early triassic and collided with asia in the late triassic and the western burma island arc system collided with asia in the jurassic upper triassic flysch and schist in the eastern indoburman ranges were accreted to western burma in the jurassic early cretaceous during eastward subduction and formation of a back arc thrust belt following collision of greater india with arc complexes to the n in the cretaceous and with tibet in the early eocene western burma moved northwards about 450 km along the sagaing namyin ridge thrust transform fault formation of the 3 major belts of tin granites and the porphyry copper deposits in the region took place in specific tectonic settings within the subduction systems and collision belts

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

gold and trace element zonation in pyrite using a laser imaging technique implications for the timing of gold in orogenic and carlin style sediment hosted deposits laser ablation icp ms imaging of gold and other trace elements in pyrite from four different sedimenthosted gold arsenic deposits has revealed two distinct episodes of gold enrichment in each deposit an early synsedimentary stage where invisible gold is concentrated in arsenian diagenetic pyrite along with other trace elements in particular as ni pb zn ag mo te v and se and a later hydrothermal stage where gold forms as either free gold grains in cracks in overgrowth metamorphic and or hydrothermal pyrite or as narrow goldarsenic rims on the outermost parts of the overgrowth hydrothermal pyrite compared to the diagenetic pyrites the hydrothermal pyrites are commonly depleted in ni v zn pb and ag with cyclic zones of co ni and as concentration the outermost hydrothermal pyrite rims are either as au rich as in moderate to highgrade deposits such as carlin and bendigo or co ni rich and as au poor as in moderate to low grade deposits such as sukhoi log and spanish mountain the early enrichment of gold in arsenic bearing syngenetic to diagenetic pyrite within black shale facies of sedimentary basins is proposed as a critical requirement for the later development of carlin style and orogenic gold deposits in sedimentary environments the best grade sediment hosted deposits appear to have the gold climax event toward the final stages of deformation related hydrothermal pyrite growth and fluid flow

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

palaeogeography of late triassic red beds in singapore and the indosinian orogeny abstract a red bed facies of the upper triassic jurong formation has been logged on sentosa island singapore an overall coarsening and thickening upward pattern is well developed the lower part of the section is dominated by purple red massive to finely laminated illite smectite kaolin rich mudstones containing thin discontinuous lenses of fine sandstone marked by low angle lamination and small ripples one dinosaur like foot print has been discovered in a loose block of red mudstone it is concluded that this is a lacustrine sequence and it is proposed to name the lake lake sentosa the upper part of the sequence consists of flat laminated to trough cross bedded medium grained sandstone and granule to cobble conglomerates alternating with purple red mudstone the mudstone sandstone packages are arranged in decametre scale coarsening upward cycles the channelling and decimetre scale cross bedding characterising the sandstone and conglomeratic beds is evidence for deposition by flashy fluvial flood processes possibly feeding into the lake as a fresh water delta one possible dinosaur trackway in granule size conglomerate has been located detrital zircon u pb ages vary from 2 7 ba to 209 ma with significant populations at 245 ma and 220 ma these ages throw light on the timing of the indosinian orogeny the molasse red beds of the jurong formation were deposited in a half graben formed in the hangingwall of the bukit timah fault when central peninsular malaysia went into extension following the climax of the indosinian orogeny in the late triassic

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

genesis of the selinsing gold deposit peninsular malaysia constraints from mineralogy geochemistry and in situ sulfur isotope compositions of sulfides abstract as a renowned orogenic lode gold deposit the selinsing gold deposit is located in the central belt of peninsular malaysia geologically the gold deposit is characterized by auriferous quartz veins and fine grained gold minerals coexisted with sulfides and the ore body is hosted by low grade metamorphic sedimentary rocks and volcanic rocks furthermore gold mineralization is closely related to tectonic deformation four main stages of vein formation have been identified namely 1 quartz pyrite arsenopyrite vein 2 quartz pyrite gold vein 3 quartz stibnite pyrite vein and 4 quartz chlorite vein the occurrence of gold includes two types i e visible gold and invisible gold the former is featured by coarse grained gold millimeter scale such as auriferous quartz veins and fine grained gold micron scale such as native gold calaverite and electrum the latter is contained in pyrite and arsenopyrite in the form of nano scale native gold particles au0 and lattice gold au1 the geothermometer of arsenopyrite and chlorite as well as temperature sulfur fugacity diagram indicate that the temperature and sulfur fugacity of hydrothermal fluid decrease gradually considering that the sulfur fugacity drops gradually and aqueous inclusions coexist with carbonic inclusions it is inferred that sulfuration reaction in which sulfur is consumed to produce sulfides and fluid immiscibility or phase separation may be responsible for gold precipitation tested by la mc icp ms the in situ sulfur isotope compositions of sulfides formed in different stages are homogenous about 1 to 1 and the calculated h2s dominated hydrothermal fluid is also consistent about 2 to 0 in sulfur isotope compositions which reflect the mantle or ultrabasic rock and basic rock or magmatic rocks may be a potential source of sulfur combined with possible source and tectonic evolution of peninsular malaysia possible metallogenic processes are proposed to explain genesis of the selinsing gold deposit and other gold deposits in the central belt i e ore forming fluid was differentiated from oceanic crust and or fertilized mantle wedge or ore forming fluid may be sourced from concealed magmatic rocks that formed by subduction of the palaeo tethys toward the east malaysia block

tectonic framework and phanerozoic evolution of sundaland abstract sundaland comprises a heterogeneous collage of continental blocks derived from the india australian margin of eastern gondwana and assembled by the closure of multiple tethyan and back arc ocean basins now represented by suture zones the continental core of sundaland comprises a western sibumasu block and an eastern indochina east malaya block with an island arc terrane the sukhothai island arc system comprising the linchang sukhothai and chanthaburi blocks sandwiched between this island arc formed on the margin of indochina east malaya and then separated by back arc spreading in the permian the jinghong nan uttaradit and sra kaeo sutures represent this closed back arc basin the palaeo tethys is represented to the west by the changning menglian chiang mai inthanon and bentong raub suture zones the west sumatra block and possibly the west burma block rifted and separated from gondwana along with indochina and east malaya in the devonian and were accreted to the sundaland core in the triassic west burma is now considered to be probably cathaysian in nature and similar to west sumatra from which it was separated by opening of the andaman sea basin south west borneo and or east java west sulawesi are now tentatively identified as the missing argoland which must have separated from nw australia in the jurassic and these were accreted to se sundaland in the cretaceous revised palaeogeographic reconstructions illustrating the tectonic and palaeogeographic evolution of sundaland and adjacent regions are presented

re os isotopic and trace element compositions of pyrite and origin of the cretaceous jinchang porphyry cu au deposit heilongjiang province ne china abstract the jinchang cu au deposit in northeast china contains more than 76 tons of au and 4683 tons of cu with average ore grades of 11 34 g t au and 1 44 cu the deposit is typical of porphyry types and consists of gold orebodies mainly hosted in a 113 ma granitic porphyry and breccia pipes within the porphyry intrusion mineralization is closely associated with early potassic alteration and late phyllic alteration pyrite is the main au bearing mineral and contains 1 48 18 9 ppb re and 11 4 38 ppt common os extremely low common os concentrations and high re os ratios are indicative of derivation of ore forming materials from the crust low re in pyrite from the jinchang deposit may indicate a mixing source of mantle and crust or a crustal source five re os isotopic analyses yield a model 1 isochron age of 114 22 ma 2 mswd 0 15 similar to the age of the host porphyry pyrite contains detectable co ni cu zn as ag au sb pb and bi pyrite has co ni ratios similar to that of volcanogenic and hydrothermal sulfide deposits indicating a magmatic hydrothermal origin and has au and as contents similar to that of porphyry epithermal systems pyrite grains from potassic and phyllic alteration stages have different trace element contents reflecting the evolution of ore forming fluids from magmatic dominated to magmatic mixed with meteoric water in combination with regional geology our new results are suggestive of origin of the jinchang cu au deposit from contemporary intrusions of granitic porphyries related to the early cretaceous subduction of the paleo pacific plate

on the relationships between slab dip back arc stress upper plate absolute motion and crustal nature in subduction zones 1 statistical analysis of modern oceanic subduction zone parameters such as the age of a downgoing plate or the absolute plate motions is performed in order to investigate which parameter controls the dip of a slab and conversely what the influence of slab geometry is on upper plate behavior for that purpose parameters have been determined from global databases along 159 transects from all subduction zones that are not perturbed by nearby collision or ridge plateau seamount subduction on the basis of tomographic images slabs that penetrate through or lie on the 670 km discontinuity are also identified the results of the statistical analysis are as follows 1 back arc stress correlates with slab dip i e back arc spreading is observed for deep dips deeper than 125 km larger than 50 whereas back arc shortening occurs only for deep dips less than 30 2 slab dip correlates with absolute motion of the overriding plate the correlation is even better when the slab lies on or even more penetrates through the 670 km discontinuity 3 slabs dip more steeply by about 20 on average beneath oceanic overriding plates than beneath continental ones 4 slabs dip more steeply on average by about 10 near edges 5 slab dip does not correlate with the magnitude of slab pull the age of subducting lithosphere at the trench the thermal regime of the subducting lithosphere the convergence rate or the subduction polarity east versus west the present study provides evidence that the upper plate absolute motion plays an important role on slab dip as well as on upper plate strain retreating overriding plates are often oceanic ones and thus may partially explain the steeper slab dips beneath oceanic upper plates one can infer that low slab dips correlate well with compression in continental advancing upper plates whereas steep dips are often associated with extension in oceanic retreating upper plates excess weight of old slabs is often counterbalanced by other forces probably asthenospheric in origin such as lateral mantle flow near slab edges or anchor forces to determine slab dip

hurricane isaac storm surges off florida observed by jason 1 and jason 2 satellite altimeters abstract storm surges can cause damage to properties and loss of life in coastal communities thus it is important to enhance our capabilities of observing understanding and forecasting storm surges for mitigating damage and loss previous studies have shown that cross shelf altimetric sea surface height profiles can be used to determine storm surge features in this study we combine satellite altimetry with tide gauge data to study storm surge features off florida in the gulf of mexico during hurricane isaac 2012 satellite observations show a storm surge of about 0 8 m near cedar key and apalachicola decreasing westward and southward in the early morning of august 28 2012 utc consistent with tide gauge measurements our analysis of satellite data reveals that the storm surge propagates northward from naples to cedar key with a phase speed of 14 16 m s and a cross shelf decay scale of 190 220 km in approximate agreement with the estimates from tide gauge data in contrast an analysis of tide gauge data reveals that the storm surge propagates westward from apalachicola to pensacola with a phase speed of 6 7 m s and a cross shelf decay scale of about 85 km it is further shown that the post storm sea level variations at these stations are associated with first mode continental shelf waves the present study shows that along shelf altimetric sea surface height profiles can be useful to observe and understand storm surge features as cross shelf ones demonstrated previously of importance to improvement of storm surge forecasting it suggests that a constellation of altimeter missions especially with wide swath altimetry could be suited to monitor storm surges

granitic magmatism basement ages and provenance indicators in the malay peninsula insights from detrital zircon u pb and hf isotope data abstract the malay peninsula lies on two continental blocks sibumasu and east malaya which are intruded by granitoids in two provinces the main range and eastern previous models propose that permian triassic granitoids are subduction related and syn to post collisional we present 752 u pb analyses that were carried out on zircons from river sands in the malay peninsula of these 243 grains were selected for hf isotope analyses our data suggest a more complex sibumasu east malaya collision history 176hf 177hfi ratios reveal that permian triassic zircons were sourced from three magmatic suites a permian crustally derived granitoids b early middle triassic granitoids with mixed mantle crust sources and c late triassic crustally derived granitoids this suggests three permian triassic episodes of magmatism in the malay peninsula two of which occurred in the eastern province although the exact timing of the sibumasu east malaya collision remains unresolved current data suggest that it occurred before the late triassic probably in late permian early triassic our data also indicate that sibumasu and east malaya basements are chronologically heterogeneous but predominantly of proterozoic age some basement may be neoarchaean but there is no evidence for basement older than 2 8 ga finally we show that hf isotope signatures of triassic zircons can be used as provenance indicators

u pb zircon geochronology of early permian to late triassic rocks from singapore and johor a plate tectonic reinterpretation article i nfo the results of u pb zircon geochronology of permian to middle triassic granitoids from singapore and neighbouring johor are presented rhyolite from pulau sibu is 276 5 ma gabbros from singapore give ages of 260 2 to 249 2 ma granites from singapore give ages from 249 2 to 230 6 ma and rhyolite from telkuma gives an age of 238 2 ma u pb detrital zircon age spectra from a late triassic conglomerate from singapore show carboniferous mid dle triassic and late triassic spikes at 350 245 and 217 ma respectively these new data when combined with published u pb zircon ages allow a revision of the plate tectonic evolution of the malaysian peninsula region a tin bearing magmatic arc evolved in the eastern malaysian peninsula part of indochina from the early permian to the middle triassic when the palaeo tethys ocean was subducted and sibumasu continental lithosphere was rifted from pangea this opened up the neo tethys ocean that the granitoid ages show a progressive decrease in age from pulau sibu 276 5 ma to singapore 230 6 ma suggests that during this andean type orogenic phase the subduction zone rolled back and steepened causing the locus of mainly i type magmatism to migrate from east to west in present day coordinates across the eastern and central belts and stretch the lithosphere as it did so in the late triassic sibumasu collided with indochina causing the western belt sibumasu to over thrust the central belt indochina along the bentong raub suture the lower half of the thickened crust formally the tin bearing indochina plate was partially melted and pre dominantly s type tin bearing granites were intruded into the upper crust formally sibumasu this late triassic collisional phase is the indosinian orogeny in peninsular malaysia

geochemistry of au bearing pyrite from the sepon mineral district laos dpr southeast asia implications for ore genesis abstract the sepon gold copper district occurs along the truong son foldbelt in a 10 km 40 km east trending corridor in southern laos this study has investigated the nature of gold in pyrite and ore forming fluid characteristics using laser ablation inductively coupled plasma mass spectrometry la icp ms and proton induced x ray emission pixe techniques gold is present as invisible gold au 1 and as nanoparticles of gold au0 in both sedimentary rock hosted gold and skarn cu au deposits gold is present in an early syngenetic pyrite generation pyrite 2b with concentrations to 0 5 ppm post sedimentation processes included formation of quartz veins which host pyrite 3b with concentrations to 1 8 ppm au the highest concentrations of gold were found in the rims of hydrothermal vein hosted pyrite 4a and in skarn related pyrite suggesting gold concentration at a later stage during the ore forming processes and not during sedimentation as rhyodacite porphyry is proximal to calcareous shale and dolomite that host ores it is plausible that the emplacement of rhyodacite porphyry introduced significant amount of hydrothermal fluids that circulated through fractures and favoured high grade to 293 ppm au in pyrite 4a and pyrite skn2 gold is preferentially concentrated in as rich zones and in areas that underwent brittle deformation as evidenced by fracture fill coarse grained pyrite 4a indicating a structural control to ore formation the predominance of se bi and te in pyrite skn1 and the elevated concentrations of bi cu se sn and mo in pyrite skn2 raise the possibility of derivation from a magmatic source the presence of primary hematite associated with the skarn suggests prevailing oxidising fluid conditions during au mineralisation in pyrite skn2 there is a striking chemical similarity between pyrite 4a core and py skn1 and rimmed zones of pyrite 4a and pyrite skn2 which indicates possibility of two types of hydrothermal fluids the as rich fluids with elevated concentrations of au se sb tl and cu recorded in pyrite 4a rims and pyrite skn2 the as poor fluids with elevated concentrations of ni and pb yielded in pyrite 4a cores and pyrite skn1 the chemistry of pyrite has also shown that both ore forming fluids are undersaturated in au similar to au bearing pyrite in the carlin type deposits nevada usa

banded tremor at miyakejima volcano japan implication for two phase flow instability 1 volcanic tremor was recorded during a period of volcanic gas emission from miyakejima volcano activity from 2001 to 2006 similar to volcanic earthquakes and long period events the source of banded tremor lies at a shallow depth beneath the summit caldera tremor packets occurred every 20 to 45 min for 1 to 2 days we modeled the source of this phenomenon with a two phase hydrothermal instability flow model consisting of subcool and superheated water regions and found two modes an excursion mode and a series of damping oscillations mode the interval between banded tremor packets can be interpreted in terms of this two phase flow oscillation with a heat supply in the order of 10 100 mw from the magma beneath the hydrothermal system

subduction rollback slab breakoff and induced strain in the uppermost mantle beneath italy differences in seismic anisotropy revealed by split sks waves that traverse the upper mantle beneath the italian region reveal four areas of internally coherent anisotropic strength providing evidence for mantle strain partitioning when compared to uppermost mantle structure imaged by tomography the sequence of these areas displays a straightforward parallelism under proper assumptions the correspondence between areas of coherent splitting degree and areas of coherent velocity perturbations offers new insights into the late evolution of subduction in italy and their effect on mantle strain

the central ailaoshan ophiolite and modern analogs abstract the central ailaoshan cal ophiolite represents an important tectonic component of the jinshajiang ailaoshan song ma suture zone separating the south china and indochina blocks in the mainland se asia the cal ophiolite occurs as a complex tectonic melange and preserves the history of the opening and closure of the once vast jinshajiang ailaoshan song ma branch of the paleotethys new and existing geological data indicate that the cal ophiolite contains magmatic rocks generated by 1 l devonian e carboniferous ca 380 330 ma volcanic passive margin breakup development in the nw gondwana margin 2 l permian ca 258 ma emeishan large igneous province related continental rift magmatism together with and intruded by 3 earliest m triassic ca 244 ma continent continent syn collisional s type granitoids the devono carboniferous suites of the cal ophiolite are highly comparable with many continental margin type alpine tethyan ophiolites in addition the various cal magmatic suites have strong south china block affinities with coeval magmatism particularly in the western south china block jinshajiang song ma and song da terranes

seismicity at old faithful geyser an isolated source of geothermal noise and possible analogue of volcanic seismicity abstract old faithful geyser in yellowstone national park u s a is a relatively isolated source of seismic noise and exhibits seismic behavior similar to that observed at many volcanoes including bubblequakes that resemble b type earthquakes harmonic tremor before and during eruptions and periods of seismic quiet prior to eruptions although old faithful differs from volcanoes in that the conduit is continuously open that rock fracturing is not a process responsible for seismicity and that the erupting fluid is inviscid h2o rather than viscous magma there are also remarkable similarities in the problems of heat and mass recharge to the system in the eruption dynamics and in the seismicity water rises irregularly into the immediate reservoir of old faithful as recharge occurs a fact that suggests that there are two enlarged storage regions one between 18 and 22 m the base of the immediate reservoir and one between about 10 and 12 m depth transport of heat from hot water or steam entering at the base of the recharging water column into cooler overlying water occurs by migration of steam bubbles upward and their collapse in the cooler water and by episodes of convective overturn an eruption occurs when the temperature of the near surface water exceeds the boiling point if the entire water column is sufficiently close to the boiling curve that the propagation of pressure release waves rarefactions down the column can bring the liquid water onto the boiling curve the process of conversion of the liquid water in the conduit at the onset of an eruption into a two phase liquid vapor mixture takes on the order of 30 s the seismicity is directly related to the sequence of filling and heating during the recharge cycle and to the fluid mechanics of the eruption short 0 2 0 3 s monochromatic high frequency events 20 60 hz resembling unsustained harmonic tremor and in some instances b type volcanic earthquakes occur when exploding or imploding bubbles of steam cause transient vibrations of the fluid column the frequency of the events is determined by the length of the water column and the speed of sound of the fluid in the conduit when these events occur damping is controlled by the characteristic and hydraulic impedances which depend on the above parameters as well as on the recharge rate of the fluid two periods of reduced seismicity of a few tens of seconds to nearly a minute in duration occur during the recharge cycle apparently when the water rises rapidly through the narrow regions of the conduit causing a sudden pressure increase that temporarily suppresses steam bubble formation a period of decreased seismicity also precedes preplay or an eruption this appears to be the time when rising steam bubbles move into a zone of boiling that is acoustically decoupled from the wall of the conduit because of the acoustic impedance mismatch between boiling water c 10 3 g cm 2 s 1 and rock c 3 10 5 g cm 2 s 1 sustained harmonic tremor occurs during the first one to one and a half minutes of an eruption of old faithful but is not detectable in the succeeding minutes of the eruption the eruption tremor is caused by hydraulic transients propagating within a sublayer of unvesiculated water that underlies the erupting two phase liquid vapor mixture the resonant frequencies of the fluid column decrease to about 1 hz when all of the water in the conduit has been converted to a water steam mixture surges are observed in the flow at this frequency but the resonance has not been detected seismically possibly because the two phase erupting fluid is seismically decoupled from the rock on which seismometers are placed if old faithful is an analogue for volcanic seismicity this study shows that because the frequency of tremor depends on the acoustic properties of the fluid and on conduit dimensions both properties must be considered in analysis of tremor in volcanic regions because magma sound speed can vary over nearly two orders of magnitude as it changes from an undersaturated liquid into a saturated two phase mixture tremor frequency might vary by this magnitude and very broad band seismographs may be required if tremor is to be monitored as magma goes from an undersaturated liquid to a vesiculated froth cessation of fluid induced seismicity may indicate that the processes that drive the transients cease but it is also possible that the processes that drive the transients continue but the fluid properties change so that the fluid becomes acoustically decoupled from the rock on which seismometers are placed