metastable olivine wedge and deep dry cold slab beneath southwest japan abstract oceanic plates subducted at trenches penetrate into the deep mantle and encounter a structural boundary at a depth of 410 km where olivine the dominant element of mantle rocks transforms into a higher density form wadsleyite this transformation may be delayed within the coldest core of subducting plates slabs due to kinetic effects and it has been suggested that metastable olivine may persist deeper than 410 km using high density seismic array data in japan we show the direct image of the structure corresponding to this metastable olivine wedge mow beneath southwest japan numerical simulation of a subducting slab including the kinetic effect of water h 2 o on the olivine wadsleyite transformation indicates that the presence of the imaged mow requires an insignificant amount of water less than 100 wt ppm be present in the slab mantle thus a deep dry cold slab we infer that the transportation of water into the deep mantle occurs along the top surface of the subducting slab but no significant amount within the slab itself we also demonstrate that a numerical simulation including the kinetics of 660 km phase transformation can reconcile the observed deep depression of the 660 km discontinuity with a gentle clapeyron slope

multistage crack seal vein and hydrothermal ni enrichment in serpentinized ultramafic rocks koniambo massif new caledonia sets of fractures and breccia sealed by ni rich silicates and quartz occur within saprock of the new caledonian regolith developed over ultramafic rocks the crystallization sequence in fractures is as follows 1 serpentine stage lizardite polygonal serpentine white lizardite 2 ni stage ni mg kerolite followed by red brown microcrystalline quartz and 3 supergene stages the red brown microcrystalline quartz corresponds to the very last stage of the ni sequence and is inferred to have precipitated within the 50 95 c temperature range it constitutes also the main cement of breccia that has all the typical features of hydraulic fracturing the whole sequence is therefore interpreted as the result of hydrothermal fluid circulation under medium to low temperature and fluctuating fluid pressure although frequently described as the result of a single downward redistribution of ni and mg leached in the upper part of the regolith under ambient temperature the ni silicate veins thus appear as the result of recurrent crack and seal process corresponding to upward medium temperature fluid convection hydraulic fracturing and subsequent fluid mixing and mineral deposition

mechanical properties of snow abstract the investigation of the mechanical properties of seasonal snow cover aims mostly at applications in avalanche release and avalanche control but also at no less important problems such as vehicle mobility in snow snow removal or construction on snow primary needs are 1 constitutive equations that is relations between the stress tensor and the motion and 2 fracture criteria which limit the region of validity of constitutive equations both can be tackled from the aspect of continiuum theories and structure theories with modern continiuum theories the characteristic nonlinear behavior of snow can be taken into account and also the strong dependence on stress and strain history when thermodynamics is introduced more insight into the deformation and fracture processes can be gained high initial deformation rates cause low dissipation elastic behavior and brittle fracture whereas when dissipative mechanisms can develop ductile fracture occurs the advantage of structural theories lies in the immediate physical insight into deformation mechanisms but the disadvantage is that only simple states of stresses acting macroscopically on a snow sample can be considered different approaches have been elaborated for low density snow the concept of chains a series of stress bearing grains or the neck growth model consideration of stress concentrations in bonds between grains and for high density snow the pore collapse model snow idealized as a material containing air voids structural constitutive equations were applied to the calculation of stress waves in snow recorded acoustic emissions indicating intergranular bond fractures can also be used for the construction of constitutive equations

the metamorphic sole of new caledonia ophiolite 40ar 39ar u pb and geochemical evidence for subduction inception at a spreading ridge amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of new caledonia termed peridotite nappe recrystallized in the high temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the eocene metamorphic complex amphibolites mostly display the geochemical features of morb with a slight nb depletion and thus are similar to the youngest late paleocene eocene babb components of the allochthonous poya terrane thermochronological data from hornblende 40ar 39ar zircon and sphene u pb suggest that these mafic rocks recrystallized at 56ma using various geothermobarometers provides a rough estimate of peak recrystallization conditions of 0 5gpa at 800 950c the thermal gradient inferred from the metamorphic assemblage 60 ckm 1 geometrical relationships and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction obduction system and recrystallized when they subducted below young and hot oceanic lithosphere they were detached from the down going plate and finally thrust onto unmetamorphosed poya terrane basalts this and the occurrence of slab melts at 53ma suggest that subduction inception occurred at or near to the spreading ridge of the south loyalty basin at 56ma 2012 american geophysical union all rights reserved

ni speciation in a new caledonian lateritic regolith a quantitative x ray absorption spectroscopy investigation abstract changes in ni speciation in a 64 m vertical profile of a new caledonian saprolitic lateritic regolith developed over ultramafic rocks under tropical weathering conditions were investigated by exafs spectroscopy quantitative analysis of the exafs spectra by linear combination least squares fitting lc lsf using a large set of model compound spectra showed that ni hosted in primary silicate minerals olivine and serpentine in the bedrock is incorporated in secondary phyllosilicates serpentine and fe oxides goethite in the saprolite unit and mainly in goethite in the laterite unit a significant concentration of ni up to 30 of total ni is also hosted by mn oxides in the transition laterite i e the lowest part of the laterite unit which contains large amounts of mn oxides however the amount of ni associated with mn oxides does not exceed 20 of the total ni in the overlying laterite unit this sequence of ni species from bedrock to laterite yields information about the behavior of ni during tropical weathering of ultramafic rocks the different ni distributions in phyllosilicates in the bedrock randomly distributed and in the saprolite unit clustered indicate two generations of ni bearing phyllosilicates the first which formed at higher temperature is related to serpentinization of oceanic crust whereas the second one which formed at lower temperature is associated with post obduction weathering of ultramafic rocks in addition the observed decrease in the proportion of ni hosted by mn oxides from the transition laterite to the upper lateritic horizons indicates dissolution of mn oxides during the last stages of differentiation of the lateritic regolith i e lateritization finally the ubiquitous occurrence of ni bearing goethite emphasizes the major role of this phase in ni speciation at the different weathering stages and suggests that goethite represents the major host for ni in the final tropical weathering stages of new caledonian ultramafic rocks

rupture characteristics of the deep bolivian earthquake of 9 june 1994 and the mechanism of deep focus earthquakes the m w 8 3 deep 636 kilometers bolivian earthquake of 9 june 1994 was the largest deep focus earthquake ever recorded seismic data from permanent stations plus portable instruments in south america show that rupture occurred on a horizontal plane and extended at least 30 by 50 kilometers rupture proceeded at 1 to 3 kilometers per second along the down dip azimuth of the slab and penetrated through more than a third of the slab thickness this extent is more than three times that expected for a metastable wedge of olivine at the core of the slab and thus appears to be incompatible with an origin by transformational faulting these large events may instead represent slip on preserved zones of weakness established in oceanic lithosphere at the earth s surface

u pb zircon dating of post obduction volcanic arc granitoids and a granulite facies xenolith from new caledonia inference on southwest pacific geodynamic models in new caledonia the occurrence of one of the world s largest and best exposed subduction obduction complex is a key point for the understanding of the geodynamic evolution of the whole southwest pacific region within the ophiolite pre and post obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes at 27 4 ma a new east dipping subduction generated the active margin magmatism along the western coast of the island saint louis massif at 24 3 ma the eastward shift of the magma activity and slightly different geochemical features koum borindi massif was either related to the older slab break off or alternatively due to the eastward migration of the mantle wedge following the collision of the eastern margin of the low howe rise finally the occurrence of a granulite facies xenolith in the koum borindi massif with comparable 24 5 ma u pb zircon age and isotopic features initial end 5 1 suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness geochronological evidence for continuous convergence during the oligocene infers an east dipping eocene oligocene subduction obduction system to have existed in the southwest pacific from the d entrecasteaux zone to the north island of new zealand

mineralization and element redistribution in the chah gheib ni laterite ore zone bavanat zagros belt iran abstract nickel laterites are supergene deposits derived from the weathering of serpentinized ultramafic rocks and they commonly accounts for over 70 of world land based ni resources serpentinized ultramafic rocks outcrop extensively in iran as result of collision between afro arabian and iranian micro plate during the late cretaceous two ni bearing laterite belts developed on the ultramafic rocks of the neyriz ophiolite have been recently discovered in the bavanat region south iran the chah gheib deposit as the biggest ni bearing laterite in the bavanat area hosts a total estimated reserve mineralization of about 102 000 tons of ore at 0 92 ni and 180 000 tons at 1 63 cr this study focuses on elemental fractionation and mineralogical control of major trace and rare earth elements in a selected profile from the chah gheib ni laterite in order to assess the conditions of ore formation and its paleo environmental significance four distinct horizons including saprolite lower limonite upper limonite and lateritic duricrust have been recognized from the bottom to the top of the studied profile iron oxy hydroxides are the dominant phases found in the laterite profile overall fe and other first raw transition metals i e cr ni v co cu and zn show abundances higher than those of the bedrock the main fe and cr carriers in the laterite deposit are fe oxy hydroxides and chromite respectively although authigenic ni and cr bearing palygorskite is also common throughout the profile elemental mobility estimated using th as immobile element showed that the major oxides are largely depleted with the exception of fe2o3 and cao among trace elements cr is the element resulting strongly enriched in those levels where large chromite crystals occurs while v co ni and zn are enriched only in some levels of the upper limonite horizon and in the lateritic duricrust likely as adsorbed cations onto iron oxy hydroxides and as a consequence of an alkaline ph environment alkaline ph conditions can also explain the cu depletion observed throughout the profile such a condition during lateritization appears further supported by both the occurrence of carbonates and palygorskite and by the distribution of the ba sr ratio carbonates and palygorskite as well as secondary quartz require dry climate to form and alternating wet dry climate may allow lateritization this study suggests that the chah gheib laterite formed in a subtropical climate possibly during the late cretaceous late paleocene period in a roughly 25 35 latitude range promoting si and mg mobilization during the wet season and carbonates quartz and mg rich silicate precipitation during the drier periods

stochastic reconstruction of the microstructure of equilibrium form snow and computation of effective elastic properties three dimensional geometric descriptions of microstructure are indispensable to obtain the structure property relationships of snow because snow is a random heterogeneous material it is often helpful to construct stochastic geometric models that can be used to model physical and mechanical properties of snow in the present study the gaussian random field based stochastic reconstruction of the sieved and sintered dry snow sample with grain size less than 1 mm is investigated the one and two point correlation functions of the snow samples are used as input for the stochastic snow model several statistical descriptors not used as input to the stochastic reconstruction are computed for the real and reconstructed snow to assess the quality of the reconstructed images for the snow samples and the reconstructed snow microstructure we also estimate the mechanical properties and the size of the associated representative volume element using numerical simulations as additional assessment of the quality of the reconstructed images the results indicate that the stochastic reconstruction technique used in this paper is reasonably accurate robust and highly efficient in numerical computations for the high density snow samples we consider

source characteristics of large deep earthquakes constraint on the faulting mechanism at great depths 1 source parameters for eight large deep earthquakes are inferred from broadband data of the global seismograph network we completed an unprecedented data set composed of 14 largest deep earthquakes mw ranging from 7 0 to 8 3 from six different subduction zones studied with identical source parameter inversion methods the study confirms earlier findings that deep earthquake source properties vary with the temperature of the subducting plate events in cold slabs show high aftershock activity high rupture velocity and high seismic efficiency in contrast earthquakes in warm slabs generally have low aftershock productivity low rupture velocity and low seismic efficiency however the 23 june 1991 argentina event has source properties that are rather characteristic for earthquakes in cold slabs and that differ from those of other large south american events we suggest that two types of deep earthquakes occur in south america and we interpret these results in the context of the shear instability model for the mechanism of deep earthquakes in this model shear failure occurs through a thermal runaway mechanism within a shear zone at great depth and low seismic efficiency might indicate significant energy dissipation due to heating and possible melt production the 1991 argentina event located in a pocket of deep seismicity within the slab core may represent a shear instability with little melting as would be the case for large deep earthquakes in cold subduction zones whereas the other known south american large deep events such as 1963 peru 1970 colombia and 1994 bolivia are located in relatively aseismic regions and may involve significant melting within warmer regions of the slab

stress distribution due to olivine spinel phase transition in descending plate and deep focus earthquakes the stress field due to olivine spinel phase transition in and around a descending plate is studied based on the calculations for an equilibrium phase transition with a constant clapeyron s slope and for a nonequilibrium transition taking a kinetic effect into consideration the material concerned is assumed to be a viscoelastic body whose physical coefficients are functions of temperature and pressures the calculated stress distribution for the equilibrium transition is characterized by a compressional stress near the upper and or lower surfaces of the plate and by a tensional stress at the central part in the depth range from 200 to 550 km the magnitude of principal stress being greater than 0 5 gpa however for the nonequilibrium transition a tensional stress predominates near the upper and lower surfaces and the central part is compressional in the depth range from 300 to 600 km unlike the case of equilibrium transition the maximum principal stress in the latter case is greater than 2 gpa which is much more than that for the equilibrium transition the principal axes in the high stressed region are oriented almost parallel to the descending direction in both cases comparison of the calculated results to the actually observed seismicity depth relation and to focal mechanisms of deep focus earthquakes in descending plates beneath island arcs shows that the nonequilibrium phase transition agrees better with the observations

evidence for a metastable olivine wedge inside the subducted mariana slab abstract an anomalous seismic velocity structure is revealed inside the subducted pacific plate at northern mariana near the deepest earthquake foci we observe anomalous later phases in the p wave coda for a small cluster of deep earthquakes and an anomalous differential p wave slowness between a few pairs of the earthquakes belonging to the cluster we interpret these observations with a 5 low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km the wedge is bounded by two steeply dipping 60 70 transition layers with the thickness of about 4 km the highly localized seismic anomaly inside the slab represents a wedge of metastable olivine embedded in dry ringwoodite deep earthquakes occur across only one of the boundaries of the metastable wedge with some of them outside the wedge the mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge

goethite aging explains ni depletion in upper units of ultramafic lateritic ores from new caledonia abstract an upward loss of ni is commonly reported in the oxide rich unit of ni laterite deposits developed over ultramafic rocks in tropical regions especially in freely drained and deeply weathered regoliths because goethite is the major mineral constituent of such oxide rich units this ni loss has been linked to compositional changes in goethite in the present study we have investigated possible correlations between ni contents in the bulk laterite and the evolution of goethite in terms of composition and crystallinity in two ni rich and one ni poor lateritic profiles from new caledonia ni k edge extended x ray absorption fine structure exafs spectroscopy indicates that goethite hosts the main fraction of ni in the three profiles investigated asbolane lithiophorite identified as accessory minerals by x ray diffraction xrd have little effect on the vertical variations in bulk ni content in spite of the fact that the ni contents of these mn oxides can be significant at certain depths the gradual decrease in ni content from the bottom to the top of the three ni lateritic profiles correlates with a decrease in the ni content of goethite as determined by electron probe micro analysis in addition xrd data show that these compositional trends are linked to an increase of the mean coherent domain size of goethite these observations support the hypothesis that ni is expelled from goethite as it ages through successive dissolution and recrystallization cycles during the lateritization process comparison of laterites having different degrees of weathering suggests that this aging process could also play a significant role in the regional variability of ni content in ni laterite deposits

morphotectonic evolution of the new caledonia ridge pacific southwest from post obduction tectonosedimentary record abstract the tectonostratigraphic and geomorphic study of two post obduction fluvial sedimentary systems on mainland new caledonia and imaged offshore on seismic reflection lines provides a new perspective on the post orogenic evolution of the new caledonia ridge relations between sedimentary sequence boundaries erosion surfaces and faults both on land and on offshore seismic reflection profiles indicate that an episode of extensional tectonics initiated in the early neogene led to the disruption and collapse of the island landsurface previously shaped during a latest oligocene phase of planation microtectonic analysis further suggests early slip on the normal faults was associated with ridge normal extension a later set of faults accompanied ridge parallel to ridge oblique extension that is interpreted to result from a shift toward a transtensional regime driven by the initiation of east verging subduction of the australian plate beneath the pacific plate starting at least in the late mid miocene

identifying microstructural deformation mechanisms in snow using discrete element modeling a dynamic model of dry snow deformation is developed using a discrete element technique to identify microstructural deformation mechanisms and simulate creep densification processes the model employs grain scale force models explicit geometric representations of individual ice grains and snow microstructure using assemblies of grains ice grains are randomly oriented cylinders of random length with hemispherical ends particle contacts are detected using a novel and efficient method based on the dilation operation in mathematical morphology grain scale ice interaction algorithms based on observed snow and ice microscale behavior are developed and implemented in the model these processes include grain contact sintering grain boundary sliding and rotation at contacts and grain contact deformation in tension compression shear torsion and bending grain scale contact force algorithms are temperature and rate dependent with both elastic and viscous components grain bonds rupture when elastic stresses exceed ice tensile or shear strengths after which intergranular friction and particle rearrangement control deformation until the snow compacts to its critical density simulations of creep settlement using 1000 grain model snow samples indicate the bulk viscosity of snow is controlled by the grain contact viscosity and area grain packing and the increased number of frozen bonds that form during settlement a linear relationship between contact viscosity and bulk snow viscosity at any specified density indicates that the linear model parameters can be accurately scaled allowing simulations to be conducted for a broad range of dynamic and viscous creep deformation problems

a deep earthquake aftershock sequence and implications for the rupture mechanism of deep earthquakes a distinguishing characteristic of deep earthquakes has been the absence of observable aftershock sequences1 2 here we report the first extensive deep earthquake aftershock sequence to be observed it was recorded by an array of eight broadband seismographs following the 9 march 1994 deep tonga earthquake the aftershocks show a power law decay with time following the main shock as is typical of shallow events most of the well located aftershocks are concentrated along a steeply dipping plane consistent with one of the nodal planes of the main shock mechanism and the mechanisms of three large aftershocks assuming these aftershocks denote the main shock rupture area they define a 50 65 km fault plane extending across the entire width of the active seismic zone and into the surrounding aseismic region the width of the aftershock zone is wider than the expected width of the metastable olivine wedge demonstrating that either the width of the metastable olivine material exceeds previous estimates or the aftershocks are not confined in such a wedge

a cascading failure during the 24 may 2013 great okhotsk deep earthquake on 24 may 2013 the largest ever recorded deep earthquake occurred beneath sea of okhotsk a multiple point source inversion procedure is applied to constrain source process of this earthquake based on waveform modeling of both direct p and sh waves and near surface reflected pp and ssh waves our results indicate that the earthquake consists of six major subevents separated in space and time encompassing a horizontal dimension of 64 4 km along n160 e and a downward depth extension of 35 4 km the geographic distribution and focal mechanisms of the inferred subevents and foreshock aftershock locations do not fit into plane rupture we suggest that the earthquake can be best explained by a cascading failure of shear instability within preexisting weak zones in the region with the perturbation of stress generated by a shear instability triggering another

paired stable isotopes o c and clumped isotope thermometry of magnesite and silica veins in the new caledonia peridotite nappe abstract the stable isotope compositions of veins provide information on the conditions of fluid rock interaction and on the origin of fluids and temperatures in new caledonia magnesite and silica veins occur throughout the peridotite nappe in this work we present stable isotope and clumped isotope data in order to constrain the conditions of fluid circulation and the relationship between fluid circulation and nickel ore forming laterization focusing on the koniambo massif for magnesite veins occurring at the base of the nappe the high 18 o values between 27 8 and 29 5 attest to a low temperature formation clumped isotope analyses on magnesite give temperatures between 26 c and 42 c that are consistent with amorphous silica magnesite oxygen isotope equilibrium the meteoric origin of the fluid is indicated by calculated 18 o water values between 3 4 to 1 5 amorphous silica associated with magnesite or occurring in the coarse saprolite level displays a narrow range of 18 o values between 29 7 and 35 3 for quartz veins occurring at the top of the bedrock and at the saprolite level commonly in association with ni talc like minerals the 18 o values are lower between 21 8 and 29 0 and suggest low temperature hydrothermal conditions 40 95 c thermal equilibration of the fluid along the geothermic gradient before upward flow through the nappe and or influence of exothermic reactions of serpentinization could be the source s of heat needed to form quartz veins under such conditions

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

parent rock and climatic evolution control on the genesis of ni bearing clays in ni co laterites new inferences from the wingellina deposit western australia abstract oxide type ni laterites seldom contain significant ni phyllosilicates reserves this study is focused on the mineralogy of ni clays mainly occurring in the saprolite zone of the wingellina oxide type ni co laterite deposit despite most of the wingellina reserves occur in the oxide zone the deposit also has a well developed high ni grade saprolite horizon this study presents a mineralogical and chemical characterization of the ni phyllosilicates of the wingellina saprolite ore aimed to understand the role of diverse bedrocks gabbro and serpentinite and the influence of climate on the formation of different clay types the main phyllosilicate in the gabbro derived saprolite consists of dioctahedral al and ni montmorillonite originated from the weathering of pyroxene the genesis of al and ni rich montmorillonite from pyroxene can be explained by an open system alterative process in which al mainly derives from the dissolution of plagioclase in the serpentinite derived saprolite the alteration pathway followed a multistage evolution i lateritic alteration of serpentine i into ni serpentine ii and tri and dioctahedral smectites saponite and nontronite ii late precipitation of interstratified ni clays chlorite smectite and talc smectite as a replacement of former phyllosilicates and as neoformed minerals the latest phenomenon may be related to the late miocene shift from humid and acid tropical climate to saline and alkaline conditions arid to semi arid climate and represents an example of post lateritization processes rarely observed in laterites located on stable cratons the aridity driven precipitation of ni rich interstratified clays in the wingellina laterite can be seen as a new model for explaining the evolution of ni laterites in stable cratonic settings experiencing post lateritization aridity

modelling snow failure with a fibre bundle model dry snow slab avalanches initiate from a failure in a weak snow layer below a cohesive slab snow is considered as a porous ice structure and the strength distribution of the single elements of this structure i e grains and bonds between grains shows a high degree of disorder on the bond or microstructural level the failure process is believed to start if the fracturing of bonds between snow grains is not balanced by the formation of new bonds we use a statistical fracture model a fibre bundle model to study the failure process in a weak snow layer the model consists of fibres of various strengths representing single snow grains between two rigid plates which represent the slab above and the substratum below the weak layer the fibres deform in a linear elastic manner and break instantly at their rupture strength broken fibres may sinter re bond and regain strength after a finite sintering time we show that the different characteristic times for breaking and sintering lead to the rate dependence of snow strength this is to our knowledge the first statistical model to reproduce the ductile to brittle transition which snow exhibits with increasing strain rate when the model is applied to simulate experimental stress strain curves for different strain rates the model and experimental results are in fair agreement

first palaeomagnetic dating of ferricrete in new caledonia new insight on the morphogenesis and palaeoweathering of grande terre terra nova 24 77 85 2012 abstract comparing palaeolatitudes estimated from remanent magnetization data of ferricrete developed over laterite at two sites goro and tiebaghi against the apparent polar wandering path of australia provides new time constraints for the peridotite weathering in new caledonia the tiebaghi massif of the west coast klippes displays a single episode of ferricrete development during latest oligocene times by contrast the goro site in the southern part of the massif du sud reveals a more complex history with several episodes of ferricrete development from latest oligocene to pliocene quaternary times these data have made it possible to constrain the post obduction geodynamics and associated morphogenesis of new caledonia since related uplift probably prevented regolith development until latest oligocene times moreover the later uplift and deep erosion of the west coast klippes during the early miocene probably prevented further regolith preservation

the 2013 okhotsk deep focus earthquake rupture beyond the metastable olivine wedge and thermally controlled rise time near the edge of a slab the 2013 m8 3 okhotsk earthquake involves two primary mechanisms of deep focus earthquake rupture mineral phase transformation of olivine to spinel and thermal shear instability backprojection imaging of broadband seismograms recorded by the north american and european networks indicates bilateral rupture toward ne and sse the rupture paths of the ne segment and other regional m7 earthquakes are confined in narrow regions along the slab contours consistent with the phase transformation mechanism however the sse rupture propagates a long distance across the slab and aftershocks are distributed across a 60 km wide zone beyond the plausible thickness of the metastable olivine wedge favoring thermal shear weakening while the ne rupture is only visible at high frequencies the sse rupture is consistently observed across a broad frequency range this frequency dependent rupture mode can be explained by lateral variations of rise time controlled by thermal thinning of the slab near its northern end

reactive transport modeling applied to ni laterite ore deposits in new caledonia role of hydrodynamic factors and geological structures in ni mineralization this study is devoted to understanding the impact of topography and hydrodynamics on the formation of high grade supergene nickel deposits the investigation proposes a new conceptual mineralization model that describes the formation of various exceptionally ni enriched hot spots observed in lateritic profiles numerical analysis of the effects of local hydrodynamics on deposits formation is performed by means of phreeqc geochemical simulator and comsol multiphysics software these are coupled through an icp java interface that allows to code their level of interaction and facilitates the exchange of parameters the model developed extends the currently existing geochemical formulation of nickeliferous laterite formation from peridotite carried out in 1 d and is additionally capable of simulating mass solute transport and geochemical processes within complex fractured porous systems the simulations improve our understanding of metal enrichment in saprolite and bedrock zones it was shown that although the initial development of nickel lateritic ores takes a few million years they are prone to relatively quick leaching and subsequent redistribution of ni when the topography changes in response to tectonic processes the latter leads to the formation of rich nickel deposits at the bottom of the slope mostly due to leaching of the saprolite material in addition to the role of changes in topography the critical impact of fractures and fracture networks on metal mobility and distribution was identified the model developed provides significant insight into the distribution of mineral resources in particular ni deposits and can be of great help for future mineral prospecting in industry

garnierites and garnierites textures mineralogy and geochemistry of garnierites in the falcondo ni laterite deposit dominican republic abstract garnierites ni mg bearing phyllosilicates are significant ore minerals in ni laterites of the hydrous silicate type in the falcondo ni laterite deposit dominican republic garnierites are found within the saprolite horizon mainly as fracture fillings and thin coatings on joints field observations indicate an important role of active brittle tectonics during garnierite precipitation different greenish colours and textures can be distinguished which correspond to different mineral phases defined according to x ray diffraction xrd and electron microprobe emp analyses a talc like 10 a type b serpentine like 7 a type c a mixture of talc and serpentine like and d sepiolite like types compositional data indicate continuous mg ni solid solution along the joins lizardite nepouite serpentine like kerolite pimelite talc like and sepiolite falcondoite sepiolite like in general talc like garnierite is dominant in falcondo ni laterite and displays higher ni contents than serpentine like garnierites emp analyses showing deviations from the stoichiometric mg ni solid solutions of serpentine and talc are best explained by talc and serpentine like mixing at the nanoscale a detailed textural study by means of quantified x ray element imaging provides a wealth of new information about the relationships between textural position sequence of crystallization and mineral composition of the studied garnierite samples these results indicate several stages of growth with variable ni content pointing to recurrent changes in the physical chemical conditions during garnierite precipitation in addition our detailed mineralogical study of the falcondo garnierites revealed that the different types identified have characteristic h 2 o content and sio 2 mgo ratios which play important roles during the pyrometallurgy process

a pressure sintering model for the densification of polar firn and glacier ice on presente les predictions de la theorie de frittage pression pour la glace pure et on les compare avec les mesures d indlandsis au groenland et en antarctique

the internal deformation of the peridotite nappe of new caledonia a structural study of serpentine bearing faults and shear zones in the koniambo massif we present a structural analysis of serpentine bearing faults and shear zones in the koniambo massif one of the klippes of the peridotite nappe of new caledonia three structural levels are recognized the upper level is characterized by a dense network of fractures antigorite and polygonal serpentine form slickenfibers along fault planes with distinct kinematics as a result the upper level keeps the record of at least two deformation events the first associated with the growth of antigorite wnw ese extension the second with the growth of polygonal serpentine nw se compression the lower level coincides with the serpentine sole of the nappe which consists of massive tectonic breccias overlying a layer of mylonitic serpentinites the sole records pervasive tangential shear with top to sw kinematics and represents a decollement at the base of the nappe the intermediate level is characterized by the presence of several meters thick conjugate shear zones accommodating ne sw shortening like the sole these shear zones involve polygonal serpentine and magnesite as the main syn kinematic mineral phases the shear zones likely root into the basal decollement either along its roof or occasionally around its base compared to top to sw shearing along the sole the two deformation events recorded in the upper level are older

deep earthquakes beneath the fiji basin sw pacific earth s most intense deep seismicity in stagnant slabs abstract previous work has suggested that many of the deep earthquakes beneath the fiji basin occur in slab material that has been detached and foundered to the bottom of the transition zone or has been laid down by trench migration in a similar recumbent position since nowhere else in the earth do so many earthquakes occur in slabs stagnated in the transition zone these earthquakes merit closer study accordingly we have assembled from historical and modern data a comprehensive catalogue of the relocated hypocenters and focal mechanisms of well located deep events in the geographic area between the bottoms of the main vanuatu and tonga wadati benioff zones two regions of deep seismogenesis are recognized there i 163 deep shocks have occurred north of 15 s in the vityaz group from 1949 to 1996 these seismological observations and the absence of other features characteristic of active subduction suggest that the vityaz group represents deep failure in a detached slab that has foundered to a horizontal orientation near the bottom of the transition zone ii another group of nearly 50 outboard deep shocks occur between about 450 and 660 km depth west of the complexly buckled and offset western edge of the tonga wadati benioff zone their geometry is in the form of two or possibly three small circle arcs that roughly parallel the inferred motion of tonga trench migration earthquakes in the southernmost of these arcs occur in a recumbent high seismic wavespeed slab anomaly that connects both to the main inclined tonga anomaly to the east and a lower mantle anomaly to the west van der hilst r 1995 complex morphology of subducted lithosphere in the mantle beneath the tonga trench nature vol 374 pp 154 157 both groups show complexity in their focal mechanisms the major question raised by these observations is the cause of this apparent temporary arrest in the descent of the tonga slab into the lower mantle we approach these questions by considering the effects of buoyant metastable peridotite in cold slab material that was detached and rapidly foundered or was buckled segmented and laid out in the transition zone

hydrothermal breccias in vein type ore deposits a review of mechanisms morphology and size distribution abstract breccias are among the most widely distributed rock textures found in hydrothermal vein type deposits previous studies have mainly been interested in developing qualitative descriptive approaches leading to a confusing profusion of terms brecciation originates in numerous ways resulting in highly complex classification systems and frequent misinterpretations of facies field observations are difficult to reconcile with physical theories of fragmentation partly due to the fact that few satisfactory quantitative tools have been developed a review of the main brecciation processes occurring in hydrothermal vein type deposits allows for the discrimination between chemical and physical mechanisms including tectonic comminution wear abrasion two types of fluid assisted brecciation hydraulic and critical volume expansion or reduction impact and collapse each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry including fragment morphology size distribution of the fragments fabric and dilation ratio the first two parameters are especially important because 1 the morphology of the fragments allows chemical and physical mechanical breccias to be distinguished and 2 the particle size distribution psd is a function of the energy input during breccia formation the slope of the cumulative psd fractal dimension ranges from high values for high energy brecciation processes to low values for low energy processes indicated by an isometric distribution the evolution of a vein system can be divided into three stages propagation wear and dilation these stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity these two thresholds also mark the transition between different types of brecciation mineralization occurs during all three stages and may display different textures due to pressure variations the use of quantitative parameters in fault related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment including structural setting and crustal level as well as fluid rock interactions recognition of the different breccia types could also be important during the early stages of mineral exploration

the evolution of crack seal vein and fracture networks in an evolving stress field insights from discrete element models of fracture sealing veins are ubiquitous in upper and middle crustal rocks due to strength and stiffness contrast to the host rock veins can influence crack propagation here we present discrete element models to investigate crack vein interactions by simulating cycles of fracturing of a rock mass sealing the cracks to form veins and refracturing the rock mass after rotating the stress field we observe different styles of interaction between new fractures and existing veins depending on the strength ratio between vein and host rock and on the changes in the stress field between the different deformation stages if the orientation of stress field does not change between deformation stages ataxial crack seal veins are produced if the veins are weak and a bundle of subparallel microveins if the veins are strong if the stress field is rotated between deformation stages the interactions include reactivation fracture deflection and crosscutting reactivation of weak veins occurs even if the vein orientation is highly unfavorable relative to the stress field relays of fractures between reactivated veins form at a higher angle to the veins than expected this demonstrates that the orientation of secondary veins does not reflect the regional stress field in a simple manner and that veins can strongly influence fracture connectivity with implications for paleostress analysis and basin modeling simulation results compare well with field examples of multiphase vein networks in carbonates from jebel akhdar oman

implications of spatial and temporal development of the aftershock sequence for the mw 8 3 june 9 1994 deep bolivian earthquake on june 9 1994 the mw 8 3 bolivia earthquake 636 km depth occurred in a region which had not experienced significant deep seismicity for at least 30 years the mainshock and aftershocks were recorded in bolivia on the banjo and seda broadband seismic arrays and on the san calixto network we used the joint hypocenter determination method to determine the relative location of the aftershocks we have identified no foreshocks and 89 aftershocks m 2 2 for the 20 day period following the mainshock the frequency of aftershock occurrence decreased rapidly with only one or two aftershocks per day occuring after day two the temporal decay of aftershock activity is similar to shallow aftershock sequences but the number of aftershocks is two orders of magnitude less additionally a mb 6 apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east southeast of the mainshock at a depth of 671 km the aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km the aftershocks define a slab striking n68 w and dipping 45 ne the strike dip and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted nazca plate the location and orientation of the aftershock sequence indicate that the subducted nazca plate bends between the nnw striking zone of deep seismicity in western brazil and the n s striking zone of seismicity in central bolivia a tear in the deep slab is not necessitated by the data a subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock favoring a horizontal fault plane the horizontal dimensions of the mainshock beck et al this issue silver et al 1995 and slab defined by the aftershocks are approximately equal indicating that the mainshock ruptured through the slab

tectonic accretion and underplating of mafic terranes in the late eocene intraoceanic fore arc of new caledonia southwest pacific geodynamic implications this paper deals with the tectonic events that result in the accretion of mafic terranes in the fore arc region and a close juxtaposition of ultramafic rocks low grade and high grade mafic terranes in many collisional orogens the example is taken from new caledonia where tectonic accretion subduction underplating and obduction of mafic terranes took place during the late eocene in an intra oceanic forearc setting the late eocene tectonic complex comprised three major terranes an overlying ultramafic mainly harzburgitic allochthon named the ophiolitic nappe an intermediate mafic mainly basaltic off scraped melange composed of kilometre scale slices of oceanic upper crust called the poya terrane parts of which have been metamorphosed into an eclogite blueschist facies complex the pouebo terrane and a lower continental basement formed by the norkolk ridge terranes based upon exhaustive sampling of the mafic terranes and field surveys our tectonic micropaleontologic and geochemical data reveal that poya and pouebo terranes rocks originally formed within one single campanian to late paleocene oceanic basin floored by tholeiitic basalt associated with some minor seamount related intraplate alkali basalt the tholeiitic basalt displays a continuous range of compositions spanning between undepleted and depleted end members the former being volumetrically predominant the overall geochemical and isotopic features indicate an origin from a prominently heterogeneous mantle source during the opening of a marginal basin the south loyalty basin which almost completely disappeared during eocene convergence the opening of this basin originally located to the east of the norfolk ridge was synchronous with that of tasman sea basin as a consequence of oceanward migration of the west dipping pacific subduction zone establishing the origin of the ultramafic ophiolitic nappe is beyond the scope of this paper however it appears to be genetically unrelated to the mafic poya and pouebo terranes although it was located in the late eocene fore arc the ophiolitic nappe and the corresponding oceanic lithosphere originated before the late cretaceous to the east of the south loyalty basin in a back arc setting or alternatively in a much older trapped basin for reasons that remain unclear a new east dipping subduction started in the eocene and consumed most of the south loyalty basin forming the intra oceanic loyalty arc due to a changing subduction regime underplating of the diahot terrane the mafic slices that now form the poya terrane were tectonically accreted in the loyalty fore arc region and remained under low pressure low temperature conditions possibly at the subsurface until the norfolk ridge reached the subduction zone diachronously this resulted in the final obduction of the fore arc area the two step obduction involved first the mafic complex forming the poya terrane and thereafter the lithospheric mantle that now forms the ophiolitic nappe in contrast pieces of the accretionnary complex were dragged down into the subduction zone underplated at depth ca 70 km and metamorphosed into high temperature eclogite to form the pouebo terrane metamorphics that display the same geochemical features as the poya terrane basalt a mid to late eocene syntectonic piggy back sedimentary basin the nepoui flysch basin mainly filled with mafic clastic material and shallow water carbonates that record the progressive uplift of the fore arc region due to the accretion and underplating of mafic ocean related and other material in contrast a slightly younger foreland basin located upon the norfolk ridge the priabonian bourail flysch basin received a massive input of detrital material derived from the norfolk ridge itself and a time increasing amount of mafic poya derived material that recorded the first step of obduction thereafter the bourail flysch was overthrust by the poya terrane and finally by the ophiolitic nappe at the same time buoyancy driven uplift and exhumation of the high pressure metamorphic complex occurred as a consequence of the diachronous blocking of the subduction zone finally for a short time a new subduction started along the west coast of new caledonia and generated small amounts of active margin related magmas these events have resulted in the close juxtaposition of unmetamorphosed and highly metamorphosed mafic and ultramafic terranes that may represent a good pre collision analogue of mafic ultramafic belts found in many collisional mountain ranges

3d modeling of the laterites on top of the koniambo massif new caledonia refinement of the per descensum lateritic model for nickel mineralization resulting from the weathering of the peridotite nappe laterites are abundant in new caledonia and host one of the largest nickel deposits worldwide this work presents a 3d model of the koniambo nickel laterite ore deposit it shows that the laterites are located along the ridges of the massif and organized as hectometric sized patches obliquely cut by the topography and distributed at various elevations three kinds of geometry were observed i a thick laterite cover between 20 and 40 m overlying saprolite and mainly localized on topographic highs ii a thin laterite cover from a few meters to 20 m mainly localized on areas with gentle slopes and iii exposure of saprolite without laterite cover our data show that ni rich and ni poor areas are organized as hectometric sized patches which broadly correlate with the distribution of the laterite thickness the highest ni areas are localized on slopes where laterite cover is thin or absent the areas with lowest ni are located in topographic highs under the thickest laterite cover the vertical ni mass balance for each borehole shows that in areas with thick laterite cover ni is sub equilibrated to slightly depleted whereas in areas with thin laterite cover ni is enriched this suggests the existence of lateral infiltration of water rich in dissolved ni from areas such as topographic highs to downstream slope areas in a process leading to enrichment of saprolite in ni in slope areas mechanical transport and leaching of laterite material on slopes including ni bearing material could also contribute to local enrichment of ni in the saprolite

inversion for anisotropy from non double couple components of moment tensors 1 an inversion method for retrieving seismic anisotropy from non double couple components of seismic moment tensors is presented the method requires a set of highly accurate moment tensors of earthquakes that occurred in a homogeneous anisotropic focal area on differently oriented faults in contrast to standard methods retrieving anisotropy from travel times or from shear wave splitting which yield an overall anisotropy averaged along a whole ray path the presented method yields a local value of anisotropy just in the focal area the method is robust being able to retrieve the orientation as well as strength of anisotropy even for low anisotropy symmetries as for orthorhombic symmetry the method can utilize the moment tensors constrained to have zero trace but using unconstrained moment tensors is advantageous the method is applied to retrieving anisotropy in the tonga subduction zone using moment tensors of deep focus earthquakes reported in the harvard centroid moment tensor catalog the inversion is complemented by tests on synthetic data to assess its stability and the accuracy of the results the inversion indicates that the subduction zone is anisotropic with orthorhombic symmetry the orientation of the intra slab anisotropy is defined by axes azimuth dip a1 320 54 a2 121 38 and a3 223 81 the errors in the azimuth and dip are about 5 the first and second axes lie along the downdip motion of the slab and along the normal to the slab respectively the strength of the p s1 and s2 anisotropy is of 7 3 1 5 13 4 2 5 and 12 6 3 5 respectively the errors of anisotropy strength are only rough estimates which reflect random but not systematic errors in the moment tensors used in the inversion the values for anisotropy strength in the slab are remarkably higher than those observed in the surrounding mantle the symmetry axes of anisotropy coincide with the principal stress directions in the slab this manifests a primary impact of stress on anisotropy formation the retrieved anisotropy in the slab can serve as an additional constraint on its structure and mineralogical composition

nickel dispersion and enrichment at the bottom of the regolith formation of pimelite target like ores in rock block joints koniambo ni deposit new caledonia in new caledonian ni deposits the richest ni silicate ores occur in fractures within the bedrock and saprolite generally several tens of meters to hundred meters below the present day surface fracture related ni silicate ore accounts for high ni grades at least a few weight percent above the average exploited grade 2 5 these ni rich veins are affected by active dissolution precipitation processes at the level of the water table ni in solution is precipitated as silicates in thin layer cementing joints this mineralization is characterized by chemical and mineralogical concentric zoning with an outer green rim around an inner white zone composed from the edge to the centre of the block i a highly oxidized and altered zone ii a green pure ni rich pimelite zone iii a zone limited to a few centimetres with a mixture of ni poor kerolite and ni rich pimelite and intermediate colours and iv a large white mg kerolite mineralization zone this study proposes that the concentric zonation results from evapo precipitation process related to alternate periods of hydration and drying induced by water table movements this extensive dispersion of ni in concentrically zoned ores can partly explain the rather monotonous ni grade of the bulk exploitation at the base of the regolith with values between 2 and 3 wt

patterns of deep seismicity reflect buoyancy stresses due to phase transitions thermal perturbation of mantle phase relations in subduction zones gives rise to significant buoyancy anomalies finite element modeling of stresses arising from these anomalies reveals transition from principal tension to compression near 400 km depth down dip compression over 400 690 km peaking at 550 km and transition to rapidly fading tension below 690 km such features even when complicated by olivine metastability are consistent with observed patterns of deep seismicity that such a simple model neglecting all effects other than buoyancy anomalies due to temperature and to thermal perturbation of olivine phase relations successfully generates so many observed features of deep seismicity suggests that these buoyancy anomalies are significant contributors to the stress field in subducting slabs it also suggests that the depth distribution of deep seismicity may largely reflect the state of stress in the slab rather than simply a particular mechanism of stress release

observations of ultra long period normal modes from the 2004 sumatra andaman earthquake abstract the great december 2004 sumatra andaman earthquake was the first giant or extreme moment magnitude mw 9 earthquake recorded by broadband digital seismometers whose data were rapidly available to investigators worldwide as a result analysis of the earth s longest period normal modes became a primary tool for studying the earthquake rather than an elegant afterthought the mode data provided the first evidence that the earthquake was much larger mw 9 3 than initially inferred from surface wave data and involved slip on a much longer fault than initially inferred from body wave data these observations in turn yielded important insight into the likely recurrence of similar earthquakes and the resulting tsunamis both on the segment of the trench that ruptured and on neighboring segments the normal mode data are more numerous and much higher quality than previously available they thus provide the first direct evidence for effects that had been theoretically predicted such as the control of the splitting pattern by receiver latitude and the splitting of torsional modes they similarly yield better results for mode properties such as the attenuation of the longest period radial modes found in agreement with existing models of intrinsic earth attenuation

from 3 hz p waves to 0 s 2 no evidence of a slow component to the source of the 2011 tohoku earthquake in the hours following the 2011 honshu event and as part of tsunami warning procedures at the laboratoire de geophysique in papeete tahiti the seismic source of the event was analyzed using a number of real time procedures the ultra long period mantle magnitude algorithm suggests a static moment of 4 1 1029 dyn cm not significantly different from the national earthquake information center neic value obtained by w phase inversion the slowness parameter uptheta 5 65 is slightly deficient but characteristic of other large subduction events such as nias 2005 or peru 2001 it remains significantly larger than for slow earthquakes such as sumatra 2004 or mentawai 2010 similarly the duration of high frequency 2 4 hz p waves in relation to seismic moment or estimated energy fails to document any slowness in the seismic source these results were confirmed in the ensuing weeks by the analysis of the lowest frequency spheroidal modes of the earth a dataset of 117 fits for eight modes including the gravest one 0s2 and the breathing mode 0s0 yields a remarkably flat spectrum with an average moment of 3 5 1029 dyn cm 1 07 this behavior of the tohoku earthquake explains the generally successful real time modeling of its teleseismic tsunami based on available seismic source scaling laws on the other hand it confirms the dichotomy among mega quakes m0 1029 dyn cm between regular events nias 2005 chile 2010 sendai 2011 and slow ones chile 1960 alaska 1964 sumatra 2004 and probably rat island 1965 whose origin remains unexplained

an implosive component to the source of the deep sea of okhotsk earthquake of 24 may 2013 evidence from radial modes and cmt inversion abstract we study the spectral amplitudes of the first two earth radial modes 0 s 0 and 1 s 0 excited by the sea of okhotsk earthquake of 24 may 2013 the largest deep event ever recorded in the search for an isotropic component to its source in contrast to the case of the 1994 bolivian earthquake we detect an implosive component m i 1 1 10 27 dyn cm equivalent to 3 of the full scalar moment but 14 of the lone deviatoric component exciting the earth s radial modes an independent moment tensor inversion using the standard globalcmt algorithm but after relaxing its zero trace constraint similarly yields an implosive isotropic component albeit with a larger amplitude while it fails to document one in the case of the 1994 bolivian deep earthquake an implosive component to the source is expected in the model of transformational faulting in which deep earthquake rupture nucleates and grows upon transformation of metastable olivine to ringwoodite in the cold subducting slab this interpretation is supported by quantitative estimates 0 9 4 m of the thickness of the transformed shear zone which scale favorably relative to earthquake fault length with the upper end of the range of laboratory results reported for ices germanates and silicates the resulting extent of the transformation in the metastable wedge is consistent with the local geometry of the deep slab as recently determined by rupture modeling and aftershock distribution our results are in contrast to those for the two runner up largest deep earthquakes the 1994 bolivian and 1970 colombian shocks for which a similar isotropic component could not be detected we attribute this difference to variability in the ratio of isotropic to deviatoric components which combined with the smaller size of the 1970 and 1994 events would make any putative implosive component fall below detection levels especially in the case of the 1970 colombian earthquake for which only analog narrow band records were available

anticrack associated faulting at very high pressure in natural olivine shallow earthquakes are produced by brittle shear fracture of rock and or fictional sliding on pre existing fault surfaces1 at very high pressures however brittle fracture and frictional sliding are impossible because frictional resistance to movement on any potential fault surface is so great that ductile stress relief processes accomodate strain at lower shear stresses than those necessary to activate faulting nevertheless more than 20 of earthquakes with magnitudes greater than five occur at depths greater than 300km where the pressure exceeds l0 gpa ref 2 possible explanations for this paradox have been offered by several recent experimental studies of shearing instabilities associated with phase transformations at high 3 8 one of these mechanisms is associated with anticrack development during the olivine spinel phase transformation in mg2geo4 at pressures of 1 2 gpa refs 4 6 it is particularly attractive because it operates between mineral structures known to occur in the mantle we show here that this mechanism also can operate in natural silicate olivine mg fe 2sio4 during onset of the transformation at the much higher pressures at which deep earthquakes occur these results lend strong support to the hypothesis that the anticrack mechanism is responsible for such earthquakes4

geodynamics of trench advance insights from a philippine sea style geometry abstract for terrestrial parameter sets trench retreat is found to be nearly ubiquitous and trench advance quite rare largely due to rheological and ridge push effects recently updated analyses of global plate motions indicate that significant trench advance is also rare on earth being largely restricted to the marianas izu bonin arc thus we explore conditions necessary for terrestrial trench advance through dynamical models involving the unusual geometry of the philippine sea region in this subduction system a slab pull force from distal subduction is transmitted to the overriding plate at the pacific trench our 2d modeling demonstrates that trench advance can occur for terrestrial rheologies in such special geometries we observe persistent trench advance punctuated by two episodes of back arc extension characteristic features of the model such as time interval between extensional episodes high back arc heat flow and stress state of philippine plate correspond to processes recorded in the region