the 2005 and 2010 earthquakes on the sumatra andaman trench evidence for post 2004 megathrust intraplate rejuvenation great earthquakes on oblique subduction zones accommodate slip on strike slip faults on the overriding and subducting plates leading to increased intraplate seismicity after the 2004 sumatra earthquake there was an increase in activity in the wharton basin wb which is considered to be part of a diffuse plate boundary here the intraplate deformation occurs in response to northwest southeast directed compression as opposed to the north northeast south southwest directed plate motion along the sumatra andaman subduction zone earthquakes here mostly occur by left lateral strike slip on north south n s trending fossil fractures although ruptures on east west planes are not uncommon here we discuss the 24 july 2005 m w 7 2 and the 12 june 2010 m w 7 5 earthquakes both of which were left lateral strike slip events sourced in the northern wb our source models for these events based on teleseismic waveform inversion favor slip on the n s fossil fracture systems consistent with previous studies in the wb although the former sourced at similar to 16 km depth was not tsunamigenic the latter similar to 34 km triggered a small tsunami possibly due to its oblique slip at similar to 5 km depth we use conceptual models of plate deformation to suggest that both these events have resulted from post 2004 redistribution of stresses and rejuvenation of intraslab fracture systems within the wb an actively deforming oceanic intraplate region

long period spectral features of the sumatra andaman 2004 earthquake rupture process summary the goal of this study is to investigate the spatial variability of the seismic radiation spectral content of the sumatra andaman 2004 earthquake we determine the integral estimates of source geometry duration and rupture propagation given by the stress glut moments of total degree 2 of different source models these models are constructed from a single or a joint use of different observations including seismology geodesy altimetry and tide gauge data the comparative analysis shows coherency among the different models and no strong contradictions are found between the integral estimates of geodetic and altimetric models and those retrieved from very long period seismic records up to 2000 3000 s the comparison between these results and the integral estimates derived from observed surface wave spectra in period band from 500 to 650 s suggests that the northern part of the fault to the north of 8 n near nicobar islands did not radiate long period seismic waves that is period shorter than 650 s at least this conclusion is consistent with the existing composite short and long rise time tsunami model with short rise time of slip in the southern part of the fault and very long rise time of slip at the northern part this complex space time slip evolution can be reproduced by a simple dynamic model of the rupture assuming a crude phenomenological mechanical behaviour of the rupture interface at the fault scales combining an effective slip controlled exponential weakening effect related to possible friction and damage breakdown processes of the fault zone and an effective linear viscous strengthening effect related to possible interface lubrication processes while the rupture front speed remains unperturbed with initial short slip duration a slow creep wave propagates behind the rupture front in the case of viscous effects accounting for the long slip duration and the radiation characteristics in the northern segment

cretaceous ridge subduction along the lower yangtze river belt eastern china the lower yangtze river belt is one of the most important metallogenic belts in china the mechanisms responsible for ore genesis and the formation of related cretaceous igneous rocks such as adakite a type granitoid and nb enriched basalt remain controversial mesozoic granitoids in the lower yangtze river belt were mostly formed in the early cretaceous 140 125 ma and three granitoid belts the inner the south and the north have been defined according to petrological and geochemical characteristics previously based mainly on negative end and high initial sr isotope values the adakitic rocks were generally attributed to partial melting of thickened or delaminated lower crust both of which require crustal thickening mesozoic crustal thickening however is not supported by the development of extensional basins in the region from the late jurassic to cretaceous eastern china was closely associated with subduction of the pacific plate in the south and the izanagi plate in the north the midocean ridge mor between these two plates was drifting toward and likely subducting under the lower yangtze river belt a ridge subduction model can therefore explain the distribution of different magmatic rocks and ore deposits in the belt partial melting of subducting young hot oceanic slabs close to the ridge formed adakitic rocks the negative end values of adakitic rocks can be plausibly interpreted by mixing between adakitic magmas and enriched components in the lithospheric mantle and or crustal materials through afc process a slab window opened during ridge subduction as indicated by a type granitoids in the center of the inner belt nb enriched basalt found in the belt was likely formed by partial melting of a mantle wedge metasomatized by fluids released from the subducting slab at shallow depths

the april 2012 indian ocean earthquakes seismotectonic context and implications for their mechanisms the 11 april 2012 earthquakes m w 8 6 and m w 8 2 were sourced within the northern wharton basin in the northeastern part of the indo australian diffuse plate boundary this unusually active oceanic intraplate region has generated many large earthquakes in the past most of which are believed to have occurred by strike slip motion triggered by the nw se oriented compressional stresses acting across the indian and australian plates in the aftermath of the 2004 megathrust earthquake along the nearby sunda trench increased seismicity in the northern wharton basin is attributed to the stress transfer from the sumatra andaman plate boundary models proposed for the april 2012 earthquakes differ somewhat in details but partly attribute their complex rupture to the reactivation of pre existing structures these structures include previously mapped n s trending fracture zones within the northern wharton basin and e w lineations across the ninetyeast ridge in this paper we review the regional tectonics and past seismicity on the indo australian plate in order to understand the seismotectonic setting of the april 2012 indian ocean earthquakes c 2014 elsevier b v all rights reserved

a review of the intracontinental porphyry deposits in the middle lower yangtze river valley metallogenic belt eastern china abstract the middle lower yangtze river valley metallogenic belt mlyb is one of the most important metallogenic belts in eastern china and contains many important porphyry deposits these deposits include the tongshankou cu mo jiguanzui cu au chengmengshan cu mo wushan cu mo fengshandong cu au dingjiashan cu yangjishan au shaxi cu au dongguashan cu au shujiadian cu and anjishan cu deposits etc in this review we summarize the geological characteristics including the stratigraphy structure ore bearing porphyry types vein characteristics and wall rock alteration metallogenic ages and petro geochemistry of representative porphyry deposits in the mlyb we conclude that porphyritic magmatism and metallogeny have occurred in three stages the early ca 149 135 ma and late ca 123 105 ma stages comprise mainly porphyry skarn mineralization whereas the middle ca 133 125 ma stage comprises porphyry mineralization ore bearing porphyries in the mlyb are the high k calc alkaline to calc alkaline series with the majority possess adakitic geochemical signature the ore bearing porphyries with adakitic signature may have originated from magma mixing produced by the delamination of enriched lithospheric mantle and partial melting of the thickened lower crust the enriched mantle derived mafic melts component are very important for generating fertile magma and the 34s and 18o values suggest that ore forming materials were magma derived compared with porphyry deposits in typical magmatic arc settings porphyry deposits in the mlyb do not contain advanced argillic lithocaps or high to intermediate sulfidation systems and the magmatic and ore forming material sources are also very different

spatial aftershock distribution of the 26 december 2004 great sumatra andaman earthquake in the northern sumatra area 1 in july 2005 about 6 months after the 2004 great sumatra andaman earthquake 20 ocean bottom seismometers were deployed in the northern sumatra area more than 1000 events were identified during the 12 day recording period after relocation the seismicity shows different patterns on each side of the lower splay fault east of this feature and beneath the aceh basin and fore arc the deep earthquakes outline the subduction megathrust fault west of it the aftershocks distribution is strongly influenced by the active n s oceanic fracture zones of the subducted plate two n s trending clusters of 10 to 50 km deep earthquakes observed below the lower wedge are interpreted as reactivated oceanic fracture zones the postseismic activity suggests a significant influence of the n s active fracture zones of the oceanic plate on the toe of the wedge explaining the dextral wrenching of wedge thrusts in the morphology the megathrust fault does not extend to the trench but outcrops east of these active oceanic fractures and seems to merge upward along the lower splay fault where shallow earthquakes are observed

geochronology and geochemistry of the fe ore bearing zhonggu intrusions of the ningwu basin implications for tectonic setting and contemporaneous cu au mineralization in the middle lower yangzte metallogenic belt abstract the zhonggu ore field is located in the southern ningwu volcanic basin the largest iron ore district within the middle lower yangtze river metallogenic belt mlyrmb of eastern china this area has produced more than 2000 mt of iron ore although comparatively little research has been done on the ore bearing intrusions in this region despite the significance of the mineralization in this area this in turn means that the petrogenesis and the links between these intrusions and the metallogenesis in this area remain unclear this study focuses on the six intrusions that are associated with almost all of the iron deposits within the zhonggu ore field namely the gushan porphyritic gabbrodiorite the longshan gabbrodiorite the hemushan diorite the baixingshan diorite the zhongjiu diorite and the taipingshan monzonite all of these rocks are either high to medium k and calc alkaline or are shoshonitic although the former dominates over the latter zircon laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating yielded ages of 132 6 1 6 to 131 6 1 6 130 7 2 2 to 129 4 1 9 131 2 0 and 132 3 2 1 ma for intrusions associated with the longshan taipingshan baixiangshan and zhongjiu deposits respectively indicating that all of these intrusions were emplaced in the early cretaceous 132 6 129 4 ma this magmatism and mineralization was contemporaneous with the second stage 135 127 ma of magmatic activity that has been documented elsewhere within the mlyrmb the mineralized intrusions associated with the zhonggu iron ore field have similar chondrite normalized rare earth element ree and primitive mantle normalized multi element variation patterns that are characterized by light ree lree and light ion lithophile element lile rb ba k and sr enrichments and heavy ree hree and high field strength element hfse nb ta zr and hf depletions these intrusions also have total ree ree concentrations that are consistent with the evolution of the magma from mafic intermediate to felsic the magmas that formed these intrusions were derived from an enriched region of the mantle and underwent contamination by the assimilation of continental crustal or lithospheric material the magmatism within the zhonggu iron ore field formed during an early cretaceous period of lithospheric thinning and extension in addition the arc affinities of the intrusions in this region indicative of a relationship to the subduction of the paleo pacific plate a process that was most likely the main factor in the generation of the mineralization within the mlyrmb the fe mineralization related intrusions in the study area are also distinctly different from intrusions in this region associated with cu au mineralization most likely as a result of the heterogeneous distribution of slab derived fluids in this period over time this research also highlights the exploration potential of this region indicating that the 132 129 ma monzonites and diorites in this area and beyond should be considered prime targets for fe exploration but are also unlikely to be related to cu au mineralization

tectonic evolution of the tancheng lujiang tan lu fault via middle triassic to early cenozoic paleomagnetic data the north striking tancheng lujiang tan lu fault is a conspicuous and controversial feature of the eastern asian landscape near the southeast extremity of the fault in anhui province we collected paleomagnetic samples at 17 middle triassic t2 and 10 upper cretaceous k2 to lower cenozoic e1 sites t2 remanent magnetizations are interpreted as primary in two of three areas the three areas are rotated 37 to 137 counterclockwise with respect to the south china block scb reference direction k2 e1 remanent magnetization directions pass regional fold and reversals tests and are not rotated with respect to surrounding areas counterclockwise rotation of t2 strata therefore ended before k2 and is attributed to left lateral shear acting along tan lu during the north china block ncb scb collision in shandong province 700 km north of the anhui sites four areas containing 33 upper jurassic j3 and cretaceous sites have negligible declination differences except for one which has dispersed directions the fold test is inconclusive for this latter area and positive for the other three regional concordance of the j3 e1 paleomagnetic data including paleolatitudes together with observed deformation patterns suggest that an extensional regime prevailed in the late cretaceous and cenozoic euler pole positions that constrain the north south china collision and account for tan lu motion suggest at least 500 km of sinistral shear took place along the fault and either 1 subduction and related ultrahigh pressure uhp metamorphism occurred near the present location of the qinling dabieshan and sulu uhp belts while tan lu acted as a transform fault that connected the two subduction zones or 2 tan lu and sulu were parts of the same transform fault system and no uhp rocks formed in situ at sulu in either case uhp rocks originally exhumed near dabieshan could have been transported by plate capture toward sulu along tan lu after north and south china impacted near dabieshan the tan lu fault grew within the scb as the dabieshan corner indented the scb causing folds in scb cover rocks to conform to the ncb margin late cretaceous to cenozoic reactivation of tan lu with both right lateral strike slip and normal fault motion occurred as the scb extruded east relative to the ncb under the influence of the india asia collision

petrogenesis and geochronology of cretaceous adakitic i and a type granitoids in the ne yangtze block constraints on the eastern subsurface boundary between the north and south china blocks abstract a careful literature investigation for the north china and yangtze precambrian basements shows a distinct overlap of the nd pb hf isotopes between these two cratonic basements the isotopes of early cretaceous adakitic granitoids from chuzhou east of the tanlu fault zone in the northeastern yangtze block fall into the overlap fields these isotopes therefore cannot be used to distinguish the derivation of the chuzhou adakitic rocks from the north china or yangtze basements moreover high resolution deep seismic probing across the dabie sulu uhp terranes and east central china all indicates the yangtze craton was thrust beneath the north china craton the chuzhou adakitic rocks were most likely derived from the archean to paleoproterozoic lower crust of the yangtze craton the north china and yangtze cratons are most probably separated by the dabie tanlu sulu imjingang belts and a subsurface north china yangtze boundary located near nanjing is unsuitable

seismology energy radiation from the sumatra earthquake we determined the duration of high frequency energy radiation from indonesia s great sumatra andaman earthquake 26 december 2004 to be about 500 seconds this duration can be translated into a rupture length of about 1 200 km which is more than twice as long as that inferred from body wave analyses performed soon after the event our analysis was able rapidly to define the extent of rupture thereby aiding the assessment of seismic hazard in the immediate future

transtension to transpression a study of strain evolution in andaman islands based on gps measurements following great sumatra andaman earthquake 2004 we use campaign mode and continuous gps data from 2005 to 2008 to examine the evolving strain pattern in andaman islands after the great sumatra andaman earthquake two and half years after the earthquake the post seismic period changes to inter seismic period at port blair post seismic displacement rate reduced to about 95 with clockwise rotation of azimuths and towards north andaman velocity vector gradually rotates towards north with drop in magnitude the inter seismic displacement was dominated by trench parallel movement strain calculations on inclined transpession model shows deformations at andaman were highly heterogeneous both in post and inter seismic periods with dominant strike slip and dip slip shearing along with layer parallel shortening and extension post seismic and inter seismic periods had suffered simultaneous subduction perpendicular extension and contraction leading to transtension and transpression deformational environments respectively occurrence of earthquakes during post and inter seismic periods were results of interplay between simple shear and pure shear components of the strain matrix

geophysical characteristics of the ninetyeast ridge andaman island arc trench convergent zone abstract the convergence tectonics of the ninetyeast ridge ner upon the andaman island arc trench system is examined through an analysis of etopo2 bathymetry satellite derived free air gravity and seismic data oblique subduction and the buoyancy forces arising from subduction of the ner render the subduction processes near the andaman arc highly complex the bathymetric expression of the ner is visible up to lat 10 n but seismic reflection data indicate that it extends up to about lat 17 n the gravity anomalies are strongly positive over the exposed segment of the ridge but are subdued over the buried portion there is a prominent break in the continuity of the trench gravity low where the ner seems to impinge upon the island arc further a strong curvilinear belt of negative anomalies just behind and running parallel to the island arc associated with the forearc basin is a dominant feature of the gravity map an offset in the continuity of this strong negative anomaly occurs at about the same latitude where the ner seems to be converging upon the island arc seismic reflection data indicate that the ner is very close to the trench flexural modeling of the gravity anomalies for the subducting indian ocean lithosphere loaded by sediments and the ner indicates that the ner is at the starting phase of its collision with the island arc and may not have started affecting the subduction process itself we infer that the en echelon block structure of the ner in the proximity of the convergent zone is a consequence of complex strike slip and subduction related tectonic forces

joint inversion of active and passive seismic data in central java seismic and volcanic activities in central java indonesia the area of interest of this study are directly or indirectly related to the subduction of the indo australian plate in the framework of the merapi amphibious experiments meramex a network consisting of about 130 seismographic stations was installed onshore and offshore in central java and operated for more than 150 days in addition 3 d active seismic experiments were carried out offshore in this paper we present the results of processing combined active and passive seismic data which contain traveltimes from 292 local earthquakes and additional airgun shots along three offshore profiles the inversion was performed using the updated lotos 06 code that allows processing for active and passive source data the joint inversion of the active and passive data set considerably improves the resolution of the upper crust especially in the offshore area in comparison to only passive data the inversion results are verified using a series of synthetic tests the resulting images showan exceptionally strong low velocity anomaly 30 per cent in the backarc crust northward of the active volcanoes in the upper mantle beneath the volcanoes we observe a low velocity anomaly inclined towards the slab which probably reflects the paths of fluids and partially melted materials in the mantle wedge the crust in the forearc appears to be strongly heterogeneous the onshore part consists of two high velocity blocks separated by a narrow low velocity anomaly which can be interpreted as a weakened contact zone between two rigid crustal bodies the recent java mw 6 3 earthquake 2006 05 26 utc occurred at the lower edge of this zone its focal strike slip mechanism is consistent with the orientation of this contact

zircon shrimp u pb ages and in situ hf isotopic analysis for the mesozoic intrusions in south taihang north china craton evidence for hybridization between mantle derived magmas and crustal components abstract the north china craton ncc was stabilized in paleo proterozoic times and the eastern part of it was remobilized in the mesozoic as is indicated by the presence of voluminous mesozoic magmas in eastern ncc in particular the lithospheric mantle beneath eastern ncc was significantly thinned during the intense mesozoic tectono magmatic activity which makes the ncc different from most other ancient cratons the mesozoic magmas may thus provide crucial evidence regarding the processes that transformed the ncc from craton to a tectonically active region the south taihang magmatic complex lies in the western part of the mesozoic magmatic zone in the ncc the complex falls into three main plutonic rocks the hongshan syenite the xishu gabbroic diorite monzonite and the wu an monzonitic rocks zircon u pb dating reveals that the three plutonic rocks were emplaced contemporaneously at 132 ma in situ hf isotopic analyses for the dated zircons indicate that the hongshan syenites show homogeneous hf t values 10 to 13 which are slightly lower than those 9 0 for the enriched subcontinental lithospheric mantle sclm as revealed by zircons from mafic rocks that originated from melting of sclm this suggests that the parental magma to the syenites was likely derived from melting of the enriched sclm and contaminated slightly by old lower continental crustal material during ascent the xishu and wu an gabbroic diorites to monzonitic rocks however show significantly varied hf isotopic compositions with hf t 9 2 to 16 and 15 5 to 24 respectively the wide range of hf t values for a single sample suggests that the xishu and wu an plutons formed through a process of hybridization between enriched mantle derived mafic magma and crustal components in variable proportions this is supported by the textural and compositional disequilibrium of plagioclase phenocrysts from the two plutons the wu an monzonitic rocks show lower hf t values than the xishu gabbroic diorite monzonite suggesting more incorporation of crustal components in the source the sudden surge of magmatic activity in the south taihang orogen took place as a result of lithospheric extension that caused partial fusion of the enriched portions of sclm generating voluminous mafic magmas underplating of the mafic magmas in the lower crust consequently caused partial melting of the old basement rocks to produce granitic melts which was followed by mixing between the mafic and granitic magmas

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

4 d evolution of se asia s mantle from geological reconstructions and seismic tomography abstract how the collision between india and asia is related to processes deeper in the mantle is unclear here we compare geological reconstructions of block motions within asia since 50 ma with the tomographically imaged three dimensional 3 d morphology of subducted lithosphere to obtain insight into the spatiotemporal evolution of mantle structure past positions of the convergent margin show remarkable similarities with slab geometry at specific depths the striking change in slab geometry from a linear structure beneath 1100 km to an increasingly distorted shape at depths of less than 700 km results from collision the slab contours match the progressive deformation of asia s margin including india s indentation and sundaland s extrusion ever since the onset of collision the indian plate appears to have overridden its own sinking mantle and it does not seem at present to underthrust tibet significantly north of the zangbo suture if correct this observation would provide further evidence against models of plateau build up involving indian lithosphere the tomographic images beneath india confirm that asian deformation has absorbed at least 1500 km of convergence since collision began from the match between the southeastward motion of sundaland between 40 and 20 ma and the principal change in slab structure between 700 and 1100 km depths we infer that lateral advection in the mantle is small and that the sinking rate beneath sunda was 2 cm yr in the lower mantle and 5 cm yr above the transition zone

seismicity gravity anomalies and lithospheric structure of the andaman arc ne indian ocean abstract the andaman arc in the northeastern indian ocean defines nearly 1100 km long active plate margin between the india and burma plates where an oblique benioff zone develops down to 200 km depth several east trending seismologic sections taken across the andaman benioff zone abz are presented here to detail the subduction zone geometry in a 3 d perspective the slab gravity anomaly computed from the 3 d abz configuration is a smooth long wavelength and symmetric gravity high of 85 mgal amplitude centering to the immediate east of the nicobar island where a prominent gravity high follows the nicobar deep the slab residual gravity anomaly srga and mantle bouguer anomaly mba maps prepared for the andaman plate margin bring out a double peaked srga low in the range of 150 to 240 mgal and a wider cum larger mba low having the amplitude of 280 to 315 mgal demarcating the andaman arc trench system the gravity models provide evidences for structural control in propagating the rupture within the lithosphere the plate margin configuration below the andaman arc is sliced by the west andaman fault waf as well as by a set of sympathetic faults of various proportions often cutting across the fore arc sediment package some of these fore arc thrust faults clearly give rise to considerably high post seismic activity but the seismic incidence along the waf further east is comparatively much less particularly in the north although the lack of depth resolution for many of the events prohibits tracing the downward continuity of these faults tectonic correlation of the gravity derived models presented here tends to favour the presence of oceanic crust below the andaman nicobar outer arc ridge

geochemistry of the siberian trap of the noril sk area ussr with implications for the relative contributions of crust and mantle to flood basalt magmatism the sequence investigated of the siberian trap at noril sk ussr consists of at least 45 flows that have been divided into six lava suites the lower three suites consist of alkalic to subalkalic basalts the ivakinsky suite overlain by nonporphyritic basalts the syverminsky suite and porphyritic and picritic basalts the gudchikhinsky suite the upper three suites are tholeiitic the uppermost 750 m of dominantly non porphyritic basalt belong to the mokulaevsky suite and are characterized by a nearly constant mg number 0 54 0 56 sio2 48 2 49 1 wt ce 12 18 ppm and ce yb 5 8 the underlying 1100 m of dominantly porphyritic basalt belong to the morongovsky and nadezhdinsky suites there is a continuous increase in sio2 48 1 55 2 wt ce 12 41 ppm and ce yb 5 18 from the top of the mokulaevsky to the base of the nadezhdinsky with little change in the mg number 0 53 0 59 mokulaevsky magmas have trace element signatures similar to slightly contaminated transitional type mid ocean ridge basalts the change in major and trace element geochemistry in the upper three suites is consistent with a decline in the degree of anatexis and assimilation of tonalitic upper crust by mokulaevsky magma the nadezhdinsky and underlaying lavas thicken within and thus appear to be related to an elongate basin centred on the noril sk talnakh mining camp the mokulaevsky and morongovsky lavas thicken to the east and appear to be related to a basin centred more than 100 km to the east of the noril sk region these magmas may have risen up out of a different conduit system

seismology speed and size of the sumatra earthquake we now have a clearer picture of the seismic features of last year s gigantic event our seismological results reveal that indonesia s devastating sumatra andaman earthquake on 26 december 2004 was 2 5 times larger than initial reports suggested second only to the 1960 chilean earthquake in recorded magnitude they indicate that it slowly released its energy by slip along a 1 200 km fault generating a long rupture that contributed to the subsequent tsunami now that the entire rupture zone has slipped the strain accumulated from the subduction of the indian plate beneath the burma microplate has been released and there is no immediate danger of a similar tsunami being generated on this part of the plate boundary although large earthquakes on segments to the south still present a threat

an evolving magmatic hydrothermal system in the formation of the mesozoic meishan magnetite apatite deposit in the ningwu volcanic basin eastern china abstract the meishan iron deposit contains 338 mt of iron ore reserves at 39 fe and represents the largest magnetite apatite deposit in the ningwu basin of eastern china controversy has long existed about whether this deposit had a hydrothermal or iron oxide melt origin iron mineralization is genetically related to plutons that are composed of gabbro diorite which were emplaced at 130 1 ma these rocks have sio2 contents of 51 72 54 60 wt na2o contents of 3 47 4 04 wt k2o contents of 2 02 2 69 wt and k2o na2o ratios of 0 51 0 73 these rocks are enriched in liles and lrees and depleted in nb ta and ti which indicates that the magma originated through partial melting of an enriched lithospheric mantle source in a subduction environment a pattern of decreasing initial sr isotopic ratios and increasing end t values with time in early cretaceous magmatic rocks of the ningwu basin may indicate incorporation of increasing proportions of asthenospheric mantle material into the source magma which is consistent with the processes of lithospheric thinning and asthenospheric upwelling in eastern china related to mesozoic subduction of the paleo pacific plate two stages of magnetite are found in the gabbro diorite 1 early crystallized magnetite as euhedral subhedral crystals in larger clinopyroxene crystals and 2 later crystallized magnetite and accompanying ilmenite grains in the voids between plagioclase and clinopyroxene crystals the formation of magnetite before clinopyroxene combined with the results of fe ti oxide geothermometry and analysis of magnetite v content indicates that the oxygen fugacity of the source magma was greater than fmq 2 2 at an early stage 640 c but decreased to fmq 2 66 as abundant magnetite crystallized at a later stage 489 c the early crystallization of magnetite at a high oxygen fugacity does not support a fenner evolution trend for the primitive magma and diminishes the likelihood of liquid immiscibility which could have generated an iron rich melt and is thus inconsistent with an iron oxide melt origin for the meishan iron deposit the 34s values of pyrite 6 6 15 1 and anhydrite 15 6 16 9 in the deposit and the occurrence of evaporites under the volcanic rocks likely indicate that the iron ores and alteration rocks of the meishan deposit were formed by the circulation of fluids of evaporitic origin driven by heat from the hypabyssal gabbro diorite intrusives in the late magmatic stage oxygen fugacity decreased to a reducing range triggering the reduction of sulfate to reduced sulfur and leading to local gold and pyrite mineralization

using earthquake source durations along the sumatra andaman subduction system to examine fault zone variations the 26 december 2004 great sumatran andaman earthquake in the indian ocean caused extensive damage and loss of life from intense shaking and the resulting tsunami several studies of this earthquake suggest that portions of the fault ruptured at variable speeds with both fast and slow rupture velocities observed along the 1200 km long rupture length variations in rupture velocity during the earthquake may indicate along strike variations in megathrust frictional conditions that may influence other earthquakes along the zone previous work on global subduction zone systems suggests depth dependent frictional conditions arising from heterogeneous conditions along the fault in many of the circum pacific subduction zones shallow earthquakes along the subduction megathrust have longer scaled source durations than deeper earthquakes possibly resulting from variations in frictional conditions with depth this study focuses on thrust mechanism earthquakes on the sumatra andaman megathrust examining aftershocks with m w 6 0 of the 2004 earthquake as well as earthquakes that occurred in the region between 1992 and 2004 source duration depth and slip distribution are determined for this set of earthquakes to explore the possibility of both along strike and depth dependent variations in source parameters and frictional conditions there is evidence of depth dependent source parameters for these events with longer scaled durations for the shallower earthquakes consistent with previous global studies no temporal change is apparent in this relationship as source parameters for previous large earthquakes are similar to those after the earthquake along strike patterns suggest long duration character for several earthquakes in the southern portion of the rupture zone but no strong evidence of slow character in the northern portion of the rupture zone it appears unlikely that any long term variations in the fault zone character influenced possible slow rupture of the 2004 earthquake

structural heterogeneity in northeast japan and its implications for the genesis of the 2004 and 2007 niigata earthquakes abstract we utilized 188 766 p wave and 179 328 s wave high quality arrival time data from 14 666 local earthquakes to determine the three dimensional 3d seismic velocity v p v s v p v s ratio crack density e and bulk velocity v structures in and around the source areas of the 2004 and 2007 niigata earthquakes japan meteorological agency magnitude m j 6 8 in japan in order to understand the generation mechanisms of the niigata mainshocks the aftershock hypocenters were relocated by applying the double difference location method simultaneously with the tomographic inversion indicating a complicated fault system that includes not only two parallel dominant faults dipping to the northeast but also some conjugate faults crossing the niigata mainshock hypocenters in general high velocity v p v s with low e at 11 km depth is visible in the southeastern part of this area in contrast to anomalous low velocity with high crack density in the northwestern part along the niigata kobe tectonic zone nktz these characteristics of the velocity and crack density are consistent with the spatial distribution of active faults along the nktz the surface geological features that indurated pre neogene rock outcrops were observed in the southeastern area whereas deep sedimentary basins were observed on the opposite side low v p and low v s zones with high v p v s anomalies were imaged in and or under the source areas showing agreement with those revealed by previous studies all the features of the velocity and v p v s structures together with the images of the crack density and bulk velocity suggest the presence of fluids under the source areas such fluids might have weakened the mechanical strength of the fault zone of the source areas thus triggering the 2004 and 2007 niigata earthquakes our present study together with other recent tomographic images reveals that fluids penetrated into the source rocks from the lower crust and uppermost mantle as a result of dehydration of the subducting pacific slab and thus may play a key role in the genesis of these large crustal earthquakes

petrogenesis of granitoids in the dewulu skarn copper deposit implications for the evolution of the paleotethys ocean and mineralization in western qinling china abstract the tethyan tectonic domain hosts numerous world class mineral deposits among these the dewulu skarn copper deposit in western qinling china belongs to the paleotethys ore belt the skarn and orebodies here occur as stratoids or lenses at the contact between the triassic dewulu intrusive complex and permian marine clastic and carbonates alteration minerals include prograde skarns garnet diopside wollastonite plagioclase hornblende actinolite tremolite epidote chlorite calcite quartz and sericite the main ore types include early disseminated skarn type replacement orebodies and late stage quartz sulfide veins chalcopyrite is the major ore mineral along with pyrite bornite and sphalerite the dewulu intrusive complex comprises quartz diorite quartz diorite porphyry and dioritic mafic microgranular enclaves mme the mmes are spheroidal in shape and have igneous mineral assemblages acicular apatites complex oscillatory zoned plagioclase and quartz megacrysts surrounded by mafic minerals the mmes are metaluminous and calc alkaline to high k calc alkaline and possess relatively high ni cr and mgo contents and mg values they display sub parallel patterns in trace element spider diagrams and rare earth element ree plots they are also characterized by the enrichment of rb u and th depletion of ba sr nb and ta and negative eu anomaly zircon la icp ms u pb dating of the dioritic mme yields an age of 247 0 2 2 ma coeval with the host quartz diorite quartz diorite porphyry and ore related sericite 40ar 39ar plateau ages within analytical uncertainties oxygen fugacity estimated from trace element compositions of zircons from the dioritic mme shows fmq 3 3 the zircons have negative ehf t values in a range of 8 0 to 3 3 corresponding to two stage model ages ranging from 1 48 to 1 78 ga the integrated data from petrology geochronology and bulk geochemistry suggest that the early triassic granitoids associated with cu skarn mineralization at dewulu were products of arc magmatism and involved magma mixing in an active continental margin setting the magma was sourced through partial melting of enriched sub continental lithospheric mantle that had been previously modified by slab derived melt during the continuous northward subduction of the paleotethys oceanic slab

40ar 39ar dating of strike slip motion on the tan lu fault zone east china abstract ne trending sinistral ductile shear belts in the southern part of the tan lu fault zone east china are exposed along the eastern edge of the northern dabie belt and southern zhangbaling belt three hornblende three phengite and 12 biotite separates from greenschist facies mylonites in the shear belts were dated by the 40ar 39ar method in this study a hornblende plateau age of 143 3 ma is interpreted as representing the time of sinistral motion on the zhangbaling part of the tan lu fault zone seven biotite samples from the same part yield 40ar 39ar cooling ages from 137 to 125 ma a phengite plateau age of 138 8 ma from the eastern edge of the dabie belt is considered as being close to the time of deformation in the tan lu strike slip zone five biotite 40ar 39ar ages from 120 to 110 ma and one phengite age of 121 ma from the same area represent cooling ages after the sinistral faulting it is concluded on the basis of these 40ar 39ar ages that the sinistral ductile shear belts in the southern part of the tan lu fault zone were produced in earliest early cretaceous this sinistral motion on the tan lu fault zone is considered to be related to high speed highly oblique subduction of the pacific plate at this time

rupture process of the 2004 sumatra andaman earthquake the 26 december 2004 sumatra andaman earthquake initiated slowly with small slip and a slow rupture speed for the first 40 to 60 seconds then the rupture expanded at a speed of about 2 5 kilometers per second toward the north northwest extending 1200 to 1300 kilometers along the andaman trough peak displacements reached 15 meters along a 600 kilometer segment of the plate boundary offshore of northwestern sumatra and the southern nicobar islands slip was less in the northern 400 to 500 kilometers of the aftershock zone and at least some slip in that region may have occurred on a time scale beyond the seismic band

in situ la icp ms trace element analyses of magnetite genetic implications for the zhonggu orefield ningwu volcanic basin anhui province china the zhonggu orefield is located within the southern ningwu volcanic basin and is one of the largest iron ore districts within the middle lower yangtze river metallogenic belt mlyrmb of eastern china the area hosts the gushan iron oxide apatite ioa deposit and the baixiangshan longshan hemushan zhongjiu and taipingshan skarn type iron deposits here we employ laser ablation inductively coupled plasma mass spectrometry la icp ms to determine trace element concentrations in magnetite from these deposits combining these new data with geological information from these deposits indicates that the iron ore within the gushan deposit has v and ti compositions that are strongly suggestive of a kiruna type ioa origin specifically the v and ti chemistry of magnetite in iron ore breccias from the gushan deposit suggests that this style of mineralization formed at a high temperature and as a result of magmatic magnetite precipitation this was followed by precipitation of lower temperature magmatic hydrothermal massive magnetite both types of magnetite host exsolved ilmenite elemental mapping also indicates that gushan breccia hosted magnetite records hydrothermal fluid activity that formed late stage vein mineralization in comparison other deposits within the zhonggu orefield all contain magnetite with compositions that are indicative of skarn mineralization this implies that these deposits formed as a result of magmatic hydrothermal rather than purely magmatic or purely hydrothermal activity contrasting with the gushan deposit finally the geochemistry of magnetite within thick anhydrite units in the longshan deposit indicates the formation by low temperature sedimentary processes and this magnetite was subsequently overprinted as a result of hydrothermal activity during the formation of the main longshan deposit overall this study indicates that the ioa skarn type and sedimentary anhydrite type iron mineralization in the zhonggu iron ore field record evolving metallogenic processes from initially orthomagmatic mineralizing systems to high to moderate temperature magmatic hydrothermal systems and finally to low temperature hydrothermal mineralization

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

lithospheric deformation under pre and post seismic stress fields along the nicobar sumatra subduction margin during 2004 sumatra mega event and its tectonic implications abstract a high resolution study was carried out under pre seismic i e static and post seismic stress fields i e dynamic in a space time frame along the nicobar sumatra margin the study reveals that the descending lithosphere records minimum stress obliquity predominant thrust movement and down dip least compressive stress axis under static stress field in northwest sumatra sector iii the imbalance between down dip component of slab pull force and viscous resistive force possibly caused cyclic stress loading in compressive field around the flexing zone 25 km and that undergone brittle failure through generation of mega thrust event on 26th december 2004 a sharp decrease in stress obliquity towards north sector ii redressing of least compressive stress axes from horizontal to down dip direction and increasing thrust movements under dynamic stress field account for continued upward shortening of the lithosphere the weak thinner zone i e between 159 and 217 km depth an age discontinuity portion possibly was collapsed through rapid enhancement of stress induced weakening and strain localization following the 2004 sumatra mega shock it is also well appreciated in the literature that such shallow disruption of the lithosphere is inevitable in the upper mantle if the slab is weakened or broken there and this phenomenon is not uncommon below the sumatra

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

molybdenite re os and albite 40ar 39ar dating of cu au mo and magnetite porphyry systems in the yangtze river valley and metallogenic implications abstract the area of the middle lower yangtze river valley eastern china extending from wuhan hubei province to western zhenjiang jiangsu province hosts an important belt of cu au mo and fe deposits there are two styles of mineralization i e skarn porphyry stratabound cu au mo fe deposits and magnetite porphyry deposits in several nne trending cretaceous fault bound volcanic basins the origin of both deposit systems is much debated we dated 11 molybdenite samples from five skarn porphyry cu au mo deposits and 5 molybdenite samples from the datuanshan stratabound cu au mo deposit by icp ms re os isotope analysis nine samples from the same set were additionally analyzed by ntims on re os results from the two methods are almost identical the re os model ages of 16 molybdenite samples range from 134 7 2 3 to 143 7 1 6 ma 2 the model ages of the five samples from the datuanshan stratabound deposit vary from 138 0 3 2 to 140 8 2 0 ma with a mean of 139 3 2 6 ma their isochron age is 139 1 2 7 ma with an initial os ratio of 0 7 8 1 mswd 0 29 these data indicate that the porphyry skarn systems and the stratabound deposits have the same age and suggest an origin within the same metallogenic system albite 40 ar 39 ar dating of the magnetite porphyry deposits indicates that they formed at 123 to 125 ma i e 10 20 ma later both mineralization styles characterize transitional geodynamic regimes i e the period around 140 ma when the main ns trending compressional regime changed to an ew trending lithospheric extensional regime and the period of 125 115 ma of dramatic ew trending lithospheric extension

earth s free oscillations excited by the 26 december 2004 sumatra andaman earthquake at periods greater than 1000 seconds earth s seismic free oscillations have anomalously large amplitude when referenced to the harvard centroid moment tensor fault mechanism which is estimated from 300 to 500 second surface waves by using more realistic rupture models on a steeper fault derived from seismic body and surface waves we approximated free oscillation amplitudes with a seismic moment 6 5 10 22 newton meters that corresponds to a moment magnitude of 9 15 with a rupture duration of 600 seconds the fault rupture models represent seismic observations adequately but underpredict geodetic displacements that argue for slow fault motion beneath the nicobar and andaman islands

origin and large scale erosional features of glacial lake spillways in the northern great plains deglaciation of the northern great plains produced two basic types of fluvial systems 1 depositional regimes produced by the action of glacial melt water that formed outwash plains and 2 highly erosive systems produced by the sudden rapid drainage of glacial lakes that formed spillways spillways are huge deeply incised trenches that display all of the characteristics of fluvial channels glacial lakes drained in weeks or months and discharges of 10 5 m 3 s were attained at bankfull stage seven spillway systems studied were formed as a consequence of the sudden rapid draining of glacial lakes many other large valleys in the mid continent area and other glaciated regions were probably formed by the same process spillways consist of deeply incised inner channels commonly flanked by broad scoured outer zones initial stages of flow produced shallow anastomosing channels continued erosion produced longitudinal grooves streamlined erosional residuals and surficial boulder lag deposits inner channels developed by the enlargement of one or more centrally located longitudinal grooves the development of erosional residuals was initiated by the incision of shallow anastomosing channels the interchannel areas were progressively modified from irregular quadrilateral or elliptical shapes to an equilibrium minimum drag lemniscate shape as glacial lake drainage proceeded correlations between length and width length and area width and area and length width ratio and k a shape parameter of the lemniscate loop are very high for all erosional residuals studied although only 20 of the residuals display an equilibrium lemniscate shape stable relationships between length width and area of erosional residuals are therefore established very early and are maintained throughout the erosional modification to the lemniscate shape the only shape factor tested which can be used to quantitatively differentiate lemniscate from nonlemniscate erosional residuals is the position of maximum width as measured by the ratio of the length from the lee to the point of maximum width to the total length xm l the mean xm l ratio for erosional residuals in a spillway segment is an indication of the relative duration of flood flows that produced the spillway

joint bulk sound and shear tomography for western pacific subduction zones abstract detailed regional body wave tomographic inversion of the western pacific region has been performed using p and s travel times from common sources and receivers with a joint inversion in terms of bulk sound and shear wave speed variations in the mantle this technique allows the separation of the influence of bulk and shear moduli and hence a more direct comparison with mineral physics information the study region is parameterized with cells of side 0 5 to 2 and 19 layers to a depth of 1500 km while the rest of the mantle was parameterized with 5 5 cells with 16 layers between the surface and the core mantle boundary a simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image a nested iterative inversion scheme is employed with local linearization and three dimensional ray tracing through the successive model updates the results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the kurile kamchatka trench while flattening of slabs above this depth is observed in the japan and izu bonin subduction zones on both the bulk sound and shear wave speed images the penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the bonin trench mariana philippine and java subduction zones fast shear wave speed perturbations associated with the subducted slabs down to the 410 km transition zone are larger than the comparable bulk sound perturbations for all these subduction zones except the philippines the bulk sound signature for the subducted slab is more pronounced than for shear in the philippines talaud new guinea solomon and tonga subduction zones where penetration of the slab into the middle mantle is observed variation in the amplitude ratio between bulk sound and shear wave speed anomalies correlates well with the subduction parameters of the descending slab slabs younger than 90 ma at the trench show bulk sound dominance in the upper mantle while older slabs have a stronger shear wave speed signature spreading of the fast shear wave speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration but has no comparable expression in the bulk sound images this high velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs

near surface expression of a young mesothermal gold mineralizing system sealy range southern alps new zealand carbonate limonite veins formed in steeply dipping fractures in the upper few hundred metres of basement greywacke in the actively rising southern alps of new zealand the veins are found commonly in extensional fractures near to but not in major faults associated with mountain uplift and or sinistral faults which bound mountain ranges some of the veins contain sulphides and minor gold deposited as part of incrementally formed fracture fillings oxygen isotope ratios of calcite range widely between 6 and 24 and calcite 13cpdb 5 5 to 11 5 the veins formed from isotopically exchanged crustal fluid with a probable meteoric water component the shallow vein network is the near surface expression of a tectonically induced hydrothermal system which has deposited gold bearing veins with a mesothermal style over several vertical kilometres this vein network has formed in a dilatational zone of the oblique collisional orogen where near vertical fractures tap deep sourced fluids similar processes acting at the southern end of the southern alps in the miocene resulted in locally rich mesothermal quartz gold veins

structural context of the great sumatra andaman islands earthquake 1 a new three dimensional seismic model and relocated regional seismicity are used to illuminate the great sumatra andaman islands earthquake of december 26 2004 the earthquake initiated where the incoming indian plate lithosphere is warmest and the dip of the wadati benioff zone is least steep along the subduction zone extending from the andaman trench to the java trench anomalously high temperatures are observed in the supra slab mantle wedge in the andaman back arc the subducting slab is observed along the entire plate boundary to a depth of at least 200 km these factors contribute to the location of the initiation of rupture the strength of seismic coupling the differential rupture properties between the northern and southern segments of the earthquake and the cause of convergence in the andaman segment

petrogenesis of dongguashan skarn porphyry cu au deposit related intrusion in the tongling district eastern china geochronological mineralogical geochemical and hf isotopic evidence the dongguashan skarn porphyry cu au deposit located in the tongling district of the middle lower yangtze river valley metallogenic belt mlyb consists of skarn ore bodies in the upper part and porphyry ore bodies in the lower part both of which are hosted in quartz diorite and quartz monzodiorite zircon u pb age and geochemical studies show that the quartz diorite of the dongguashan intrusion formed at 140 3 2 0 ma mswd 0 19 and belongs to the high potassium calc alkaline series it is enriched in large ion lithophile elements lile and light rare earth elements lree depleted in high field strength elements hfse and heavy rare earth elements hree and has a slightly negative eu anomaly 176hf 177hf values of the rims of zircons show a variable range 0 282087 0 282391 corresponding with calculated ehf t values of 10 72 to 21 46 plagioclases in the quartz diorite have unbalanced structure characterized by bright andesine and labradorite an 37 0 65 5 cores with higher contents of fe and sr and are corroded by dark oligoclase an 13 8 27 6 rim major elements trace elements hf isotope and the composition of plagioclases indicate that the parental magma of the dongguashan intrusion was produced by the mixing of underplating mafic magma and felsic magma formed by remelting of paleoproterozoic and neoarchean crustal rocks neoproterozoic crust may also provide some material to the felsic magma mafic magma played a key role and made the parental magma rich in water sulfur metals cu au and gave it a high oxygen fugacity during its magmatic evolution the parental magma underwent fractional crystallization of hornblende apatite sphene and other mafic minerals some quartz diorite and quartz monzodiorite samples that show adakitic signatures may result from injection of mafic magma some inherited zircons of the quartz diorite in the dongguashan intrusion gave ages of 2 40 2 50 ga 1 95 2 05 ga and 0 74 0 81 ga coming from ultramafic mafic and andesitic igneous rocks and this indicates that there may have been three periods 2 4 2 0 and 0 8 ga of magmatic activity in the tongling district

coda q estimates in the andaman islands using local earthquakes the attenuation property of andaman island has been investigated analyzing coda waves from 57 local earthquakes in the magnitude range of 2 0 4 9 using the single backscattering model these earthquakes waveforms recorded on five broadband seismographs sited over the island from north to south during nov 2003 to march 2004 have been used to calculate the frequency dependent coda q q c applying the time domain coda decay method the coda q computed at central frequencies from 0 5 12 hz and five lapse time windows from 40 to 80 s progressively increases from 105 f 0 88 in the north andaman to 135 f 0 79 in the south andaman with an average of 119 f 0 80 the average q c values vary from 75 42 at 0 5 hz to 697 54 at 12 hz central frequency for 40 s lapse time window while for 80 s lapse time window its variation is from 117 38 at 0 5 hz to 1256 115 at 12 hz the q c estimated at different lapse times manifests a significant variation from 122f 0 75 to 174f 0 73 corresponding to lapse time window lengths of 40 and 80 s respectively the variation of q c with frequency lapse time and also with the location of seismograph reflects the marked structural and compositional inhomogeneity with depth along the andaman islands these observations are well correlated with the seismicity pattern and distinct high angle subduction beneath the island

the relationship of the seismic source and subduction zone structure for the 2004 december 26 sumatra andaman earthquake abstract studies of the 2004 december 26 sumatra andaman earthquake indicate that the rupture and subsequent down dip slip of the mw 9 3 event propagated with variable speed as it progressed northwards the transitions between different behaviour for the source correspond to changes in the physical properties of the subducted slab along the sumatra andaman arc revealed by multi wavespeed seismic tomography the transition from rapid slip to dominantly slower slip near 6 5 n and the end of the main zone of tsunamigenic source at 10 n lies in each case just to the south of localised features where changes in the physical properties of the slab are indicated from the ratio of shear wavespeed to bulk sound speed these features are associated mainly with bulk modulus variations the changing morphology of the subduction zone is associated with changes in physical properties that are manifested in the tomographic images and have modified the character of the slip along the 1500 km long arc segment that ruptured during this great earthquake

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

the lower changjiang yangzi yangtze river metallogenic belt east central china intrusion and wall rock hosted cu fe au mo zn pb ag deposits abstract the lower valley of changjiang from wuhan of the hubei province in the west to zhenjiang of the jiangsu province in the east contains more than 200 polymetallic cu fe au mo zn pb ag deposits and is one of the most important metallogenic belts in china this metallogenic belt situated at the northern margin of the yangzi craton and bordered by the dabieshan ultrahigh pressure metamorphic belt to the north consists mainly of cambrian triassic marine clastic sedimentary rocks and carbonate and evaporite rocks which overlay a precambrian basement and are intruded by yanshanian 205 to 64 ma granitoid intrusions and subvolcanic complexes repeated tectonism from late proterozoic to triassic resulted in extensively developed networks of faults and folds involving the cambrian triassic sedimentary strata and the precambrian basement the yanshanian granitoid intrusions and subvolcanic complexes in the lower changjiang metallogenic belt are characterized by whole rock 18 o of 8 to 10 initial 87 sr 86 sr of 0 704 to 0 708 and ndt from 10 to 17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials also the yanshanian granitoids exhibit eastward younging and increase in alkalinity i e from older calc alkaline in the west to younger subalkaline alkaline in the east which are related to oblique collision between the yangzi and sino korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes most polymetallic deposits in the lower changjiang metallogenic belt are clustered in seven districts where the yanshanian magmatism is particularly extensive from west to east edong jiurui anqing guichi luzhong tongling ningwu and ningzhen mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits orebodies in yanshanian granitoid intrusions skarn orebodies at the contact zones between the yanshanian intrusions and late paleozoic early mesozoic sedimentary rocks and stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata the most important host sedimentary strata are the middle carboniferous huanglong formation lower permian and lower middle triassic carbonate and evaporite rocks the intrusion hosted and skarn orebodies exhibit well developed zonation in alteration assemblages metal contents and isotopic compositions within individual deposits and apparently formed from hydrothermal activities related to the yanshanian magmatism the stratabound massive sulfide orebodies in the late paleozoic early mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano sedimentary exhalative processes in shallow marine environments however extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization on the basis of geological relationships and isotope geochemical characteristics we propose a carbonate hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies this model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the yanshanian intrusions with carbonate and evaporite wall rocks mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion hosted orebodies the stratabound massive sulfide deposits of the lower changjiang metallogenic belt share many features with the well studied high temperature carbonate hosted replacement deposits of northern mexico and western united states particularly with respect to association with small shallow granitoid complexes structural and stratigraphic controls on mineralization alteration assemblages geometry of orebodies metal association metal zonation and isotopic systematics

slow rupture in andaman during 2004 sumatra andaman earthquake a probable consequence of subduction of 90 e ridge summary one of the most enigmatic features of the 2004 sumatra andaman earthquake was the slow rupture speed and low slip on the northern part of the rupture under the andaman region we propose that the aseismic 90 e ridge ner on the indian plate obliquely subducts under the andaman frontal arc region though other possibilities also exist we hypothesized that this ridge probably acted as a structural barrier influencing rupture characteristics of the earthquake here we present several features of the andaman region that favour ner subduction under the region which include i comparatively shallow bathymetry and trench depth ii low seismicity iii significant variation in the azimuths of coseismic horizontal offsets due to the 2004 sumatra andaman earthquake iv lack of post seismic afterslip on the coseismic rupture in the andaman frontal arc region v low p wave with only small decrease in s wave speed from tomographic studies vi gravity anomalies on the indian plate indicating continuation of the ridge under the andaman frontal arc and vii lack of back arc volcanoes in the andaman region

2008 little andaman aftershock genetic linkages with the subducting 90 e ridge and 2004 sumatra andaman earthquake we analyse the june 27 2008 little andaman aftershock mw 6 6 of december 26 2004 sumatra andaman earthquake mw 9 2 that occurred near the trench in the subducting india plate beneath the sunda plate unlike majority of the other aftershocks in the frontal arc the little andaman aftershock and its own aftershocks occurred through normal slip on the north south oriented steep planes we use the coseismic and ongoing postseismic deformation due to the 2004 sumatra andaman earthquake at a gps site nearest to the little andaman aftershock and compute changes in the coulomb stresses due to the coseismic slip and postseismic afterslip the coulomb stress on the little andaman aftershock fault plane progressively increased since the 2004 sumatra andaman earthquake which probably led to the occurrence of the little andaman aftershock on the pre existing n s oriented strike slip steep planes of the subducting 90 e ridge that were reactivated through normal slip

constraints on 2004 sumatra andaman earthquake rupture from gps measurements in andaman nicobar islands the 26 december 2004 sumatra andaman earthquake mw 9 0 9 3 is the greatest earthquake of the modern seismological era the rupture characteristics of the earthquake particularly in the andaman nicobar region are not well resolved from seismological or far field geodetic data here in this article we present campaign mode global positioning system gps measurements of coseismic displacements at 13 sites in the andaman nicobar islands before and after the 2004 sumatra andaman earthquake these measurements provide improved estimates of rupture characteristics in the region coseismic horizontal ground displacement of 1 5 6 5 m towards the southwest and coseismic vertical displacement mostly subsidence of 0 5 2 8 m occurred along the andaman nicobar islands with maximum displacements in the nicobar islands we estimate coseismic slip under the andaman and nicobar islands as 3 8 7 9 m and 11 15 m respectively the length of the rupture is estimated to be about 1500 km with a width varying from 120 km under middle andaman island to 160 km under great nicobar island gps measurements during january 11 22 2005 from port blair suggest rapid afterslip in the postseismic period limited gps data available from 1995 measurements at two sites in andaman provide evidence of strain accumulation that varied significantly in the 10 yr preceding the earthquake d 2005 elsevier b v all rights reserved

tears or thinning subduction structures in the pacific plate beneath the japanese islands abstract the nature of a subduction zone at depth is affected by the evolution of its tectonic system and the geometry of the trench line can change over time due to slab roll back or the arrival of a distinctive feature with the incoming oceanic lithosphere the configuration of the plate has to accommodate such changes with buckling thinning or the formation of tears depending on the rate of influx to the trench tomographic imaging is commonly used to recognise the presence of such tears through marked reductions in wavespeed anomalies in localised zones a good example is provided by pacific plate subduction beneath the japanese islands a horizontal tear in the plate below 300 km depth can be recognised at the southern end of the izu bonin arc associated with the change in slab morphology to the much steeper mariana arc beneath southern honshu a break in the fast wavespeeds associated with the pacific plate has been described as a tear based on the evidence of converted phases from the edge of the zone and tensional focal mechanisms for seismic events in the tear zone in the north close to the hokkaido bend in the subduction zone the reduction in the shear wavespeed anomaly is just as dramatic but here the characteristics of high frequency guided waves from deep earthquakes indicate continuity of slab material with thinning of the slab the thinned slab has less wavespeed contrast within the affected cells and so appears in the tomographic images as a weakened anomaly the various modes of slab deformation represent different ways in which the subducted material accommodates the strains imposed by the evolution of the geometry of the subduction scenario not all significant reductions in wavespeed anomalies represent tears and thus it is important that such interpretations be checked against the characteristics of wave propagation through the zone

origin of mesozoic adakitic intrusive rocks in the ningzhen area of east china partial melting of delaminated lower continental crust to the best of our knowledge modern adakites have not been documented in a nonarc environment we report geochemical and isotopic data for early cretaceous anjishan adakitic intrusive rocks that are in a continental setting unrelated to subduction the anjishan adakitic intrusive rocks which are exposed in the ningzhen area of east china have high sr y and la yb ratios coupled with low yb and y as well as relatively high mgo contents and mg numbers mg 0 4 0 6 similar to products from slab melting however low n d t values 6 8 to 9 7 and high 8 7 sr 8 6 sr i 0 7053 0 7066 are inconsistent with an origin by slab melting the tectonics and geochemistry lead us to conclude that adakitic magmas were most likely derived from partial melting of mafic material at the base of the continental crust high sr y and la yb ratios of the adakitic intrusive rocks suggest that garnet was stable as a residual phase during partial melting implying that the crustal thickness exceeded 40 km in the early cretaceous the present thickness of the crust in the ningzhen area is only 30 km and therefore the crust appears to have been thinned by at least 10 km since the early cretaceous the relatively high mgo contents and mg of the anjishan intrusive rocks suggest that adakitic magmas interacted with mantle rocks possibly coinciding with lower crustal delamination which would also account for the observed thinning

a genetic link between iron oxide apatite and iron skarn mineralization in the jinniu volcanic basin daye district eastern china evidence from magnetite geochemistry and multi mineral u pb geochronology various styles of ore deposits may form from a single magmatic hydrothermal system identification of a possible genetic link between different ore types in a region is not only of critical importance for a better understanding of the magmatic hydrothermal processes but can also help in successful mineral exploration both iron oxide apatite ioa and iron skarn deposits are closely associated with intrusive rocks of intermediate to felsic in composition but whether these two ore types can form from the same magmatic intrusion remains poorly understood in this study we present a comparative study between a newly identified subsurface ioa ore body located at the apex of a diorite porphyry and the iron skarn ore bodies located immediately above it in the jinniu volcanic basin of the daye district middle lower yangtze river metal logenetic belt mlyrmb eastern china in order to highlight a genetic link between these two styles of mineralization the ioa ores are dominated by ti rich magnetite with variable amounts of fluorapatite diopside and actinolite this mineralogical assemblage is distinctly different from the iron skarn ores which consist mainly of ti depleted magnetite and subordinate pre ore garnet and diopside and post ore quartz chlorite calcite and pyrite in addition magnetite from the ioa ores is characterized by well developed ilmenite lamellae and has high concentrations of ni v co and ga consistent with high temperature crystallization whereas magnetite grains from the iron skarn ores usually exhibit oscillatory growth zones and contain much lower ni v co and ga indicating their formation under relatively low temperatures titanite and fluorapatite from the ioa ores have u pb ages of 132 5 2 4 ma to 128 4 3 0 ma which match a titanite u pb age for the associated iron skarn ores 1323 2 0 ma and are consistent with zircon u pb ages for the ore hosting diorite porphyry 130 4 0 7 ma to 130 3 0 5 ma this age consistency supports a possible genetic link among the diorite porphyry ioa ores and iron skarn ores we propose that the ioa and skarn ores are the products of two consecutive mineralization stages of the same magmatic hydrothermal system involving a high temperature hypersaline fluid coexisting with the diorite porphyry magma during emplacement and a subsequent low temperature diluted hydrothermal fluid other ioa and iron skarn deposits of similar ages 130 ma are found in a series of volcanic basins in the mlyrmb which forms one of the world s largest ioa metallogenic belts the close association of the two ore styles identified at daye provides a useful exploration guide for ioa and iron skarn deposits both on a local and regional scale

a tectono genetic model for porphyry skarn stratabound cu au mo fe and magnetite apatite deposits along the middle lower yangtze river valley eastern china abstract the middle lower yangtze river valley metallogenic belt yrb situated along the northern margin of the yangtze craton is characterized by porphyry skarn stratabound cu au mo fe deposits in the areas of uplift and magnetite apatite deposits in cretaceous fault basins following detailed field investigations and a review of published data we recognize two episodes of magmatism and mineralization in the yrb 1 156 137 ma high k calc alkaline granitoids associated with 148 135 ma porphyry skarn stratabound cu au mo fe deposits and 2 135 123 ma shoshonitic series associated with 134 9 122 9 ma magnetite apatite deposits a type granitoids and associated alkaline volcanic have a small age range from 126 5 to 124 8 ma and are temporally spatially and genetically associated with the second episode the geodynamic history of the yrb did not experience the paleozoic to mesozoic lithospheric thickening that took place in the north china craton this process is inferred to be linked to partial melting of the delaminated lower crust at high pressures resulting in the development of c type adakitic rocks the petrochemical and sr nd isotopic data show that both the shoshonitic series and a type granitoids are quite different from adakites with only some of the k calc alkaline granitoids having adakitic signatures previous ore genesis models were established based on an assumed relationship with adakites and a continuous tectono thermal evolution from 150 to 100 ma all data obtained for the middle lower yangtze river region consistently show that the tan lu regional strike slip fault zone initiated at 233 6 to 225 6 ma from the collision between the north china and yangtze cratons and was reactivated at ca 160 ma the tan lu fault was caused by the oblique subduction of the izanagi plate which along the yrb the low angle subducted slab and the overlying crust was disrupted or broken due to the disharmonious movement of the two blocks the high k calc alkaline granitoids magmas were derived from melting of the subducted slab with some input of crustal material these magmas were emplaced at the intersections between ne and ew trending faults and formed porphyry skarn stratabound cu au mo fe deposits between 156 and 137 ma after 135 ma the subducted plate changed its direction of motion to northeast now running parallel to the eurasian continental margin and leading to large scale continental extension the shoshonitic series and subsequent a type granitoids magmatism and the development of magnetite apatite ores in the yrb took place in both fault basins and ne trending rifts between 135 and 124 ma

partial melting of thickened or delaminated lower crust in the middle of eastern china implications for cu au mineralization abstract field relations isotope systematics and plate tectonic reconstructions require that felsic adakites in the yangtze block and the dabie orogen eastern china were not derived from a subducting slab despite the signature of a mantle component in the contemporaneous mafic adakite hosts of cu au deposits in the same areas the apparently contradictory requirements are accounted for by a a deep crustal melting origin for barren adakites and b a crustal delamination origin followed by ascent through lithospheric mantle for adakites associated with mineralization the crustal delamination process associated with the prospective porphyries duplicates the metallogenically essential aspects of the subduction environment the importance of adakitic magmas in the genesis of porphyry style cu au deposits is affirmed by these findings but the range of prospective tectonic environments is extended to include an important intraplate postsubduction setting the porphyries of eastern china demonstrate

complex slab subduction beneath northern sumatra 1 new data provided by the 2004 2005 sumatra andaman great earthquake sequences allow us to image with improved detail the p wave velocity structure beneath sumatra and adjacent regions below northern sumatra we find that the slab is folded at depth exhibiting geometry similar to that of the volcanic arc and the trench at the surface we speculate that this fold plays a major role in the segmentation of the sumatra megathrust and may impede rupture propagation in the region north of sumatra significant slab material in the mantle transition zone is imaged for the first time and we infer the presence of a major tear between the upper mantle and transition zone there

ore formation at the washan iron oxide apatite deposit in the ningwu ore district eastern china insights from in situ la icp ms magnetite trace element geochemistry abstract iron oxide apatite ioa deposits are an important type of iron deposit that may host large reserves of iron and other elements the washan deposit in the ningwu ore district is a classic giant ioa deposit hosted by porphyritic diorite at washan four fe mineralization stages have been identified with clear crosscutting relationships forming four types of ores disseminated ores breccia ores and magnetite actinolite and magnetite apatite actinolite veins trace element concentrations and single grain geochemical profiles of magnetite from the four fe mineralization stages were obtained via laser ablation inductively coupled plasma mass spectrometry la icp ms the geochemical profiles show consistent ti v mg and al contents from cores to rims indicating that magnetite might have crystallized quickly under relatively stable conditions in each stage compatible element e g co v ni and cr contents of the washan magnetite are similar to those of magmatic fe ti v deposits with high v and ti contents indicating a close magmatic link increasing mg al mn ni and ga contents and decreasing cr content from early to late stages imply increasingly intense reactions between fe bearing fluids and country rocks e g diorite and evaporites which also suggests a magmatic hydrothermal origin we propose a new genetic model for ore formation at the washan ioa deposit first an fe rich liquid which may have formed via liquid immiscibility ascended through the magma system resulting in the disseminated ores and albite alteration in the porphyritic diorite with cooling and crystallization of the magma the intrusive rocks developed fractures and brecciation which may have provided pathways for fe bearing fluids after the breccia or massive ores formed the pathways would have been quickly sealed by mineral precipitation continuous liquid immiscibility and magma crystallization may have produced similar fluids with more sedimentary material involved and its markers displayed when the fluid pressure overcame the lithostatic pressure the fractures that developed may have provided the necessary conduits for emplacement of the magnetite actinolite and magnetite actinolite apatite veins subsequently the magmatic hydrothermal system might have remained active during cooling and differentiation while pyrite quartz and calcite veins formed

long period toroidal earth free oscillations from the great sumatra andaman earthquake observed by paired laser extensometers in gran sasso italy summary strain data recorded by two crossed laser extensometers operating in the gran sasso underground observatory recorded seismic free oscillations excited by the 2004 december 26 sumatra andaman earthquake the main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods t 1000 s we reconstruct the time evolution of selected free oscillations for comparison with synthetic seismograms that include normal mode coupling effects from coriolis force attenuation and ellipticity envelopes estimated for the gran sasso differential data set for free oscillations with period t 1 mhz are approximated adequately by a composite centroid moment tensor cmt source with five subevents and an aggregate mw 9 3 moment magnitude envelopes for several toroidal free oscillations with t 1000 s are predicted less well the amplitude of the rarely observed mode 0t2 is overpredicted at gran sasso by roughly a factor of two and other modes are underpredicted the amplitude discrepancy for 0t2 is confirmed at selected exceptionally low noise seismic stations hypothetical explanations include a slow slip component of the seismic moment release errors in the composite cmt source model unmodelled coupling effects to earth s secular modes and feedback from the sumatra andaman tsunami on indian ocean coastlines of these hypotheses either an extended duration strain release or tsunami feedback seem most plausible the viability of the tsunami feedback mechansim deserves further investigation

mantle transition zones mtz discontinuities beneath the andaman subduction zone abstract we study the mantle transition zone discontinuities beneath the andaman subduction zone using receiver functions generated from broadband seismic stations the receiver functions were geographically binned using the common conversion point ccp technique moveout corrected receiver functions shows that p sv phase conversions from 410 km discontinuity arrives around 5 to 7 s earlier than expected 44 s migrating and projecting these receiver functions along a depth profile shows that the mean apparent depth of 410 and 660 km discontinuities is 357 5 km and 660 7 km respectively this translates to around 53 6 km elevation in 410 km discontinuity we attribute this elevation to the perturbation in isotherm caused by the young and steep subducting slab which results in phase transformation of olivine phase to wadsleyite phase at much earlier depth there is no substantial topographical variation in depth of discontinuity at 660 km we infer this flat topography of the 660 km discontinuity due to the termination of the descending slab as evidenced in recent tomographic studies the apparent mean mtz thickness beneath the andaman subduction zone asz is 296 6 km

bearing of plate geometry and rheology on shallow focus mega thrust seismicity with special reference to 26 december 2004 sumatra event abstract we propose a model pertaining to the generation of 26th december 2004 off sumatra mega event in the backdrop of other similar type earthquakes along subduction zones around the world reconstructions of benioff trajectories through the hypocenters of historical earthquakes including six mega earthquakes indicate i confinement of hypocenters right within the descending lithosphere and ii natural coincidence of foci of the mega events around the zones of plate flexing these observations are discussed in detail with special emphasis on the sumatra margin considering the role of rheological anomaly across the cross section of the descending lithosphere yield strength envelope and residual stress accumulation through time the intraplate origin of shallow mega thrust earthquakes allowed us to advocate the zone of flexing along the profiles of the subducting plates as nodal area for stress concentration we propose here that at elevated confining pressure and temperature loading of unidirectional cyclic stress on time average bending stress enhanced the material yield strength i e strain hardening and leads the semi brittle portion of the lithosphere into near brittle condition through rheological transformation under subsequent rise in neutral surface and increase in compressive stress field non coaxial deformation triggered shear failure on 26th december 2004 preferably at the rheological interface between strain hardened near brittle layer and deformed ductile layer within the sub oceanic mantle a two stage fracture mechanism viz a slow 1 1 km s bilateral initiation in an essentially strain hardened near brittle domain and a follow up very rapid progression 3 3 km s in the brittle crustal domain was mainly involved in the generation of 2004 off sumatra mega event estimation shows an amount of 3 38 10 22 to 4 50 10 22 n m seismic moment m o and 8 95 9 03 moment magnitude m w for the southern part of the 1300 km extended rupture i e between the north andaman to the north and the sumatra at its south the study necessitates the reassessment of other shallow focus mega thrust earthquakes along the subduction margins around the globe

kinematics and source zone properties of the 2004 sumatra andaman earthquake and tsunami nonlinear joint inversion of tide gauge satellite altimetry and gps data 1 we re analyzed the source of the 26 december 2004 sumatra andaman earthquake and tsunami through a nonlinear joint inversion of an inhomogeneous data set made up of tide gauges satellite altimetry and far field gps recordings the purpose is twofold 1 the retrieval of the main kinematics rupture parameters slip rake and rupture velocity and 2 the inference of the rigidity of the source zone we independently estimate the slip from tsunami data and the seismic moment from geodetic data to derive the rigidity our results confirm that the source of the 2004 sumatra andaman earthquake has a complex geometry constituted by three main slip patches with slip peaking at 30 m in the southern part of the source the rake direction rotates counterclockwise at the northern part of the source according to the direction of convergence along the trench the rupture velocity is higher in the deeper than in the shallower part of the source consistent with the expected increase of rigidity with depth it is also lower in the northern part consistent with known variations of the incoming plate properties and shear velocity our model features a rigidity 20 30 gpa that is lower than the preliminary reference earth model prem average for the seismogenic volume the source rigidity is one of the factors controlling the tsunami genesis for a given seismic moment the lower the rigidity the higher the induced seafloor displacement the general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation

teleseismic relocation and assessment of seismicity 1918 2005 in the region of the 2004 mw 9 0 sumatra andaman and 2005 mw 8 6 nias island great earthquakes the m w 9 0 2004 sumatra andaman islands and m w 8 6 nias island great earthquake sequences have generated over 5000 catalog reported earthquakes along 1700 km of the sumatra andaman and western sunda regions studies of prior regional seismicity have been limited to global catalog locations that often have poorly constrained epicenters and depths approximately 3650 teleseismically well recorded earthquakes occurring in this region during the period 1918 2005 are relocated with special attention to focal depth reduced uncertainties of epicenters and depths in the region on the order of 15 and 10 km respectively foster interpretation of focal mechanism data and provide additional details about the subducting indian and australian plates the revised earthquake dataset reveals a sharp delineation between aftershocks of the 2004 and 2005 earthquakes near simeulue island and a steepening in slab dip from south to north the downdip width of the aftershock zone of the 2004 m w 9 0 earthquake varies from 200 km at its northern end to 275 km at its southern end and events located between 35 and 70 km focal depth occur more frequently in the southernmost section of this aftershock zone outer rise and near trench normal and strike slip faulting earthquakes also increase in frequency following the 2004 and 2005 earthquakes earthquake swarms triggered along the andaman backarc spreading center both north of sumatra and near siberut island 100 km south of the nias island aftershock sequence illustrate the complex and variable nature of seismicity following these great earthquakes

the june 2010 nicobar earthquake fault reactivation on the subducting oceanic plate the similar to 1300 km long rupture zone of the 2004 andaman sumatra megathrust earthquake continues to generate a mix of thrust normal and strike slip faulting events the 12 june 2010 m w 7 5 event on the subducting plate is the most recent large earthquake on the nicobar segment the left lateral faulting mechanism of this event is unusual for the outer rise region considering the stress transfer processes that follow great underthrusting earthquakes another earthquake m w 7 2 with a similar mechanism occurred very close to this event on 24 july 2005 these earthquakes and most of their aftershocks on the subducting plate were generated by left lateral strike slip faulting on north northeast south southwest oriented near vertical faults in response to north northwest south southeast directed compression pre 2004 earthquake faulting mechanisms on the subducting oceanic plate are consistent with this pattern post 2004 left lateral faulting on the subducting oceanic plate clusters between 5 degrees n and 9 degrees n where the 90 degrees e ridge impinges the trench axis our study observes that the subducting plate off the sumatra and nicobar segments behaves similarly to a chip of the india australia plate deforming in response to a generally northwest southeast oriented compression an aspect that must be factored into the plate deformation models

geologic and geochemical insights into the formation of the taiyangshan porphyry copper molybdenum deposit western qinling orogenic belt china abstract taiyangshan is a poorly studied copper molybdenum deposit located in the triassic western qinling collisional belt of northwest china the intrusions exposed in the vicinity of the taiyangshan deposit record episodic magmatism over 20 30 million years pre mineralization quartz diorite porphyries which host some of the deposit were emplaced at 226 6 6 2 ma syn collisional monzonite and quartz monzonite porphyries which also host mineralization were emplaced at 218 0 6 1 ma and 215 0 5 8 ma respectively mineralization occurred during the transition from a syn collisional to a post collisional setting at ca 208 ma a barren post mineralization granite porphyry marked the end of post collisional magmatism at 200 7 5 1 ma the ore bearing monzonite and quartz monzonite porphyries have a e hf t range from 2 0 to 12 5 which is much more variable than that of the slightly older quartz diorite porphyries with t dm2 of 1 15 1 23 ga corresponding to the positive e hf t values and t dm1 of 0 62 0 90 ga corresponding to the negative e hf t values molybdenite in the taiyangshan deposit with 27 70 to 38 43 ppm re suggests metal sourced from a mantle crust mixture or from mafic and ultramafic rocks in the lower crust the 34 s values obtained for pyrite chalcopyrite and molybdenite from the deposit range from 1 3 to 4 0 0 2 to 1 1 and 5 3 to 5 9 respectively suggesting a magmatic source for the sulfur calculated 18 o fluid values for magmatic k feldspar from porphyries 13 3 hydrothermal k feldspar from stockwork veins related to potassic alteration 11 6 and hydrothermal sericite from quartz pyrite veins 8 6 to 10 6 indicate the taiyangshan deposit formed dominantly from magmatic water hydrogen isotope values for hydrothermal sericite ranging from 85 to 50 may indicate that magma degassing progressively depleted residual liquid in deuterium during the life of the magmatic hydrothermal system alternatively d variability may have been caused by a minor amount of mixing with meteoric waters we propose that the ore related magma was derived from partial melting of the ancient mesoproterozoic to neoproterozoic middle to lower continental crust this crust was likely metasomatized during earlier subduction and the crustal magmas may have been contaminated with lithospheric mantle derived magma triggered by mash e g melting assimilation storage and homogenization processes during collisional orogeny in addition a significant proportion of the metals and sulfur supplied from mafic magma were simultaneously incorporated into the resultant hybrid magmas

patterns of faulting in the ethiopian rift valley abstract some typical and some unusual fault patterns are described from the ethiopian rift valley they include arcuate faults convex in plan towards the downthrown side lines of obliquely tilted faulted blocks up horsts horizontally stratified rhomb horsts athwart tilted strata faults whose polarity switches in conjunction with development of small horsts intersecting fault sets and re entrant and semi circular faults explanations remain wanting for many of these phenomena which show that crustal extension can be complex at the meso scale

geochronology petrogenesis and metallogenic implications of mineralization related intrusive rocks in the xuancheng ore district eastern china abstract the xuancheng ore district is a newly discovered ore district within the middle and lower yangtze river metallogenic belt mlyrmb of eastern china this district contains numerous skarn porphyry deposits and this study focuses on four intrusions associated with known skarn mineralization within this district namely the shizishan pyroxene diorite spd the changshan biotite pyroxene diorite cbpd the maweishan quartz diorite mqd and the magushan porphyritic granodiorite mpg new u pb zircon age data indicate that all of these intrusions formed between 136 and 132 ma they are all calc alkaline enriched in the large ion lithophile elements lile and the light rare earth elements lree are depleted in the high field strength elements hfse and the heavy ree hree and have slightly negative eu anomalies the spd and cbpd have similar 87sr 86sr i 0 7060 0 7068 and 0 7065 0 7068 end t 10 6 to 9 5 and 10 1 to 9 9 and zircon ehf t 16 5 to 10 3 and 13 2 to 9 9 values whereas the mqd intrusion has similar 87sr 86sr i 0 7062 0 7076 values but higher end t 8 7 to 8 2 and zircon ehf t values 11 9 to 6 2 than the spd and the cbpd this indicates that the magmas were predominantly derived from the enriched lithospheric mantle but the mqd magmas incorporated less crust derived material than the spd and cbpd magmas the mpg intrusion has different 87sr 86sr i 0 7079 0 7086 end t 6 0 to 5 7 and zircon ehf t values 5 1 to 2 1 than the other intrusions indicating this intrusion formed from magmas derived from the lithospheric mantle that assimilated upper crustal material prior to and or during emplacement the compositions of plagioclase within the mqd and mpg intrusions provide no evidence of magma mixing these new data indicate that the 136 132 ma magmatism within the xuancheng region formed from magmas generated by the partial melting of an enriched region of the lithospheric mantle that was previously metasomatized by fluids derived from a subducted oceanic lithospheric slab the magmas then underwent fractional crystallization e g the mqd intrusion and or the assimilation of crustal material e g the mpg intrusion these processes generated parental magmas that were enriched in h2o s and metals e g cu increasing their mineralizing potential and potentially leading to the formation of the skarn deposits within the xuancheng ore district identifying intrusions with similar characteristics may be a useful exploration tool for skarn type mineralization within this region and the wider mlyrmb

tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins an assessment based on plate boundary kinematics interseismic coupling and historical seismicity we assess the tsunami hazard posed to new zealand by the kermadec and southern new hebrides subduction margins neither of these subduction zones has produced tsunami large enough to cause significant damage in new zealand over the past 150 years of well recorded history however as this time frame is short compared to the recurrence interval for major tsunamigenic earthquakes on many of the earth s subduction zones it should not be assumed that what has been observed so far is representative of the long term for each of these two subduction zones we present plate kinematic and fault locking results from block modelling of earthquake slip vector data and gps velocities the results are used to estimate the current rates of strain accumulation on the plate interfaces where large tsunamigenic earthquakes typically occur we also review data on the larger historical earthquakes that have occurred on these margins as well as the global cmt catalogue of events since 1976 using this information we have developed a set of scenarios for large earthquakes which have been used as initial conditions for the comcot tsunami code to estimate the subsequent tsunami propagation in the southwest pacific and from these the potential impact on new zealand has been evaluated our results demonstrate that there is a significant threat posed to the northland and coromandel regions of new zealand should a large earthquake m w 8 5 occur on the southern or middle regions of the kermadec trench and that a similarly large earthquake on the southern new hebrides trench has the potential to strongly impact on the far northern parts of new zealand close to the southern end of the submarine three kings ridge we propose logic trees for the magnitude frequency parameters of large earthquakes originating on each trench which are intended to form the basis for future probabilistic studies

a flying start then a slow slip the human tragedy caused by the sumatra andaman earthquake moment magnitude 9 3 on 26 december 2004 and its companion nias earthquake moment magnitude 8 7 on 28 march 2005 is difficult to comprehend these earthquakes the largest in 40 years have also left seismologists searching for the words and tools to describe the enormity of the geological processes involved four papers in this issue discuss aspects of a rupture process of surprising complexity the first such event to test the sensitivity and range of many new technologies a surprising feature of the earthquake is that after the initial rapid rupture subsequent slip of the plate interface occurred with decreasing speed toward the north

40 ar 39 ar dating of fuchsite and sericite from altered rocks close to ore veins in shagou large size ag pb zn deposit of xiong ershan area western henan province and its significance the tieluping ore district comprising shagou tieluping and haopinggou ag pb zn deposits is the largest silver area in western henan province with controlled reserves of 4 000 tons of silver metal and extreme high grade the ore veins extending along a large group of ne trending fractures are several kilometers long several hundred meters deep and several to 20 centimeter thick showing a significant economic value these deposits are hence a rare type of silver deposits in the world 40ar 39 dating was performed on fuchsite and sericite from the altered rocks close to the ore veins which yielded a set of age data i e plateau ages of 145 0 1 1 ma and 147 0 1 5 ma and isochronal ages of 145 2 2 5 ma and 147 6 2 3 ma these age data correspond to re os dating data of molybdenite from the ores in the sandaozhuang nannihu and shangfanggou porphyry skarn mo w deposits in xiong ershan area a group of pb zn ag deposits surround the three mo w deposits exhibiting zoning in space as more and more molybdenum appears downward in the shagou ag pb zn mine it is inferred that there possibly exists a mo ore body at the depth