seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

high speed rupture in the first 20 s of the 2011 tohoku earthquake japan 1 the 2011 tohoku earthquake produced tens of meters of fault slip near the japan trench which generated devastating tsunami the rupture process before the huge slip is still unclear due to a lack of resolution here i perform a multiscale slip inversion analysis to examine the first 10 and 20 s of the rupture process and the whole rupture process at different scales the result shows that 4 s after the initiation this earthquake started with a relatively high speed rupture that had a peak slip rate faster than 1 m s and a rupture velocity comparable to 3 km s fourteen seconds after the initiation the rupture propagation direction changed from northward to westward near the edge of the m 7 3 foreshock coseismic slip area the stress release by the foreshock may contribute to the complex small scale rupture propagation which may appear to be slow rupture propagation when only looking at long period data

source parameters of the shallow 2012 brawley earthquake imperial valley resolving earthquake parameters especially depth is difficult for events occurring within basins because of issues involved with separating source properties from propagational path effects here we demonstrate some advantages of using a combination of teleseismic and regional waveform data to improve resolution following a bootstrapping approach local ss s differential arrivals from a foreshock are used to determine a local layered model which can then be used to model teleseismic depth phases pp sp and ss using the cut and paste cap method for which all strike dip rake and depth variations are sampled for several crustal models we find that regional data prove the most reliable at fixing the strike whereas the depth is better constrained by teleseismic data weighted solutions indicate a nearly pure strike slip mechanism 59 1 with a centroid depth of about 4 0 km and an m w of 5 4 for the mainshock of the 2012 brawley earthquake

coseismic radiation and stress drop during the 2015 mw 8 3 illapel chile megathrust earthquake on 16 september 2015 an mw 8 3 earthquake struck middle chile due to the subduction of the nazca plate beneath the south america plate this earthquake is the consequence of 72 years of strain accumulation in the region since the 1943 m 8 3 event in this study we apply the compressive sensing method cs to invert for the spatiotemporal distribution of the coseismic radiation at different frequencies of this event the results show clear frequency dependent feature of earthquake rupture with low frequency lf radiation located in the updip region while high frequency hf radiation concentrated in the downdip region of the megathrust we also compare the cs results with three coseismic slip models as well as the stress drop distributions inferred from these slip models the comparison confirms our understanding of coseismic radiation that energy sources are mostly located in the margin of large coseismic slip regions furthermore we find that the lf radiation sources are mainly within the stress decreasing releasing regions while the hf radiation sources are mainly located in the stress increasing loading regions due to rupturing of relatively large asperities nearby stress decreasing and releasing these results help to better understand the physics of the rupture process during megathrust earthquakes moreover our results do not show radiation sources south of the epicenter suggesting that the subducting juan fernandez ridge probably stopped the rupture of this earthquake toward the south

mineralogical evidence for magmatic and hydrothermal processes in the qitianling oxidized tin bearing granite hunan south china emp and mc la icpms investigations of three types of titanite abstract the qitianling granite which is located in hunan province southern china is a metaluminous sn granite that crystallized at relatively oxidized conditions between the ni nio nno and fe 2 o 3 fe 3 o 4 mh buffers titanite sphene catisio 5 is a common tin carrier mineral in the qitianling granite based on electron microprobe emp and multi collector mc laser ablation la icpms investigations we describe three types of titanite with various textures and sno 2 contents which probably formed during the magmatic and hydrothermal processes responsible for the granite crystallization and later evolution the form of type i titanite ranges from subhedral to euhedral coarse grained crystals and typically exhibits an envelope like shape and sector zoning it is characterized by a high fe 2 o 3 content on average 2 44 wt and low sno 2 0 43 wt which indicates crystallization during an early magmatic stage its formation temperature is estimated to have been 721 to 780 c from emp and la icpms using the zr in titanite geothermometer type ii titanite occurs as both discrete grains and symplectitic intergrowths and typically fills interstices between other minerals it contains up to 26 wt sno 2 which suggests a late magmatic origin chondrite normalized ree patterns for type ii titanite reveal a lanthanide tetrad effect that was linked to differentiation of the granite magma type iii titanite is restricted to cleavage cracks in chlorite and is rich in al 2 o 3 it is obviously the secondary product of biotite alteration at a temperature that is estimated to be lower than 400 c during the hydrothermal stage this hydrothermal activity also impacted the primary titanites type i titanite experienced alteration to different degrees via coupled dissolution reprecipitation which gave rise to the formation of secondary minerals including cassiterite micro grains some grains of the type ii titanite reacted with fluids along the grain boundary which led to the gradual leaching of sn based on information from these types of titanite and their sn behavior we discuss the progressive enrichment of sn during and after granite crystallization under a high oxidation state as well as the predominant role of fluids in the leaching concentration and transportation of sn during hydrothermal processes which favors vein type sn mineralization

contrasting evolution of fluorine and boron rich tin systems individual sn provinces or regions within provinces are sometimes enriched in fluorine or boron giving rise to fluorine rich and boron rich environments the structural styles of mineralisation within these environments are similar except that hydrothermal intrusive breccia pipes are more common in boron rich environments and apogranite massive greisen systems are more common in fluorine rich environments the increased solubility of h2o in b bearing magmas compared to f bearing magmas may play a role in the structural evolution of the mineralising systems the greater mechanical energy produced during crystallisation of b rich magmas provides a mechanism for breccia pipe and stockwork formation while the more passive crystallisation of f rich magmas often results in the formation of disseminated mineralisation the partitioning of boron toward the aqueous fluid phase and the enhanced solubility of silica in the fluid phase frequently results in tourmalinisation and silicification of the wall rocks in b rich environments in contrast feldspathic and sericitic alterations usually predominate in f rich environments

inversion of source parameters for moderate earthquakes using short period teleseismic p waves in this paper we introduce a new method for estimating the source parameters of moderate earthquakes mw 5 0 by modeling short period teleseismic waveforms this method uses a grid search algorithm to minimize misfits between observed data and synthetic seismograms in depth magnitude and mechanism domain in a relative high frequency range of 0 8 2 0 hz similar to the traditional cut and paste method used in regional modeling zhu and helmberger bull sesimol soc am 86 1634 1641 1996 in this frequency range a significant challenge is determining the initial p wave polarity because of a low signal to noise ratio snr therefore we first determine source properties for a master earthquake with a relative strong snr both the travel time and amplitude corrections are developed relative to the reference 1d model along each path used in inverting the master event we then applied these corrections to other earthquakes clustered in the same area to constrain the initial p polarities thus the focal mechanisms can be determined reasonably well we inverted focal mechanisms for a small set of events beneath qeshm island in southern iran and demonstrate the importance of radiation pattern at short periods

initiation of the great mw 9 0 tohoku oki earthquake abstract we determined the location size mechanism and the frequency content of the first 4 0 s of the 2011 tohoku oki earthquake since the beginning of this earthquake is very small we develop a comparative approach against a near by reference earthquake the master event we first determined the water depth near the master event using the differential timing between the water phase pwp reflected from the air water interface and the depth phase pp reflected from the water crust interface then we located the master event using the well known ocean bathymetry in the area after calibrating teleseismic arrays 30 to 90 at short periods for timing and amplitude with respect to the master event we were able to determine the initiation of the main event it began as a small m w 4 9 thrust event located at 38 19 n 142 68 e at a depth of 21 km and a few seconds later evolved into a slower extremely large slip event up dip

mineralogy geochemistry and ore genesis of kanawa uranium mineralization hawal massif eastern nigeria terrane implications for uranium prospecting in nigeria and cameroon abstract the kanawa area eastern nigeria terrane ent located proximal to pan african shear zone has u prospects with an average u concentration of 0 1 wt samples taken from the fault breccia mylonite cataclasite and ore zone show increasing u contents of 2 2 6 7 ppm 4 7 ppm 36 253 ppm and 165 1000 ppm respectively u pb dating of magmatic zircons from the granite hosting the u prospect yield 206pb 238u concordia age of 603 5 9 ma suggesting pan african ediacaran age for the host granite in contrast zircon grains from the u ore zone yield 206pb 238u concordia age of 228 2 ma considered here as the estimated age of u mineralization an interpretation that need to be supported by additional data the pan african granite hosting kanawa u mineralization has very low u content u 1 0 6 7 ppm and therefore could not have been the main source of the u mineralization considering that the kanawa u ore zone shows broadly similar geochemical signature and yield roughly similar age with its spatially associated mesozoic rocks in area we suggest that the u mineralization was probably sourced from the mesozoic volcanics rocks uranium zr v may have been leached out from the mesozoic volcanic by hydrothermal fluid circulating along the channel ways provided by pan african wrench fault taken together our combined major and trace element data in conjunction with previously reported data of u mineralization from western cameroon allow us re evaluate the geochemical signatures of pan african granite hosting u mineralization in these regions and reassess their u potential in relation to some well known u deposits elsewhere in the world it is noteworthy that the kanawa u mineralization shows broadly similar geochemical features with the volcanic related streltsovskoye antei u deposit transbaikalia russia the highly evolved ekomedion granites in cameroon have high u and f content and exhibit geochemical features typical of u fertile granite suggesting that u mineralization ekomedion area was probably sourced from the granites in contrast pan african granites from kitongo have low u and f content and may not have been the primary source of the kitongo u mineralization as suggested for kanawa u mineralization the kitongo u mineralization was probably sourced from the mesozoic rocks in the area these chains of mesozoic volcanic and plutonic suites largely emplaced within pan african mega shear zones extend from nigeria into cameroon and niger and could be linked to other mega shear zones in egypt and saudi arabia where similar u mineralization have been reported this study therefore allows for an initial correlation of u occurrences and provides a framework for further regional investigation

thermal effects of thrust faulting abstract calculations based on simple models of overthrust sheets in crystalline basement rocks show that significant thermal effects may result from their movements if rates are sufficiently high e g plate tectonic rates the thrust sheets sufficiently thick 5 10 and 15 km are modelled here the distances moved sufficiently large and for reasonable values of the coefficient of friction along the thrust plane overthrusting can cause metamorphic mineral zonations and heat flow anomalies observable in the field regions where large scale overthrusting has occurred should be characterized by a decrease with depth of grade of metamorphic mineral assemblages and anomalously low heat flow the theoretical effects are presented as a series of maximum temperature vs depth and heat flow vs time plots

ferric ferrous ratios h 2 o contents and d h ratios of phlogopite and biotite from lavas of different tectonic regimes complete chemical analyses including ferric and ferrous iron h2o contents and dd values for 16 phlogopite and biotite and 2 hornblende separates are presented samples were obtained from volcanic rocks from four localities 1 phlogopite phenocrysts from minette lavas from the western mexico continental arc 2 biotite and hornblende phenocrysts from andesite lavas from mono basin california 3 phlogopite and biotite from clinopyroxenite nodules entrained in potas sic lavas from the east african rift uganda and 4 phlogopite phenocrysts from a wyomingite lava in the leucite hills wyoming the fe 2 o 3 contents in the mi cas range from 0 8 to 10 5 wt corresponding to 0 09 to 1 15 fe 31 per formula unit pfu water contents vary from 1 6 to 3 0 wt corresponding to 1 58 to 3 04 oh pfu significantly less than would be expected for a site fully occupied by hydroxyl cation and anion based normalization procedures provide accurate mineral for mulae with respect to most cations and anions but are unable to generate accurate estimates of fe 31 yfe t a nd overestimate oh at the expense of o on the hydroxyl site these inaccuracies are present despite acceptable adjust ed totals and stoichiometric calculated site occupancies the phlogopite and biotite phenocrysts in arc related lavas from western mexico and eastern california have the highest fe 31 yfe t ratios 56 87 reflecting high magmatic oxygen fugacities dnno 51 2t o 15 in contrast to those from uganda 25 40 and the leucite hills 23 there is no correlation between the oh content and the fe 31 yfe t ratio in the micas values of k mgyfe 21 d 2s errors were calculated for three phlogo pite olivine pairs 0 12 0 12 0 26 0 14 0 09 0 12 two biotite hornblende pairs 0 73 0 08 and 1 22 0 10 and a single phlogopite augite pair 1 15 0 12 values of k fyoh d for two biotite and hornblende pairs could not be determined without significant error because of the extremely low f contents 0 2 wt of the four phases the dd values obtained in this study encompass a large range 2137 to 243 the phlogo pite and biotite separates from uganda have dd values of 270 to 249 which overlap those believed to represent primary mantle there is a larger range in dd values 2137 to 243 for phlogopite phenocrysts from west ern mexico minette lavas although their range in d 18 o values 5 2 6 2 is consistent with normal mantle it is unlikely therefore that the variable dd values reflect heterogeneity in the mantle source region of the minette magmas nor can the extremely low dd values reflect degassing of h2 or h2o since almost 100 loss of dis solved water in the magma is required an unrealistic scenario given the stability of the hydrous phenocrysts the very low dd values of the mascota minette phlogo pites require that the hydrogen be introduced from an external source e g meteoric water whatever the pro cess responsible for the observed hydrogen isotope com position it had no effect on the d 18 o value fo2 ah2o or bulk composition of the host magmas

magmatic oxidation in the syenitic murdock creek intrusion kirkland lake ontario evidence from the ferromagnesian silicates the syenitic murdock creek intrusion of late archean age lies within one of the major lode gold camps of the world at kirkland lake ontario there is a strong spatial association between syenitic intrusions gold mineralization and carbonatization hydrothermal fluids that carried the gold had an unusually high oxygen fugacity f o 2 notwithstanding a wide range in rock compositions within the intrusion from clino pyroxenite to alkali feldspar syenite clinopyroxene and biotite have consistently low fe fe mg and high fe 3 fe 2 fe 3 ratios these compositional features indicate a deficiency of fe 2 in the magma during crystallization together with the presence of abundant early formed magnetite and titanite this is interpreted to result from an intrinsically high magmatic f o 2 that remained constant during pluton evolution f o 2 approx 10 12 bars mineral compositions proportions of crystallizing mineral phases and textural features i

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

forearc slope deformation above the japan trench megathrust implications for subduction erosion abstract subduction erosion is a commonly invoked model that is used to explain the tectonic subsidence of the japan trench forearc slope although other models have explained the morphology and history of the margin new multichannel seismic reflection and bathymetric data collected after the 2011 tohoku earthquake provide the opportunity to investigate the detailed structure of the overriding plate near the earthquake epicenter and obtain new constraints on tectonic models we use regional residual separation of the local bathymetry to constrain fault scarp extents and local landward dipping forearc basins seismic images of these basins clearly show landward dipping horizons in the shallow section the strata in these basins imply a different mechanism for formation than the surrounding forearc slope and we propose that these basins formed from local uplift a regional basal unconformity mapped 150 km along trench has highly variable relief indicating that forearc slope subsidence occurs at multiple wavelengths in response to multiple different sources we characterize the upper to middle slope transition and propose that this region may be the landward limit of major subduction erosion and also the main region for large mass wasting normal faults found in this setting have maximum lengths of 20 km limiting their role in margin processes our results place constraints on the extent of major subduction erosion at the japan trench margin and indicate that subduction erosion should be revisited as the sole model of formation to include additional tectonic processes

hydrothermal alteration and mineral chemistry of the giant baiyanghe be u deposit in xinjiang northwest china implications for its mineralization abstract the baiyanghe be u deposit is located in the xuemisitan volcanic belt of the northwest margin of the junggar plate nw china it is the largest beryllium deposit in asia but the physicochemical conditions of ore precipitation and mechanisms of transportation and precipitation of be and u are still poorly constrained here we present detailed petrographic study whole rock major and trace elements of the host rocks and mineral chemistry of this deposit to address these issues the alteration minerals associated with be u mineralization mainly include fluorite hematite quartz chlorite manganese oxides and muscovite fluorite is generally colorless green or light purple to dark purple in this deposit the colorless and green fluorite and calcite display low concentrations of be and u the light purple to purple fluorite is characterized by high be concentration but low u concentration the dark purple fluorite shows high concentrations of be and u both primary mica in the yangzhuang granite porphyry and hydrothermal muscovite in the ore are enriched in f 4 26 7 78 wt 4 22 6 70 wt respectively these results indicate that the ore forming fluids were enriched in f and this deposit might have experienced at least two hydrothermal events that are responsible for the precipitation of be and u minerals all investigated chlorites are trioctahedral and belong to fe chlorites and they precipitated at temperatures of 125 to 200 c thermochemical constraints suggest that the ore forming fluids had log f o 2 about 25 to 30 and ph about 4 5 to 5 2 our study indicates that the yangzhuang granite porphyry may represent the primary sources of be and u and that post magmatic hydrothermal processes accompanied with extensive hydrothermal alteration caused remobilization of be u and other elements from the granite porphyry both be and u were mainly transported as fluoride complex ions as indicated by the abundant fluorite and other f bearing gangue minerals the contact zones between the granite porphyry and devonian volcanic rocks provide favorable reservoirs for be and u minerals the precipitation of be was mainly resulted from the decreasing temperature and fluorine concentration in fluids and the decreasing f o 2 and increasing ph were responsible for the precipitation of u

the 2010 mw 8 8 chile earthquake triggering on multiple segments and frequency dependent rupture behavior 1 multi frequency back projection results of the february 27 2010 mw 8 8 chile earthquake reveal that this earthquake consists of distinct subevents with different slip characteristics the subevent south of the epicenter releases its energy at low frequencies 0 05 0 1 hz implying slow slip and has a rupture speed around 0 8 km s two subevents north of the epicenter are characterized by high frequency energy 1 5 hz release the first of these subevents appears to trigger slip on the second segment to the north which has higher amplitude energy release and a fast propagation speed of about 2 9 km s in addition to these rupture details high frequency energy release is observed at the rupture front followed by lower frequency energy release this observation suggests that the rupture of large earthquakes involves dynamic weakening of faults and hence their rupture properties may not be related easily to those of small earthquakes these distinct slip behaviors point out the need to consider data from a wide range of frequencies to fully assess the rupture process and associated hazards of giant earthquakes

in situ sims uraninite u pb dating and genesis of the xianshi granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province china is host to numerous granite hosted vein type hydrothermal uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because the uranium minerals in these deposits are usually fine grained and may have formed in several stages therefore the ages previously obtained by the bulk dating techniques are possibly a mixed age the xianshi uranium deposit located in the southeastern part of the guidong granite complex is a major uranium deposit in south china the uranium mineralization from this deposit is mainly fine grained uraninite in quartz or calcite veins which are spatially associated with the cretaceous mantle derived mafic dykes micro raman spectroscopy and x ray diffraction analyses indicate that the dominant uranium mineral occurs as a rare form of uraninite u 3 o 7 three distinct generations of uranium minerals have been identified based on petrographic and field relations stage 1 uraninite has the lowest uo 2 and highest pbo contents whereas stage 3 uraninite has the highest uo 2 and lowest pbo contents uraninite from the xianshi deposit was dated using an in situ sims u pb dating technique the results show three distinct age groups 135 4 ma 113 2 ma and 104 2 ma which are in excellent agreement with the ages of three episodes of mantle derived mafic dykes therefore the xianshi uranium deposit has experienced at least three hydrothermal events that are responsible for the deposition of uranium ores which are genetically related to the emplacement of three sets of mafic dykes

aftershocks near the updip end of the 2011 tohoku oki earthquake abstract the march 2011 m w 9 0 tohoku oki earthquake activated shallow aftershocks with normal faulting focal mechanisms near the trench axis to investigate stress state in the shallow subduction zone near the trench axis we used ocean bottom seismographs obss to record earthquakes from august to october 2011 we estimated hypocenter locations and focal mechanisms of the recorded earthquakes by using a grid search method in a 2 d velocity model based on an active seismic survey the results show that most of the earthquakes occurred within both the overriding and subducting plates with very few on the plate interface and none in the most seaward 45 km of the overriding plate aseismic wedge the low seismicity along the plate interface is consistent with the nearly complete stress drop on the megathrust fault in the m w 9 0 earthquake focal mechanisms indicate that trench normal tension is pre dominant in both plates and extends to a depth of about 30 km at least on the other hand several trench normal compressional earthquakes were located at the landward end of the aseismic wedge these earthquakes suggest horizontal compression of the overriding prism that may be caused by a strengthening of the shallowest part of the megathrust

isotope geochronology geochemistry and mineral chemistry of the u bearing and barren granites from the zhuguangshan complex south china implications for petrogenesis and uranium mineralization abstract the zhuguangshan complex carries some of the most important granite hosted uranium deposits in south china here we investigate the changjiang and jiufeng granites which represent typical u bearing and barren granites in the complex using zircon u pb ages whole rock geochemistry sr nd isotopic and zircon hf isotopic data and mineral chemistry to constrain the petrogenesis and uranium mineralization la icp ms zircon u pb dating shows that both the changjiang and jiufeng granites were emplaced ca 160 ma these rocks show high silica weakly to strongly peraluminous compositions enrichment in rb th and u and depletion in ba nb sr p and ti these features coupled with the high initial 87 sr 86 sr ratios negative end t values and ehf t values and the paleoproterozoic two stage model ages of these two granites suggest that the two granites belong to s type granites and the parental magmas of the two granites were derived from the paleoproterozoic metasedimentary rocks however the granitoids show different mineralogical characteristics the biotite in the changjiang granite belongs to siderophyllite marking higher degree of chloritization whereas the biotite in the jiufeng granite is ferribiotite characterized by only slight chloritization compared with the jiufeng granite the biotite in the changjiang granite has lower crystallization temperature and oxygen fugacity but higher f content and the uraninite has higher uo 2 content but lower tho 2 content and stronger corrosion the chemical ages of uraninites from both granites are within error consistent with the zircon u pb ages and are considered to represent the emplacement ages of granites chemical ages of pitchblende in the changjiang granite yield 118 8 ma 87 4 ma and 68 6 ma representing multiple episodes of hydrothermal events that are responsible for the precipitation of u ores in the changjiang uranium ore field our study suggests that the degree of magma differentiation and physicochemical conditions of the magmatic hydrothermal system are the key factors that control the different u contents of these two granites the mineralogical characteristics of uraninite and biotite can be used to distinguish between u bearing and barren granites and serve as a potential tool for prospecting granite hosted uranium deposits

petrogenesis of triassic granite from the jintan pluton in central jiangxi province south china implication for uranium enrichment abstract numerous triassic biotite granites and two mica granites crop out in the interior of south china and some of them possess high u contents which have been regarded as the sources for later hydrothermal mineralization their petrogenesis is therefore crucial for constraining the possible origins of the u enrichment here we report new la icpms zircon u pb ages mineral geochemistry of biotite and muscovite whole rock geochemical results and sr nd and zircon hf isotope data from the jintan pluton in central jiangxi province south china la icpms zircon u pb dating indicates that both biotite granite bg and two mica granite tmg in the jintan pluton crystallized at 220 ma the tmg have higher u contents 7 85 to 48 90 ppm average18 44 ppm than thebg 4 99 to 17 72 ppm average 8 64 ppm both bg and tmg show negative whole rock end t and zircon ehf t values and contain some inherited zircons the tmg are strongly peraluminous a cnk 1 13 1 33 contain abundant primary muscovite and display s type affinity on plots of yvs rb and th vs rb suggesting that they are s type granites the bg also display s type granite affinities on plots of yvs rb and th vs rb the suites display similar sr nd isotope compositions bg initial 87sr 86sr values 0 711389 to 0 714225 and end t 9 91 to 9 16 tmg initial 87sr 86sr values 0 711832 and end t 10 02 and are spatially associated suggesting that the bg should also be classified as s type granites the tmg have higher zircon ehf t values 6 4 to 1 1 than the bg 8 7 to 3 7 indicating the tmg and bg might be derived from similar sediments but possibly with some distinct characteristics in their sources the bg exhibit linear covariations in chemical compositions with relatively high total ree and light ree contents and mgo contents while the tmg displays broader compositional variations but with relatively low total ree light ree and mgo contents biotite geochemistry indicates the tmg formed in a more reduced magmatic system than the bg the temperatures estimated by zircon saturation thermometry indicate the bg had distinctly higher magmatic temperatures than the tmg the tmg display relatively high al2o3 tio2 ratios and low cao na2o ratios than the bg but have higher sr y and la yb ratios the geochemical and petrological data suggest the bg were derived from clay poor psammite sources at deeper levels with higher temperatures and higher oxygen fugacity and underwent an extensive fractional crystallization while the tmg was derived from clay rich pelitic sources at higher levels and lower temperatures and oxygen fugacity with only limited fractional crystallization we conclude that the combination of u rich sources physical chemical conditions such as low partial melting temperature or low degrees of partial melting a reduced environment and low ree and lree contents of magmas controlled the u enrichment in tmg

the seismic cycle at subduction thrusts 1 insights from laboratory models 1 subduction megathrust earthquakes occur at the interface between the subducting and overriding plates these hazardous phenomena are only partially understood because of the absence of direct observations the restriction of the instrumental seismic record to the past century and the limited resolution completeness of historical to geological archives to overcome these restrictions modeling has become a key tool to study megathrust earthquakes we present a novel model to investigate the seismic cycle at subduction thrusts using complementary analog paper 1 and numerical paper 2 approaches here we introduce a simple scaled gelatin on sandpaper setup including realistic tectonic loading spontaneous rupture nucleation and viscoelastic response of the lithosphere particle image velocimetry allows to derive model deformation and earthquake source parameters analog earthquakes are characterized by quasi periodic recurrence consistent with elastic theory the interseismic stage shows rearward motion subsidence in the outer wedge and uplift of the coastal area as a response of locked plate interface at shallow depth the coseismic stage exhibits order of magnitude higher velocities and reversal of the interseismic deformation pattern in the seaward direction subsidence of the coastal area and uplift in the outer wedge like natural earthquakes analog earthquakes generally nucleate in the deeper portion of the rupture area and preferentially propagate upward in a crack like fashion scaled rupture width slip proportionality and seismic moment duration scaling verifies dynamic similarities with earthquakes experimental repeatability is statistically verified comparing analog results with natural observations we conclude that this technique is suitable for investigating the parameter space influencing the subduction interplate seismic cycle

mesozoic large scale magmatism and mineralization in south china preface abstract south china is famous for its polymetallic deposits with more than 50 of the world s w and sb reserves and 20 of the sn reserves as well as abundant cu mo pb zn au ag ta nb hree and u this special issue reports recent progress on the tectonic evolution magmatism and ore deposits of south china which leads to a more comprehensive understanding of the mesozoic large scale magmatism and mineralization events 1 south china has been located in backarc settings during multiple subductions since the paleozoic which may have contributed to pre enrichments of the ore forming materials 2 the pacific plate subduction was a principle factor that controlled the late mesozoic large scale magmatism and mineralization in south china through flat subduction ridge subduction slab tearing and slab rollbacks

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

lateral mixing in the equatorial pacific the importance of inertial instability 1 mixing in the ocean plays a key role in the ocean s dynamics and thermodynamics and how the ocean interacts with the atmosphere here we focus on lateral mixing in the equatorial ocean and in particular the part played by inertial instability we demonstrate the effectiveness of the instability in promoting mixing in the equatorial thermocline that is sufficient to affect the large scale structure of the equatorial ocean and which rectifies problems in existing ocean models the spatial and temporal variability of the process is likely to impinge on interannual variations of the ocean and el nino

fault interactions and triggering during the 10 january 2012 mw 7 2 sumatra earthquake the 10 january 2012 mw 7 2 sumatra earthquake in the wharton basin occurred 3 months before the great mw 8 6 and mw 8 2 earthquakes in the same region which had complex ruptures and are the largest strike slip earthquakes ever recorded teleseismic p wave back projection of the mw 7 2 earthquake images a unilateral rupture lasting 40 s without observable frequency dependency low frequency 0 05 0 3 hz high frequency 0 3 1 hz in addition to radiation bursts during the mw 7 2 main shock coherent energy releases from 50 to 75 s and from 100 to 125 s are observed about 143 km northeast of the main shock rupture and landward of the trench analysis of globally recorded p waves in both 0 02 0 05 hz velocity records and 1 5 hz stacked envelope functions confirms the presence of coherent sources during the time windows the observed energy bursts are likely to be large early aftershocks occurring on or near the subduction interface both dynamic and static triggering could have induced these early aftershocks as they initiated after the surface wave passed by and the coulomb stress perturbations from the mw 7 2 main shock promote earthquakes in the observed locations the earthquake sequence is a clear example of a seaward intraplate strike slip earthquake triggering landward intraplate earthquakes in the same region in contrast to previously reported normal reverse or reverse normal interactions at subduction zones

eastern asia and the western pacific timing and spatial distribution of rifting in china abstract a compilation of recognized rifts in china indicates that five distinct episodes of rifting have occurred these episodes occurred at approximately 2 3 ga 1 85 1 7 ga 1 0 0 7 ga 550 190 ma and 175 ma to present the timing and location of rifting has largely been a function of tectonic activity along the margins of the various chinese paleocontinents some of the oldest rocks in china are found in the sino korean and tarim cratons and most of the identified precambrian rifts are found within or on the margins of these cratons these cratons are viewed as the continental nucleus of china and fold belts and microcontinents have been accreted to this nucleus through time much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin especially in the paleozoic beginning in the middle mesozoic rifting commenced along the entire eastern margin of china extension occurred concomitantly with subduction in a backarc setting this is the dominant cenozoic extensional regime in china and is still active today to date few cenozoic rifts have been found in western china where most tectonism is probably a consequence of the collision between india and china but it seems likely that more rifts will be discovered in this area as it becomes better studied

genesis of the guangshigou pegmatite type uranium deposit in the north qinling orogenic belt china abstract the guangshigou uranium deposit is an important pegmatite type uranium deposit located in the north qinling orogenic belt nqb china the characteristics pertaining to its chronology petrogenesis and geodynamic setting remain unclear till date in this study we present systematic zircon u pb ages lu hf isotopic data and mineral chemistry of uranium rich biotite pegmatite dikes in situ zircon u pb dating of the biotite pegmatite dikes yielded early caledonian ages 422 417 ma the initial 176hf 177hf ratios of the zircons from the biotite pegmatites showed a narrow range 0 282378 0 282590 with ehf values ranging from 5 1 to 2 8 and paleoproterozoic to mesoproterozoic two stage hf model ages between 1723 and 1227 ma the bulk and mineral chemistries of the pegmatites also indicate that the pegmatite dikes were derived from low degree partial melting of qinling group rocks with monazite as the residual mineral differences between the normal biotite pegmatite and the mineralized biotite pegmatite dikes with respect to mineralogy texture structure and mineral chemistry indicate that the assimilation between the pegmatite dikes and the wall rock may be the primary mechanism for the mineralization of the uranium with the fractional crystallization process being another important mechanism amphibolite facies metamorphism which was most likely caused by the exhumation of the subducted slab in the nqb may have been a key factor in the genesis of the uranium rich pegmatitic magma

teleseismic inversion for rupture process of the 27 february 2010 chile mw 8 8 earthquake the 27 february 2010 chile m w 8 8 earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation the faulting geometry slip distribution seismic moment and moment rate function are estimated from broadband teleseismic p sh and rayleigh wave signals we explore some of the trade offs in the rupture process estimation due to model parameterizations limited teleseismic sampling of seismic phase velocities and uncertainty in fault geometry the average slip over the 81 500 km 2 rupture area is about 5 m with slip concentrations down dip up dip and southwest and up dip and north of the hypocenter relatively little slip occurred up dip offshore of the hypocenter the average rupture velocity is 2 0 2 5 km s

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

zircon u pb geochronology and geochemistry of granites in the zhuguangshan complex south china implications for uranium mineralization abstract the zhuguangshan complex composed of caledonian indosinian and yanshanian granites and cretaceous mafic dykes is one of the most important granite hosted uranium producers in south china here we present la icp ms zircon u pb and hornblende 40ar 39ar geochronology and whole rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization samples collected from the fuxi youdong longhuashan chikeng qiling and sanjiangkou intrusions yield zircon weighted 206pb 238u ages of 426 7 5 4 ma 226 4 3 5 ma 225 0 2 7 ma 152 2 3 0 ma 153 9 2 1 ma and 155 2 2 1 ma respectively a new ar ar dating of the hornblende of the diabase from the changjiang uranium ore field yields a plateau age of 145 1 1 5 ma these results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420 435 ma 225 240 ma 150 165 ma 140 ma 105 ma and 90 ma both u bearing and barren granites occur in this complex and they display differences in whole rock and biotite geochemistry the barren granites show higher al2o3 cao tfmm rb zr ba si mg la yb n and eu eu but lower sio2 alk rb di rb sr and tio2 mgo than those of the u bearing granites biotites in the u bearing granites are close to the fe rich siderophyllite annite end member with fe fe mg ratios higher than 0 66 whereas those in the barren granites are relatively close to the mg rich eastonite phlogopite end member with fe fe mg ratios

fmnear determination of focal mechanism and first estimate of rupture directivity using near source records and a linear distribution of point sources abstract the fmnear method is based on both the waveform inversion of near source seismic records and on a linear finite source model the primary source parameters that are determined are the moment magnitude m w the double couple focal mechanism strike dip and rake and the distribution of seismic moment along strike which provides a first order estimate of rupture length and directivity source depth is also explored an advantage of the approach is the use of the finite source model directly within the search of the focal mechanism this strategy allows the inclusion of strong motion records at short distances for moderate to very large earthquakes m w 5 5 however for moderate to small earthquakes m w m w 4 5 to 9 0 test cases incorporate continental events recorded by a large number of well distributed stations and less favorable cases in its present form the fmnear approach is very well adapted to continental earthquakes surrounded by seismic stations but it can also give informative results in more difficult configurations the fmnear method is now ready for fully automated determinations and is already implemented in near real time online material details on inversion parameters flow charts of the fmnear method figures of waveform modeling and sensitivity for selected events and table of velocity models

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

diffusion in zircon despite its low abundance in most rocks zircon is extraordinarily useful in interpreting crustal histories the importance of u th pb isotopic dating of zircon is well and long established davis et al this volume parrish et al this volume zircon also tends to incorporate trace elements useful as geochemical tracers such as the ree y and hf a number of characteristics of zircon encourage the preservation of internal isotopic and chemical variations often on extremely fine scale which provide valuable insight into thermal histories and past geochemical environments the relative insolubility of zircon in crustal melts and fluids as well as its general resistance to chemical and physical breakdown often result in the existence of several generations of geochemical information in a single zircon grain the fact that this information is so frequently retained as evidenced through backscattered electron or cathodoluminescence imaging that often reveal fine scale zoning down to the sub micron scale has long suggested that diffusion of most elements is quite sluggish in zircon in this chapter we present an overview of the findings to date from laboratory measurements of diffusion of cations and oxygen in zircon because of its importance as a geochronometer attempts have been made to measure diffusion especially of pb for over 30 years but only in the last decade or so have profiling techniques with adequate depth resolution been employed in these studies resulting in a plethora of new diffusion data these findings have important implications for isotopic dating interpretation of stable isotope ratios closure temperatures and formation and preservation of primary chemical composition and zoning in zircon efforts have been made for some time to quantify and characterize diffusion in zircon most notably of pb in deference to its significance in interpreting pb isotopic signatures and refining understanding of thermal histories as is evident from

petrogenesis of adakitic porphyries in an extensional tectonic setting dexing south china implications for the genesis of porphyry copper mineralization the dexing adakitic porphyries quartz diorite granodiorite porphyries associated with giant porphyry cu deposits are located in the interior of a continent south china they exhibit relatively high mgo cr ni and sr contents high la yb and sr y ratios but low yb and y contents similar to adakites produced by slab melting associated with subduction however they are characterized by bulk earth like nd sr isotope compositions end t 1 14 to 1 80 and 87 sr 86 sr i 0 7044 0 7047 and high th 12 6 27 2ppm contents and th ce 0 19 0 94 ratios which are different from those of cenozoic slab derived adakites sensitive high resolution ion microprobe shrimp geochronology studies of zircons reveal that the dexing adakitic porphyries have a crystallization age of 171 3ma this age is contemporaneous with middle jurassic extension within the shi han rift zone and within plate magmatism elsewhere in south china indicating that the dexing adakitic porphyries were probably formed in an extensional tectonic regime in the interior of the continent rather than in an arc setting their high th contents and th ce ratios and middle jurassic age argue against an origin from a neoproterozoic 1000ma stalled slab in the mantle taking into account available data for the regional metamorphic magmatic rocks and the present day crustal thickness 31km in the area we suggest that the dexing adakitic porphyries were most probably generated by partial melting of delaminated lower crust which was possibly triggered by upwelling of the asthenospheric mantle due to the activity of the shi hang rift zone moreover the dexing adakitic magmas must have interacted with the surrounding mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity fo2 of the mantle the high fo2 could have induced oxidation of metallic sulfides in the mantle and mobilization of chalcophile elements which are required to produce associated cu mineralization therefore the cu metallogenesis associated with the dexing adakitic porphyries is probably related to partial melting of delaminated lower crust similar to the metallogenesis accompanying slab melting

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

late triassic u bearing and barren granites in the miao ershan batholith south china petrogenetic discrimination and exploration significance abstract the miao ershan uranium ore district is one of the most important granite hosted uranium producers in south china there are several triassic granite plutons in the miao ershan batholith but uranium ore deposits mainly occur within the douzhashan granitic body precise zircon u pb dating indicated that these triassic granite plutons were emplaced during 204 to 215 ma the douzhashan u bearing granite lies in the central part of the miao ershan batholith and has higher u contents 8 0 to 26 1 ppm average 17 0 ppm than the nearby xiangcaoping granite 5 0 to 9 3 ppm average 7 0 ppm and the yangqiaoling granite 6 4 to 18 3 ppm average 11 5 ppm in the south part of the batholith the douzhashan granite is composed of medium grained two mica granite whereas the xiangcaoping and yangqiaoling granites are composed of porphyritic biotite granite both the xiangcaoping and douzhashan granites have high a cnk ratios 1 10 high 87 sr 86 sr i ratios 0 720 and low e nd t values 11 3 to 10 4 suggesting that they belong to strongly peraluminous s type granites the douzhashan granite has low cao na 2 o ratios high rb sr and rb ba ratios indicating a partial melting origin of clay rich pelitic rocks in contrast the xiangcaoping granite formed from clay poor psammite derived melt the yangqiaoling granite shows different geochemical characteristics with the douzhashan and xiangcaoping granites indicating a different magma source the yangqiaoling granite has higher e nd t of 9 4 to 8 3 and variable a cnk values from 0 98 to 1 19 suggesting a mixture source of meta sedimentary rocks and meta igneous rocks crystallization fractionation is not the main mechanism for u enrichment in the douzhashan granite we suggest that u rich pelitic rock sources may be the key factor to generate peraluminous u bearing granites in south china searching for those granites which are reduced strongly peraluminous and were derived from u rich pelitic rocks is the most effective way for exploring granite hosted u deposits

compressive sensing of the tohoku oki mw 9 0 earthquake frequency dependent rupture modes 1 compressive sensing cs is a technique for finding sparse signal representations to underdetermined linear measurement equations we use cs to locate seismic sources during the rupture of the 2011 tohoku oki mw9 0 earthquake in japan from teleseismic p waves recorded by an array of stations in the united states the seismic sources are located by minimizing the l2 norm of the difference between the observed and modeled waveforms penalized by the l1 norm of the seismic source vector the resulting minimization problem is convex and can be solved efficiently our results show clear frequency dependent rupture modes with high frequency energy radiation dominant in the down dip region and low frequency radiation in the updip region which may be caused by differences in rupture behavior more intermittent or continuous at the slab interface due to heterogeneous frictional properties

tsunamigenic earthquake simulations using experimentally derived friction laws abstract seismological tsunami and geodetic observations have shown that subduction zones are complex systems where the properties of earthquake rupture vary with depth as a result of different pre stress and frictional conditions a wealth of earthquakes of different sizes and different source features e g rupture duration can be generated in subduction zones including tsunami earthquakes some of which can produce extreme tsunamigenic events here we offer a geological perspective principally accounting for depth dependent frictional conditions while adopting a simplified distribution of on fault tectonic pre stress we combine a lithology controlled depth dependent experimental friction law with 2d elastodynamic rupture simulations for a tohoku like subduction zone cross section subduction zone fault rocks are dominantly incohesive and clay rich near the surface transitioning to cohesive and more crystalline at depth by randomly shifting along fault dip the location of the high shear stress regions asperities moderate to great thrust earthquakes and tsunami earthquakes are produced that are quite consistent with seismological geodetic and tsunami observations as an effect of depth dependent friction in our model slip is confined to the high stress asperity at depth near the surface rupture is impeded by the rock clay transition constraining slip to the clay rich layer however when the high stress asperity is located in the clay to crystalline rock transition great thrust earthquakes can be generated similar to the mw 9 tohoku 2011 earthquake

petrogenesis of u and mo bearing a2 type granite of the gattar batholith in the arabian nubian shield northeastern desert egypt evidence for the favorability of host rocks for the origin of associated ore deposits abstract hydrothermal ore deposits associated with granitic rocks are the result of combinations and series of successive processes events and conditions in a magma system and at post magmatic stage the metal content of a granitic magma as well as fractional crystallization metal ligand complexation emplacement mechanisms and tectonic processes influence the metal precipitation and content of a hydrothermal ore deposit the present study of the gattar batholith evaluates how these processes contribute to the generation of an ore deposit gattar batholith in the north eastern desert of egypt as part of the northern region of the arabian nubian shield ans is geographically mineralogically and geochemically divided into two distinctive areas the southern part mainly consists of syenogranite while the northern part is dominated by highly evolved alkali feldspar granite uranium and mo mineralization occurring here is mostly limited to the margin of the highly evolved alkali feldspar granites new u pb zircon geochronology within this study indicates an age of 620 600 ma although high common pb and discordant age data of many zircon grains reflect alteration by f rich fluids some zircons with distinct older u pb ages were considered to be inherited from the wall rocks representing juvenile crust of the ans the two different granitic rocks are comagmatic in origin and have a type characteristics generated by partial melting of lower juvenile crust of the ans geochemical data are in good agreement with a magmatic origin of the alkali feldspar granites suggesting fractional crystallization of a syenogranitic source as the most favorable process of their formation petrography geochemistry and geochronology studies of the gattar granites along with field observations provide evidence for multiple intrusions as a result of successive magma pulses with different chemical composition this led to the formation of reverse zoning within the intrusive complex this kind of magma emplacement promotes the escape of exsolved metal bearing volatile rich fluids into the boundary of the hammamat sedimentary rocks hsr and gattar granite at the northern part of the batholith build up of volatiles is a common phenomenon in granitic rocks and typically results in enhanced contents of f alkalis and ore metals released at subsolidus stage

probabilistic imaging of tsunamigenic seafloor deformation during the 2011 tohoku oki earthquake diverse observations from the 2011 m w 9 0 tohoku oki earthquake pointed to large coseismic fault slip proximal to the japan trench this seismic failure prompted a reevaluation of the conventional view that the outer forearc is generally aseismic however the nature of near trench fault slip during this event remains debated without consensus on whether slip peaked at the trench or at greater depths here we develop a probabilistic approach to image the spatiotemporal evolution of coseismic seafloor displacement from near field tsunami observations in a bayesian framework we sample ensembles of nonlinear source models parameterized to focus on near trench features incorporating the uncertainty in modeling dispersive tsunami waves in addition to nominal observational errors our models indicate that seafloor in the region of the earthquake was broadly uplifted and tilted seaward approaching the deep ocean trench over length scales of 40 km seafloor uplift peaks at 5 0 6 m near the inner outer forearc transition and decreases to 2 m at the trench axis over a distance of 50 km corresponding to a seafloor tilt of 0 06 0 02 m km over length scales of 20 km peak uplift reaches 7 2 m at the similar location but uplift at the trench is less constrained elastic modeling that reproduces the observed tilt requires a coseismic slip deficit at the trench such a deficit is effectively consistent with a metastable frictional model for the shallowest megathrust while large shallow earthquakes in the region cannot be completely ruled out aseismic deformation is the most likely mode for satisfying the long term slip budget

forgotten major elements hydrogen and oxygen variation in biotite from metapelites variations in the h sup and o sup 2 minus content of minerals have been virtually ignored since the advent of the electron microprobe in the mid 1960s such studies do not serve as a basis for consideration of the variation of other major constituents such as fe sup 3 h sup and o sup 2 minus the authors report results of a comprehensive study of all major element compositional variation in biotite using samples from a suite of metapelites ranging from lower garnet to sillimanite k feldspar grades the data show that fe sup 3 remains constant within analytical error while percentages by weight of h sub 2 o and o decrease and increase respectively with increasing metamorphic grade h sup and o sup 2 minus contents of biotite appear to be highly sensitive to temperature and pressure samples from low metamorphic grades contain bulk h sup contents 4 h sup formula unit excess h sup probably occupies vacancies in the interlayer sites as either h sub 2 o or h sub 3 o these results will have an impact on geoscience disciplines that make assumptions about stoichiometry of hydrous phases for example the temperature range of reactions involving the breakdown of hydrous phases with more or less h sup than predicted will change more in some cases dramatically and any calculations involving water activities must be modified to consider h sup variation partitioning of h sup among coexisting hydrous phases delta d studies may be affected by both amount of h sup and its location and bonding interlayer h sub 2 o or h sub 3 o vs oh sup minus ar diffusivities calculated for sup 40 ar sup 39 ar work will be influenced by the h sup occupancy in the interlayer sites cation substitution models for h sup bearing phases need to consider exchanges involving both h sup and o sup 2 minus less

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

element geochemistry mineralogy geochronology and zircon hf isotope of the luxi and xiazhuang granites in guangdong province china implications for u mineralization abstract the luxi and xiazhuang granitic plutons are parts of the guidong granite belt in northern guangdong province china they occur next to each other and have similar crystallization ages however the xiazhuang pluton hosts several important uranium u ore deposits whereas the luxi pluton does not this study compares the two plutons using whole rock geochemistry biotite compositions zircon u pb ages by la icpms and in situ zircon hf isotope data by la mc icpms to understand the fundamental controls results show that the two plutons have similar ages 237 ma for the luxi pluton and 234 ma for the xiazhuang pluton they also have similar geochemical features that are characteristic of s type granites zircons from both plutons have negative e hf t values 9 to 12 and a paleoproterozoic two stage hf model age t dm2 1838 ma to 2025 ma suggesting that their parental magmas were all derived from paleoproterozoic metasedimentary rocks the geochemical and petrological data suggest that these two plutons crystallized from magmas derived from the same parent at different stages the parental magma of the xiazhuang pluton is more evolved than that of the luxi pluton this factor plus different physical chemical conditions such as temperature volatile components and oxidation state resulted in higher u content and favorable u bearing species in the xiazhuang magmatic hydrothermal system u occurs mainly as uraninite in the xiazhuang pluton which facilitates u transfer from granite into co 2 rich hydrothermal fluid to form u ore deposits in contrast u occurs mainly as ree bearing minerals in the luxi magmatic system preventing u transfer to associated hydrothermal fluids as a result the xiazhuang pluton hosts several important uranium ore deposits whereas the luxi pluton is ore barren

frictional properties of fault zone gouges from the j fast drilling project mw 9 0 2011 tohoku oki earthquake smectite rich fault gouges recovered during integrated ocean drilling program expedition 343 japan trench fast drilling project j fast from the plate boundary slip zone of the 2011 mw 9 0 tohoku oki earthquake were deformed at slip velocities of 10 m s 1 to 3 5 m s 1 and normal stresses up to 12 mpa water dampened gouges 1 are weaker apparent friction coefficient 0 1 m s 1 a significant amount of amorphous material formed in room humidity experiments at low and high slip velocities likely by comminution and disordering of smectite our results indicate that the frictional properties of water dampened gouges could have facilitated propagation of the tohoku oki rupture to the trench and large coseismic slip at shallow depths

anelasticity of the crust and upper mantle beneath north and central india from the inversion of observed love and rayleigh wave attenuation data the fundamental mode love and rayleigh waves generated by earthquakes occurring in kashmir nepal himalaya northeast india and burma and recorded at hyderabad new delhi and kodaikanal seismic stations are analysed love and rayleigh wave attenuation coefficients are obtained at time periods of 15 100 seconds using the spectral amplitude of these waves for 23 different paths along northern across burma to new delhi and central across kashmir nepal himalaya and northeast india to hyderabad and kodaikanal india love wave attenuation coefficients are found to vary from 0 0003 to 0 0022 km 1 for northern india and 0 00003 km 1 to 0 00016 km 1 for central india similarly rayleigh wave attenuation coefficients vary from 0 0002 km 1 to 0 0016 km 1 for northern india and 0 00001 km 1 to 0 0009 km 1 for central india backus and gilbert inversion theory is applied to these surface wave attenuation data to obtainq 1 models for the crust and uppermost mantle beneath northern and central india inversion of love and rayleigh wave attenuation data shows a highly attenuating zone centred at a depth of 20 80 km with lowq for northern india similarly inversion of love and rayleigh wave attenuation data shows a high attenuation zone below a depth of 100 km the inferred lowq value at mid crustal depth high attenuating zone in the model for northern india can be by underthrusting of the indian plate beneath the eurasian plate which has caused a low velocity zone at this shallow depth the gradual increase ofq 1 from shallow to deeper depth shows that the lithosphere asthenosphere boundary is not sharply defined beneath central india but rather it represents a gradual transformation which starts beneath the uppermost mantle the lithospheric thickness is 100 km beneath central india and below that the asthenosphere shows higher attenuation a factor of about two greater than that in the lithosphere the very lowq can be explained by changes in the chemical constitution taking place in the uppermost mantle

source models of great earthquakes from ultra low frequency normal mode data abstract we present a new earthquake source inversion technique based on normal mode data for the simultaneous determination of the rupture duration length and moment tensor of large earthquakes with unilateral rupture we use ultra low frequency f m w 8 5 i sumatra andaman 26th december 2004 ii nias sumatra 28th march 2005 iii bengkulu 12th september 2007 iv tohoku japan 11th march 2011 v maule chile 27th february 2010 and vi the 24 may 2013 m w 8 3 okhotsk sea russia deep 607 km event while finite source inversions for rupture length duration magnitude and fault mechanism are possible for the sumatra andaman and tohoku events for all the other events their lower magnitudes only allow stable point source inversions of mode multiplets we obtain the first normal mode finite source model for the 2011 tohoku earthquake which yields a fault length of 461 km a rupture duration of 151 s and hence an average rupture velocity of 3 05 km s giving an independent confirmation of the compact nature of this event for all the other earthquakes studied our new source models agree well with previous studies we do not find any unexplained systematic differences between our results and those in the literature suggesting that for the wave frequencies considered the moment magnitude and the fault mechanism of the earthquakes studied do not show a strong frequency dependence

derivation of 3 d coseismic surface displacement fields for the 2011 mw 9 0 tohoku oki earthquake from insar and gps measurements

uranium metallogenesis in south china and its relationship to crustal extension during the cretaceous to tertiary south china is rich in vein type hydrothermal uranium deposits hosted in granitic volcanic and carbonaceous and siliceous pelitic sedimentary rocks the uranium deposits are spatially associated with extensional structures and or mantle derived mafic dikes both the uranium deposits and mafic dikes are cretaceous to tertiary in age temporally coincident with the crustal extension carbon isotope analyses of calcite deposited in the main stage mineralization in the veins from 12 representative uranium deposits yield 13c values of ore forming fluids mainly from 4 to 8 per mil which are permissive of a mantle origin for the co2 in the ore forming fluids a mantle origin is consistent with the association of the deposits with mafic dikes and the 3he 4he ratios of ore forming fluids e g 0 10 2 02 ra for the volcanic hosted xiangshan uranium deposit isotopic compositions of h and o demonstrate that water in the ore forming fluids is predominantly meteoric in origin ore forming temperatures ranged approximately from 150 to 250 c uranium rich crustal rocks in south china may have been the sources for the uranium crustal extension and associated mafic magmatism are considered to have heated the rocks and allowed co2 possibly from mantle sources to migrate upward and to mix with co2 poor meteoric water the co2 rich hydrothermal fluids mobilized uranium from the source rocks and then the uranium was deposited in various host rocks to form the uranium deposits

modeling the 2012 wharton basin earthquakes off sumatra complete lithospheric failure a sequence of large strike slip earthquakes occurred west of sunda trench beneath the wharton basin first reports indicate that the main shock was extremely complex involving three to four subevents m w 8 with a maze of aftershocks we investigate slip models of the two largest earthquakes by joint inversion of regional and teleseismic waveform data using the m w 7 2 foreshock we developed hybrid green s functions for the regional stations to approximate the mixture of oceanic and continental paths the main shock fault geometry is defined based on the back projection results point source mechanisms aftershock distribution and fine tune of grid searches the fault system contains three faults labeled f1 89 289 for dip strike f2 74 20 and f3 60 310 the inversion indicates that the main rupture consisted of a cascade of high stress drop asperities up to 30 mpa extending as deep as 50 km the rupture propagated smoothly from one fault to the next f1 f2 and f3 in sequence with rupture velocities of 2 0 2 5 km s the whole process lasted about 200 s and the major moment release 70 took place on the n s oriented f2 the m w 8 2 aftershock happened about 2 h later on a n s oriented fault with a relatively short duration 60 s and also ruptured as deep as 50 km the slip distributions suggest that the earthquake sequence was part of a broad left lateral shear zone between the australian and indian plates and ruptured the whole lithosphere these earthquakes apparently reactivated existing fracture zones and were probably triggered by unclamping of the great sumatran earthquake of 2004

deep crustal extensional faulting in the ivrea zone of northern italy abstract the ivrea zone in northern italy consists of amphibolite and granulite facies metasedimentary metabasic and ultrabasic rocks and is thought to represent a section through the deep continental crust detailed mapping of the high grade part of this zone has revealed a series of high temperature shear zones which after the effects of later low temperature faulting and folding have been removed appears to accommodate extension of the sequence the shear zones formed at temperatures similar to those at which thermal equilibration occurred in the host rocks and locally show evidence for development under prograde conditions these observations fit well with thermal effects calculated from a simple heat flow model for extensional faulting in this model the effects of shear heating and displacement of cool hanging wall rocks against hotter footwall rocks are calculated these observations indicate that faulting as a mode of failure may be important during extension of the lower continental crust especially when basic rocks are the dominant components of the rock pile a restored section through the extended lower crust as observed in the ivrea zone is presented and the extent to which the features observed are able to explain seismic reflectivity of the lower crust is discussed

trace elements u pb ages and hf isotopes of zircons from mesozoic granites in the western nanling range south china implications for petrogenesis and w sn mineralization abstract the e w trending nanling range located in the southern part of the south china block scb is characterized by widespread intra continental mesozoic granitoids and accompanying w sn polymetallic ore deposits detailed studies are presented on trace elements u pb ages and lu hf isotopes in zircons from the mesozoic a2 type like granitoids including the qianlishan qitianling xianghualing huashan guposhan niumiao tong an jinziling and jinjiling plutons from the western nanling range la icp ms u pb analyses of zircon indicate that these granites intruded mainly from ca 160 150 ma two types of zircon magmatic and late magmatic hydrothermal with similar ages can be distinguished based on their zircon trace element compositions the late magmatic hydrothermal zircons have high contents of metallogenic elements e g w and sn and may be closely related with the ore deposits the ehf t values of zircons from the mesozoic granitoids are mildly negative to positive indicating the reworking of both old and young crustal components the significant involvement of mesozoic juvenile mantle derived materials in the source can be excluded because of the rare occurrences of mafic rocks with radiogenic isotopic signatures in the area the average crustal residence age patterns of the mesozoic granites in the western nanling range are similar to those of the neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen which may represent the neoproterozoic collisional belt between the yangtze and cathaysia blocks considering the specific isotopic and metallogenic features of the mesozoic granitoids in the study area we propose that the western nanling range may represent a western extension of neoproterozoic arc continent collisional belt in south china the mesozoic granitoids of this area may have been generated mainly by reworking of deeply buried neoproterozoic arc related volcanic sedimentary materials due to thermal perturbations triggered by the subduction of the paleo pacific plate in mesozoic time

precise molybdenite re os and mica ar ar dating of the mesozoic yaogangxian tungsten deposit central nanling district south china the yaogangxian deposit in the central nanling region south china consists of vein type ore bodies hosted in cambrian to jurassic strata and mesozoic granitic intrusions wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz feldspar phlogopite and muscovite we have carried out molybdenite re os and phlogopite and muscovite 40ar 39ar dating to better understand the timing and genesis of mineralization re os dating of eight molybdenite samples yielded model ages ranging from 152 0 3 5 to 161 1 4 5 ma with an average of 156 0 ma the re os analyses give a well defined 187re 187os isochron with an age of 154 9 2 6 ma mswd 2 4 hydrothermal phlogopite and muscovite display extremely flat 40ar 39ar age spectra phlogopite yields a 40ar 39ar plateau age of 153 0 1 1 ma whereas muscovite yields a plateau age of 155 1 1 1 ma both 40ar 39ar ages are in good agreement with the re os ages placing the timing of tungsten mineralization at about 154 ma this age is consistent with the field relationships our new data when combined with published geochronological results from other major deposits in this region suggest that large scale w sn mineralization occurred throughout the central nanling region in the late jurassic

importance of the lu hf isotopic system in studies of planetary chronology and chemical evolution the 176lu 176hf isotope method and its applications in earth sciences are discussed greater fractionation of lu hf than sm nd in planetary magmatic processes makes 176hf177hf a powerful geochemical tracer in general proportional variations of 176hf177hf exceed those of 143ndl44nd by factors of 1 5 3 in terrestrial and lunar materials lu hf studies therefore have a major contribution to make in understanding of terrestrial and other planetary evolution through time and this is the principal importance of lu hf new data on basalts from oceanic islands show unequivocally that whereas considerable divergences occur in 176hf177hf 87sr86sr and 143ndl44nd 87sr86sr diagrams 176hf177hf and 143nd144nd display a single linear isotopic variation in the suboceanic mantle these discordant 87sr86sr relationships may allow with the acquisition of further hf nd sr isotopic data a distinction between processes such as mantle metasomatism influence of seawater altered material in the magma source or recycling of sediments into the mantle in order to evaluate the hf nd isotopic correlation in terms of mantle fractionation history there is a need for measurements of hf distribution coefficients between silicate minerals and liquids and specifically for a knowledge of hf behavior in relation to rareearth elements for studying ancient terrestrial hf isotopic variations the best quality hf isotope data are obtained from granitoid rocks or zircons new data show that very u pb discordant zircons may have upwardly biased 176hf177hf but that at least concordant to slightly discordant zircons appear to be reliable carriers of initial 176hf177hf until the controls on addition of radiogenic hf to zircon are understood combined zircon whole rock studies are recommended lu hf has been demonstrated as a viable tool for dating of ancient terrestrial and extraterrestrial samples but because it offers little advantage over existing methods is unlikely to find wide application in pure chronological studies

seismic structure and seismogenesis off sanriku region northeastern japan summary in 1997 a seismic experiment using an airgun array and ocean bottom seismographs obss was performed in the forearc region of the northeastern japan nej arc the objectives of this experiment were to clarify seismic structures of the forearc region off sanriku japan using airgun obs data and to understand the nature of the japan trench seismogenic zone fundamental features of the structure are as follows i the subduction angle becomes steeper from east to west from 3 to 8 to 11 with the top of the plate located at depths of 11 km 40 km west from the trench 21 km 120 km west from the trench and 28 km 140 km west from the trench respectively ii the nej moho beneath the forearc is defined at a depth of approximately 20 km iii p wave velocity of the island arc upper mantle is approximately 8 km s 1 iv the p wave velocity of the cretaceous sedimentary layer exhibits significant lateral variability 4 0 5 5 km s 1 i nthe e w direction v the upper crust of nej forearc also has the significant lateral heterogeneity 5 0 6 3 km s 1 i nthe e w direction but not in the n s direction vi the middle crust defined on land extends in some locations 40 km east of the coastline vii lateral variability in the p wave velocity of the lower crust 6 7 7 0 km s 1 i ssmall compared with that of the upper crust according to these results it is suggested that the rupture areas of large earthquakes m7 in this region are limited within the contact zone between the nej arc crust and the subducting oceanic crust although a thin layer with low velocity is probably present within this contact zone the serpentinization of uppermost mantle wedge of the nej arc by reaction between the mantle materials and the water from the thin layer beneath forearc region is limited this might indicate that a significant volume of water and sediments subduct with the slab to depths of over 20 km

impact of additional dead carbon on the circulation estimation of thermal springs exposed from deep seated faults in the dongguan basin southern china abstract in hydrothermal systems the dissolved carbon of thermal groundwater may contain components derived from mineral alterations under high temperatures metamorphic source and or from magmatic gases additionally from carbonate dissolution most common these components are known as additional dead carbon which dilutes the modern carbon used for dating leading to the overestimation of 14c ages four typical geothermal springs hosted by deep seated faults and eighteen non thermal springs and wells from the dongguan basin of southern china were investigated to assess the circulation times of the hydrothermal system based on their radiocarbon contents for the thermal springs the circulation depth approximately 3648 m the apparent 14c ages 20 15 to 12 97 ka and the 13c calibrated 14c ages 16 02 to 8 55 ka were estimated the circulation speed of the thermal groundwater was as low as 0 46 m a which was too slow for a fracture hydrothermal system hosted by deep faults the analysis of the helium and carbon isotopes in the thermal groundwater revealed the existence of mantle derived carbon and thermally altered carbon from limestones a 13c 3he 4he illustration was proposed to correct for the additional dead carbon content according to the reassessed 14c ages the groundwater circulation time was overestimated and the circulation speed of the thermal groundwater was underestimated in hydrothermal system the reassessed 14c ages can provide a more reasonable result than the initial slow estimate in the context of a fracture hydrothermal system hosted by deep faults we conclude that measured 14c contents should be reassessed during the use of radiocarbon dating for thermal groundwater if additional dead carbon exists in the water

genetically related mo bi ag and u f mineralization in a type granite gabal gattar eastern desert egypt abstract molybdenum bismuth silver and uranium fluorine mineralization in the gabal gattar area are genetically related both are hosted in fractionated and hydrothermally altered a type granite while mo bi ag ore is hosted in ns striking quartz veins the u f mineralization forms batches and micro veinlets controlled by nne to nw trending structures u was incorporated in late magmatic hypogene minerals e g zircon and xenotime and in u th minerals closely associated with fluorite molybdenite native bismuth galena chalcopyrite sphalerite aikinite pbcubis 3 berryite s 16 cu ag 6 bi 7 pb 3 and native silver were identified in the quartz veins fluid inclusions occur in fluorite type 1 associated with u minerals and in quartz type 2 from mo bearing veins type 1 and 2 inclusions homogenize at temperatures between 220 c and 106 c their salinity ranges from 1 3 to 10 wt nacleq respectively f rich fluids accumulated at the last stage of granite crystallization extracted ore metals and deposited them in a shallow hydrothermal system mo bi and ag precipitated earlier from saline fluids due to cooling fluid mixing and wallrock sulfidation u f minerals precipitated from low salinity fluids after high input of meteoric water

compressive sensing of frequency dependent seismic radiation from subduction zone megathrust ruptures megathrust earthquakes rupture a broad zone of the subducting plate interface in both along strike and along dip directions the along dip rupture characteristics of megathrust events e g their slip and energy radiation distribution reflect depth varying frictional properties of the slab interface here we report high resolution frequency dependent seismic radiation of the four largest megathrust earthquakes in the past 10 y using a compressive sensing sparse source recovery technique resolving generally low frequency radiation closer to the trench at shallower depths and high frequency radiation farther from the trench at greater depths together with coseismic slip models and early aftershock locations our results suggest depth varying frictional properties at the subducting plate interfaces the shallower portion of the slab interface above 15 km is frictionally stable or conditionally stable and is the source region for tsunami earthquakes with large coseismic slip deficient high frequency radiation and few early aftershocks the slab interface at intermediate depths 15 35 km is the main unstable seismogenic zone for the nucleation of megathrust quakes typically with large coseismic slip abundant early aftershocks and intermediate to high frequency radiation the deeper portion of the slab interface 35 45 km is seismically unstable however with small coseismic slip dominant high frequency radiation and relatively fewer aftershocks

shallow subduction zone earthquakes and their tsunamigenic potential summary we have examined the source spectra of all shallow subduction zone earthquakes from 1992 to 1996 with moment magnitude 7 0 or greater as well as some other interesting events in the period range 1 20 s by computing moment rate functions of teleseismic p waves after comparing the source spectral characteristics of tsunami earthquakes earthquakes that are followed by tsunamis greater than would be expected from their moment magnitude with regular events we identified a subclass of this group slow tsunami earthquakes this subclass consists of the 1992 nicaragua the 1994 java and the february 1996 peru earthquakes we found that these events have an anomalously low energy release in the 1 20 s frequency band with respect to their moment magnitude although their spectral drop ov is comparable to those of the other earthquakes from an investigation of the centroid and body wave locations it appears that most earthquakes in this study conformed to a simple model in which the earthquake nucleates in a zone of compacted and dehydrated sediments and ruptures up dip until the stable sliding friction regime of unconsolidated sediments stops the propagation sedimentstarved trenches e g near jalisco can produce very shallow slip because the fault material supports unstable sliding the slow tsunami earthquakes also ruptured up dip however their centroid is located unusually close to the trench axis the subduction zones in which these events occurred all have a small accretionary prism and a thin layer of subducting sediment ocean surveys show that in these regions the ocean floor close to the trench is highly faulted we suggest that the horst and graben structure of a rough subducting oceanic plate will cause contact zones with the overriding plate making shallow earthquake nucleation and up dip propagation to the ocean floor possible the rupture partly propagates in sediments making the earthquake source process slow two factors have to be considered in the high tsunami generating potential of these events first the slip propagates to shallow depths in low rigidity material causing great deformation and displacement of a large volume of water second the measured seismic moment may not represent the true earthquake displacement because the elastic constants of the source region are not taken into account in the standard cmt determination

no clear evidence for localized tidal periodicities in earthquakes in the central japan region we search for possible localized tidal triggering in earthquake occurrence near japan by testing for tidal periodicities in seismicity within a variety of space time bins we examine 74 610 earthquakes of m 3 in the japan meteorological agency jma catalog from january 2000 to april 2013 because we use many earthquakes for which accurate focal mechanisms are not available we do not compute tidal stresses on individual fault planes but instead assume that the mechanisms are likely to be similar enough among nearby events that tidal triggering will promote earthquake occurrence at specific tidal phases after dividing the data into cells at a range of spatial 0 2 0 5 1 0 and temporal dimensions 100 200 400 days we apply schuster s test for non random event occurrence with respect to both the semi diurnal and semi monthly tidal phases because the resulting p values will be biased by temporal clustering caused by aftershocks we apply a declustering method that retains only one event per tidal cycle per phase increment our results show a wide range of p values for the localized earthquake bins but the number of bins with very small p values e g p 0 05 is no more than might be expected due to random chance and there is no correlation of low p value bins with the time of the 2010 m 9 0 tohoku oki earthquake

using repeated sources to quantitatively determine temporal change of medium properties theory and an example 1 we develop a theory of using difference wavefields of repeated sources to locate and quantify temporal medium change and apply the theory to locate temporal change of seismic properties beneath the japan subduction zone using repeated earthquakes our theory states the difference wavefields of two repeated sources in a temporally changed medium can be equivalently treated as wavefields propagating from conceptual sources with their location at the place of temporal change and their strengths equal to the product of magnitude of medium property change and magnitude of the initial wavefields from the repeated sources when the medium change extends to a finite region the conceptual sources become volumetric sources distributed over the region of the medium change and propagating in the direction of the initial wave the conceptualization establishes a theoretical framework for possible applications of using difference wavefields to locate and quantify temporal medium changes in geological sciences ultrasonic experiments civil engineering and medical imaging we search repeating earthquakes occurring in the japan subduction zone formulate an empirical procedure to extract the difference wavefields between repeating earthquakes and determine temporal change of seismic properties using a back projection method we locate the temporal change of seismic properties beneath the japan subduction zone to be at 37 2 n 142 e and estimate the magnitude of the conceptual body force associated with the temporal change to be 1 15 1010n or as a reference a 0 87 density change for an assumed volume of temporal change of 103 km3

an adjoint based fem optimization of coseismic displacements following the 2011 tohoku earthquake new insights for the limits of the upper plate rebound the 11 march 2011 tohoku earthquake was the strongest event recorded in recent historic seismicity in japan several researchers reported the deformation and possible mechanism as triggered by a mega thrust fault located offshore at the interface between the pacific and the okhotsk plate the studies to estimate the deformation in detail and the dynamics involved are still in progress in this paper coseismic gps displacements associated with tohoku earthquake are used to infer the amount of slip on the fault plane starting from the fault displacements configuration proposed by caltech jpl aria group and geoazur cnrs an optimization of these displacements is performed by developing a 3d finite element method fem model including the data of gps acoustic stations located offshore the optimization is performed for different scenarios which include the presence of topography and bathymetry dem as well as medium heterogeneities by mean of the optimized displacement distribution for the most complete case heterogeneous with dem a broad slip distribution not narrowly centered east of hypocenter is inferred the resulting displacement map suggests that the beginning of the area of subsidence is not at east of mygw gps acoustic station as some researchers have suggested and that the area of polar reversal of the vertical displacement is rather located at west of mygw the new fault slip distribution fits well for all the stations at ground and offshore and provides new information on the earthquake generation process and on the kinematics of northern japan area

isotopic geochemistry of shituling uranium deposit northern guangdong province china the shituling uranium deposit is located on the granitic side of the contact zone between the southeastern part of guidong granite and the precambrian low grade metamorphic rocks there occur many nww and nne striking basic veins in this area the veinlike ore bodies mainly hosted in maofeng granite are controlled by ew trending fissure structures the u pb age of uraninite 135 ma is obviously different from the formation age of maofeng granite but close to the age of nww trending diabase veins the initial 87 sr 86 sr values of pyrite 0 71315 0 72579 in the ore are between those of nww striking diabase 0 70449 0 70632 and maofeng and xiazhuang granites 0 75058 0 99507 at 135 ma the linear pb isotope distribution of pyrite from the ore indicates that pb in the ore was a mixture of pb derived from the basement metamorphic rock maofeng granite and diabase the sr and pb isotopes show multiple source characteristics of the ore forming components the ore forming fluids have 18 o h 2o of 2 0 8 1 and d h 2o of 63 51 suggesting that the ore forming fluids were mainly composed of mantle fluids the calcite 13 c of 8 3 suggests that the co 2 in the fluids came from the mantle therefore the mantle fluids might have played an important role in uranium mineralization of the shituling uranium deposit

fate of trace elements during alteration of uraninite in a hydrothermal vein type u deposit from marshall pass colorado usa alteration of uraninite from a hydrothermal vein type u deposit in marshall pass colorado has been examined by electron microprobe analysis in order to investigate the release and migration of trace elements w as mo zr pb ba ce y ca ti p th fe si al during alteration under both reducing and oxidizing conditions the release of trace elements from uraninite is used to establish constraints on the release of fission product elements from the uo2 in spent nuclear fuels uraninite occurs with two different textures 1 colloform uraninite and 2 fine grained uraninite the colloform uraninite contains 1 04 1 75 wt of wo3 0 16 1 70 wt of as2o3 0 06 0 88 wt of moo3 whereas the fine grained uraninite retains 2 25 4 93 wt of wo3 up to 5 76 wt of moo3 and 0 26 0 60 wt of as2o3 the near constant concentration of incompatible w in the colloform uraninite suggests w incorporation into the uraninite structure or homogeneous distribution of w rich nano domains incorporation of w and mo into the uraninite and subsequent precipitation of uranyl phases bearing these elements are critically important to understanding the release and migration of cs during the corrosion of spent nuclear fuel as there is a strong affinity of cs with w and mo zoning in the colloform texture is attributed to variation in the amount of impurities in uraninite for unaltered zones the calculated amount of oxygen ranges from 2 08 to 2 32 apfu atom per formula unit and defines the stoichiometry as uo2 x and u4o9 whereas for the altered zones of the colloform texture the oxygen content is 2 37 2 48 apfu which is probably due to the inclusion of secondary uranyl phases mainly schoepite the supergene alteration resulted in precipitation of secondary uranyl minerals at the expense of uraninite four stages of colloform uraninite alteration are proposed i formation of an oxidized layer at the rim ii corrosion of the oxidized layer iii precipitation of u6 phases with well defined cleavage and iv fracture of the uraninite surface along the cleavage planes of the u6 phases

origin of topaz bearing and related peraluminous granites of the late devonian davis lake pluton nova scotia canada crystal versus fluid fractionation abstract the davis lake pluton in the late devonian south mountain batholith in southwestern nova scotia canada is composed of peraluminous leucomonzogranites and subordinate topaz bearing leucogranites that host greisens and a primary tin deposit the concentrations of incompatible trace elements e g rb li u f ta and sn and element e g k rb nb ta and la sm and isotopic ratios e g 206 pb 204 pb and 87 sr 86 sr display a spatial zonation the granitic rocks were generated by extensive fractional crystallization of major phases feldspars and biotite and accessory minerals monazite apatite and zircon in a compositionally zoned magma chamber fractional crystallization of the evolving f rich peraluminous granitic magma was accompanied particularly in later stages by fluid fractionation involving fluorine complexing fluid fractionation was a major differentiation process during the terminal stages of the pluton s evolution it played an important role in the genesis of the evolved rocks which are characterized by low k rb 24 150 nb ta 1 6 la sm 1 5 4 and eu eu 0 01 0 3 ratios these ratios as well as the enhanced concentrations of li rb u ta and sn in these rocks correlate with f fluorine rich fluids modified the rb sr and u pb ratios which produced the distinct variations of 87 sr 86 sr and 206 pb 204 pb isotopic ratios the parent magma was formed by dehydration melting of lower crustal metasedimentary rocks the melting was related to crustal thickening in association with terrane and collision along the eastern margin of the appalachians

the bermuda earthquake of march 24 1978 a significant oceanic intraplate event the bermuda earthquake m 6 occurred near the westerly extension of the kane fracture zone roughly 370 km southwest of the island of bermuda it is one of the largest oceanic intraplate earthquakes to occur off the eastern coast of north america because of its size and location it has provided an excellent set of wwssn body waves they can be used to infer its depth and faulting parameters by waveform modeling techniques the results indicate a north northwest striking thrust mechanism strike n20 w dip 42 ne rake 90 with the hypocenter located at a depth of 11 km which for an oceanic crust places it predominantly in the mantle the event had a seismic moment of 3 4 1025 dyne cm and its time history was modeled with a symmetric trapezoidal time function 3 s in duration the north northwest strike of the event is in good agreement with the bathymetry of the area the epicenter being close to the southwestern edge of the bermuda rise the strike of the event is also close to that of the inferred extensions of the present ridge fracture zones in the region the presence of such fracture zones is indicative of local weak zones in the lithosphere the bermuda earthquake most likely is associated with one of these zones of weakness and is the result of the application of present day stress imposed on the region by the north american plate in the direction of its absolute motion this is an important event in terms of understanding and estimating seismic hazard on the eastern seaboard of north america

trace element and isotope sr nd geochemistry of porphyry and skarn mineralising late cretaceous intrusions from banat western south carpathians romania geochemical and isotopic strontium neodymium data have been obtained from 24 samples of seven late cretaceous intrusions associated with skarn tincova bocsa ocna de fier dognecea and porphyry copper molybdenum skarn deposits oravi a ciclova sasca and moldova nou in the south carpathians of romania the intrusions cut the supragetic getic nappes and form a 100 km long nne ssw trending lineament in the banat metallogenic province the samples range in composition from gabbro to granodiorite and define in major and trace element variation diagrams a calc alkaline to high potassium calc alkaline trend ranging from 50 to 67 sio2 they are magnetite bearing i type granitoids enriched in lile lree and depleted in nb ta and zr common features for magmas associated with subduction zones the lack of cumulate textures and of positive europium anomalies seems to indicate that the samples represent liquid compositions the observed trend thus approximates a liquid line of descent resulting from fractional crystallisation of parental magmas with similar major and trace element compositions initial strontium isotopic ratios sri vary from 0 7042 to 0 7058 and end t values range from 3 9 to 0 2 variations of sri and end t values with sio2 show minor crustal assimilation the generally positive end t values together with moderate sri indicate that the parental magmas result from partial melting of a rubidium enriched and lree depleted source such as a heterogeneous lithospheric mantle or a young mafic lower crust derived from it selective rubidium enrichment probably occurred during a previous subduction event by metasomatism of the overlying mantle wedge either in the early cretaceous or earlier as suggested by tdm model ages ca 600 ma the cu mo pb zn fe deposits are intimately associated with the intrusions and the banat romania region can be subdivided in two metallogenic zones in northern banat fe cu pb zn skarns occur whereas in southern banat porphyry style copper and molybdenum deposits predominate these differences result from a combination of several parameters 1 magma composition whereby copper and molybdenum rich deposits tend to be associated with calc alkaline compositions 2 an increase of the present day erosion level from south to north as indicated by the presence of large equigranular plutons in northern banat and of porphyritic cupolas and apophyses associated with porphyry style mineralisation in southern banat 3 the nature of the host rocks with skarns preferentially developed in calcareous host rocks and 4 local variations of conditions controlling the infiltration of fluids and the precipitation of ore minerals

coherent seismic arrivals in the p wave coda of the 2012 m w 7 2 sumatra earthquake water reverberations or an early aftershock

he pb and s isotopic constraints on the relationship between the a type qitianling granite and the furong tin deposit hunan province china abstract the furong tin deposit located in southern hunan province china is a large newly discovered deposit with an estimated sn reserve of about 700 000 tons the deposit is spatially and temporally associated with the a type qitianling granite the 3he 4he ratios of fluid inclusions trapped in sulfides from the deposit range from 0 13 to 2 95 ra indicating a mixed crust mantle source similar to that of the qitianling granite complex lead isotopes in feldspars of the granite mostly in the range of 206pb 204pb 18 547 19 180 207pb 204pb 15 598 15 825 208pb 204pb 37 912 39 068 and in sulfide minerals 206pb 204pb 18 467 18 836 207pb 204pb 15 503 15 772 208pb 204pb 38 607 39 099 are essentially the same indicating that the lead in both was derived mainly from the upper crust with a small mantle component the sulfur isotopic values of the ore minerals vary widely ranging from 26 1 to 10 4 but are mainly within the range of 0 2 to 10 4 implying that the s in the hydrothermal fluids was derived mainly from magmatic fluids with minor contributions from the mantle sedimentary rocks and biogenic material the he pb and s isotopes all confirm that the ore forming fluids of the furong deposit were magmatic in origin derived from the melts that produced the qitianling a type granite the tin mineralization occurs within or along the margins of the qitianling granite complex and the timing of the mineralization coincides with the intrusive age of the granite the available data suggest that the emplacement of the granites and the mineralization was related to mantle upwelling and extension of the lithosphere in south china during the mesozoic

subevent location and rupture imaging using iterative backprojection for the 2011 tohoku mw 9 0 earthquake summary knowledge of the rupture speed and spatial temporal distribution of energy radiation of earthquakes is important for earthquake physics backprojection of teleseismic waves is commonly used to image the rupture process of large events the conventional backprojection method typically performs temporal and spatial averaging to obtain reliable rupture features we present an iterative backprojection method with subevent signal stripping to determine the distribution of subevents large energy bursts during the earthquake rupture we also relocate the subevents initially determined by iterative backprojection using the traveltime shifts from subevent waveform cross correlation which provides more accurate subevent locations and source times a bootstrap approach is used to assess the reliability of the identified subevents we apply this method to the mw 9 0 tohoku earthquake in japan using array data in the united states we identify 16 reliable subevents in the frequency band 0 2 1 hz which mostly occurred around or west of the hypocentre in the downdip region analysis of tohoku aftershocks shows that depth phases can often produce artefacts in the backprojection image but the position and timing of our main shock subevents are inconsistent with depth phase artefacts our results suggest a complicated rupture with a component of bilateral rupture along strike the dominant energy radiation between 0 2 and 1 hz is confined to a region close to the hypocentre during the first 90 s a number of subevents occurred around the hypocentre in the first 90 s suggesting a low initial rupture speed and repeated rupture or slip near thehypocentre therupturereachedthecoastalregionabout106kmnorthwestofthehypocentreat43sandtheregionabout110kmnorthofthehypocentreat105swithanorthwardrupture speed 2 0 kms 1 at 60 110 s after 110 s a series of subevents occurred about 120 220 km southwest of the hypocentre consistent wit ha3k ms 1 along strike rupture speed the abundant high frequency radiation in the downdip region close to the coast suggests intermittent rupture probably in the brittle ductile transition zone the lack of high frequency radiation in the updip region suggests the rupture near the trench was more continuous probably due to more homogeneous frictional properties of the shallow slab interface the lack of early aftershocks in the updip region indicates that most of the accumulated slip in the updip region during the interseismic period was probably released during the main shock

rock magnetic investigation and its geological significance for vein type uranium deposits in southern china to characterize the metallogenic environment of a typical vein type uranium deposit samples from diabase dykes alteration zones including metamorphic diabase and uranium ore and granites were systematically investigated for six boreholes from southeastern china rock magnetic results indicate that coarse grained magnetites pseudosingle domain psd and multidomain md are dominant magnetic carriers in diabase in contrast the uranium ore is dominated by fine grained magnetites superparamagnetic sp and single domain sd the concentration of magnetic particles in fresh granites is low magnetic properties of metamorphic diabases exhibit much greater variability of magnetic properties and higher degrees of sulfuration than unaltered diabase and granite due to contact metasomatism and reduction effects close to the vein compared with diabase magnetic remanence of the uranium ore is much lower but displays much higher stability the koenigsberger ratio q peaks in the uranium ore with a value of 1 00 using the systematic rock magnetic results to constrain the interpretation the contribution of the intersection zone of diabase dyke and silicified fault to magnetic anomalies was further modeled and the effects of the ore body are significant for magnetic exploration overall rock magnetic investigations of vein type uranium deposit provide a better understanding of the interactions between different rock types and further facilitate regional magnetic surveys on the ground

newly discovered uranium mineralization at 2 0 ma in the menggongjie granite hosted uranium deposit south china abstract the southeastern part of the nanling metallogenic province south china contains numerous economically important granite hosted hydrothermal vein type uranium deposits the miao ershan mes uranium ore field is one of the most important uranium sources in china hosts the largest chanziping carbonaceous siliceous pelitic rock type uranium deposit and several representative granite hosted uranium deposits the geology and geochemistry of these deposits have been extensively studied however accurate and precise ages for the uranium mineralization are scarce because uranium minerals in these deposits are usually fine grained and may have formed in several stages thus hindering the understanding of the uranium metallogenesis of this province the menggongjie mgj uranium deposit is one of the largest granite hosted uranium deposits in the mes ore field uranium mineralization in this deposit occurs at the central part of the mes granitic complex accompanied with silicification fluorination k metasomatism and hematitization the ore minerals are dominated by uraninite occurring in quartz or fluorite veinlets along fractures in altered granite in situ sims u pb dating on the uraninite yields the u pb isotopic age of 1 9 0 7 ma which is comparable to the chemical u th pbtol uraninite age of 2 3 0 1 ma such ages agree well with the eruption ages of the extension related quaternary volcanics 2 1 1 2 ma in south china suggesting that the uranium mineralization have formed at an extensional setting possibly related to the quaternary volcanic activities therefore our robust new dating results of the mgj uranium deposit make it the youngest granite hosted uranium deposit reported so far in south china and the mineralization event represents a newly identified mineralization epoch