volcanic plutonic parity and the differentiation of the continental crust the continental crust is central to the biological and geological history of earth however crustal heterogeneity has prevented a thorough geochemical comparison of its primary igneous building blocks volcanic and plutonic rocks and the processes by which they differentiate to felsic compositions our analysis of a comprehensive global data set of volcanic and plutonic whole rock geochemistry shows that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics in both tectonic settings our results indicate that fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas emphasizing the role of mafic cumulates as a residue of crustal differentiation a global geochemical data set of volcanic and plutonic rocks indicates that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but are divergent in continental rifts brenhin keller and co authors present a global geochemical dataset of the two fundamental building blocks of the continental crust volcanic externally erupted and plutonic internally solidified rocks their results indicate that differentiation trends from primitive basaltic to felsic compositions for volcanic versus plutonic samples are generally indistinguishable in subduction zone settings but divergent in continental rifts offsets in major and trace element differentiation patterns in rift settings suggest higher water content in plutonic magmas and reduced eruptibility of hydrous silicate magmas relative to dry rift volcanics this work indicates that in both tectonic settings fractional crystallization rather than crustal melting is predominantly responsible for the production of intermediate and felsic magmas

evaluation of tsunami risk from regional earthquakes at pisco peru we evaluate tsunami risk for the port city of pisco peru where major liquefied natural gas facilities are planned we use a compilation of instrumental and historical seismicity data to quantify the sources of six earthquakes that generated tsunamis resulting in minor inundation 1974 to catastrophic destruction 1687 1746 1868 in pisco for each of these case scenarios the seismic models are validated through hydrodynamic simulations using the most code which compute both flow depth on virtual offshore gauges located in pisco harbor and the distribution of runup in the port and along the nearby beach space time histories of major earthquakes along central and southern peru are used to estimate recurrence times of tsunamigenic earthquakes we conclude that pisco can expect a metric tsunami capable of inflicting substantial damage every 53 years and a dekametric tsunami resulting in catastrophic destruction of infrastructures every 140 years the last such event occurred 138 years ago an important result of our study is that total destruction of the city of pisco during the famous 1868 arica tsunami requires an earthquake rupture straddling the nazca ridge which thus constitutes at best an imperfect barrier for the propagation of rupture during megathrust events this gives a truly gigantic size to the 1868 arica earthquake with a probable seismic moment reaching 1030 dyne cm

large pre digital earthquakes of the bonin mariana subduction zone 1930 1974 abstract the bonin mariana subduction zone is the end member example of a decoupled system as described by uyeda and kanamori 1979 with no interplate thrust solutions of moments greater than 8 10 25 dyn cm known in the cmt catalog although a number of earthquakes are reported with assigned magnitudes around or above 7 both during the wwssn period and the historical pre 1962 era we present a systematic study of these events including relocation and inversion of moment tensors we obtain 15 new moment tensor solutions featuring a wide variety of focal mechanisms both in the fore arc and the outer rise and most importantly a shallow dipping interplate thrust mechanism with a moment of 4 10 27 dyn cm for the event of 28 december 1940 at a location 175 km east of pagan our results show that the modern cmt catalog still undersamples the seismicity of the mariana arc which is thus not immune to relatively large albeit rare interplate thrust events with moments 40 times that of the largest global cmt solution frequency magnitude relations would then suggest a return time of 320 years for a magnitude 8 interplate thrust faulting earthquake in the bonin mariana system

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

a 1 78 ga large igneous province in the north china craton the xiong er volcanic province and the north china dyke swarm abstract the 1 78 ga xiong er volcanic province xvp and coeval north china giant mafic dyke swarm ncds are the most important magmatic events occurring after the amalgamation of the north china craton ncc the xvp consists of 3 7 km of extrusive volcanics and some feeder dykes sills located along the southern margin of the ncc and extending over an area 0 06 m km2 compositions vary from basalt to rhyolite but are predominantly intermediate in terms of silica content there are also minor sedimentary intercalations and pyroclastic units the sedimentary interlayers indicate an environment changing from continental facies to oceanic facies up section the xvp is characterized by fractional crystallization from an em i type mantle source and both continental arc andean type and rift environments have been proposed the ncds is widespread in the central ncc with an outcrop area 0 1 m km2 and are exposed at variable depths up to 20 km deepest in the north dyke compositions vary from basalt to andesite and dacite but are dominantly mafic and comprise two series of magmatism previous studies revealed that the ncds recorded assimilation and fractional crystallization of an em i type magma source with a minor dm contribution in the younger magmas both syn collisional and intra continental anorogenic environments have been proposed spatial and petrogenic correlations suggest a cogenetic relationship between the ncds and xvp and considered together they define a large igneous province lip of 0 1 m km2 in area and 0 1 m km3 in volume which is also notable for its continuous compositional range from mafic to felsic with no gap at intermediate compositions the petrology is explained by a common magma source that undergoes a silica poor and iron enriched fractionation trend at depth followed by a silica rich and iron poor fractionation trend in shallow level magma conduits dykes and surface lavas a mantle plume is favored as the cause of this 1 78 ga north china lip

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

ultralong period seismic study of the december 2004 indian ocean earthquake and implications for regional tectonics and the subduction process analysis of the earth s longest period normal modes shows that the december 2004 sumatra andaman earthquake was much larger mw 9 3 than ini tially inferred from surface wave data and involved slip on a much longer fault than initially inferred from body wave data the seismic moment and relative excitation of the normal modes indicate that the entire aftershock zone ruptured consistent with the large tsunami amplitudes in thailand sri lanka and india an apparent increase in seismic moment with period results from interference between parts of the fault the earthquake resulted from subduction of the indian plate beneath the burma microplate a sliver plate between the indian and sunda plates hence the rate and direction of convergence depends on the motion of the burma plate which is not well known convergence would be highly oblique if the rate of motion between burma and sunda is that inferred from spreading in the andaman sea and less if a slower rate is inferred from the sagaing fault the december earthquake was much larger than expected from a previously proposed relation based on the idea of seismic coupling in which such earthquakes occur only when young lithosphere subducts rapidly moreover a global reanalysis finds little support for this correlation hence we suspect that much of the apparent differences between subduction zones such as some trench segments but not others being prone to m w 8 5 events and hence oceanwide tsunamis may reflect the short earthquake history sampled this possi bility is supported by the variability in rupture mode at individual trench segments

petrology and geochemistry of the loch ba ring dyke mull n w scotland an example of the extreme differentiation of tholeiitic magmas the loch ba ring dyke in the tertiary igneous central complex of mull n w scotland is composed predominantly of a banded rhyolitic welded tuff the rhyolite contains numerous inclusions of dark aphanitic rock the textural relationships between the different rocks indicate rapid violent and intimate mixing during emplacement of the dyke the dark glassy component varies continuously from basaltic andesite to andesite dacite and rhyolite these glasses are enriched in feo and depleted in mgo at a given sio2 content in comparison to other tholeiitic highly differentiated volcanic rocks the rhyolite contains an average of 4 phenocrysts and is associated with the mineral assemblage plagioclase an32 to an21 sanidine or50 60 hedenbergite fayalite magnetite ilmenite apatite zircon mineral aggregates involving either plagioclase hedenbergite ilmenite or plagioclase fayalite magnetite are common but aggregates containing fayalite and hedenbergite together are scarce the dark glassy components are either phenocryst free or contain less than 0 2 phenocrysts the main phenocrysts associated with the dark glasses are plagioclase an65 an30 high calcium clinopyroxene ranging continuously from augite to pure hedenbergite pigeonite magnetite ilmenite and rare apatite zoning in minerals is generally weak or absent the plagioclase feldspar high calcium clinopyroxenes and pigeonites have similar compositional ranges to the minerals observed in the middle and upper zones of the skaergaard intrusion the mineral compositions are systematically related to sio2 content and mg number of the glasses the data demonstrate that mineral compositions and assemblages similar to the skaergaard form from silica rich andesitic to rhyolitic liquids the various mafic glasses are interpreted to have been derived from a zoned magma chamber underlying an upper layer of rhyolitic magma differentiation is attributed to fractional crystallization of the observed mineral assemblages causing sio2 enrichment and feo depletion however glasses with less than 57 sio2 have unusual compositions with very low mgo and p2o5 as well as variable al2o3 and tio2 their peculiarities could be explained by andesitic magmas assimilating cumulate mineral aggregates precipitated from more differentiated dacite and rhyolite magmas the bulk compositions of these cumulates have high feo low sio2 and negligible mgo and p2o5 it is suggested that the high density of the mineral aggregates containing fayalite hedenbergite magnetite and ilmenite caused them to settle through the zoned chamber to be assimilated by high temperature less differentiated magmas

the mechanism of great banda sea earthquake of 1 february 1938 applying the method of preliminary determination of focal mechanism to a historical event abstract a moment tensor solution is derived for the great 1938 banda sea earthquake one of the largest events for which no definitive focal geometry has been published we apply the method of preliminary determination of focal mechanism which consists of inverting for a moment tensor using exclusively the spectral amplitudes of mantle rayleigh and love waves while discarding the phase information which can be affected by uncertainties in relative timing between historical records from a dataset of 17 records at seven stations we obtain a robust solution featuring a very large moment of 8 37 10 28 dyn cm the centroid depth being constrained around 60 km by minimizing the rms residual of the inversion the method involves an inherent two fold 180 indeterminacy on the orientations of strike and slip which is lifted by the examination of the polarization of long period body waves read individually on original records resulting in a mostly thrust faulting mechanism strike 276 dip 63 slip 70 this approach coupled with more traditional relocation efforts allows a rare glimpse of this exceptional event confirmed here to rank among the 10 largest moments ever published within the extremely complex regional plate tectonics pattern the 1938 event took place in a region of sparse seismicity and away from the presumed locations of block boundaries the deeper than normal focus of the event agrees well with the generally minor level of reported damage and with the generation of a relatively benign tsunami available modern focal mechanisms in its vicinity are too few and too scattered to allow any meaningful comparison but the 1938 event shares its compressional axis with that of the smaller and deeper 1963 shock to the southwest which probably expresses coherence in the regional contortion of the subducting australian plate lithosphere

relationships between chamber margin accumulates and pore liquids evidence from arrested in situ processes in ejecta latera caldera italy biotite and clinopyroxene rich mafic nodules occur together with syenite ejecta in ca 235 to 155 ka tuffs surrounding the latera caldera clinopyroxenites and leucite monzosyenites crystallized along the lower margins of a crustal magma system and record complex crystallization histories of potassic magmas that were parental to a range of lava and tuff compositions the mafic nodules have the mineral assemblage clinopyroxene biotite anorthite orthoclase leucite hauyne titanite apatite amphibole olivine phlogopite and comprise mesocumulate and orthocumulate layers that commonly alternate on the scale of several centimeters despite the apparently ultramafic nature of the early cumulate assemblage the common occurrence of intercumulate orthoclase leucite hauyne salitic clinopyroxene and vesicular glass indicates that interstitial liquids underwent late stage differentiation at relatively shallow depths but under highly variable conditions of volatile saturation many of the mafic nodules exhibit pronounced variations in the type and abundance of mineral reaction textures these range from unreacted assemblages to nodules in which cumulate megacrysts are surrounded by well developed symplectite halos the textural variability indicates strongly localized disequilibrium between cumulate frameworks and vapor saturated pore fluids and is attributed to convective fractionation of liquids through permeable crystal mush lithologic discontinuities exhibited by the xenolith suite and host magmas are best explained by variable communication between a compositionally stratified magma reservoir and its partly crystallized lower chamber margins periodic replenishment of this system by less evolved magmas subsequently promoted mixing and hybridization that are characteristic features of many latera lavas and tephra

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

outer rise earthquakes and seismic coupling outer rise earthquakes can be separated into two basic categories based on focal mechanism compressional and tensional events reflecting compressional and tensional outer rise stress regimes we propose a model that connects the stress regime in the outer rise to the behavior of large subduction earthquakes and explains the focal mechanisms and both the temporal and spatial occurrence of outer rise earthquakes we find that compressional outer rise events tend to occur oceanward of seismic gaps in seismically coupled subduction zones or equivalently just prior to large subduction zone earthquakes the compressional stress regime is probably caused by slip in adjacent subduction zone segments there are two modes of occurrence for tensional outer rise earthquakes depending on whether they occur in coupled or uncoupled subduction zones in coupled subduction zones tensional events tend to occur after large subduction events as tensional stress from slab pull is temporarily transmitted to the outer rise in subduction zones that are inherently uncoupled tensional events can occur at any time therefore in uncoupled subduction zones the outer rise is always in tension and only tensional outer rise events occur there while in coupled subduction zones the outer rise is in a compressional state prior to large subduction earthquakes and a tensional state afterwards due to the large displacements

crystallization and textural evolution of a closed system magma chamber insights from a crystal size distribution study of the lilloise layered intrusion east greenland the recognition that postcumulus processes significantly modify primary textures in layered mafic intrusions has thrown into question many early observations on which classical crystallization theories are based petrographic observations combined with quantitative textural analysis of samples from various stratigraphic levels of the lilloise intrusion east greenland demonstrate that postcumulus textural modification of cumulates formed during the solidification of a closed system magma chamber may be detected crystal size distribution csd measurements of lilloise cumulates and the resulting csd profiles are compared to predicted theoretical closed system csd profiles similarities between the measured csd profiles and published predicted csd profiles support lilloise magma evolving in a closed system chamber and indicate that primary crystallization processes can be distinguished using quantitative textural techniques textural coarsening driven by syn magmatic deformation is suggested to be the dominant postcumulus process affecting csd plot morphology csd slope values and profiles plot shapes remain relatively constant for a given liquidus mineral particularly olivine and clinopyroxene so that the number of phases on the liquidus at any one time affects mineral modal abundances as a result csds generally exhibit overall smaller grainsizes and progressively lower nucleation densities at higher levels in the intrusion

intraplate seismicity of the pacific basin 1913 1988 we establish here a comprehensive database of intraplate seismicity in the pacific basin relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913 1988 these numbers do not include earthquake swarms which account for another 838 events most of the remainder 304 events are actually plate boundary earthquakes that have been erroneously located in intraplate regions a significant number occur in recent years when location capabilities should have guarded against this situation relocations involve a careful linear inversion of p and s arrivals accompanied by a monte carlo statistical analysis we have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins

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

preliminary determination of focal mechanisms from the inversion of spectral amplitudes of mantle waves abstract we present a method for the preliminary determination of focal mechanisms pdfm based on the inversion of deviatoric moment tensor components from depleted datasets of mantle wave spectral amplitudes the latter are found to be largely insensitive to errors in epicentral estimates which can hamper the inversion of the full complex spectrum under real time operational conditions robust solutions can be obtained from rayleigh wave spectra at as few as three stations and from a combination of rayleigh and love waves at only two stations provided they sample 60 in azimuth the systematic application of this method to a dataset of 43 large earthquakes during 1996 1999 yielded mechanisms rotated an average of only 17 from the published harvard cmt a figure comparing favorably with the case of other catalogues such as the usgs moment tensor solutions

multiple cmt source analysis of the 2004 sumatra earthquake while it is agreed that the great sumatra earthquake of december 26 2004 was among the largest earthquakes of the past century there has been disagreement on how large it was which part of the fault ruptured and how the rupture took place we present a centroid moment tensor cmt analysis of the earthquake in which multiple point sources are used in the inversion to mimic a propagating slip pulse the final model consists of five point sources with the southernmost sources accounting for the majority of the moment release the presumed fault planes of the southern sources strike northwest while those in the north strike northeast consistent with the geometry of the subduction trench slip on the fault is found to be more oblique in the north than in the south the inversion with five sources leads to a moment magnitude for the sumatra earthquake of m w 9 3 consistent with estimates from long period normal mode amplitudes

on an improved method to obtain the moment tensor and depth of earthquakes from the amplitude spectrum of rayleigh waves abstract a new method is presented to invert for the moment tensor and depth using the amplitude spectra of vertical component rayleigh waves in the period range 20 to 100 sec the technique follows a similar approach to that suggested by romanowicz 1982a to invert for the moment tensor from the complex spectra of rayleigh waves and presents some distinct advantages to the method proposed originally by mendiguren 1977 it eliminates some biases and errors in the data arising for example from inaccurate propagation corrections furthermore it is substantially faster computationally and permits us to study independently the variance reduction as a function of depth of each of the momenttensor elements resulting in better focal depth resolution the method is applied to three earthquakes in the tien shan mountains of central asia the eastern cordillera of peru and the gibbs transform fault in the north atlantic in all three cases the results of the moment tensor inversion agree with those determined using long period body wave modeling

a discussion of hunter and sparks contrib mineral petrol 95 451 461 silica poor iron rich liquids like those estimated for skaergaard by wager and brown are preserved in labrador as chilled pillows iron rich rocks in the kiglapait intrusion have likewise been produced by liquids poor in silica there is no reason to expect such liquids in volcanoes so their absence as lavas means nothing about their possible plutonic occurrence successful tests of the siliceous liquid hypothesis would include showing that the proposed rhyolitic liquids can produce the observed olivines in the range fo 10 40 they would require showing that the observed low f o 2 oxide mineral assemblages can occur at the high silica contents proposed and that the silicate mineral assemblages and compositions can represent high silica liquids i doubt very much that these critical tests can be met

compositional and kinetic controls on liquid immiscibility in ferrobasalt rhyolite volcanic and plutonic series we present major element compositions of basalts and their differentiation products for some major tholeiitic series the dry low pressure liquid lines of descent are shown to approach or intersect the experimentally defined compositional space of silicate liquid immiscibility ferrobasalt rhyolite unmixing along tholeiitic trends in both volcanic and plutonic environments is supported by worldwide occurrence of immiscible globules in the mesostasis of erupted basalts unmixed melt inclusions in cumulus phases of major layered intrusions such as skaergaard and sept iles and oxide rich ferrogabbros closely associated with plagiogranites in the lower oceanic crust liquid immiscibility is promoted by low pressure anhydrous fractional crystallization that drives the low al2o3 high feo liquids into the two liquid field kinetic controls can be important in the development of two liquid separation the undercooling that occurs at the slow cooling rates of plutonic environments promotes early development of liquid immiscibility at higher temperature in contrast rapid cooling in erupted lavas leads to large undercoolings and liquid immiscibility develops at significantly lower temperatures unmixing leads to the development of a compositional gap characterized by the absence of intermediate compositions a feature of many tholeiitic provinces the compositions of experimental unmixed silica rich melts coincide with those of natural rhyolites and plagiogranites with high feotot and low al2o3 suggesting the potential role of large scale separation of immiscible si rich liquid in the petrogenesis of late stage residual melts no trace of the paired ferrobasaltic melt is found in volcanic environments because of its uneruptable characteristics instead fe ti p rich gabbros are the cumulate products of immiscible fe rich melts in plutonic settings the immiscibility process may be difficult to identify because both melts crystallize the same phases with the same compositions the two liquids might form incompletely segregated emulsions so that both liquids continue to exchange as they crystallize and remain in equilibrium even if segregated both melts evolve on the binodal surface and exsolve continuously with decreasing temperature the two liquids do not differentiate independently and keep crystallizing the same phases with differentiation further evolution by fractional crystallization potentially drives the bulk liquid out of the twoliquid field so that very late stage liquids could evolve into the single melt phase stability field

fluid motions and compositional gradients produced by crystallization or melting at vertical boundaries the results of a continuing series of laboratory experiments designed to model the fluid motions which accompany crystallization are both described and related in a preliminary way to prototype flows in magma chambers previous experiments have demonstrated the importance of compositional inhomogeneity produced by crystallization and melting in a thermal gradient and coupled with double diffusive effects in driving convective flows which result in thermal and compositional stratification in an originally homogeneous fluid the present experiments examine effects produced in tanks cooled at the side by the upward flow of a less dense boundary layer depleted in the crystallizing component as crystals grow on the side wall these processes are examined in simple two and three component aqueous systems h2o na2co3 h2o na2co3 k2co3 h2o cuso4 na2so4 with one and two crystallizing phases in each of these systems an initially downward flow of a cooled boundary layer against the side wall is reversed as crystallization commences and depletes the boundary layer in the crystallizing component accumulation of this cooler but lighter depleted fluid at the top of the chamber produces thermal and compositional layering by a filling box mechanism partly modified by interchange between the boundary layer and the convecting layers outside when more than one component is present in the solution the crystallization process produces a differentiated fluid column i e one with compositional gradients which are different for each of the components the compositional and thermal distributions within the fluid change with time but finally appear to reach a steady state these distributions are the integrated result of compositional changes produced by crystallization from a thin boundary layer a small proportion of the bulk fluid which evolves in composition and temperature independently of the bulk fluid in a manner controlled by the dynamics of the system the paths of fluid evolution and the resulting sequence and abundance of crystalline products are very different from those predicted on the basis of simple thermally driven crystallization in the static system disequilibrium effects probably involving different kinetics of crystallization of different crystals in part determine crystallization in the experimental system these may or may not be important in real magmatic systems there is still much to learn before even the behaviour in these simple experimental systems is understood fully and the application of the results to the interpretation of the behaviour in real magma chambers in even further away however it is apparent that dynamic effects provide an additional degree of freedom in crystallization processes and allow evolution of small increments of solution to compositions much further along crystallization paths than that allowed in static equilibrium systems petrologists will have to free their thinking from classical constraints of static systems in order to interpret many magmatic phenomena

silicate liquid immiscibility within the crystal mush late stage magmatic microstructures in the skaergaard intrusion east greenland late stage microstructures developed during the last stages of solidification of the skaergaard intrusion comprise a wide array of reactive and non reactive intergrowths reactive microstructures ascribed to open system behaviour include serrated grain boundaries between pyroxene and plagioclase primocrysts fish hook pyroxenes and mafic symplectites they form by the addition of fe and ca and removal of alkalis and silica other microstructures include those formed by internally generated redox reactions between olivine fe ti oxides and pyroxene non reactive microstructures include closely spatially associated granophyric intergrowths and previously undescribed ilmenite rich intergrowths that are interpreted as a consequence of crystallization of separated conjugate immiscible liquids the open system reactive microstructures occur predominantly in the cumulates on the chamber floor appearing in lzb and disappearing to be replaced by a granophyre ilmenite rich intergrowth association in the upper zone they are not common in the marginal border series their distribution mirrors that of efficient expulsion of trapped liquid and can be attributed to the gravitationally driven loss of a si rich immiscible component from the interstitial liquid the loss of the si rich component causes the remaining fe rich liquid to react with the primocrysts bulk rock major element data are consistent with little or no preferential loss of the si rich liquid from the mush but the resolution of the available data is not sufficient to assess the effect of this relative movement on the liquid line of descent of the bulk magma the first appearance of the paired conjugate non reactive intergrowths in mz marginal border series points to the early onset of immiscibility in the bulk liquid

plagioclase in the skaergaard intrusion part 1 core and rim compositions in the layered series the anorthite content of plagioclase grains xan in 12 rocks from the layered series of the skaergaard intrusion has been studied by electron microprobe typically 30 core and 70 rim analyses per thin section mean core compositions vary continuously from an66 at the base of the layered series lza to an32 30 at the top on the other hand crystal rims are of approximately constant composition an50 1 from the lza to the lower middle zone mz above the mz core and rim compositions generally overlap profiles across individual plagioclase grains from the lower zone show that most crystals have an external zone buffered at xan 50 1 the simplest explanation for these features is that during postcumulus crystallization in the lower zone interstitial liquids passed through a density maximum this interpretation is consistent with proposed liquid lines of descent that predict silica enrichment of the liquid associated with the appearance of cumulus magnetite

avian remains from the early middle pleistocene of the so a basin central flores indonesia and their palaeoenvironmental significance the so a basin in central flores contains the earliest known evidence for hominins on this remote indonesian island with stone tools from this region dating back at least 1 0 ma at least 16 late early to early middle pleistocene terrestrial fossil localities record evidence for highly insular endemic faunas and proxy evidence for hominins the hominin presence in the so a basin raises many questions as to how when and from where hominins arrived on the island and key issues regarding their adaptation to this insular environment remain poorly understood here we provide palaeoenvironmental data based on avian remains recovered during recent systematic excavations of late early to early middle pleistocene deposits at mata menge and bo a leza in the so a basin at least six species of birds in five avian orders were recovered forming the oldest bird remains recovered from wallacea two species a swan cygnus sp and an eagle owl bubo sp no longer occur on flores the avian assemblage from mata menge and bo a leza described here is indicative of an open environment with a strong open freshwater component and nearby grasslands and with forests at a distance in that it differs from the late pleistocene limestone cave site of liang bua the find locality of homo floresiensis and is more similar to the early pleistocene homo erectus sites of the sangiran dome on java although little is known regarding the identity of the so a basin toolmakers the presence of an open savannah type environment in the late early to early middle pleistocene of flores may have facilitated their dispersal from the asian shelf into wallacea

evolution of the skaergaard magma evidence from crystallized melt inclusions polymineralic aggregates composed of clinopyroxene fe ti oxide minerals apatite and accessory k feldspar biotite and amphibole are enclosed in cumulus plagioclase grains in the middle zone of the skaergaard intrusion the chemistry of the minerals in the aggregates and the textural relations between the aggregates and the host plagioclase grains indicate that they represent inclusions of the contemporaneous melt of the skaergaard intrusion through mass balance calculations a quantitative estimate of the melt composition for this level in the intrusion can be obtained and this estimate confirms that the silica content in the middle zone melt was similar to or possibly even lower than the silica content in the initial skaergaard melt and relatively enriched in iron

faulting within the pacific plate at the mariana trench implications for plate interface coupling and subduction of hydrous minerals we investigate faulting within the incoming pacific plate at the mariana subduction trench to understand stresses within the bending plate regional stresses acting upon the plate interface and the extent of possible faulting induced mantle serpentinization we determine accurate depths by inverting teleseismic p and sh waveforms for earthquakes occurring during 1990 2011 with global centroid moment tensor gcmt solutions for earthquakes with mw 5 0 we determine centroid depths and source time functions and refine the fault parameters results from central mariana indicate that all earthquakes are extensional and occur at centroid depths down to 11 km below the moho at the southern mariana trench extensional earthquakes continue to 5 km below the moho one compressional earthquake at 34 km below the seafloor suggests stronger plate interface coupling here in addition we model the stress distribution within the pacific plate along two bathymetric profiles extending seaward from the mariana subduction trench axis to better understand whether our earthquake depth solutions match modeled scenarios for plate bending under applied external forces results from our flexure models match the locations of extensional and compressional earthquakes and suggest that the pacific plate at southern mariana is experiencing larger compressional stresses possibly due to greater interplate coupling additionally we conclude that if extensional faulting promotes the infiltration of water into the subducting plate mantle then the top 5 15 km of the pacific plate mantle are partially serpentinized and a higher percentage of serpentinization is located near the central mariana trench where extensional events extend deeper

crystallization sequence and magma chamber processes in the ferrobasaltic sept iles layered intrusion canada the sept iles layered intrusion quebec canada 564 ma is a large plutonic body with a diameter of 80 km and a thickness of 6 km made up from its base to top of a layered series with troctolite and gabbro and an upper border series with anorthosite capped by cupolas of a type granite chilled margin compositions suggest a ferrobasaltic parental magma close to that of the skaergaard intrusion but much richer in iron and titanium samples from drill cores and surface sampling of the 4 7 km thick layered series reveal a succession of massive troctolites and layered gabbros that contain 24 fe ti oxide layers cm to m thick and many anorthositic autolithic blocks the sequence of crystallization in the layered series is plagioclase an72 34 and olivine fo75 21 followed by magnetite and ilmenite then ca rich pyroxene and finally apatite an olivine gap is observed between fo66 and fo59 the saturation of fe ti oxides before ca rich pyroxene is interpreted to be the result of the high feot and tio2 contents and the low cao content of the parental magma contamination by old continental crust has occurred during crystallization of the layered series as indicated by sr isotopic compositions 87sr 86sr564 0 70360 0 70497 the differentiation trend of the intrusion is interrupted by two large and many small reversals to more primitive compositions of cumulus phases cr content of magnetite and lower sr isotope ratios these reversals and the intermittent disappearance of some phases are interpreted as resulting from magma chamber replenishments by undifferentiated primitive basaltic magma and mixing with the resident magma the author 2010 published by oxford university press all rights reserved for permissions please e mail journals permissions oxfordjournals org

archaeological implications of the geology and chronology of the soa basin flores indonesia the timing of arrival of early hominids in southeast asia has major implications for models of hominid evolution the majority of evidence for the earliest appearance of hominids in the region has previously come from java in western indonesia much of this evidence remains controversial owing to a poor understanding of the stratigraphic and chronologic relationships of the depositional units from which the material was derived before artifacts may be placed into their proper archaeological context the geologic history of archaeological sites must be thoroughly understood and deposits containing artifacts must be properly dated an extensive investigation has been undertaken on the island of flores in eastern indonesia to determine the depositional and chronological history of stratigraphic units within the soa basin many of the units are associated with stone artifacts attributed to homo erectus zircon fission track dates of tuffaceous deposits within this lacustrine basin now provide the most reliable data concerning the true time of arrival of homo erectus into southeast asia and indicate that these early hominids must have successfully begun colonizing eastern indonesia by ca 840 ka

landscape development preceding homo erectus immigration into central java indonesia the sangiran formation lower lahar abstract the sangiran dome is the primary stratigraphic window for the solo basin a coastal feature on the pliocene pleistocene sunda subcontinent south margin in the dome the lower lahar unit llu is a lahar type debris flow overlying near shore marine sediments the event that emplaced the llu likely originated from sector collapse on a neighboring volcanic edifice freshwater mollusc fossils in the llu indicate that swamps or shallow lakes lay between the edifice and the current dome area 40ar 39ar analyses on hornblende separates from six pumice lenses suggest that the llu was deposited as early as 1 90 0 02 ma the event resulting in deposition of the llu transformed late pliocene near shore marine environments into estuarine and marsh settings shortly thereafter glacioeustatic sea level falls completed the local transition to fully terrestrial environments that attracted homo erectus to southernmost sunda in the early pleistocene

xenoliths of gneisses and the conformable clot like granophyres in the marginal border group skaergaard intrusion east greenland results of this research and the earlier work of wager and his colleagues indicate that contamination influenced the overall character of the marginal border group of the skaergaard intrusion precambrian gneisses were a major source of contamination and are identifiable as xenoliths in the marginal border a variety of other xenoliths occur with a wide compositional range

differentiation of ferro basaltic magmas under conditions open and closed to oxygen implications for the skaergaard intrusion and other natural systems because processes such as fractional crystallization and crystallization under conditions closed to oxygen are difficult to simulate in the laboratory there is a need for quantitative models of magma crystallization behaviour comparison of experimental data on an iron rich basaltic composition with predictions of the melts free energy minimization algorithm shows that although liquidus temperatures and silicate mineral equilibria are predicted relatively well the saturation of fe ti oxides is not we have used the same experimental data to construct an alternative crystallization model based on known equilibrium phase relations mineral melt partitioning of major elements and mass balance constraints the model is used to explore the consequences of equilibrium and fractional crystallization in systems open and closed to oxygen liquid lines of descent for perfect equilibrium and perfect fractional crystallization are predicted to be very similar in a system open to oxygen the model predicts that magnetite saturation leads to strongly decreasing iron and increasing silica contents of residual liquids whereas systems closed to oxygen crystallize less abundant magnetite leading to a less pronounced iron depletion in the liquid predicted bulk solid compositions and variations offo with falling temperature agree well with those observed or inferred from the cumulates of the skaergaard intrusion but none of the predicted liquid lines of descent are consistent with the extreme iron enrichment proposed for this intrusion based on mass balance calculations compositional factors such as water and phosphorus are not thought to be the source of the discrepancy as the cumulates of the basistoppen sill which closely resemble those of skaergaard may be used to calculate a liquid line of descent in agreement with that predicted by the model for fractional crystallization closed to oxygen a comparison of the predicted t io paths and liquid lines of descent with those inferred from natural systems suggests that volcanic centres such as iceland and hawaii evolve under conditions open to oxygen whereas evidence from plutonic environments e g skaergaard and kiglapait layered intrusions suggests that they evolved under conditions more closed to oxygen the compositional evolution of the melt phase in volcanic and plutonic systems may therefore be different although the results of this study suggest that magnetite saturation will limit fe enrichment in all environments to 20wt feo consistent with enrichments reported for volcanic glasses

parental liquids of the skaergaard intrusion cumulates petrogenetic relationships between compositions advocated as possible liquids parental to the skaergaard layered series cumulates have been investigated using equations for the prediction of liquidus temperature and liquid path followed during fractional crystallization given a suitably defined sequence of primocryst mineral assemblages a variation of the fractionation scheme provides a new method for the calculation of the parent liquid composition

mm a variable period mantle magnitude this paper lays the theoretical groundwork for a variable period mantle magnitude mm based on the measurement of the spectral amplitude x of very long period rayleigh waves we retain the concept of magnitude by restricting ourselves to single station measurements ignoring the focal mechanism and the exact depth of the shallow earthquakes considered our measurements are made at a series of periods in all cases greater than 40 s and the largest value is retained this procedure effectively avoids the well known interference effects leading to saturation of magnitude scales defined at a fixed period two corrections are used a period dependent distance correction cd and a source correction cs also period dependent compensating for the variation of the excitation of rayleigh waves with period both of these corrections are fully predictable on the basis of standard surface wave excitation and dispersion theory the result is a formula of the type mm log10 x cd cs c0 in which all coefficients including the constant c0 are justifiable on sound theoretical grounds the analysis of a data set of 256 records from the broadband seismograph at papeete tahiti the ultra long period system at pasadena and stations of the geoscope network shows that the mean error in the estimation of the seismic moment is on the order of 0 1 0 2 units of magnitude with the standard deviation at each station also on the order of 0 2 units of magnitude no significant trend with either distance period or station can be identified the method can also be transposed to the time domain under some simple assumptions which are justifiable theoretically for typical teleseismic distances across the pacific basin both versions of the method lend themselves well to automation thus by providing a real time estimate of the seismic moment of distant earthquakes mm has considerable potential for tsunami warning purposes its concept can easily be extended to love waves and also to intermediate and deep earthquakes

subduction seismicity and tectonics in the lesser antilles arc we have studied the mechanisms of 17 earthquakes along the lesser antilles subduction zone to examine a site where very old lithosphere subducts at a slow convergence rate no large thrust earthquakes occurred during the 1950 1978 study period the three large magnitude seven events are all normal faults one is a normal faulting event seaward of the trench its aftershock sequence includes strike slip events on differently oriented faults probably due to lateral block motion in response to the main shock a second indicates extension within the slab at depth these observations suggest that subduction in this region is primarily decoupled and aseismic unless the time interval studied is unrepresentative the third normal fault earthquake occurred within the upper plate with fault planes perpendicular to the arc and trench this unusual geometry may represent a flexural response to the subduction of the barracuda ridge a major bathymetric high with uncompensated excess mass at depth which seems analogous to flanking ridges found along some mid atlantic ridge fracture zones thus the barracuda ridge is not buoyant and does not affect benioff zone dip strike slip faulting occurs at depth in the subduction zone along a concentration normal to the arc and maymore indicate a fossil fracture zone there is no direct evidence in the shallow seismicity for the hypothetical north america south america caribbean triple junction through some of the oceanic intraplate seismicity is consistent with such a boundary less

mechanism for normal faulting in the subducting plate at the mariana trench we investigate the mechanisms of normal fault initiation and evolution in the subducting pacific plate near the mariana trench through bathymetry analysis and geodynamic modeling we model the subducting plate as an elastoplastic slab subjected to tectonic forcing at the trench including vertical load bending moment and horizontal tensional force in our simulations normal faults initiate within the outer rise region and reach maximum throw toward the trench this result holds over a wide range of tectonic forcing and is consistent with observations of the challenger deep region where multibeam bathymetry data indicate faults initiate near the outer rise at 70 110 km from the trench and reach maximum throw at 10 35 km from the trench however models require a horizontal tensional force with magnitude comparable to axial vertical load to jointly explain the observed seafloor bathymetry location of maximum normal fault throw and prevalence of normal faults dipping toward the trench

crustal contamination and the granite problem in the british tertiary volcanic province isotopic studies on the british tertiary volcanic province have shown that the granites contain both mantle derived and crustal components while basic rocks display pronounced crustal contamination in order to study contamination mechanisms in greater detail isotopic and chemical variations in skye plateau lavas and cuillins complex intrusive units were examined as a function of time in both cases degrees of crustal contamination generally fall with time which it is argued reflects the progressive melting and sweating out9 of lewisian acid gneissic sheets from the more refractory intermediate basement during repeated intrusion and contamination of sheet like magma reservoirs long lived developing magma chambers do not fit the data well skye granites had basic precursors that suffered similar types of contamination in the lower crust but tended to form longer lived developing magma chambers in the upper crust nevertheless skye granites display similar crustal pb contents to associated basic intrusions and are argued not to be the products of crustal anatexis but the differentiates of preshal mhor basic magmas contaminated by ca 10 with large degree partial melts of lewisian acid gneisses

frequency moment distribution of deep earthquakes implications for the seismogenic zone at the bottom of slabs abstract we present a systematic investigation of the variation with depth of the frequency of earthquake occurrence vs seismic moment based on 16 years of harvard centroid moment tensor cmt solutions we analyze depth variations of earthquake size distribution in terms of variations in the absolute value of the slope of the regression of the logarithm of the population vs seismic moment a quantity known as the parameter the shallowest earthquakes 0 50 km depth exhibit a well defined and robust size distribution regime characterized by a discontinuous increase in with increasing moment others have shown that this increase probably represents the effects of a physical limit in the dimensions of the area of seismogenic slip of shallow earthquake sources the population of deep earthquakes in the depth interval 500 600 km shows two markedly different distributions the deep earthquakes in the tonga region feature an initially high value 0 92 at small moments and a lower value 0 41 at high moments in contrast the size distribution of non tonga deep events shows the reverse of those changes 0 41 at low moment and 1 17 at higher moment to help explain these observations we propose a model of deep seismogenesis that assumes three dimensional earthquake source regions that vary principally in their transverse dimensions the two segment behavior in the tonga region and other subduction zones is thought to represent in part constraints owing to the threshold of completeness of the cmt catalog and to its short time interval of sampling we interpret the differences between tonga and other deep wadati benioff zones as being a consequence of tonga s markedly higher subduction rate and hence its colder thermal structure and presumably thicker region of seismogenesis we interpret the critical moments at which values change in terms of variations in the transverse thickness of deep seismogenic zones and estimate that it is about 11 km for the tonga region and about 3 km for other zones at depths of 500 600 km these results are generally consistent with deep earthquakes being restricted to wedge shaped regions of peridotite persisting metastably to as deep as 700 km in old rapidly descending and hence cold slabs failure is thought to occur in metastable peridotite by transformational faulting great deep earthquakes present special challenges to any theory of deep earthquakes based on slab thermal structure for example a continuing question is how such large events can fit in a thermally controlled seismogenic zone that is diminishing in its transverse dimensions with increasing depth the very concept of a scale invariant earthquake size distribution may be inappropriate for these rare events and the unusual settings in which they are found

sidewall differentiation in an alkalic magma chamber evidence from syenite xenoliths in tuffs of the latera caldera italy feldspathoidal and quartz bearing syenite xenoliths in c 235 to 155 ka tuffs surrounding the latera caldera have textures and mineral assemblages that indicate an origin from the crystalline margins of a shallow magma chamber this lithic suite exhibits a diversity of plutonic fabrics unaltered glass bearing nodules with undeformed sanidine frameworks coexist with completely crystallized clasts many of which show evidence of subsolidus modification the syenites comprise eutectic mineral assemblages with high percentages of titanite apatite and melanite garnet as accessory minerals ubiquitous reaction textures in syenite accompany progressive changes in mineral assemblages and they show the decreasing influence of limestone contamination with distance from the contact of syenite and skarn wallrock diagnostic mineral assemblages include nepheline rich in calcite inclusions coexisting titanite and metamorphic perovskite zircon with baddeleyite inclusions fluorapatite mantled by a possible carbonate bearing apatite francolite melanite garnet intergrown with clinopyroxene and interstitial hauyne rich in pyrrhotite inclusions at latera pumice fragments in the same deposit can exhibit up to ten fold differences in vesicularity and crystal content from 50 vol phenocrysts these clasts in conjunction with glass bearing syenite and skarn xenoliths may represent a range of progressively crystallized magmas that were quenched at the instant of their eruptive entrainment the major element abundances of pumices and syenite reflect the fractionation of plagioclase and sanidine with lesser amounts of fassaitic diopside leucite biotite apatite and alkali amphibole trace element ratios e g rb sr nb ta zr hf lree hree on the other hand are highly variable for crystalline and pumiceous ejecta and some element variations e g li ta nb th cannot be entirely reconciled with simple crystal liquid fractionation the syenite clasts span a range of compositions from strongly fractionated assemblages rich in accessory minerals to compositions that more closely approximate quenched reservoir liquids these features reflect processes that range from pure fractional crystallization to in situ crystallization where fractionated liquid was trapped in the pores of sidewall cumulates along the chamber roof and walls

crystallization and compositional convection in a porous medium with application to layered igneous intrusions growing crystals can provide a local source of buoyancy by depleting melt of certain chemical components and vigorous convective motions in the fluid can result we report a quantitative experimental study in which saturated aqueous solutions of cuso4 and na2so4 in porous media of either glass balls or cuso4 5h2o crystals were crystallized by cooling from below the crystals growing in the pore space released light chemically depleted solution which had the potential to convect out of the porous medium and be replaced by additional saturated solution from above we explore the physical and chemical effects of compositional convection during the complete solidification of the interstitial solution by varying the permeability of the porous medium the cooling rate and the initial composition of the solution this type of convection can form adcumulate rocks by enabling continuous circulation of melt from the main magma reservoir through the pores of a cumulus pile adcumulus growth can occur by this mechanism as long as the convective velocity in the porous medium is greater than the velocity of the solidification front we scale the experimental results to magmatic conditions and infer that this process should occur commonly in layered igneous intrusions when our porous media had a small permeability compositional convection enabled the adcumulate growth of a completely solid contact between melt and cumulate trapping of dynamically unstable melt beneath this impermeable layer of crystals also occurred in these experiments and may be important geologically small shallowly emplaced intrusions and the cumulate zones at the base of komatiites are probably cooled too rapidly for significant intercumulus convection to occur

the differentiation of the skaergaard intrusion mcbirney and naslund have missed the two central points that we reiterate for clarity first the composition of the cotectic cumulate extract for the lzc best estimated from the average composition of adcumulate rocks had a substantially lower silica content than any conceivable basaltic liquid so silica enrichment is unavoidable this is true of all the dyke compositions reported by brooks and nielsen even the anomalous rock e with sio2 46 second it is the normal behaviour of tholeiite basaltic magma to produce increasingly iron rich cumulate extracts with little change in silica until feti oxide precipitation occurs when silica enrichment and compositional divergence begins such divergence between equivalent cumulate plutonic and fractionated volcanic rocks hads been widely documented skaergaard magmas do have some uncommon features however similar assemblages exist in volcanic rocks as in the andesitic to rhyolitic glasses of the loch ba ring dyke mull sparks 1988 it is also a basic principle that elements enriched in cumulate rocks often become depleted in the corresponding liquids iron enrichment in the skaergaard cumulates is complementary to iron depletion in liquids

m m a variable period mantle magnitude for intermediate and deep earthquakes we extend to the case of intermediate and deep earthquakes the mantle magnitude developed for shallow shocks byokal andtalandier 1989 specifically from the measurement of the spectral amplitude of rayleigh waves at a single station we obtain a mantle magnitude mm theoretically related to the seismic moment of the event through m m log 10 m 0 20 the computation ofmminvolves two corrections the distance correction is the same as for shallow shocks for the purpose of computing the frequency dependent source correction we define three depth windows intermediate a 75 to 200 km intermediate b 200 400 km and deep over 400 km in each window the source correctioncs is modeled by a cubic spline of log10t

petrogenesis and tectonic implications of the iron rich tholeiitic basalts in the hutuo group of the wutai mountains central trans north china orogen abstract the hutuo group located in the wutai mountains area is characteristic of paleoproterozoic strata in the north china craton and plays an important role in establishing evolutionary processes in the trans north china orogen we present petrological observations along with geochemical and nd isotopic data for basalts in the qingshicun and hebiancun formations of the hutuo group these basalts are enriched in tfeo 11 97 18 01 wt consistent with occurrences of iron rich basalt world wide they also display relatively high mgo 4 95 12 25 wt ni 79 121 ppm and cr 37 101 ppm and low in sio 2 41 37 51 95 wt therefore the iron rich character of the hutuo group basalts originated with their parental magma rather than via shallow crustal fractionation at low oxygen fugacity as inferred for many high iron basalts the hutuo group basalts exhibit weak to moderate differentiation of light ree over heavy ree la lu cn 2 61 6 79 with minor or slight eu anomalies eu eu 0 77 1 41 and also show the nb and ti troughs without obvious zr and hf anomalies the nd t values of the basalts range from 1 23 to 0 81 with t dm of 2489 2664 ma the basalts most plausibly originated from the fertile subcontinental lithosphere mantle and in the case of the qingshicun formation basalts also underwent the crustal contamination basalts in the hutuo group also have the high zr hf ratios and present high ti v values of 24 55 and zr y ratios ranging from 4 6 to 13 6 suggesting that they were emplaced in a within plate setting considering the sedimentary associations and detrital fragments in the hutuo and gantaohe groups and bimodal magmatism along the trans north china orogen we propose that 2 2 2 0 ga geological events within the orogen were rift related but did not result from subduction or island arc processes

the depth of the deepest historical earthquakes we usep ands times listed in the international seismological summary to relocate 23 historical earthquakes 1927 1963 reported as occurring at or below 670 km in all cases our relocated hypocenters are shallower than the starting depths furthermore all events converge to 691 km or less with a precision estimated at 10 km this study upholds the results of stark and frohlich who had usedpp p times of post wwssn earthquakes to constrain reliable hypocentral depths to no greater than 684 km in particular we reject rothe s claim that a 1963 event in the vicinity of new guinea occurred at a depth of more than 780 km

stress transfer and seismic phenomena in coupled subduction zones during the earthquake cycle an elementary mechanical model of a coupled subduction zone is presented it is used to study the transfer of extensional stresses along the underthrusting plate and shear stress interactions between the plate itself and its thrust contact zone with the overriding plate during the earthquake cycle the model assumes an elastic plate which deforms one dimensionally has shear drag interactions treated approximately by the elsasser procedure with a maxwellian viscoelastic mantle and is subject to steady gravitational sinking forces great thrust earthquakes are simulated as sudden stress relieving displacements at the contact zone between the slab and overriding plate the model allows analysis of the space and time variable stresses in the main thrust zone the adjacent oceanic plate and the subducting slab over each earthquake cycle stress variations leading to outer rise events are discussed as well as stress changes responsible for intraplate seismicity downdip from the main thrust zone based on simulations of periodic great earthquakes the results of simulated slow progression of deformation slip from below into the thrust contact zone are also presented such preslip occurring over a time scale that is small in comparison with the whole seismic cycle e g of the order of a tenth or so is shown to transiently slow the rate of buildup of or even relieve extensional stresses in the slab in the absence of preslip those stresses build up steadily in time during the latter part of the cycle the results have implications for induction of sesimic quiescence as well as for explaining patterns of seismicity in relation to spatial position along the underthrusting plate and to time throughout the cycle correlations are reported between the model simulations and seismicity observations from coupled subduction zones around the world the observations include tensional outer rise events after large subduction earthquakes and compressional ones in the latter parts of the cycle normal tensional intraplate earthquakes preceding the main thrust events and positioned downdip from the thrust zones and interlaced periods of seismic activity in the lower part of the main thrust zone and in the descending slab

the south of java earthquake of 1921 september 11 a negative search for a large interplate thrust event at the java trench summary we present a detailed study of the earthquake of 1921 september 11 located between the two anomalous tsunami earthquakes of 1994 and 2006 south of java based on modern relocation techniques a compilation of focal mechanism constraints from historical seismograms a quantification of mantle surface waves and a numerical simulation of its mediocre tsunami only 10 cm at cilacap we conclude that the 1921 earthquake occurred at a depth of 30 km as an intraplate earthquake in the outer rise featuring a mostly strike slip mechanism expressing tensional stress parallel to the direction of convergence with a moment of 5 1027 dyn cm two other large historical earthquakes south of java in 1937 and 1943 are also shown to be intraplate shocks so that the java subduction zone lacks large interplate thrust events for the entire era of instrumental seismicity however this does not violate the extrapolation to large sources of the frequency moment characteristics of modern digital data 1976 2011 thus leaving open the possibility that the java trench might entertain occasional if rare mega thrust events

the youngest stegodon remains in southeast asia from the late pleistocene archaeological site liang bua flores indonesia stegodon remains originating from late pleistocene layers of the archaeological cave site liang bua on the indonesian island of flores are described as a new endemic dwarf subspecies stegodon florensis insularis subsp nov some fossil stegodon fragments were found in association with the recently described remains of homo floresiensis but many occur in levels with high artefact concentrations the direct ancestor is the larger sized s florensis florensis known from early pleistocene and early middle pleistocene sites on flores the assemblage from liang bua comprises mostly dental and skeletal elements of juvenile individuals s f insularis is characterized by an advanced molar ridge formula and diminutive size on average the molars are 30 per cent smaller in linear dimensions as compared to the ancestral species hominin activities are likely to have played a role in the stegodon bone accumulation at liang bua

seismic coupling and uncoupling at subduction zones seismic coupling has been used as a qualitative measure of the interaction between the two plates at subduction zones kanamori 1971 introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern pacific subduction zones a quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables age of the subducting lithosphere and convergence rate the largest earthquakes occur in zones with young lithosphere and fast convergence rates while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane asperities are strong regions that resist the motion between the two plates the zones with the largest earthquakes have very large asperities while the zones with smaller earthquakes have small scattered asperities this observation can be translated into a simple model of seismic coupling where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface while the variation in asperity size is used to establish a connection between earthquake size and tectonic stress it also implies that plate age and rate affect the asperity distribution plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the preferred trajectory i e the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity indirect influences are many including oceanic plate topography and the amount of subducted sediments all subduction zones are apparently uncoupled below a depth of about 40 km and we propose that the basalt to eclogite phase change in the down going oceanic crust may be largely responsible this phase change should start at a depth of 30 35 km and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change

do trench sediments affect great earthquake occurrence in subduction zones seismic energy release is dominated by the underthrusting earthquakes in subduction zones and this energy release is further concentrated in a few subduction zones while some subduction zones are characterized by the occurrence of great earthquakes others are relatively aseismic this variation in maximum earthquake size between subduction zones is one of the most important features of global seismicity previous work has shown that the variation in maximum earthquake size is correlated with the variation in two other subduction zone properties age of the subducting lithosphere and convergence rate these two properties do not explain all the variance in maximum earthquake size i propose that a third subduction zone property trench sediments explains part of the remaining variance in maximum earthquake size subduction zones are divided into two groups 1 those with excess trench sediments and 2 those with horst and graben structure at the trench thirteen of the 19 largest subduction zone events including the three largest occur in zones with excess trench sediments about half the zones with excess trench sediments are characterized by great earthquake occurrence most of the other zones with excess trench sediments but without great earthquakes are predicted to have small earthquakes by the age rate correlation two notable exceptions are the oregon washington and middle america zones overall the presence of excess trench sediments appears to enhance great earthquake occurrence one speculative physical mechanism that connects trench sediments and earthquake size is that excess trench sediments are associated with the subduction of a coherent sedimentary layer which at elevated temperature and pressure forms a homogeneous and strong contact zone between the plates

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

characterization of bone surface modifications on an early to middle pleistocene bird assemblage from mata menge flores indonesia using multifocus and confocal microscopy abstract island southeast asia isea is a key region for the study of human evolution new fossil and archaeological evidence from several islands suggests an early to middle pleistocene colonisation date by hominins a taphonomic framework however such as that exists for africa is currently lacking and taphonomical studies of isea vertebrate assemblages are very limited in this paper we apply multifocus and confocal microscopy to surface modifications on an early to middle pleistocene avian assemblage from mata menge in the so a basin of central flores indonesia with the aim of characterizing material and testing the relevance of 3d reconstructions to study the taphonomy of isea bone assemblages our observations document a number of bone surface modifications including individual parallel grooves overlapping spindle like striations elongated impacts short composite grooves and rows of pits these features suggest that several taphonomic agents were at play during and after the accumulation of the mata menge small vertebrate assemblage we find no unambiguous evidence for the exploitation of birds by the so a basin hominins or for hominins being a significant accumulating agent of avian remains at mata menge however our work should be seen as preliminary as direct comparative data on relevant biological agents are lacking the markedly distinct faunal composition and climatic regimes of many southeast asian islands and the potential use of different tools by hominins warrants the development of a comprehensive taphonomical framework that is specifically relevant for isea

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

can crystallization of olivine tholeiite give rise to potassic rhyolites an experimental investigation experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica saturated potassic suites could be genetically related through crystallization extreme crystallization 96 97 of a high mgo 10 62 wt olivine tholeiite from the snake river plain with an initial bulk water content of 0 4 wt at a mid crustal pressure of 4 3 kbar generated potassic rhyolitic liquids similar in major element chemistry to those found in the quaternary rhyolite domes of the snake river plain and their plutonic equivalents in the proterozoic laramie anorthosite complex residual liquids comparable in composition to the bulk rock compositions of intermediate rocks found at the craters of the moon and cedar butte eruptive centers in the snake river plain are also generated along this crystallization path