influence of rotation on the metal rain in a hadean magma ocean 1 today it is widely accepted that during its early evolution the earth experienced a magma ocean that covered most of its surface the separation of metal from silicate was much facilitated in the environment of such a magma ocean the differentiation mechanism is known as the metal rain scenario our study will focus on the settling dynamics of these metal droplets because of the low viscosity of molten silicate and a higher rotation period of the earth at that time the rotation has a potentially strong influence on the dynamics of the magma ocean we use numerical 3d fluid simulations to analyze the combined effects of strong rotation and convection on the settling of the iron droplets we show that the influence of rotation on the settling depends on the latitude at the poles the influence of rotation is only marginal at the equator three different scenarios can be distinguished first at low rotation rates the particles form a dense layer at the bottom second for strong rotation the particles stay mostly suspended and layers form in the temperature field third at higher rotation rates the particles form a ribbon like structure in the middle of the box the influence of rotation on the iron droplets may lead to a scenario where part of the iron is kept in the mantle instead of transported to the core this would have a strong influence on the later states of the differentiation process and the amount of siderophile elements in the mantle

comment on mid cretaceous extensional fragmentation of a jurassic early cretaceous compressional orogen alaska by e l miller and t l hudson

collapse of the luzon volcanic arc during onset of arc continent collision evidence from a miocene pliocene unconformity eastern taiwan a regional miocene pliocene unconformity in the coastal range of eastern taiwan provides information about vertical motions that affected the colliding volcanic arc during initiation of arc continent collision the unconformity separates precollisional volcanic and volcaniclastic rocks of the miocene luzon arc and forearc basin from an overlying thick sequence of syncollisional pliocene pleistocene sedimentary rocks derived from the metasedimentary accretionary wedge of taiwan the duration of time represented by the unconformity averages 1 2 m y and locally ranges up to 4 m y the basal unit of the younger syncollisional sequence consists of bathyal mega slump folded mudstone pebbly mudstone and thin bedded turbidites sharp stratigraphic juxtaposition of these deep marine deposits directly above shallow marine limestone and epiclastic rocks upper part of the older arc sequence requires extremely rapid subsidence during initiation of the collisional basin the coastal range unconformity is interpreted to represent a period of latest miocene nondeposition and or erosion in the luzon arc that was related to initial subduction of the eurasian continental margin along the manila trench this period was followed in pliocene time by very rapid subsidence or collapse of the arc platform to 1 2 km water depth there are two dissimilar mechanisms of basin subsidence that may have controlled initiation of the collisional basin 1 extension rifting and crustal thinning in the luzon arc massif to form a series of small rift or pull apart subbasins or 2 flexural subsidence of oceanic lithosphere in a foreland style basin due to crustal loading in the expanding accretionary wedge of proto taiwan although data are insufficient to provide a unique solution the flexural subsidence model is supported by systematic younging of the initial subsidence event from west to east which may record eastward migration of an outer flexural bulge notable differences between the unconformity and paleogeography of the early collisional basin and analogous present day basins in the offshore region to the south suggest that arc continent collision and basin development in eastern taiwan have experienced secular change since late pliocene time

connectivity of molten fe alloy in peridotite based on in situ electrical conductivity measurements implications for core formation in terrestrial planets abstract the connectivity of molten fe s in peridotite has been experimentally investigated by means of in situ electrical conductivity measurements at high temperatures and 1 gpa starting materials were powdered mixtures of peridotite klb 1 with various amounts 0 3 6 13 19 24 vol of the 1 gpa eutectic composition in the fe fes binary system at temperatures above the eutectic point in the fe fes system 980 c and below the solidus of klb1 1200 c molten fe s in a solid silicate matrix interconnects when the volume fraction is over 5 conductivity temperature paths indicate that in the presence of partial silicate melting the connectivity of molten fe s in a peridotite matrix is inhibited based on observations of retrieved samples the percolation threshold of fe s melts in the presence of low to moderate degrees of silicate melt is estimated at 13 2 vol these results indicate that if the volume fraction of fe alloy in a planetesimal was initially greater than 5 and if early heating by decay of radionuclides raised the temperature of the interior above the fe alloy melting point initial metal segregation was controlled by permeable flow of molten iron alloy in a solid silicate matrix these conditions were likely met by many terrestrial objects in the early solar nebula efficient removal of residual fe alloy 5 vol from silicate requires high degree melting of silicate so that metal can segregate as droplets giant impacts during the final stage of accretion of large planetary objects could supply the energy required for high degrees of melting alternatively if initial metal segregation were delayed until a planetary object grew to large size 1000 km in diameter release of gravitational potential energy due to metal segregation could contribute enough heat to form a magma ocean

slumping and sliding in miocene and recent developing arc basins onshore and offshore sumba indonesia abstract neogene slidemasses in eastern sumba are discussed and compared to neogene and quaternary analogues in seismic profiles from the offshore lombok and savu basins the onshore examples were deposited in deep marine base of slope environments within the reach of large amounts of clastics derived from a volcanic arc i e in a setting comparable to that of the recent slides onshore three types of slides are distinguished ranging from mud clast rich debris flows type 1 their possible seismic origin is discussed elongate lenticular slumps type 2 to over 100 m thick slide masses of intimately mixed and folded strata together with rafts of less deformed sediments type 3 the offshore analogues may be twice as thick both in the field and in the seismic profiles such slides are found at various superimposed levels five superimposed units can be distinguished in a seismic profile in the savu basin near the westernmost extension of the offshore sumba ridge a giant blocky slide occurs all slide masses are located on slopes with increasing gradients due to differential vertical movements tectonically induced oversteepening is therefore considered a main cause of failure in outcrops the upper surfaces of the slides are almost flat this contrasts with a hummocky topography seen in some of the offshore examples

coupled core mantle thermal evolution of early mars 1 several arguments point out that at the end of planetary accretion the core of mars was likely to be much hotter than its mantle resulting in the formation of a completely or partially molten thermal boundary layer at the base of the mantle here we address the following questions how did the superheated core cool and what role did it play in the early mantle dynamics of mars we divide the coupled core mantle evolution of early mars into two stages during the first stage vigorous convection within the molten boundary layer removes the heat from the core so that the boundary layer expands up as the boundary layer gets thicker the temperature of the layer decreases eventually the temperature of the molten boundary layer drops down to the temperature for the rheological transition melt fraction 40 within 100 years this stage is described by a parameterized convection approach the second stage is modeled in spherical shell geometry using the fully three dimensional finite element code citcoms a single plume superplume forms by the instability of the thermal boundary layer the superplume stage lasts much longer on the scale of millions to hundreds of millions of years depending on the mantle viscosity during both stages of evolution the heat flux can easily satisfy the requirements for the dynamo

dynamics of core formation and equilibration by negative diapirism 1 we investigate dynamically the timing and metal silicate equilibration processes during core formation by negative diapirism using numerical modeling in 3 d axisymmetric geometry we follow the sinking of iron rich diapirs through a viscous silicate mantle we carried out a parameter study in which shear heating as well as several viscous rheologies are considered and systematically varied general scaling laws are derived for the diapir sinking velocity as well as for the silicate melt generation and distribution around the diapir using these scaling laws we show that metal diapirs of a radius 1 100 m sinking through a partially molten silicate mantle can chemically equilibrate within the timescales suggested by geochemical constraints therefore negative diapirism can contribute significantly to metal silicate equilibration processes during core formation

structural expression of forearc crust uplift due to subducting asperity abstract new structural observations and mapping of reefal terraces carried out both on the field and on satellite remote sensing data indicate that sumba island is presently undergoing a large amount of extension associated with a significant regional uplift this crustal uplift may have been created by a major thrust emerging in the south of the island the uplift which partly accommodated the australian plate south west banda arc convergence is associated with the general northeastward tilt of the island the consequent anomalous positive topography along the southern coast of the island is being compensated by significant tectonic erosion along large scale curvilinear normal faults in the southeastern half of the island the most important expression of this gravitational collapse is located at the receding side of an advancing circular dome showing striking similarities with accretionary wedges being affected by seamount subduction the part of the forearc basin known as the savu basin is moderately deformed mostly in its central part and appears to act as a rigid buttress in the convergence between the banda arc and the australian plate as a result the convergence appears to be transferred northward within the actively shortening back arc domain which goes from the north of the flores island to the southwest of the timor block the convergent plate boundary shows a transition between a stable domain west of sumba and a tectonized domain east of sumba the latter coinciding with the subduction of the outer australian passive margin the subduction of the ocean continent boundary of the austral indian plate below the banda arc since the lower pliocene may have incorporated some crustal fragments in the plunging benioff zone most likely the integration of the stretched continental lithosphere in the subduction zone caused the uplift the entire forearc domain exhibiting inherited structures of the upper plate

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

contextualising the dead combining geoarchaeology and osteo anthropology in a new multi focus approach in bone histotaphonomy abstract histotaphonomy has become an important area of research in funerary archaeology it focuses on diagenetic alterations in bone microstructure and the reconstruction of post mortem processes microbial bioerosion is the most common diagenetic change observed in archaeological bone and its probable causes have been the subject of ongoing discussions this paper presents a new integrative approach that combines methods from physical anthropology and geoarchaeology the aim is to contextualise samples in regard to their sedimentary milieu sediment type the sedimentation processes they underwent and the specific archaeological features they originate from the analysis is based on 208 human and animal skeletal fragments from the late la tene site of basel gasfabrik recovered from various feature types and embedded in different sediments both 80 m and 30 m thin sections were graded semi quantitatively on a scale of 0 or 1 to 5 in regard to bacterial attack bai wedl tunnels wti cyanobacterial attack cai the formation of cracks cri the collagen content coi and thermal alterations hei our results evinced no correlations between the intensity of bacterial attack and sediment types or sedimentation processes respectively we therefore deduce that bacterial degradation of bone is mainly caused by endogenous gut bacteria wedl tunnels on the other hand are chiefly found in bones from exposed surfaces bone collagen content as measured by birefringence is dependent on a variety of factors with thermal alteration being among the most important unlike the 80 m sections used in anthropological investigations the 30 m thin sections typically utilized in geoarchaeological analyses permitted a reliable distinction of microbial bioerosion types our context oriented histotaphonomic approach allows detailed conclusions on the causes of microbial bioerosion in bone moreover it provides an important tool for reconstructing the post mortem biographies of human and animal remains especially in regard to multi stage mortuary practices and the analysis of sedimentation processes thus this novel approach generates a wealth of information from individual skeletal elements as well as from bone fragments embedded in soil samples

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

dynamics of metal silicate separation in a terrestrial magma ocean in a terrestrial magma ocean the metal silicate separation involved small metal droplets our goal is to better understand the dynamics of the metal droplet scenario the mechanism of sedimentation in a vigorously convecting and strongly rotating magma ocean may differ significantly from settling droplets in a still fluid in order to systematically study the parameter dependence on the style of motion we utilize two dimensional and three dimensional numerical convection models combined with a tracer based sedimentation method we investigate the characteristic flow patterns resulting from the competing effects of convection and droplet settling and find three styles of motion a temperature dominated style where most droplets remain suspended a droplet dominated style where the droplets separate from the fluid and a style of repetitive motion we find that the droplet dominated style is relevant to the magma ocean in this scenario the droplets settle and form a dense bottom layer one of the key findings of this work is that the formation of the dense bottom layer and therefore the separation of metal droplets from the liquid silicate occurs on a characteristic timescale which is identical with the stokes settling time finally we study the chemical interaction of settling metal droplets and liquid silicate and discuss how accurately a simple parameterized model can describe the chemical equilibration in the metal rain scenario of a terrestrial magma ocean we find agreement between the parameterized model and our two dimensional model our simulations which include thermal convection into the metal rain model confirm the fundamental observation that metal droplets are not permanently suspended in the convecting silicate melt but that they sink and rapidly form a dense layer at the base of the magma ocean

a multi phase model of runaway core mantle segregation in planetary embryos abstract a classic scenario of core formation suggests that growing proto planets are heated by the impacts of accreting planetesimals at their surface until their shallow layers reach the melting temperature of their metallic components or even of the silicates in this partially molten shell metal and silicates differentiate and the metallic phase ponds on top of the still undifferentiated inner planet later a gravitational instability brings dense metallic diapirs to the center of the planet we test this multi phase scenario by using a formalism that self consistently accounts for the presence of solid silicates solid and liquid iron at each point of the mixture an average velocity and a separation velocity of the solid and liquid phases are defined the energy balance accounts from the changes in potential energy associated with the segregation we show that core formation starts before a significant melting of the silicates as soon as impact heating is large enough to reach the melting temperature of the metallic component segregation proceeds in a few thousand years by a runaway process due to the conversion of gravitational energy into heat that occurs necessarily in all undifferentiated embryos of moon to mars sizes the first metallic diapirs leave behind them a trailing conduit along which most of the further melting occurs the cores of large planets do not form at the end of accretion but must result from the merging of the already differentiated hot cores of embryos

the wetar back arc thrust belt eastern indonesia the effect of accretion against an irregularly shaped arc the 350 km long east west trending wetar back arc thrust belt in eastern indonesia is a result of the collision of australia with the indonesian island arc along the northwest margin of wetar island a short 50 km section of the thrust belt trends northeast coincident with the offset of the indonesian arc by the newly discovered left lateral wetar atauro fault which runs along the shelf region and trends northeast the wetar atauro fault may be viewed as a large scale lateral ramp or wrench fault separating the eastern wetar thrust belt from the western wetar thrust belt the interaction of strike slip faulting and back arc thrust faulting creates several arc blocks whose geometry strongly affects the structure of the deformed wedge of sediment accreting in the wetar back arc thrust belt the varying orientations of the arc backstop make the wetar back arc thrust belt a perfect laboratory for the study of oblique convergence along most of its length the wetar thrust belt parallels the arc slope however along the northeast trending offset in the thrust belt seamarc ii side scan sonar plus seismic reflection data show that the trend of the thrust belt is not parallel to the trend of the arc slope rather it is intermediate between the trend of the arc slope and the perpendicular to the expected convergence direction the side scan images allow us to map the geometry of four main thrust faults the wetar liran atauro and alor faults the wetar liran and atauro faults trend northeast parallel to the thrust front and do not have an en echelon relationship the westernmost fault in the survey area the alor fault trends almost east west the orientation of the wetar atauro fault is consistent with a maximum principal stress within the arc oriented between 8 and 23 west of north depending on the internal coefficient of friction this agrees well with the p axes of nearby earthquake focal mechanisms which trend consistently west of north suggesting that the regional principal tectonic compression is oriented west of north because the thrust belt is oblique to the arc slope we infer the structural directions are influenced by both the arc backstop and by the regional tectonic stress the tectonic compression due to arc continent collision in this region may be modified by the arc geometry in several ways 1 the stress necessary to support the arc topography may be significant close to the arc 2 the change in thickness of the elastic part of the lithosphere may cause a concentration of tectonic stress and 3 the difference in material properties between the relatively rigid arc bulldozer and the weak basin sedimentary fill may be an important factor in producing a thrust belt that conforms roughly to the shape of the arc the structure of the wetar back arc thrust zone demonstrates that the development of small rigid blocks within a major collision zone may produce complex structural patterns and local directions of shortening that are highly oblique to the main direction of plate convergence

melt flow in a variable viscosity matrix it is often assumed that the molten regions of planetary interiors can be modeled as a compacting viscous matrix permeated by a less viscous melt phase in order to assess the true behaviour it is important to test as many different aspects of these models as possible in the calculations presented here the matrix viscosity is made to decrease as the proportion of melt increases new results in two dimensions show that if only gravity drives the flow pockets of melt travel upwards as solitary waves and the behaviour is similar to the well known constant viscosity case however when an external shear strain is applied an instability occurs and melt flows into elongated pockets or veins perpendicular to the least compressive stress whilst veins much greater than a compaction length in width are suppressed their minimum width is not clearly constrained the growth rate of veins is directly proportional to the applied strain rate so that their degree of development is proportional to the total strain it is suggested that under mid ocean ridges the total strain may be enough for such veins to be important

stratigraphic constraints on the development and timing of arc continent collision in northern papua new guinea abstract the finisterre mountains of northern papua new guinea are the site of an active southeast propagating collision between the finisterre terrane and the australian continental margin the clastic sedimentary sequence on the southern flank of the range records the history of the collision the age of initial collision can be deduced from the second of two provenance shifts that occur in the sequence as revealed by a study of 69 dated sandstones the first shift at about 16 18 ma was from volcanolithic sediments to mixed provenance sediments rich in quartz and metasedimentary lithic fragments these latter sediments were probably derived from the orogenic belt active along the australian continental margin at that time at 3 0 3 7 ma the volcanic source was rejuvenated initial collis on at this time uplifted the finisterre terrane causing the provenance shift here we break the stratigraphic sequence into three units the sarawaget beds the erap structural complex and the leron formation the sarawaget beds are middle eocene to early miocene volcanolithic sandstones that were deposited as clastic aprons un the flanks of the finisterre volcanic are volcanic activity ceased in the early miocene the erap complex is divided into two clastic subunits the sukurum and nariawang units and one basaltic subunit the gorambampan unit the sukurum unit consists of turbidites deposited south of the extinct finisterre arc from the latest early miocene through the early pliocene much of the sediment in the unit was derived from low to medium grade metasedimentary units on the active northern margin of the australian continent renewed subduction i the late miocene or pliocene occurred along the new britain trench just south of the remnant finisterre arc closing an eastward widening small ocean basin the sukurum unit probably represents an accretionary prism that formed at this subduction zone scattered seamounts that were scraped off the downgoing plate are preserved as the gorambampan unit initial collision of the finisterre terrane with the continental margin at 3 0 3 7 ma uplifted the paleogene volcanic rocks which were rapidly eroded and deposited as the volcanolithic turbidites of the nariawang unit southeastward propagation of the collision tip caused incorporation of the nariawang unit into the accretionary wedge rapid uplift raised the terrane foreland above sea level sometime after 1 3 mo the fluvial lacustrine and marginal marine deposits of the leron formation accumulated in a terrane foreland basin that developed south of the collision zone further propagation of the thrust front toward the foreland incorporated the leron formation into the fold and thrust belt rapid uplift of the finisterre range and voluminous volcanolithic sedimentation continue to the present in the finisterre range arc continent collision is marked by a provenance shift from metasedimentary and quartzose detritus to volcanic detritus in another modern arc continent collision on taiwan collision has caused a shift from volcanic to metasedimentary detritus we attribute this discrepancy to the presence of the finisterre terrane an extinct arc in the forearc region of the finisterre arc continent collision and the absence of a similar terrane in the forearc area on taiwan the very different evolution of sandstone provenance in the active taiwan and finisterre collision zones shows that local factors can profoundly influence the provenance histories of collision zones no one model of sediment provenance evolution can characterize all collision zones whether modern or ncient

deformation induced metal melt networks in silicates implications for core mantle interactions in planetary bodies abstract previous analyses of texturally equilibrated hydrostatically annealed olivine rocks containing metal and metal sulfide melts have determined that these melts do not form interconnected networks at low volume fractions to characterize the change in connectivity of metal melt in response to deformation we used optical microscopy and electron microprobe analyses to investigate the microstructures of samples of olivine gold sheared to shear strains of 200 deformation causes the development of a strong melt preferred orientation 13 15 to the shear plane and antithetic to the shear direction this melt preferred orientation consists of previously isolated pockets of gold melt that have connected into networks extending for many grain lengths as well as linear trails of isolated pockets melt was observed to have migrated 125 200 m in response to pressure gradients induced by serrations in the pistons in contact with the sample proving that finite permeability exists during deformation well below the critical melt fraction for connectivity consideration of the balance between differential and interfacial stresses on melt pockets indicates that melt channels formed in response to deformation can drain rocks to a very small melt fraction in a direction subparallel to the shear direction stranding less melt than drainage under hydrostatic conditions therefore core formation by percolative flow of non wetting melt in actively deforming planets and planetesimals may be accomplished more efficiently than previously believed in addition core material entrained in the mantle at the core mantle boundary will be strongly aligned sub horizontally in regions of horizontal shear and have little to no permeability in the vertical direction providing a mechanism to trap core material in d

petrology and geochemistry of ordovician k bentonites in new york state constraints on the nature of a volcanic arc altered volcanic ashes k bentonites in the late ordovician caradocian utica shale of new york state are the product of explosive arc volcanism most of the 30 k bentonites examined in this investigation contain fragmental crystals and rock fragments microliths up to 600 mu m in diameter that generally are neither detrital contamination from the surrounding black shale nor igneous phenocrysts the dominant phases are garnet two groups gr sub 15 20 alm sub 45 75 py sub 35 0 sp sub 2 5 gr sub 2 5 alm sub 55 85 py sub 10 40 sp sub 1 plagioclase feldspar an sub 80 10 alkali feldspar or sub 99 0 clinopyroxene wo sub 50 40 en sub 50 30 fs sub 0 30 and orthopyroxene wo sub 1 2 en sub 77 32 fs sub 32 66 accompanied by lesser quantities of hornblende aluminosilicate quartz sphene fe ti oxides apatite and zircon most of the fragmental crystals appear to be derived from the same source as the metamorphic microliths which possess minerals with similar compositions both crystals and microliths are interpreted as xenocrysts and xenoliths from the ancient continental crust on which the ordovician arc was constructed they became entrained in the volcanic plume during explosive eruptions a precambrian age acquired on k feldspars from one k bentonite using the sup 40 ar sub 39 ar method shows that these xenocrysts were derived from depths of less than 5 10 km in the microcontinent at the time of late ordovicianmore volcanism the occurrence of xenocrysts and xenoliths in these k bentonites underscores the importance of performing detailed petrology on ash layers prior to the onset of more sophisticated tasks e g isotopic age determinations regional stratigraphic correlations of k bentonites based upon chemical compositions less

earth s core formation aided by flow channelling instabilities induced by iron diapirs abstract the core formation mechanism remains poorly known an unstable gravitational configuration of a dense molten metallic layer overlying a cold chondritic protocore is predicted by most studies which leads to the formation of a rayleigh taylor rt instability recent results dahl t w 2005 turbulent mixing during planet accretion and core formation interpretation of the hf w chronometer and implications for the age of the moon m sc thesis university of copenhagen indicate that additionally iron cores of predifferentiated planetesimals are also able to plunge mostly intact into the cold protocore and create large iron diapirs for both scenarios we propose the application of the stress induced melt channelling mechanism stevenson d j 1989 spontaneous small scale melt segregation in partial melts undergoing deformation geophys res lett 16 1 067 1 070 in the region surrounding an incipient iron diapir we therefore perform numerical experiments solving the two phase two composition flow equations within a 2d rectangular box with symmetrical boundary conditions we apply the compaction boussinesq approximation cba and include a depth dependent gravity for simplicity we use a constant viscosity for the solid phase and a melt fraction dependent rheology for the partially molten region around the diapir we investigate the physical conditions under which the melt channels can form and whether they are applicable to the early earth as a result for sufficiently small melt retention numbers iron rich melt channels develop within a region of approximately twice the diapir s size this could lead to effective draining of the surrounding region and might initiate cascading daughter diapirs the region of the protocore drained by this cascading mechanism is expected to significantly increase with depth and thus indicates an effective mechanism to also extract iron melt from deeper parts of the initially chondritic protocore this mechanism could effectively accelerate the process of core formation

how to make a planet an introduction the special collection building planets the dynamics and geochemistry of core formation aims to combine cutting edge experimental analytical and modeling results with review articles defining the state of the science and current challenges to our understanding of the origin geophysics and geochemistry of planetary cores our goal is to highlight novel and interdisciplinary approaches that address aspects of core formation and evolution at the atomic grain and planetary scales

nature and distribution of deformation across the banda arc australian collision zone at timor recently acquired seismic reflection and seamarc ii side scan and swath bathymetry profiles near timor show that the banda arc australia collision zone has a tectonic framework similar to that of a typical oceanic subduction system deformation is occurring at present most intensely at the foot of the inner slope of the timor trough this deformation front is discontinuously advancing southward as new thrust slices develop within the subducted australian margin strata in contrast present deformation is apparently negligible in the savu basin the complex fore arc basin north of timor a possible significant exception is a postulated right lateral northeast trending fault zone offsetting the outer arc high between savu and roti although back arc thrusting has been documented north of the volcanic arc this component of convergence is minor compared with the scale of ongoing deformation in the timor trough the detailed nature of these surveys has also led to the recognition of along strike variations in deformation in the timor trough and in the savu basin these variations may be related to the variable degree of involvement of the australian continental margin along the arc

the west pacific geodynamic model abstract between the asian and australian continents on the western side and the general subduction of the central pacific on the eastern side the west pacific presents two types of subduction towards the continents and towards the ocean as a consequence at the present day there are two main types of marginal seas the japan sea and the south china sea and in the geological past two types of orogenesis the japanese and the taiwanese types these are the models of the two main orogenic belts respectively the circum pacific and tethyan for a long period of the past the alps and the mediterranean sea were the tectonic model of reference however with the increase in geological studies oceanographic research geophysical surveying the west pacific gradually became an alternative model which grew more useful with each passing day the present day trench island arc marginal sea system appears to be a good model for the first stages of orogenic belts whereas the mountains of the east eurasian margins provide an example of the completion of formation of such belts the coexistence of different stages of mountain building is the main reason for the increasing interest shown by earth scientists in the west pacific

continental margin tectonics submarine accretionary prisms submarine accretionary prisms are sites of incipient mountain building where sediments and rocks of the deep ocean are uplifted deformed and ultimately transformed to continental crust accretionary prisms develop at sites of lithospheric convergence that is subduction zones commonly accretionary prisms form along continental margins although accretionary prisms may also occur adjacent to island arcs which are ultimately coalesced into continental landmasses here we review the studies of submarine accretionary prisms during the past four years with primary focus on the contributions of geoscientists from the united states

two dimensional stokes flow around a heated cylinder a possible application for diapirs in the mantle 1 it is widely assumed that the separation of metal and silicates in a homogeneously accreted protoplanet occurred rather rapidly the process of core formation through the descent of large hot iron rich bodies through a cold silicate protoplanet is discussed if iron diapirs sink toward the planet center with the stokes velocity they would require more than 800 ma to form a core in the case of a planet similar to the earth we therefore implement a temperature dependent rheology for the silicate material surrounding the diapir which leads to a reduction of the drag force exerted on the iron drop we compare the drag force for different sinking velocities to the body force on the diapir and find that the terminal velocity in the temperature dependent viscosity model is a factor of 30 higher than that in an isoviscous medium on the basis of these results the core formation time for the earth could be as little as 30 ma

direct numerical simulation of an iron rain in the magma ocean core formation in terrestrial planets is a complex process possibly involving several mechanisms this paper presents a direct numerical simulation of one of these the separation of an emulsion of metal in a magma ocean the model using a fully lagrangian approach called the moving particle semi implicit method solves the equations of fluid dynamics including a proper treatment of surface tension it allows investigation of the balances controlling the distribution of drop size and velocity in both two and three dimensional situations a scaling analysis where buoyancy is balanced by both surface tension and inertia correctly predicts the average values in these quantities the full calculation gives an average drop radius of 1 5 cm falling at a velocity of about 30 cm s 1 analysis of the full distribution remains interesting and shows that a significant part of the smallest droplets is entrained upward by the return flow in molten silicate and might be entrained by succeeding thermal convection in addition we investigate the conversion of gravitational energy into viscous heating and the thermal equilibration between both phases we find that viscous heating is essentially produced at the surface of iron drops and that thermal equilibration is dominated by advection scaling thermal diffusion to chemical diffusion leads to the estimation that the latter would happen in less than 100 m in the magma ocean

formation of a solid inner core during the accretion of earth the formation of an inner core during the accretion of earth is investigated using self gravitating and compressible earth models formed by accreting a total of 25 or 50 moon to mars size planetary embryos the impact of an embryo heats the proto earth s interior differentially more below the impact site than elsewhere the rotating core dynamically overturns and stratifies shortly after each impact creating a spherically symmetric and radially increasing temperature distribution relative to an adiabatic profile merging of an embryo to the proto earth increases the lithostatic pressure that results in compressional temperature increase while further enhances the melting temperature of the core causing solidification a total of 36 thermal evolution models of the growing proto earth s core are calculated to investigate effects of major physical parameters no solidification is considered in the first 21 models where modified two body escape velocities are used as the impact velocities of the embryos at the end of accretion temperatures in the upper part of the core are significantly different among these models whereas temperatures in the deeper parts are similar the core solidification considered in the remaining 15 models where impact velocities higher than the modified two body escape velocities are adopted drastically changes the temperature distribution in the deeper parts of the core all of the models produce partially solidified stiff inner cores 1000 2100 km in radius at the end of accretion where the solid fraction is larger than 50 the innermost of the stiff inner cores are completely solidified to radii 250 1500 km

segregation of core melts by permeable flow in the lower mantle we measured the dihedral angle of molten iron in mg fe sio3 perovskite aggregate with increasing pressure and temperature using laser heated diamond anvil cell results demonstrate that it decreases from 94 at 27 gpa and 2400 k to 51 at 47 gpa and 3000 k this value is smaller than the critical angle of 60 thus allowing iron melt to wet the grain boundaries of silicate perovskite and develop an interconnected melt network within the perovskite dominant matrix even at very small melt fractions the quenched liquid iron contained substantial amounts of oxygen and silicon as pressure and temperature increase such a decrease in the dihedral angle is likely due to a reduction in the iron perovskite interfacial energy by dissolving oxygen and silicon into the liquid iron from coexisting silicate perovskite these suggest that a wetting behaviour of core melts in the solid silicate mantle changes above 40 gpa corresponding to 1000 km depth in the present earth and efficient metal segregation may have proceeded by permeable flow in a late stage of accretion oxygen and silicon incorporated during core formation and later by core mantle boundary process may be important light elements in the earth s core

quaternary hinterland evolution of the active banda arc surface uplift and neotectonic deformation recorded by coral terraces at kisar indonesia abstract coral terrace surveys and u series ages of coral yield a surface uplift rate of 0 5 m ka for kisar island which is an emergent island in the hinterland of the active banda arc continent collision based on this rate kisar first emerged from the ocean as recently as 450 ka these uplifted terraces are gently warped in a pattern of east west striking folds these folds are strike parallel to more developed thrust related folds of similar wavelength imaged by a seismic reflection profile just offshore this deformation shows that the emergence of kisar is influenced by forearc closure along the south dipping kisar thrust however the pinnacle shape of kisar and the protrusion of its metamorphic rocks through the forearc basin sediments also suggest a component of extrusion along shear zones or active doming coral encrusts the island coast in many locations over 100 m above sea level terrace morphology and coral ages are best explained by recognizing major surfaces as mostly growth terraces and minor terraces as mostly erosional into older terraces all reliable and referable coral u series ages determined by mc icp ms correlate with marine isotope stage mis 5e 118 128 ka the only unaltered coral samples are found below 6 m elevation however an unaltered tridacna giant clam shell in growth position at 95 m elevation yields a u series age of 195 31 ka which corresponds to mis 7 this age agrees with the best fit uplift model for the island loose deposits of unaltered coral fragments found at elevations between 8 and 20 m yield u series ages of

active deformation in eastern indonesia and the philippines from gps and seismicity data in this study we combine global positioning system gps velocities with information on the style of regional seismicity to obtain a self consistent model velocity and strain rate field for the entire eastern indonesia and philippines region in the process of interpolating 93 previously published gps velocities the style and direction of the seismic strain rate field inferred from earthquakes with m0 1 1020 n m from the harvard centroid moment tensor catalog are used as constraints on the style and direction of model strain rates within the plate boundary zones the style and direction of the seismic strain rate field are found to be self similar for earthquakes up to m0 1 1020 n m equivalent to mw 7 3 our inversion result shows the following the java trench which lacks any significant historic seismicity delineates the australian plate au sunda block sunda plate boundary west of the island of sumba east of sumba convergence is distributed over the back arc and banda sea and there is no subduction at the timor trough suggesting that the northern boundary of the au plate runs north of this part of the banda arc through the banda sea in new guinea most motion is taken up as strike slip deformation in the northern part of the island delineating the pacific plate pa au boundary however some trench normal convergence is occurring at the new guinea trench evidence that the strain is partitioned in order to accommodate oblique pa au motion pa au motion is consistent with nuvel 1a direction but 8 mm yr 1 slower than the nuvel 1a estimate for pa au motion the sulawesi trench and molucca sea delineate zones of high strain rates consistent with high levels of active seismicity the sulawesi trench may take up some of the au sunda motion philippine sea plate motion is in a direction slightly northward of the nuvel ia estimate and is partitioned in some strike slip strain rates along the philippine fault and relatively larger trench normal convergence along the philippine trench and on the philippine mainland in the southern philippines and along the manila trench in the northern philippine islands the high level of strain rate along the manila trench is not released by any significant historic seismic activity for the entire eastern indonesia philippines region seismicity since 1963 has taken up 40 of the total moment rate inferred from our model

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

a model of metal silicate separation on growing planets abstract the thermal evolution of planets during their accretionary growth is strongly influenced by impact heating the temperature increase following a collision takes place mostly below the impact location in a volume a few times larger than that of the impactor impact heating depends essentially on the radius of the impacted planet when this radius exceeds 1000 km the metal phase melts and forms a shallow and dense pool that penetrates the deep mantle as a diapir to study the evolution of a metal diapir we propose a model of thermo chemical readjustment that we compare to numerical simulations in axisymmetric spherical geometry and with variable viscosity we show that the metallic phase sinks with a velocity of order of a stokes velocity the thermal energy released by the segregation of metal is smaller but comparable to the thermal energy buried during the impact however as the latter is distributed in a large undifferentiated volume and the former potentially liberated into a much smaller volume the diapir and its close surroundings a significant heating of the metal can occur raising its temperature excess by at most a factor of 2 or 3 when the viscosity of the hot differentiated material decreases the proportion of thermal energy transferred to the undifferentiated material increases and a protocore is formed at a temperature close to that of the impact zone

heat partitioning in terrestrial planets during core formation by negative diapirism article i nfo we investigate the gravitational heat partitioning between silicate and metallic phases during core formation by negative diapirism in terrestrial planets we model the dynamic evolution of an iron diapir sinking through a solid silicate proto mantle our calculations include viscous heating and strong temperature and composition dependence of viscosity we show that the diapir mean temperature evolves towards an asymptotic value td which depends on the efficiency of viscous heating and heat transfer between the diapir and its surroundings and on the viscous rheology we derived a simple analytic model that captures the thermal evolution observed in our numerical experiments this model can be applied to determine the heat distribution within terrestrial planets with a large number of diapirs during their growth and early differentiation we show that the partitioning of core formation heating during negative diapirism depends strongly on the size distribution of the iron diapirs a large number of small sinking iron diapirs favors metal silicate heat exchange and leads to a relatively hot core which allows a sustainable dynamo as on earth a small number of large diapirs have the opposite effect and could correspond to a mars like planet with an early dynamo that is no longer active in all cases negative diapirism tends to leave the lowermost mantle significantly hotter than its upper part which could trigger large amounts of melting in the early deep mantle

structural styles and tectonic evolution of the seram trough indonesia abstract the seram trough is located in the northern part of the banda arc australian collision zone in eastern indonesia and is currently the site of contraction between the bird s head of new guinea and seram island it has been interpreted as a subduction trench an intra continental thrust zone and foredeep and a zone of strike slip faulting recently acquired 2d seismic lines clarify its tectonic evolution and relationship to the bird s head folding in the early pliocene formed an anticlinorium running from misool to the onin peninsula of irian jaya and produced a newly recognised angular unconformity the unconformity truncates sediments as old as middle jurassic and is an ancient topographic surface with significant relief it was later folded and now dips south towards the trough where it is covered by up to 3 km of sediments initial tilting of the unconformity surface was accompanied by deposition of a transgressive sequence which can be traced into the trough this is overlain by two sequences which prograde towards the trough these sequences show progressive rotation of the unconformity surface gravitational displacement of sediments into the trough and thrusting which continues to the present day contraction occurred in the trough after the early pliocene and is younger than the previously suggested late miocene age thrust faults in the trough deform sediments deposited above the unconformity and detach at the unconformity surface on seram thrust faults repeat mesozoic miocene sequences and probably detach at their contact with metamorphic basement the detachment surface must cut through the mesozoic miocene sequence between seram and the trough this work suggests the seram trough is not a subduction trench but a foredeep produced in response to loading by the developing fold and thrust belt of seram with an associated peripheral bulge to the north the seram trough is interpreted to be a very young zone of thrusting within the australian continental margin

polydiapirs multiwavelength gravity structures polydiapirs domes in domes result from the evolution of a multiwavelength rayleigh taylor gravitational instability the present work investigates the initiation and development of polydiapirs by means of two dimensional finite difference models of gravitationally unstable triple layered sequences of newtonian fluids the values of viscosities thicknesses and densities were systematically varied for selected examples in triple layered sequences only two types of density stratification are likely to result in multiwavelength instabilities that will eventually develop into polydiapiric structures the limiting factors and evolution of such structures were studied for both these types of density stratifications finite difference calculations on models with physical parameters appropriate to evaporitic sequences and covered by a viscous clastic overburden showed that a very small downward density decrease in the evaporitic source may cause an internal overturn that will compete with the main overturn between source and overburden this may lead to the development of sequential or simultaneous polydiapirs the mature polydiapirs in the models exhibit spines curtain folds pendant repetitions of the source layers inside the large diapirs and anomalous interdiapiric distances all these features are known in natural salt diapirs suggesting that polydiapirs may be far more common in nature than hitherto recognized

arc continent collisional orogenesis in the sw pacific and the nature source and correlation of emplaced ophiolitic nappe components abstract southwest pacific ophiolitic nappes emplaced upon the former margin of eastern australia provide a record of cyclical episodes of arc continent collisional orogenesis that occurred throughout the paleogene cenozoic nappes in papua new guinea new caledonia and northland new zealand consist of two key components 1 a basal and apparently older late cretaceous eocene metamorphosed normal to weakly enriched morb like basaltic ocean floor terrane and 2 an uppermost supra subduction zone ssz ophiolite that represents basement of the associated magmatic forearc a detailed comparison of geochemical characteristics of unequivocal ssz basalts with those considered as representative of the basaltic ocean floor terranes illustrates that formation of the majority of the latter is consistent with melting of a source transitional to normal n and enriched e morb these slight ree enriched or transitional t morb have generally been considered as the result of seafloor spreading in a back arc basin bab or basins to the east of australia in the late cretaceous paleocene 85 55 ma the enrichment recorded by the bab basalts is likely a result of upwelling plumes associated with initial fragmentation of eastern gondwana that left their signature on the mantle source consequently tapped by the bab basalts a subset of slightly more enriched basalts may owe their enrichment to source contamination minor assimilation of thinned gondwana derived continental crust associated lree depleted n mor basalts previously considered as part of the basaltic ocean floor terranes on the other hand are similar to ssz basalts of the northland and papuan ultramafic belt ophiolites refinement of existing tectonic models is hindered by ambiguities in the stratigraphic relationships of the underlying basaltic ocean floor terranes with the overlying ssz ophiolites a paucity of age data and uncertainties in the tectonomagmatic affinities of the underlying basalts nonetheless the geochemical characteristics displayed by lree depleted basalts of the basaltic ocean floor terranes suggest that these may instead represent younger magmatic forearc basement components subsequently overthrust by lower sections of a genetically related ophiolite whether these and for that matter the majority of basalts of the basaltic ocean floor terranes indeed represent complementary forearc crust to the ssz ophiolite as opposed to a slice of late cretaceous eocene bab floor backthrust beneath the ssz ophiolite upon emplacement will have to await the acquisition of corresponding radiometric age data