amphibole as an archivist of magmatic crystallization conditions problems potential and implications for inferring magma storage prior to the paroxysmal 2010 eruption of mount merapi indonesia amphibole is widely employed to calculate crystallization temperature and pressure although its potential as a geobarometer has always been debated recently ridolfi et al contrib mineral petrol 160 45 66 2010 and ridolfi and renzulli contrib mineral petrol 163 877 895 2012 have presented calibrations for calculating temperature pressure fo2 melt h2o and melt major and minor oxide composition from amphibole with a large compositional range using their calibrations we have i calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations and ii calculated crystallization conditions for amphibole from basaltic andesitic pyroclasts erupted during the paroxysmal 2010 eruption of mount merapi in java indonesia to infer pre eruptive conditions our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates calculated fo2 and melt sio2 content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions however calculated crystallization pressure and melt h2o content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters amphibole from merapi s pyroclasts yields calculated conditions of 200 800 mpa 900 1 050 c nno 0 3 nno 1 1 3 7 7 2 wt melt h2o and 58 71 wt melt sio2 we interpret the variations in calculated temperature fo2 and melt sio2 content as reasonable estimates but conclude that the large calculated pressure variation for amphibole from merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range in contrast bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas respectively and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth

subsalt imaging using tti reverse time migration tti depth imaging technology is routinely applied to image structures that lie beneath dipping anisotropic overburden in the canadian foothills vestrum and vermeulen 2004 the north sea hawkins et al 2002 and offshore west africa ball 1995 until now ray based migration algorithms served as the only choice for tti imaging because upgrading ray based imaging algorithms for tti is straightforward and incurs minor additional computational cost unlike ray based algorithms tti wave based algorithms are difficult to formulate and their implementations are often unstable and computationally intensive unfortunately ray based algorithms perform poorly in comparison to wave based algorithms in imaging structures beneath a complex overburden such as the salt canopy in the gulf of mexico however the use of tti imaging in this area is impeded by the lack of appropriate check shots and offset vsps that can constrain anisotropic parameters

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

retrieving both the impedance contrast and background velocity a global strategy for the seismic reflection problem recorded seismic reflection waveforms contain information as to the small scale variations of impedance and the large scale variations of velocity this information can be retrieved by minimizing the misfit between the recorded waveforms and synthetic seismograms as a function of the model parameters because of the different physical characters of the velocity and the impedance we update these parameters in an alternating fashion which amounts to a relaxation approach to the minimization of the waveform misfit as far as the impedance is concerned this minimization can be performed efficiently using gradient algorithms for the inversion for seismic velocities gradient methods do not work nearly as well therefore we use different minimization methods for determining impedances and velocities however the determination of the impedance and the determination of the velocity are strongly coupled relaxation is most effective when this coupling is as weak as possible weak coupling can be achieved par

geology geochemistry geochronology and economic potential of neogene volcanic rocks in the laguna pedernal and salar de aguas calientes segments of the archibarca lineament northwest argentina abstract this study presents new geochemical geochronological isotopic and mineralogical data combined with new geological mapping for a 2400 km 2 area of neogene volcanic rocks in northwestern argentina near the border with chile between 25 10 s and 25 45 s the area covers the zone of intersection between the main axis of the cordillera occidental and a set of nw se trending structures that form part of the transverse archibarca lineament this lineament has localized major ore deposits in chile e g the late eocene la escondida porphyry cu deposit and large volcanic centers such as the active llullaillaco and lastarria volcanoes on the border between chile and argentina and the neogene archibarca antofalla and cerro galan volcanoes in argentina neogene volcanic rocks in the laguna pedernal and salar de aguas calientes areas are mostly high k calc alkaline in composition and range from basaltic andesites through andesites and dacites to rhyolites magmatic temperatures and oxidation states estimated from mineral compositions range from 1000 c and fmq 1 0 1 5 in andesites to 850 c and fmq 1 5 2 0 in dacites and rhyolites the oldest rocks consist of early middle miocene andesite dacite plagioclase pyroxene phyric lava flows and ignimbrites with 40 ar 39 ar ages ranging from 17 14 0 10 ma to 11 76 0 27 ma their major and trace element compositions are typical of the andean central volcanic zone and show strong crustal contamination trends for highly incompatible elements such as cs rb th and u these rocks are geochemically grouped as sub suite 1 this widespread intermediate composition volcanism was followed in the middle late miocene by a period of more focused rhyodacitic flow dome complex formation these felsic rocks are characterized by less extreme enrichments in highly incompatible elements and increasing depletion of heavy rare earth elements these rocks are geochemically grouped as sub suite 2 the youngest rocks in this sub suite show the highest la yb ratios and are characterized by abundant hornblende phenocrysts not commonly seen in other rocks from the area in the pliocene pleistocene there was a return to more typical andesite dacite volcanism with geochemical characteristics similar to the early middle miocene lavas and are also grouped in sub suite 1 finally extensional tectonics in the quaternary led to localized outpouring of mafic basaltic andesitic to andesitic monogenetic lava flows and cones one particularly large flow the vega aguas calientes lava flow covers approximately 90 km 2 and samples form two groupings with affinities similar to the least evolved samples from sub suites 1 and 2 sub groups ba1 and ba2 respectively nd and sr isotopic compositions indicate moderate to strong crustal contamination especially in more felsic rocks and extend from 87 sr 86 sr 0 706 and end 2 4 values typical of central volcanic zone rocks to more evolved compositions 0 709 and 6 8 respectively typical of large volume ignimbrites of the altiplano puna volcanic complex and cerro galan the latter compositions are thought to be derived by extensive interaction between mantle derived arc magmas and paleozoic granitoid rocks that form much of the crustal column in this region the distinctive mineralogy and geochemistry of the sub suite 2 middle late miocene rhyodacitic flow dome complexes indicate that these magmas had higher water content than both the earlier and later sub suite 1 andesites dacites they were erupted during a period of tectonic quiescence following the quechua orogenic phase and geophysical evidence suggests that they were proximally derived from a large upper crustal magma chamber which partially collapsed to form a trap door caldera strong fumarolic alteration associated with the youngest of these felsic volcanoes cerro abra grande suggests the potential for the existence of epithermal type mineralization within the volcanic edifice or porphyry type mineralization at depth

skilful predictions of the winter north atlantic oscillation one year ahead the north atlantic oscillation profoundly influences european and north american winter weather dynamical model predictions now exhibit skill in prediction of the winter north atlantic oscillation more than one year in advance

migration velocity analysis from locally coherent events in 2 d laterally heterogeneous media part i theoretical aspects we present a new method based on migration velocity analysis mva to estimate 2 d velocity models from seismic reflection data with no assumption on reflector geometry or the background velocity field classical approaches using picking on common image gathers cigs must consider continuous events over the whole panel this interpretive step may be difficult particularly for applications on real data sets we propose to overcome the limiting factor by considering locally coherent events a locally coherent event can be defined whenever the imaged reflectivity locally shows lateral coherency at some location in the image cube in the prestack depth migrated volume obtained for an a priori velocity model locally coherent events are picked automatically without interpretation and are characterized by their positions and slopes tangent to the event even a single locally coherent event has information on the unknown velocity model carried by the value of the slope measured in the cig the velocity is e

decadal evolution of ocean thermal anomalies in the north atlantic the effects of ekman overturning and horizontal transport basin scale thermal anomalies in the north atlantic extending to depths of 1 2km are more pronounced thanthebackgroundwarmingover thelast 60years a dynamicalanalysis basedonreanalyses ofhistorical data from1965to2000suggeststhat thesethermalanomaliesare formedbyocean heat convergences augmented by the poorly known air sea fluxes the heat convergence is separated into contributions from the horizontal circulation and the meridional overturning circulation moc the latter further separated into ekman and moc transport minus ekman transport moc ekman cells the subtropical thermal anomalies are mainly controlled by wind induced changes in the ekman heat convergence while the subpolar thermal anomalies are controlled by the moc ekman heat convergence the horizontal heat convergence is generally weaker only becoming significant within the subpolar gyre these thermal anomalies often have an opposing sign between thesubtropicalandsubpolargyres associatedwithopposingchangesinthemeridionalvolumetransportdriving the ekman and moc ekman heat convergences these changes in gyre scale convergences in heat transport are probably induced by the winds as they correlate with the zonal wind stress at gyre boundaries

experimentally derived high pressure cumulates from hydrous arc magmas and consequences for the seismic velocity structure of lower arc crust 1 this contribution explores the consequences of experimentally derived ultramafic plutonic rocks for estimates of continental crust composition the formation of high pressure cumulates from primitive to evolved hydrous arc magmas was investigated in the range 0 8 1 5 gpa and 1350 800 c to provide constraints on solid assemblages that form the roots of island arc crust at pressures exceeding 0 8 gpa 25km 40 60 of ultramafic cumulates are produced to obtain andesite to dacite compositions that are typical for evolved island arc volcanic and plutonic rocks calculated cumulate densities are comparable or higher than upper mantle values while seismic velocities vp vary continuously between 7 3 and 8 km s resulting in a broad crust mantle transition the moho represents a plagioclase saturation boundary our results are consistent with seismic imaging from continental margins and island arcs revealing that beneath an active volcanic front a sharp geophysical moho signature is sometimes absent

studies of labrador sea water formation and variability in the subpolar north atlantic in the light of international partnership and collaboration abstract labrador sea water lsw the lightest contribution to north atlantic deep water nadw and one of the most prominent water masses of the subpolar north atlantic has seen remarkable changes over the past century lsw originates in the labrador sea where it is formed through wintertime ocean convection of varying intensity depth and spatial extent formation of lsw followed by its respective injection into the mid depth circulation system is mandatory for ventilating and renewing water layers of the interior ocean indispensably important for unraveling the history of variability in formation and properties of lsw as well as for mapping its large scale spreading and export are sustained physical and chemical observations from the deep ocean these observations started at the beginning of the 20th century from occasional mostly national surveys and today constitute large scale multi national collaborative efforts including a vast arsenal of sophisticated instrumentation in a historical context we revisit major milestones over the past 100 years which have established and are constantly adding to shaping today s knowledge on lsw and present first details on the latest vintage of lsw generated during the strong winter of 2013 2014 respective argo data reveal mixed layer depths greater than 1700 m marking formation of a new cold and fresh anomaly that has spread since then over the subpolar north atlantic we further summarize the on going observational efforts in the subpolar north atlantic and present a compilation of hydrographic standard lines that serve to provide top to bottom information on nadw components

changes in arctic melt season and implications for sea ice loss the arctic wide melt season has lengthened at a rate of 5 days decade 1 from 1979 to 2013 dominated by later autumn freezeup within the kara laptev east siberian chukchi and beaufort seas between 6 and 11 days decade 1 while melt onset trends are generally smaller the timing of melt onset has a large influence on the total amount of solar energy absorbed during summer the additional heat stored in the upper ocean of approximately 752 mj m 2 during the last decade increases sea surface temperatures by 0 5 to 1 5 c and largely explains the observed delays in autumn freezeup within the arctic ocean s adjacent seas cumulative anomalies in total absorbed solar radiation from may through september for the most recent pentad locally exceed 300 400 mj m 2 in the beaufort chukchi and east siberian seas this extra solar energy is equivalent to melting 0 97 to 1 3 m of ice during the summer

interdecadal variations of the thermohaline circulation in a coupled ocean atmosphere model abstract a fully coupled ocean atmosphere model is shown to have irregular oscillations of the thermohaline circulation in the north atlantic ocean with a time scale of approximately 50 years the irregular oscillation appears to be driven by density anomalies in the sinking region of the thermohaline circulation approximately 52 n to 72 n combined with much smaller density anomalies of opposite sign in the broad rising region the spatial pattern of see surface temperature anomalies associated with this irregular oscillation bears an encouraging resemblance to a pattern of observed interdecadal variability in the north atlantic the anomalies of sea surface temperature induce model surface air temperature anomalies over the northern north atlantic arctic and northwestern europe

the impact of labrador sea temperature and salinity variability on density and the subpolar amoc in a decadal prediction system labrador sea density variability is important for atlantic meridional overturning circulation amoc dynamics and hence decadal variability in the atlantic we investigate whether temperature or salinity dominate top 500m interannual labrador sea density variability in gridded observations an assimilation of the observations and a set of multi annual hindcasts we find that salinity dominates in the observations and assimilation in the hindcasts salinity remains dominant for the first year but from year three these revert to the same temperature dominance seen in the underlying climate model this is due to damping of the interannual salinity variability possibly caused by unrealistically large convection that develops crucially the hindcasts have high correlation skill in temperature salinity throughout but no skill in density dynamic sea level or the subpolar amoc due to the incorrect drivers this highlights the importance of correctly simulating both the sign and magnitude of temperature salinity variability in a prediction system

high sr y magmas reflect arc maturity high magmatic water content and porphyry cu mo au potential examples from the tethyan arcs of central and eastern iran and western pakistan the temporal and geochemical evolution of arc magmatism that culminated in porphyry cu mo au deposit formation has been studied in three separate neo tethyan arc systems in central and eastern iran and western pakistan porphyry cu au deposits in the lut block of eastern iran formed in the middle eocene at the end of a period of extensive paleocene eocene volcanism porphyry cu mo deposits in the kerman belt of central iran formed in the middle miocene at the end of a period of voluminous eocene oligocene volcanism and porphyry cu au deposits in the chagai belt of western pakistan formed in four pulses during the eocene early miocene middle late miocene and late miocene pliocene after a prolonged period of arc magmatism that began in the late cretaceous and is still active in each region the late porphyry related magmas are more geochemically evolved and more hydrous as evidenced by the presence of hornblende phenocrysts than the preceding volcanic rocks we suggest that this reflects maturation of the arc magmatic system over a period of tens of millions of years leading to the generation of more evolved volatile rich magmas at later stages of the arc s history high magmatic water contents are a prerequisite for the shallow crustal emplacement of arc magmas and the subsequent generation of potentially ore forming subvolcanic magmatic hydrothermal systems it is thus suggested that the fertility of arc magmas within a given arc terrane can be assessed by observing the relative timing of plutonic suites later suites are more prospective noting the common presence of hornblende or biotite phenocrysts indicating high magmatic water contents and through lithogeochemical fingerprinting of magmatic fractionation processes relatively high sr y and la yb ratios and eun eu ratios 1 indicating abundant early hornblende fractionation and suppression of plagioclase crystallization in hydrous magmas

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

magmatic evolution and porphyry epithermal mineralization in the taftan volcanic complex southeastern iran abstract the taftan volcanic complex is located above the makran subduction zone in sistan and baluchestan province southeastern iran the earliest volcanic activity at taftan started in the late miocene 8 ma with eruption of andesitic to dacitic lava onto a cretaceous to eocene volcanic and sedimentary paleosurface 20 km to the northwest of the current volcanic edifice later plio pleistocene volcanism consisted of voluminous andesitic and dacitic lavas and pyroclastic flows 3 1 to 0 4 ma taftan and the neighbouring bazman volcano are the southeasternmost and youngest manifestations of arc related volcanism in iran which began with the eocene miocene urumieh dokhtar magmatic arc udma in northwest and central iran and extends into western pakistan chagai arc major porphyry cu mo au deposits are associated with miocene to pliocene intrusive rocks in the kerman section of the eocene neogene urumieh dokhtar magmatic arc in southeastern iran e g sar cheshmeh meiduk and at reko diq and saindak in the late cretaceous quaternary chagai arc in western pakistan in a gap of 300 km between these two belts several porphyry and epithermal prospects are exposed in the miocene pliocene sections of the taftan volcanic complex including the kharestan 6 10 0 80 ma and bidester porphyry epithermal cu au deposits 4 3 ma and the siah jangal epithermal au deposit late miocene in addition several argillic to advanced argillic and fumarolic alteration zones occur in plio pleistocene volcanic rocks around the current volcanic edifice these deposits have received limited exploration electron microprobe analyses of amphibole magnesio hastingsite phenocrysts and magnetite ilmenite mineral pairs from the taftan and bazman volcanic rocks indicate a change of crystallization temperature and magmatic oxidation state from 1000 c and fmq 1 in andesitic rocks to 900 c and fmq 2 in dacitic rocks magmatic water content was 4 wt as indicated by the ubiquitous presence of amphibole phenocrysts major and trace element compositions of the taftan and bazman volcanic rocks show calc alkaline to high k calc alkaline affinity with relative depletions of nb ta and ti and enrichments of large ion c elements lile th and u on normalized diagrams these trace element patterns including listric shaped normalized rare earth element profiles and relatively high sr y and la yb ratios are similar to those of fertile miocene igneous rocks from the kerman belt and chagai arc and suggest that the taftan suite in particular should be prospective for porphyry cu ore formation regionally there is no clear geochemical difference between the neogene kerman belt rocks which are thought to post date the onset of collision between the afro arabian and eurasian plates late oligocene to earliest miocene and the subduction related bazman taftan and chagai belt magmas the porphyry deposits formed in these distinct settings are also virtually indistinguishable this suggests that most of the processes affecting the geochemistry and metallogeny of the magmas in both settings take place in the lithosphere albeit that the ultimate source of the magmas is in the supra subduction zone asthenospheric mantle wedge in collisional environments subduction related material previously crystallized in the deep lithosphere is simply being remobilized

an anatomy of the cooling of the north atlantic ocean in the 1960s and 1970s abstractin the 1960s and early 1970s sea surface temperatures in the north atlantic ocean cooled rapidly there is still considerable uncertainty about the causes of this event although various mechanisms have been proposed in this observational study it is demonstrated that the cooling proceeded in several distinct stages cool anomalies initially appeared in the mid 1960s in the nordic seas and gulf stream extension before spreading to cover most of the subpolar gyre subsequently cool anomalies spread into the tropical north atlantic before retreating in the late 1970s back to the subpolar gyre there is strong evidence that changes in atmospheric circulation linked to a southward shift of the atlantic itcz played an important role in the event particularly in the period 1972 76 theories for the cooling event must account for its distinctive space time evolution the authors analysis suggests that the most likely drivers were 1 the great salinity anomaly of the late 1960s 2 an earlier

the evolution of aqueous vapor from silicate melts effect on oxygen fugacity abstract the simplest possible aqueous vapor evolved from an iron bearing magma under normal conditions is an h 2 o h 2 mixture hydrogen is produced by the oxidation of fe ii to fe iii by water in the magma yielding an increase in f o 2 equations are derived which model this mass transfer process the resulting differential equation expresses the change in magmatic f o 2 as a function of a change in n 1 h 2 o the vapor evolution progress variable the calculations demonstrate that in this simple scheme very iron poor magmas h 2 o feo are required to produce significant increases in magmatic f o 2 the incremental increase in o 2 during vapor evolution becomes progressively smaller as o 2 increases with this process becoming highly inefficient as the hematite stability field is approached other more complete processes involving meteoric water assimilation of altered rocks and subsolidus processes may produce the observed increase in f o 2 inferred to have occurred in systems of normal iron contents in low iron systems such as the high silica rhyolitic magmas associated with climax type porphyry molybdenum systems high oxygen fugacities may be obtained by this mechanism

propagation pathways of classical labrador sea water from its source region to 26 n 1 more than two decades of hydrography on the abaco line east of the bahamas at 26 n reveals decadal variability in the salinity of classical labrador sea water clsw despite the long distance from its source region in the north atlantic ocean hydrographic time series from the labrador sea and from the abaco line show a pronounced step like decrease in salinity between 1985 and 1995 in the labrador sea and between 1995 and 2010 at the abaco line suggesting a time lag between the two locations of approximately 9 years the amplitude of the anomaly at the abaco line is 50 of the amplitude in the labrador sea a similar time lag and reduction of amplitude is found in the high resolution ofes model in which salinity anomalies can be observed propagating through the deep western boundary current as well as through a broad interior pathway on its way south to the abaco line the clsw becomes 8 standard deviations saltier due to isopycnal mixing with mediterranean outflow water mow climatological data in the north atlantic suggests that the mixing ratio of mow to clsw at the abaco line is 1 4 and that no variability in mow is required to explain the observed variability at the abaco line the data studied here suggest that decadal clsw anomalies stay relatively coherent while getting advected despite the important role of interior pathways

a multimodel study of sea surface temperature and subsurface density fingerprints of the atlantic meridional overturning circulation abstractthe atlantic meridional overturning circulation amoc is an important component of the north atlantic climate system here simulations from 10 coupled climate models are used to calculate patterns of sea surface temperature sst and subsurface density change associated with decadal amoc variability the models are evaluated using observational constraints and it is shown that all 10 models suffer from north atlantic deep water transports that are too shallow although the biases are least severe in the community climate system model version 4 ccsm4 in the models that best compare with observations positive amoc anomalies are associated with reduced labrador sea stratification and increased midocean 800 1800 m densities in the subpolar gyre maximum correlations occur when amoc anomalies lag labrador sea stratification and subsurface density anomalies by 2 6 yr and 0 3 yr respectively in all 10 models north atlantic warming follows positive amoc anomalies but the patterns and magnitud

offset and angle domain common image point gathers for shot profile migration prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially cost effective for sparse shot wide azimuth geometries the interpretation of offset as the displacement between the downward propagating shot wavefield and upward propagating receiver wavefield enables us to extract offset domain common image point cip gathers during shot profile migration the offset domain gathers can then be transformed to the angle domain with a radial trace mapping originally introduced for shot geophone migration the computational implications of this procedure include both the additional cost of multioffset imaging and an implicit transformation from shot geophone to midpoint offset coordinates although this algorithm provides a mechanism for imaging angle dependent reflectivity via shot profile migration for sparse shot geometries the fundamental problem of shot aliasing may severely impact the quality of cip gathers

iterative resolution estimation in least squares kirchhoff migration we apply iterative resolution estimation to least squares kirchhoff migration reviewing the theory of iterative optimization uncovers the common origin of different optimization methods this allows us to reformulate the pseudo inverse model resolution and data resolution operators in terms of effective iterative estimates when applied to kirchhoff migration plots of the diagonal of the model resolution matrix reveal low illumination areas on seismic images and provide information about image uncertainties synthetic and real data examples illustrate the proposed technique and confirm the theoretical expectations

a decadal prediction case study late twentieth century north atlantic ocean heat content an ensemble of initialized decadal prediction dp experiments using the community climate system model version 4 ccsm4 shows considerable skill at forecasting changes in north atlantic upper ocean heat content and surface temperature up to a decade in advance coupled model ensembles were integrated forward from each of 10 different start dates spanning from 1961 to 2006 with ocean and sea ice initial conditions obtained from a forced historical experiment a coordinated ocean ice reference experiment with interannual forcing core ia which exhibits good correspondence with late twentieth century ocean observations from the north atlantic subpolar gyre spg region north atlantic heat content anomalies from the dp ensemble correlate highly with those from the core ia simulation after correcting for a drift bias in particular theobservedlarge rapid rise in spgheatcontentin themid 1990sis successfullypredicted in the ensemble initialized in january of 1991 a budget of spg heat content from the core ia experiment sheds light on the origins of the 1990s regime shift and it demonstrates the extent to which low frequency changes in ocean heat advection related to the atlantic meridional overturning circulation dominate temperature tendencies in this region similar budgets from the dp ensembles reveal varying degrees of predictive skill in the individual heat budget terms with large advective heat flux anomalies from the south exhibiting the highest correlation with core ia the skill of the dp in this region is thus tied to correct initialization of ocean circulation anomalies while external forcing is found to contribute negligibly and for incorrect reasons to predictive skill in this region over this time period

angle domain common image gathers for migration velocity analysis by wavefield continuation imaging we analyze the kinematic properties of offset domain common image gathers cigs and angle domain cigs adcigs computed by wavefield continuation migration our results are valid regardless of whether the cigs were obtained by using the correct migration velocity they thus can be used as a theoretical basis for developing migration velocity analysis mva methods that exploit the velocity information contained in adcigs we demonstrate that in an adcig cube the image point lies on the normal to the apparent reflector dip that passes through the point where the source ray intersects the receiver ray the image point position on the normal depends on the velocity error when the velocity is correct the image point coincides with the point where the source ray intersects the receiver ray starting from this geometric result we derive an analytical expression for the expected movements of the image points in adcigs as functions of the traveltime perturbation caused by velocity errors by applying this ana

the geotectonic history of the makran and adjacent areas of southern iran abstract the makran mountain range in southern iran has been entirely covered by regional mapping on a scale of 1 250 000 but in contrast to the mapping of oman on the other side of the gulf the recent mapping is little known the cenozoic accretionary prism in the south fronts onto a mesozoic melange zone representing earlier subduction and to the north of this is an eastwards tapering microcontinental sliver which is followed by a zone of largely intact mesozoic ophiolite complexes to the north of this lies the jaz murian depression a desert expanse with no bedrock outcrop the sanandaj sirjan bajgan dur kan microcontinental sliver which extends from turkey through the zagros to the makran is one of a number of microcontinents which detached from gondwana no later than the early triassic nw iran yazd tabas lut birk helmand farah during the mesozoic these were enclosed by tracts of ocean now represented by ophiolites and the sectors closed at different times ranging from early cretaceous to end palaeogene an analogy is drawn with the present day mediterranean the sistan ocean in the east was infilled with an immense thickness of abyssal turbidites during the eocene before it closed the field evidence indicates that there was a second cenozoic accretionary prism here but sedimentation ceased after the eocene on its collision with the back of the main makran prism this eastern sistan trough now completely occluded is compared with the still open tract separating the makran from oman at the present time and its northern extension which has been similarly occluded by collision beneath the zagros some residual very shallow inland seas persisted inland from the makran through the neogene the occurrence of blueschists in the inner ophiolite belt of the makran is discussed abyssal turbidite sedimentation continued in the main southern zone of the makran into the early miocene to be succeeded by thick shallow water sequences including reefal limestones intense tectonic dislocation at the end of the miocene was accompanied by a shift of the subduction front to its present position out in the indian ocean and uplift leading to the deposition of spectacular pliocene pleistocene fanglomerates

crustal forensics in arc magmas abstract the geochemical characteristics of continental crust are present in nearly all arc magmas these characteristics may reflect a specific source process such as fluid fluxing common to both arc magmas and the continental crust and or may reflect the incorporation of continental crust into arc magmas either at source via subducted sediment or via contamination during differentiation resolving the relative mass contributions of juvenile mantle derived material versus that derived from pre existing crust of the upper plate and providing these estimates on an element by element basis is important because 1 we want to constrain crustal growth rates 2 we want to quantitatively track element cycling at convergent margins and 3 we want to determine the origin of economically important elements and compounds traditional geochemical approaches for determining the contributions of various components to arc magmas are particularly successful when applied on a comparative basis studies of suites from multiple magmatic systems along arcs for which differentiation effects can be individually constrained can be used to extrapolate to potential source compositions in the lesser antilles arc for example differentiation trends from individual volcanoes are consistent with open system evolution however such trends do not project back to a common primitive magma composition suggesting that differentiation modifies magmas that were derived from distinct mantle sources we propose that such approaches should now be complemented by petrographically constrained mineral scale isotope and trace element analysis to unravel the contributing components to arc magmas this innovative approach can 1 better constrain true end member compositions by returning wider ranges in geochemical compositions among constituent minerals than is found in whole rocks 2 better determine magmatic evolution processes from core rim isotopic or trace element profiles from the phases contained in magmas and 3 constrain rates of differentiation by applying diffusion controlled timescales to element profiles an example from nguaruhoe volcano new zealand underscores the importance of such a microsampling approach showing that mineral isotopic compositions encompass wide ranges that whole rock isotopic compositions are consequently simply element weighted averages of the heterogeneous crystal cargo and that open system evolution is proved by core rim variations in sr isotope ratios nguaruhoe is just one of many systems examined through microanalytical approaches the overwhelming conclusion of these studies is that crystal cargoes are not truly phenocrystic but are inherited from various sources the implication of this realization is that the interpretation of whole rock isotopic data including the currently popular u series needs careful evaluation in the context of petrographic observations

a differential semblance criterion for inversion of multioffset seismic reflection data mean square error leading to least squares inversion of multioffset reflection seismograms is insensitive to velocity trend information except in the immediate vicinity of a kinematically correct model in contrast differential semblance retains sensitivity to velocity trend changes over a wide range of models the differential semblance criterion combines mean square error with the mean square differences of inverted models from data sets at neighboring shot positions or offsets or slownesses differential semblance compares model estimates at nearby acquisition parameters which are similar even when the model velocity trends are incorrect because the method inverts the data so that the estimated model amplitudes are meaningful simple differences between the unstacked model estimates give a reliable measure of velocity error a mathematical investigation indicates that the differential semblance criterion is smooth and convex over a large range of velocity models numerical simulation using synthetic data sets verifies this contention

subaqueous pyroclastic flows and ignimbrites an assessment an assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary hot gas rich pyroclastic flows mass flows which resulted from the transformation of gassupported flows into water supported ones and secondary mass flows carrying redeposited pyroclastic debris based on subaerial pyroclastic flows the term pyroclastic flow should be restricted to demonstrably hot gas rich mass flows of pyroclastic debris using this definition very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described in the majority of these cases the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate the only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the ordovician nearshore shallow marine ignimbrites of ireland and wales and miocene ignimbrites of southwest japan resulting from the passage of subaerially erupted pyroclastic flows into shallow water other possible examples are near vent dense clast deposits in the donzurobo formation of japan possible submarine intra caldera ponded ignimbrite successions in california and wales and near vent pumiceous deposits of ramsay island wales all other purported cases are either clearly the result of water supported mass flow transportation and deposition debris avalanches debris flows turbidity currents or lack adequate supporting evidence regarding the heat state or the palaeoenvironment only the shallow marine ignimbrites of ireland and wales show adequate evidence of welding but even these could have been nearly wholly exposed above sea level when welding occurred we conclude that when pyroclastic flows enter water they are generally disrupted explosively and or ingest water and transform into water supported mass flows and we suggest the various scenarios in which this occurs there is no evidence to suggest that welding in wholly subaqueous environments is common

migration by extrapolation of time dependent boundary values migration of an observed zero offset wavefield can be performed as the solution of a boundary value problem in which the data are extrapolated backward in time this concept is implemented through a finite difference solution of the two dimensional acoustic wave equation all depths are imaged simultaneously at time 0 the imaging condition and all dips right up to vertical are correctly migrated numerical examples illustrate this technique in both constant and variable velocity media

accommodation of arabia eurasia convergence in the zagros makran transfer zone se iran a transition between collision and subduction through a young deforming system 1 at iranian longitude the arabian plate is moving northward relative to eurasia 20 mm yr 1 according to gps to the east this relative motion is accommodated by northward subduction under the e w makran emerged accretionary prism to the west it is accommodated partly by the zagros fold and thrust belt and partly by the alborz kopet dagh deforming zones further north this work investigates the nnw striking transition zone that connects zagros and makran the minab zendan fault system satellite images and structural and geomorphic field observations show a distributed deformation pattern covering a wide domain five north to nw trending major faults were identified they exhibit evidence for late quaternary reverse right lateral slip and correspond to two distinct fault systems the western one transferring the zagros deformation to the makran prism and the eastern one northward transferring the deformation to the alborz kopet dagh tectonic study and fault slip vector analyses indicate that two distinct tectonic regimes have occurred successively since the miocene within a consistent regional ne trending compression 1 an upper miocene to pliocene tectonic regime characterized by partitioned deformation between reverse faulting and en echelon folding 2 a ne trending 1 axis transpressional regime homogeneously affecting the region since upper pliocene the change is contemporaneous with major tectonic reorganization regionally recorded therefore this study provides evidence for active deformation that is not localized but distributed across a wide zone it accommodates the convergence and transfers it from collision to subduction by transpressional tectonics without any partitioning process in the present day period

tectonic magmatic and metallogenic evolution of the tethyan orogen from subduction to collision abstract this paper reviews the tectonic magmatic and metallogenic history of the tethyan orogen from the carpathians to indochina focus is placed on the formation of porphyry cu mo au deposits as being the most characteristic mineral deposit type formed during both subduction and collisional processes in this region relatively little is known about the history of the paleotethys ocean which opened and closed between gondwana and eurasia in the paleozoic and few ore deposits are preserved from this period the neotethyan ocean opened in the permian early triassic as the cimmerian continental fragments the cores of turkey iran tibet and indochina rifted from the northern gondwana margin and drifted northwards these microcontinents docked with the eurasian margin at various points in the mesozoic and cenozoic and formed a complex archipelago involving several small back arc basins and remnants of the paleotethyan ocean the main neotethyan ocean and these smaller basins were largely eliminated by collision with india and africa arabia in the early eocene and early mid miocene respectively although neotethyan subduction continues beneath the hellenic arc and the makran the majority of porphyry type deposits are found in association with neotethyan subduction mainly in the mesozoic and paleogene and syn to post collisional events in the mid paleogene to neogene they are found throughout the orogen but some sections are particularly well endowed including the carpathians balkans rhodopes eastern turkey lesser caucasus nw iran se iran sw pakistan southern tibet and se tibet indochina other sections that appear barren may reflect deeper levels of erosion young sedimentary cover or lack of exploration although there may also be real reasons for low prospectivity in some areas such as minimal subduction e g the western mediterranean region or lithospheric underthrusting as proposed in western tibet over the last decade improved geochronological constraints on the timing of ore formation and key tectonic events have revealed that many porphyry deposits that were previously assumed to be subduction related are in fact broadly collision related some forming in back arc settings in advance of collision some during collision and others during post collisional processes such as orogenic collapse and or delamination of subcontinental mantle lithosphere while the formation of subduction related porphyries is quite well understood collisional metallogeny is more complex and may involve a number of different processes or sources these include melting of orogenically thickened crust previously subduction modified lithosphere including metasomatized mantle underplated mafic rocks or lower crustal arc plutons and cumulates or upwelling asthenosphere e g in response to delamination slab breakoff back arc extension or orogenic collapse the most fertile sources for syn and post collisional porphyry deposits appear to be subduction modified lithosphere because these hydrated lithologies melt at relatively low temperatures during later tectonomagmatic events and retain the oxidized and relatively metalliferous character of the original arc magmatism unusually metallically enriched lithospheric sources do not seem to be required but the amount of residual sulfide phases in these rocks may control metal ratios e g cu au in subsequent magmatic hydrothermal ore deposits relatively au rich deposits potentially form in these settings as observed in the carpathians e g rosia montan turkey kisladag copler and iran sari gunay dalli although the majority of syn and post collisional porphyries are cu mo rich and resemble normal subduction related deposits e g in the gangdese belt of southern tibet this similarity extends to the associated igneous rocks which being derived from subduction modified sources largely retain the geochemical and isotopic character of those original arc magmas while still retaining a broadly calc alkaline character these rocks may extend to mildly alkaline shoshonitic compositions and may display adakite like trace element signatures high sr y and la yb ratios reflecting melting of deep crustal garnet amphibolitic sources but they are otherwise hard to distinguish from normal subduction related magmas small post collisional mafic alkaline volcanic centers are common throughout the orogen but for the most part appear to be barren however similar rocks in other post subduction settings around the world are associated with important alkalic type porphyry and epithermal au cu deposits and the potential for discovery of such deposits in the tethyan orogen should not be overlooked

locally and remotely forced subtropical amoc variability a matter of time scales mechanisms driving the north atlantic meridional overturning circulation amoc variability at low frequency are of central interest for accurate climate predictions although the subpolar gyre region has been identified as a preferred place for generating climate timescale signals their southward propagation remains under consideration complicating the interpretation of the observed time series provided by the rapid climate change meridional overturning circulation and heatflux array western boundary time series rapid mocha wbts program in this study we aim at disentangling the respective contribution of the local atmospheric forcing from signals of remote origin for the subtropical low frequency amoc variability we analyze for this a set of four ensembles of a regional 208s 558n eddy resolving 1 128 north atlantic oceanic configuration where surface forcing and open boundary conditions are alternatively permuted from fully varying realistic to yearly repeating signals their analysis reveals the predominance of local atmospherically forced signal at interannual time scales 2 10 years whereas signals imposed by the boundaries are responsible for the decadal 10 30 years part of the spectrum due to this marked timescale separation we show that although the intergyre region exhibits peculiarities most of the subtropical amoc variability can be understood as a linear superposition of these two signals finally we find that the decadal scale boundary forced amoc variability has both northern and southern origins although the former dominates over the latter including at the site of the rapid array 26 58n

a role of the atlantic ocean in predicting summer surface air temperature over north east asia we assess the ability of the depresys3 prediction system to predict the summer jjas surface air temperature over north east asia depresys3 is based on a high resolution ocean atmosphere coupled climate prediction system 60 km in the atmosphere and 25 km in the ocean which is full field initialized from 1960 to 2014 26 start dates we find skill in predicting surface air temperature relative to a long term trend for 1 and 2 5 year lead times over north east asia the north atlantic ocean and eastern europe depresys3 also reproduces the interdecadal evolution of surface air temperature over the north atlantic subpolar gyre and north east asia for both lead times along with the strong warming that occurred in the mid 1990s over both areas composite analysis reveals that the skill at capturing interdecadal changes in north east asia is associated with the propagation of an atmospheric rossby wave which follows the subtropical jet and modulates surface air temperature from europe to eastern asia we hypothesise that this circumglobal teleconnection pattern is excited over the atlantic ocean and is related to atlantic multi decadal variability and the associated changes in precipitation over the sahel and the subtropical atlantic ocean this mechanism is robust for the 2 5 year lead time for the 1 year lead time the pacific ocean also plays an important role in leading to skill in predicting sat over northeast asia increased temperatures and precipitation over the western pacific ocean was found to be associated with a pacific japan like pattern which can affect east asia s climate

kirchhoff modeling inversion for reflectivity and subsurface illumination because of its computational efficiency prestack kirchhoff depth migration is currently one of the most popular algorithms used in 2 d and 3 d subsurface depth imaging nevertheless kirchhoff algorithms in their typical implementation produce less than ideal results in complex terranes where multipathing from the surface to a given image point may occur and beneath fast carbonates salt or volcanics through which ray theoretical energy cannot penetrate to illuminate underlying slower velocity sediments to evaluate the likely effectiveness of a proposed seismic acquisition program we could perform a forward modeling study but this can be expensive we show how kirchhoff modeling can be defined as the mathematical transpose of kirchhoff migration the resulting kirchhoff modeling algorithm has the same low computational cost as kirchhoff migration and unlike expensive full acoustic or elastic wave equation methods only models the events that kirchhoff migration can image kirchhoff modeling is also

noise removal by migration of time shift images abstractwhen using seismic data to image complex structures the reverse time migration rtm algorithm generally provides the best results when the velocity model is accurate with an inexact model moveouts appear in common image gathers cigs which are either in the surface offset domain or in subsurface angle domain thus the stacked image is not well focused in extended image gathers the strongest energy of a seismic event may occur at non zero lag in time shift or offset shift gathers based on the operation of rtm images produced by the time shift imaging condition the non zero lag time shift images exhibit a spatial shift we propose an approach to correct them by a second pass of migration similar to zero offset depth migration the proposed approach is based on the local poststack depth migration assumption after the proposed second pass migration the time shift cigs appear to be flat and can be stacked the stack enhances the energy of seismic events that are defocused at zero time lag

a multimodel comparison of centennial atlantic meridional overturning circulation variability a mechanism contributing to centennial variability of the atlantic meridional overturning circulation amoc is tested with multi millennial control simulations of several coupled general circulation models cgcms these are a substantially extended integration of the 3rd hadley centre coupled climate model hadcm3 the kiel climate model kcm and the max plank institute earth system model mpi esm significant amoc variability on time scales of around 100 years is simulated in these models the centennial mechanism links changes in the strength of the amoc with oceanic salinities and surface temperatures and atmospheric phenomena such as the intertropical convergence zone itcz 2 of the 3 models reproduce all aspects of the mechanism with the third mpi esm reproducing most of them a comparison with a high resolution paleo proxy for sea surface temperatures ssts north of iceland over the last 4 000 years also linked to the itcz suggests that elements of this mechanism may also be detectable in the real world

attenuation compensation for least squares reverse time migration using the viscoacoustic wave equation strong subsurface attenuation leads to distortion of amplitudes and phases of seismic waves propagating inside the earth conventional acoustic reverse time migration rtm and least squares reverse time migration lsrtm do not account for this distortion which can lead to defocusing of migration images in highly attenuative geologic environments to correct for this distortion we used a linearized inversion method denoted as qp lsrtm during the leastsquares iterations we used a linearized viscoacoustic modeling operator for forward modeling the adjoint equations were derived using the adjoint state method for back propagating the residual wavefields the merit of this approach compared with conventional rtm and lsrtm was that qp lsrtm compensated for the amplitude loss due to attenuation and could produce images with better balanced amplitudes and more resolution below highly attenuative layers numerical tests on synthetic and field data illustrated the advantages of qp lsrtm over rtm and lsrtm when the recorded data had strong attenuation effects similar to standard lsrtm the sensitivity tests for background velocity and qp errors revealed that the liability of this method is the requirement for smooth and accurate migration velocity and attenuation models

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

3d angle gathers from reverse time migration reverse time migration rtm based on directly solving the two way wave equation provides a natural way to deal with large lateral velocity variations and imposes no dip limitations on the seismic images it has become a standard migration tool for subsalt imaging in the gulf of mexico in addition the adoption of wide azimuth waz data acquisition provides better subsurface illumination and more azimuthal information which significantly aids imaging beneath complex overburdens because waz data are richer in the propagation directions of the waves recorded rtm and waz acquisition go hand in hand

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

least squares migration of incomplete reflection data a least squares migration algorithm is presented that reduces the migration artifacts i e recording footprint noise arising from incomplete data instead of migrating data with the adjoint of the forward modeling operator the normal equations are inverted by using a preconditioned linear conjugate gradient scheme that employs regularization the modeling operator is constructed from an asymptotic acoustic integral equation and its adjoint is the kirchhoff migration operator we tested the performance of the least squares migration on synthetic and field data in the cases of limited recording aperture coarse sampling and acquisition gaps in the data numerical results show that the least squares migrated sections are typically more focused than are the corresponding kirchhoff migrated sections and their reflectivity frequency distributions are closer to those of the true model frequency distribution regularization helps attenuate migration artifacts and provides a sharper better frequency distribution of estimated reflectivity the least squares migrated sections can be used to predict the missing data traces and interpolate and extrapolate them according to the governing modeling equations several field data examples are presented a ground penetrating radar data example demonstrates the suppression of the recording footprint noise due to a limited aperture a large gap and an undersampled receiver line in addition better fault resolution was achieved after applying least squares migration to a poststack marine data set and a reverse vertical seismic profiling example shows that the recording footprint noise due to a coarse receiver interval can be suppressed by least squares migration