replenishment crystal accumulation and floor aggradation in the megacrystic kameruka suite australia detailed field evidence indicates that the kameruka suite plutons of the bega batholith eastern australia grew by crystal accumulation on the floor of a magma chamber depositional features in the plutons including mafic enclave channels asymmetric enclave pillows and exotic rafts load casts and flame structures and graded and trough cross beds indicate that the pluton built progressively upward the general eastward dip of depositional features in the main pluton implies a lower western and upper eastern contact consistent with a basal granite migmatite contact in the west and a sharp hornfelsic sidewall contact in the east mafic felsic and composite dykes most common near and below the basal western contact are interpreted as conduits for magma chamber replenishment and imply open system behaviour during pluton construction textural relations are also consistent with an open system cumulate origin typically centimetre scale grains of quartz plagioclase and megacrystic alkali feldspar form a touching framework with interstices filled with smaller biotite flakes and smaller intercumulus quartz and feldspar crystals alkali feldspar megacrysts vary from euhedral and unzoned to mantled and partially replaced by plagioclase to ovoid and completely pseudomorphed by quartz albite aggregates the common occurrence of mantled and pseudomorphed alkali feldspar in mafic enclaves and in hybrid tonalitic rocks forming the matrix to enclave swarms suggests that replacement or resorption of granitic primocrysts was associated with mafic replenishments the occurrence of all megacryst types at outcrop scale implies extended alkali feldspar crystallization in different parts of the chamber thorough stirring during or after periodic replenishment and final settling in a cumulate mush the bulk composition of the cumulate mush represented by granodiorite cannot represent the emplaced magma compositional variation can be modelled by variable degrees of crystal accumulation from a parental silica rich melt represented by the silicic dykes as dykes periodically fed the magma chamber crystals accumulated on the floor and more evolved melts probably erupted from its roof thus the average composition of the magma and the cumulus minerals may have remained relatively constant and the sublinear chemical trends that typify the kameruka suite simply reflect differing proportions of melt and cumulate material sublinear chemical trends can also be explained by a restite model however the distinctive ba light rare earth element and zr spikes at high silica can be explained only by a cumulate model which also explains why the low silica granites of the suite share the same chemical characteristics as the high silica granites

dehydration melting of amphibolite at 10 kbar the effects of temperature and time we have simulated the dehydration melting of a natural low k calcic amphibolite 67 4 hornblende 32 5 anorthite in piston cylinder experiments at 10 kbar and 750 1000 c for 1 9 days the solidus temperature is lower than 750 c garnet appears at 850 c the overall reaction is hb p l cpx al hb ca hb ga opx three stages of reaction are 1 melting dominated by the growth of clinopyroxene and garnet with little change in composition of liquid or garnet 2 a reversal of this reaction between 875 c and 900 c with decreases in the amounts of liquid and garnet and 3 a large increase in liquid along with the loss of hornblende and decrease of plagioclase while clinopyroxene and garnet increase garnet is enriched in pyrope and zoned from fe cores to mg edges range 3 mol pyrope liquid composition is enriched first in an to 950 c and then in ab the liquids are more calcic and aluminous than natural tonalites which is attributed to the plagioclase composition an90 the formation of peraluminous liquid from the metaluminous amphibolite is caused by anorthite not h2o saturated conditions the results are consistent with an amphibolite phase diagram with relatively high solidus temperatures in the garnet absent field 900 1000 c but with a solidus backbend at 7 9 kbar coincident with the garnet in boundary hornblende breakdown due to garnet formation in a closed system must make h2o available for h2o undersaturated melting right down to the h2o saturated solidus below 700 c which defines a large low temperature pt area where hydrous granitoid melts can be generated with residual garnet and hornblende

mountain waves over mont blanc influence of a stagnant boundary layer abstract a stationary mountain wave embedded in southwesterly flow over mont blanc in the alps was observed simultaneously by three research aircraft and three types of remote sensing gps dropsondes airborne light detecting and ranging lidar and rapid scan satellite imagery these observations provide a basis for testing linear and nonlinear theories of how mountain waves over complex terrain are controlled by the ambient wind profile especially the effects of a low level stagnant layer and the jet stream aloft the layer of blocked flow near the ground reduced the amplitude of the wave generation the strong wind and weak stability in the upper troposphere forced the wave into a decaying evanescent state in spite of this evanescent condition no lee waves were observed the authors resolve this paradox by demonstrating that the stagnant layer below 3 km played an additional role it was able to absorb downward reflected waves preventing the formation of a resonant cavity linear theory inclu

gravity wave excitation during the coastal transition of an extreme katabatic flow in antarctica abstractthe offshore extent of antarctic katabatic winds exerts a strong control on the production of sea ice and the formation of polynyas in this study we make use of a combination of ground ba

katabatic jumps in the martian northern polar regions abstract martian polar regions host active regional wind circulations such as the downslope katabatic winds which develop owing to near surface radiative cooling and sloped topography many observations stratigraphy from radar profiling frost streaks spectral analysis of ices concur to show that aeolian processes play a key role in glacial processes in martian polar regions a spectacular manifestation of this resides in elongated clouds that forms within the polar spiral troughs a series of geological depressions in mars polar caps here we report mesoscale atmospheric modeling in martian polar regions making use of five nested domains operating a model downscaling from horizontal resolutions of twenty kilometers to 200 m in a typical polar trough we show that strong katabatic jumps form at the bottom of polar troughs with an horizontal morphology and location similar to trough clouds large vertical velocity up to 3 m s and temperature perturbations up to 20 k propitious to cloud formation this strongly suggests that trough clouds on mars are caused by katabatic jumps forming within polar troughs this phenomena is analogous to the terrestrial loewe phenomena over antarctica s slopes and coastlines resulting in a distinctive wall of snow during katabatic events our mesoscale modeling results thereby suggest that trough clouds might be present manifestations of the ice migration processes that yielded the internal cap structure discovered by radar observations as part of a cyclic step process this has important implications for the stability and possible migration over geological timescales of water ice surface reservoirs and overall for the evolution of mars polar caps over geological timescales

origin of biotite apatite rich enclaves achala batholith argentina the achala batholith of argentina contains very unusual layered enclaves containing up to 30 apatite and 50 biotite in some layers this modal mineralogy produces bulk rock compositions that cannot represent liquids having as little as 29 sio2 and up to 8 p2o5 nor can the enclaves represent metasedimentary xenoliths because 1 none of the precambrian wall rocks has these compositions 2 none of the metasedimentary xenoliths present within the batholith shows any degree of transition to the mica apatite rich enclaves 3 the compositions and textures in the enclaves are inconsistent with metasediments 4 a geochronological study of zircon from an enclave gives an age of 368 2 ma the exact age of zircons in the granitic host rocks for these reasons we conclude that the enclaves are neither xenoliths of precambrian wall rocks nor restite of a precambrian source the identical age of the enclave and the host granites coupled with textural mineralogical and bulk rock characteristics of the enclaves indicates that the enclaves are magmatic segregations i e cumulates the f rich nature of the stubby shaped apatites and biotites indicates a high f content of the magma parental to the enclaves we infer that the viscosity of the melt was lowered sufficiently to allow cumulates to form in spite of the granitic composition of the melt

constraints from zircon u pb ages o and hf isotopic compositions on the origin of neoproterozoic peraluminous granitoids from the jiangnan fold belt south china zircon textures and micro chemical compositions precisely record the origin and petrogenesis of granitoids which are crucial for evaluating crustal growth and reworking thermal and geodynamic evolution zircons in peraluminous granitoids from the three largest 820 ma complexes guibei yueyang and jiuling in the jiangnan fold belt in south china are used to constrain their sources and petrogenetic processes zircons in the guibei granitoids have complex internal structures nearly all magmatic and inherited zircons have similar ehf 6 8 to 5 6 and 18o values 8 8 11 6 and dominantly lie between ehf evolution vectors for a crust created between 1 7 and 2 1 ga suggesting that the guibei granitoids were produced by partial melting of recycled heterogeneous supracrustal material however the yueyang granitoids contain zircons with high ehf 0 5 to 9 7 and relatively low 18o values 5 9 8 4 and two stage model ages of 1 1 1 8 ga and thus may have been formed by melting of mafic rocks from the lower crust the jiuling granitoids and their enclaves contain more complex zircons with more variable ehf 7 2 to 9 7 and 18o values 7 0 10 6 and lie along the mixing trend between the above proposed infracrustal and supracrustal granitoids therefore the neoproterozoic peraluminous granitoids in the jiangnan fold belt were produced by melting and mixing of continental crust compared with extremely low 4 and negative 18o values of neoproterozoic igneous zircons formed in its northern active continental margin the high 18o peraluminous granitoids in the southeastern yangtze block are considered to have been formed by melting of hydrothermally unaltered continental crust triggered by asthenosphere upwelling in the nanhua back arc basin

microgranular enclaves as evidence of rapid cooling in granitoid rocks the case of the los pedroches granodiorite iberian massif spain microgranular enclaves from the los pedroches granodiorite lpg los pedroches batholith iberian massif spain have sr nd isotopic and mineral chemical compositions close to those of their host this similarity is not related to restite unmixing as indicated by the igneous textures of the enclaves a number of other geological and geochemical lines of evidence including the high ree and hfse contents of the microgranular enclaves relative to the host granitoid strongly suggest that this similarity cannot be explained by magma mixing alternatively a crystallization process by rapid cooling within the host granitoid magma could explain the geochemical and textural characteristics of the microgranular enclaves including shape grain size mineralogy texture chemistry and sr nd isotopic composition such a crystallization occurred at the walls of the magma conduits through which the granitic magmas were emplaced in the upper crust this process should be considered as an alternative hypothesis to magma mixing for the generation of some microgranular enclaves especially where no direct evidence exists for the presence of basic magmas coeval with granitoids and where there is a lack of isotopic contrast between hosts and enclaves as the process is favoured by feeder dyke related emplacement we suggest that abundance of microgranular enclaves can be related to the mechanism of emplacement of granitoid bodies

origin of high potassium talc alkaline i type granitoids many i type granitoid magmas are generated through partial melting of older metaigneous rocks and the compositions of such melts are broadly calc alkaline and metaluminous these melts are granitic to tonalitic and result from thermal extremes in their lower crustal source regions data on the experimental partial melting of common crustal rocks suggest that high k i type granitoid magmas can be derived only from the partial melting of hydrous calc alkaline to high k calc alkaline mafic to intermediate metamorphic rocks in the crust because of their low k2o contents metabasaltic rocks of all kinds are unsuitable as sources and models that propose mixing of mantle derived basaltic magmas and crustal melts are also inadequate there is no requirement that i type calc alkaline magmatism be related in any way to subduction processes

melting of continental crust during subduction initiation a case study from the chaidanuo peraluminous granite in the north qilian suture zone the chaidanuo granite batholith is a similar to 500 km 2 homogeneous high level intrusion in the north qilian oceanic suture zone three types of enclaves have been recognized including 1 supracrustal xenoliths 2 biotite gneiss that represents restite of the upper crustal melting and 3 coeval mantle derived mafic magmatic enclave mme the batholith consists dominantly of peraluminous biotite monzogranite with sio2 69 73 wt and a cnk 1 05 1 28 and shows geochemical affinity with the upper continental crust e g enrichment of large ion lithophile elements liles k rb u th pb depletion of high field strength elements hfses nb ta ti p eu and sr and enriched sr sr 87 sr 86 i 0 731 to 0 744 nd epsilon nd t 6 0 to 7 1 isotopes zircon u pb dating indicates that this batholith formed at 516 505 ma coeval with the mmes 510 ma which represent the early stage of seafloor subduction in the north qilian suture zone the hf isotopic composition of the mme epsilon hf t 6 0 to 2 1 is more depleted than that of the host granite epsilon hf t 14 8 to 4 7 suggesting mixing of mantle and crust derived melts the inherited zircon cores in the host granite yield an age peak at similar to 750 ma with a few detritals of 591 1683 ma zircons from a biotite gneiss enclave yield a protolith age of 744 ma and a metamorphic melting event at 503 ma sr nd isotopic modeling reveals that the batholith was generated by melting of neoproterozoic granitic rocks with the addition of 10 18 mantle derived magma therefore peraluminous granite can be produced by melting of crustal materials heated by mantle derived magmas during the early stage of subduction initiation at the site of a prior passive continental margin c 2014 elsevier ltd all rights reserved

some aspects of the effect of surface friction on flows over mountains the effect of surface friction on flow over mountains in stratified fluids is investigated using a two dimensional version of the naval research laboratory s non hydrostatic coupled ocean atmosphere mesoscale prediction system coamps without surface friction flow over a mountain attains a maximum speed at the surface on the lee slope with surface friction the flow speed vanishes at the surface and reaches a maximum near the top of the boundary layer bl corresponding to this wind distribution is a shallow layer of very large vertical wind shear beneath the jet maximum and a weaker but deeper sheared layer elsewhere this strong shear generates maximum turbulent kinetic energy tke at the jet maximum region meanwhile the buoyancy effect associated with the mountain gravity wave inhibits the production of the tke above the jet maximum region the combined effects of shear and buoyancy lead to a very shallow bl on the lee slope in general surface friction reduces the amplitude of mountain gravity waves comparison of the flow fields with the outline of the bl height indicates that flow characteristics correspond closely to the distribution of the bl height it is hypothesized that the reduction in mountain wave amplitude in the presence of surface friction is due to the reduction in the slope of the bl height as compared to the terrain height for narrower and or higher mountains the bl height exhibits a secondary peak on the lee side that further modifies the wave simulations using the bl height as a solid mountain without surface friction confirm that characteristics of flow over the mountain are associated with the distribution of bl height rather than the terrain height field as the non dimensional mountain height increases the magnitude of the effect of surface friction decreases due to decreasing bl depth on the lee side with the result that the bl height profile becomes closer to the terrain height field the effect of surface friction on asymmetric mountains is also investigated without surface friction the pressure drag shows distinctive reduction with a secondary peak on the downstream side but the effect is less when the secondary peak is on the upstream side with surface friction all three mountains have similar pressure drag corresponding to their similar bl height profiles copyright 2003 royal meteorological society

effects of inversion height and surface heat flux on downslope windstorms abstractsimulations are presented focusing on the role of temperature inversions in controlling the formation and strength of downslope wind storms three mechanisms are examined depending on the relative height of the inversion with respect to the mountain and the stability of vertically propagating mountain waves for low level inversions flows are generated that closely resemble a reduced gravity shallow water hydraulic response with a large vertical displacement of the inversion on the lee side of the mountain for higher level inversion cases simulated flows more closely followed a stratified hydraulic behavior with the inversion acting as a rigid reflective lid in the third mechanism downslope winds were forced by a self induced critical layer located below the inversion height the presence of the inversion in this case had little effect on the resulting downslope winds observations made on the falkland islands show that downslope windstorms may preferentially occur in early morning even withou

evolution of the bangong nujiang tethyan ocean insights from the geochronology and geochemistry of mafic rocks within ophiolites abstract the bangong nujiang suture zone bnsz is located in the central tibetan plateau and represents the relict of the bangong nujiang tethyan ocean bnto this paper presents zircon u pb ages and whole rock geochemical and sr nd isotope data for the ophiolitic rocks from the rutog dongco dongqiao amdo and dengqen areas from west to east in the bnsz zircon u pb ages obtained from five gabbros and one leucogabbro from the five areas are 169 2 167 2 187 2 184 2 177 3 and 164 2 ma respectively mafic rocks gabbros and basalts in the bnsz can be divided into morb like and oib type based on geochemical data the morb like rocks are tholeiitic and can be further divided into n and e morb subtypes marked by depleted and flat ree patterns respectively all morb like rocks show supra subduction zone ssz geochemical affinities such as mild enrichment in the large ion lithophile elements and depletion in the high field strength elements coupled with high and positive whole rock e nd t values 8 1 to 5 4 the oib type rocks which formed in the early cretaceous 132 108 ma are exposed in the dongco dongqiao and tarenben areas and they consist mostly of alkali basalts with within plate geochemical characteristics and positive e nd t values 5 9 to 4 5 on the basis of these new data combined with information from the literature we further support that the bnto was an intra oceanic arc backarc basin that existed between the north lhasa subterrane nlt and the south qiangtang subterrane sqt during the early middle jurassic this basin may have been active until the early cretaceous when the oib type basalts erupted

a new theory for downslope windstorms and trapped mountain waves abstractlinear mountain gravity waves forced by a nonlinear surface boundary condition are derived for a background wind that is null at the surface and increases smoothly to reach a constant value aloft and for a constant buoyancy frequency in this configuration the mountain waves have a critical level just below the surface that is dynamically controlled by the surface and minimum richardson number j when the flow is very stable and when the depth over which dissipations act is smaller than the mountain height this critical level dynamics easily produces large downslope winds and foehns the downslope winds are more intense when the stability increases and much less pronounced when it decreases when j goes below 1 in contrast the trapped lee waves are very small when the flow is very stable start to appear when and can become pure trapped waves e g not decaying downstream when the flow is unstable for for the trapped waves these results are explained by the fact that the critical l

do s type granites commonly sample infracrustal sources new results from an integrated o u pb and hf isotope study of zircon in contrast to i type granites which commonly comprise infracrustal and supracrustal sources s type granites typically incorporate predominantly supracrustal sources the initial aim of this study was to identify the sources of three scottish caledonian 460 ma s type granites kemnay cove and nigg bay by conducting oxygen u pb and hf isotope analyses in zircon in order to characterise one potential end member magma involved in the genesis of the voluminous late caledonian 430 400 ma i type granites field whole rock geochemical and isotopic data are consistent with the generation of the s type granites by melting their dalradian supergroup country rocks while hf isotope compositions of magmatic zircon u pb data of inherited zircons and high mean zircon 18o values of 9 0 2 7 2sd and 9 8 2 0 for the kemnay and cove granites support this model the nigg bay granite contains zircons with much lower 18o values 6 8 2 1 similar to those found in scottish i type granites this suggests that the nigg bay granite contains low 18o material representing either altered supracrustal material or more likely an infracrustal source component with mantle like 18o mixing trends in plots of 18o vs ehf for s type granite zircons indicate involvement of at least two sources in all three granites this pilot study of scottish caledonian s type granites demonstrates that while field and whole rock geochemical data are consistent with local melting of only supracrustal sources the oxygen isotopic record stored in zircon reveals a much more complex petrogenetic evolution involving two or more magma sources

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

topographic control of stratified flows upstream jets blocking and isolating layers optimal solutions to the nonlinear hydrostatic boussinesq equations are developed for steady density stratified topographically controlled flows characterized by blocking and upstream influence these flows are jet like upstream of an isolated obstacle and are contained within an asymmetric thinning stream tube that is accelerated as it passes over the crest a stagnant nearly uniform density isolating layer surrounded by a bifurcated uppermost streamline separates the accelerated flow from an uncoupled flow above the flows are optimal in the sense that for a given stratification the solutions maximize the topographic rise above the blocking level required for hydraulic control while minimizing the total energy of the flow hydraulic control is defined mathematically by the asymmetry of the accelerated flow as it passes the crest a subsequent analysis of the taylor goldstein equation shows that these sheared non uniformly stratified flows are indeed subcritical upstream critical at the crest and supercritical downstream with respect to gravest mode long internal waves the flows obtained are relevant to arrested wedge flows selective withdrawal stratified towing experiments tidal flow over topography and atmospheric flows over mountains

the mixing of magmas in plutonic and volcanic environments analogies and differences abstract magma mixing processes have been widely recognized in both the plutonic and volcanic environments but the quality and quantity of information that can be extracted from the two environments are substantially different understanding the advantages and limits associated with the study of plutonic and volcanic rocks is essential to establish precise methodological approaches to build the most complete conceptual model by merging information from these two complementary igneous environments in this work we review magmatic interaction processes in the plutonic and volcanic environments by considering several aspects of these geological phenomena in particular we first briefly report on the structural and geochemical evidence for magma mixing in both plutonic and volcanic rocks with the aim to provide a general picture of this natural phenomenon successively we discuss some recent results about magma mixing achieved using the concepts from chaos theory and discuss their potential impact on magma differentiation finally we attempt to build a general picture of this igneous process by merging present day information from both the plutonic and volcanic environments it emerges from the general picture that the time spent by the magmatic system in the molten or partially molten state is the crucial factor for the preservation of the fingerprints of magma mixing in the two environments we propose a conceptual model that may be useful to understand what kind of information we can obtain from volcanic and plutonic rocks and ultimately to maximize our knowledge about magma mixing

on the diurnal variation of mountain waves abstract the diurnal variation of mountain waves and wave drag associated with flow past mesoscale ridges has been examined using the coupled ocean atmosphere mesoscale prediction system coamps and an analytical boundary layer bl model the wave drag exhibits substantial diurnal variation in response to the change in the atmospheric bl characteristics such as the bl depth shape factor and stability during daytime a convective bl develops characterized by a shallow shear layer near the surface and a deep well mixed layer aloft both of which tend to decrease the wave drag as a result the convective bl could significantly weaken mountain waves and reduce the momentum flux by up to 90 near the surface the flow pattern resembles a potential flow with a surface wind maximum located near the ridge crest during nighttime a shallow stable bl develops and the modulation of wave drag by the stable nocturnal bl is governed by the bl froude number fr if the bl flow is supercritical the drag incr

elemental and sr nd isotope geochemistry of microgranular enclaves from peralkaline a type granitic plutons of the emeishan large igneous province sw china abstract microgranular enclaves are common within intermediate to felsic granitic rocks that have i and s type affinity however they are rare within alkaline anorogenic granitoids of a type affinity the permian 260 ma emeishan large igneous province elip of southwest china contains two peralkaline silica saturated a type granitic plutons that host microgranular enclaves the enclaves from the baima pluton are intermediate in composition and have lower sio 2 and higher tio 2 cao and mg sio 2 57 2 to 63 0 wt tio 2 0 8 to 1 8 wt cao 1 7 to 3 3 wt mg 28 to 44 than their host sio 2 62 6 to 67 8 wt tio 2 0 5 to 1 4 wt cao 0 4 to 1 8 wt mg 15 to 31 the enclaves from the taihe pluton are more felsic sio 2 63 8 to 71 3 wt tio 2 0 3 to 0 6 wt cao 0 6 to 2 3 wt mg 8 to 22 but are still less evolved than their host sio 2 69 8 to 75 1 wt tio 2 0 2 to 0 6 wt cao 0 4 to 0 8 wt mg 3 to 12 in both cases the enclaves have very similar end t values baima end t 2 8 to 3 2 taihe end t 1 0 to 2 0 as their hosts baima end t 3 0 to 3 2 taihe end t 1 5 to 1 9 the major and trace element trends of the enclave host pairs suggest that fractional crystallization occurred and that element diffusion was likely minimal the enclaves are interpreted as entrained accumulations of early formed crystals of a silicic magma which was originally produced by fractional crystallization of a mafic magma

megabreccia shedding from modern low relief carbonate platforms nicaraguan rise single channel seismic reflection data from the margins of lowrelief 150 250 m measured from edge of bank to basin carbonate platforms on the northern nicaraguan rise reveal complex seismic intervals consisting of mounded chaotic seismic facies interspersed with discontinuous parallel laminated seismic facies we interpret that these intervals contain megabreccias chaotic facies and sandy turbidites parallel laminated facies one megabreccia is exposed on the sea floor displaying an overall fan shape having individual blocks measuring nearly 300 m across and 110 m high the source area consists of a scalloped embayment with a headwall scarp 180 m high reflections within the platform are sharply truncated by this escarpment this single megabreccia is 120 m thick and extends 27 km along slope and 16 km out into the basin other megabreccias within the basin have individual blocks measuring 400 m across rocks from dredge hauls are a mixture of shallow and deep water facies shallow water facies consist of mixed skeletal grain stones and halimeda packstones deep water facies are massive chalks chalks with shallow water skeletal grains and chalk block breccias this indicates that the megabreccias formed as a result of bank margin collapse during which the ensuing debris flow eroded into slope and basin facies mixing rock types together we speculate that bank margin collapse events resulting in megabreccia formation may have been seismically triggered and we emphasize that these large scale mass wasting events occurred along margins of low relief carbonate platforms

identifying the crystal graveyards remaining after large silicic eruptions abstract the formation of crystal poor high silica rhyolite via extraction of interstitial melt from an upper crustal mush predicts the complementary formation of large amounts of typically unerupted silicic cumulates however identification of these cumulates remains controversial one hindrance to our ability to identify them is a lack of clear predictions for complementary chemical signatures between extracted melts and their residues to address this discrepancy we present a generalized geochemical model tracking the evolution of trace elements in a magma reservoir concurrently experiencing crystallization and extraction of interstitial melt our method uses a numerical solution rather than analytical thereby allowing for various dependencies between crystallinity partition coefficients for variably compatible and or incompatible elements and melt extraction efficiency results reveal unambiguous fractionation signatures for the extracted melts while those signatures are muted for their cumulate counterparts our model is first applied to a well constrained example searchlight pluton usa and provides a good fit to geochemical data we then extrapolate our results to understanding the relationship between volcanic and plutonic silicic suites on a global scale utilizing the navdat database to identify crystal accumulation or depletion signatures for each suite we suggest that many large granitoids are indeed silicic cumulates although their crystal accumulation signature is expected to be subtle

interactions between dioritic and granodioritic magmas in mingling zones plagioclase record of mixing mingling and subsolidus interactions in the gesiniec intrusion ne bohemian massif sw poland dioritic and granodioritic rocks coexist in the gesiniec intrusion in sw poland showing typical relationships in many mafic felsic mingling zones worldwide such as dioritic syn putonic dykes and microgranular enclaves within granodioritic host plagioclase zonation from granodioritic rocks suggests late stage mixing probably with dioritic magma whereas no magma mixing is recorded in plagioclase from dioritic rocks the diorites seem to show effects of interaction with evolved leucocratic melts derived from granodiorite not with the granodioritic melt itself we conclude that the diorites compositions were modified after their emplacement within the granodioritic host when the diorites were essentially solidified and injection of evolved melt from granodiorite did not involve marked modification of plagioclase composition compositional zoning patterns of plagioclase in diorites can be modeled by closed system fractional crystallization interrupted by resorption induced probably by decompression granodioritic plagioclase seems to be affected by the same resorption event plagioclase that crystallized in dioritic magma before the resorption does not record interaction between dioritic and granodioritic magmas suggesting that both magmas evolved separately

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

fractional crystallization of primitive hydrous arc magmas an experimental study at 0 7 gpa differentiation of mantle derived hydrous basaltic magmas is a fundamental process to produce evolved intermediate to sio2 rich magmas that form the bulk of the middle to shallow continental and island arc crust this study reports the results of fractional crystallization experiments conducted in a piston cylinder apparatus at 0 7 gpa for hydrous calc alkaline to arc tholeiitic magmas fractional crystallization was approached by synthesis of starting materials representing the liquid composition of the previous higher temperature experiment temperatures ranged from near liquidus at 1 170 c to near solidus conditions at 700 c h2o contents varied from 3 0 to more than 10 wt the liquid line of descent covers the entire compositional range from olivine tholeiite 1 170 c to high silica rhyolite 700 c and evolves from metaluminous to peraluminous compositions the following crystallization sequence has been established olivine clinopyroxene plagioclase spinel orthopyroxene amphibole titanomagnetite apatite quartz biotite anorthite rich plagioclase and spinel are responsible for a marked increase in sio2 content from 51 to 53 wt at 1 040 c at lower temperatures fractionation of amphibole plagioclase and fe ti oxide over a temperature interval of 280 c drives the sio2 content continuously from 53 to 78 wt largest crystallization steps were recorded around 1 040 c and at 700 c about 40 of ultramafic plutonic rocks have to crystallize to generate basaltic andesitic liquids and an additional 40 of amphibole gabbroic cumulate to produce granitic melts andesitic liquids with a liquidus temperature of 1 010 c only crystallize 50 over an 280 c wide range to 730 c implying that such liquids form mobile crystal mushes 50 crystals in long lived magmatic systems in the middle crust allowing for extensive fractionation assimilation and hybridization with periodic replenishment of more mafic magmas from deeper magma reservoirs

pre eruptive reheating during magma mixing at quizapu volcano and the implications for the explosiveness of silicic arc volcanoes effusive explosive transitions are observed in volcanoes erupting water rich magmas that lack mineralogical evidence of degassing suggesting that gas loss occurred rapidly and ascent was fast despite the high viscosity of rhyodacitic to rhyolitic melts here we show that pre eruptive heating of water rich silicic magma by mixing with hot recharge in subvolcanic chambers controls the effusive explosive transition volcan quizapu chile emitted a 5 km3 mingled dacite andesite lava flow in a d 1846 1847 that was 130 c hotter than the 5 km3 of the same dacite that lead to a plinian eruption in a d 1932 we explain the suppression of explosive fragmentation in the 1846 1847 lavas by enhanced syneruptive magma degassing as a consequence of late reheating following mixing with andesite recharge higher magma temperatures led to the transitioning into effusive eruptive behavior by significantly accelerating volatile diffusion and lowering melt viscosity which facilitated bubble nucleation growth and coalescence while also inhibiting brittle fragmentation thus recharge by mafic magmas in subvolcanic magma chambers may reduce the risk of explosive eruptions in cases where heat can be efficiently transferred to cold volatile rich silicic magmas

oxygen isotope systematics of the banda arc low delta o 18 despite involvement of subducted continental material in magma genesis abstract this study reports new laser fluorination oxygen isotope data for 60 volcanic rocks and 15 sediments distributed over the whole length of the banda arc eastern indonesia the melt oxygen isotope values 18omelt were calculated from phenocryst 18o data using theoretical and empirical mineral melt fractionation factors the 18omelt of individual volcanic centers within the arc varies between 5 57 and 6 54 except for serua 18omelt 6 13 7 48 and ambon 18omelt 8 12 8 38 these 18omelt values are up to 2 lower than new and previously published oxygen isotope data obtained on whole rock powders by conventional methods we attribute this discrepancy to post emplacement low temperature alteration and or to a systematic deviation of the bulk analysis sediment 18owr calculated from the 18o carbonate and silica fractions both measured conventionally range between 12 9 and 24 2 the low 18omelt values excluding serua and ambon overlap with the mantle range and are in agreement with simple two component source mixing models that predict 1 5 addition of subducted continental material to a depleted morb type source in the sub arc mantle this percentage is consistent with previous models based on sr nd pb th he hf isotope data however correlations between incompatible trace element ratios and oxygen isotope systematics requires involvement of partial melts derived from subducted continental material as the major slab component rather than bulk addition the contribution of hydrous fluids from both subducted altered oceanic crust and continental material is probably of minor importance magma mantle wedge interaction models could account for the observed low 18o signatures but predicted effects are difficult to distinguish from models without mantle wedge interaction assimilation of arc crust material is thought to be important for the high 18omelt values of serua and ambon afc modelling suggests up to 20 and 80 assimilation at serua and ambon respectively inclusions of meta sedimentary material and whole rock sr nd isotopes point to assimilation processes at nila but this probably had little effect on the 18o of phenocrysts which record original source values according to radiogenic isotope data magma sources in the banda arc are the most heavily influenced by fluxes of subducted continental material among currently active oceanic island arcs hence the results of this study suggest that high 18o 6 5 in arc lavas are difficult to reconcile with addition of subducted components to magma sources but must reflect assimilation of arc crustal material

the combined effects of water and fluorine on the viscosity of silicic magmas abstract the newtonian viscosity of water plus fluorine bearing silicate melt of haplogranitic composition hpg8 has been determined viscosities of hpg8 melt with addition of 3 11 and 4 25 wt of f and up to 3 wt h2o have been obtained using a micropenetration technique in the interval 109 74 to 1011 84 pa s and temperatures varying from 370 to 700 c at ambient pressure determination of the temperature dependence of viscosity from this and previous studies permits the parameterization of the viscosity of melts containing water and fluorine having similar composition within a 0 3 log units standard error the viscosity of water bearing f rich haplogranitic samples is represented by a modified vogel fulcher tammann vft equation which provides a non arrhenian description of the temperature dependence of the viscosity the results of this study indicate that taken individually or together both h2o and f have a strong and similar effect on the viscosity of sio2 rich compositions this similarity between f2o 1 and h2o greatly simplifies the task of predicting viscosity for volatile rich highly silicic magmas the low viscosities of hydrous fluorine bearing granitic melts favour efficient crystallization fractionaction paths for these liquids controlling degassing paths and consequently the eruptive behaviour numerical simulations of eruptive events normally do not take into account the contribution of fluorine this may introduce a significant error in the description of the fluid dynamic properties of magma and therefore in the accurate prediction of eruptive scenarios as well as in hazard assessment studies fluorine unlike water remains dissolved in the melt at high concentrations and low confining pressures the incorporation of fluorine data and the modelling of fluorine bearing viscosity data are therefore of fundamental importance for simulations of magma dynamics and prediction of eruptive scenarios

high silica granites terminal porosity and crystal settling in shallow magma chambers abstract high silica 70 wt sio2 granites hsgs are important carriers of highly incompatible elements thus understanding their origin is relevant to understanding how the composition of the continental crust evolves we examined a large scale geochemical study of plutons in the peninsular ranges batholith in southern california usa to better understand the petrogenetic relationships between hsgs and the batholith using highly incompatible and compatible elements we show that hsgs represent residual liquids within a felsic 69 72 wt sio2 magmatic crystal mush at crystal fractions of 50 60 and residual liquid fractions of 40 50 trace element systematics show that separation of the hsg liquid from the crystal mush is inefficient such that no more than 70 80 of the hsg is fully extracted and the remaining greater than 20 30 remains trapped in cumulate mush we find little evidence of more efficient liquid crystal segregation which suggests that compaction induced segregation may be too slow to be important on a large scale instead the terminal porosity of 20 30 coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension 0 74 which may indicate that crystal settling perhaps in the form of hindered settling drives segregation of viscous silicic melts and crystals unlike compaction settling operates on timescales of 1 10 ky fast enough to generate large volumes of hsg and complementary cumulates with trapped melt before magma chambers freeze many felsic plutons may thus be cumulates but because of trapped melt they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent the approach here using a combination of highly incompatible and compatible elements provides a way of identifying and quantifying trapped melt fractions finally we show that hsgs appear to form only in the shallow crust

an intercomparison of t rex mountain wave simulations and implications for mesoscale predictability abstractnumerical simulations of flow over steep terrain using 11 different nonhydrostatic numerical models are compared and analyzed a basic benchmark and five other test cases are simulated in a two dimensional framework using the same initial state which is based on conditions during intensive observation period iop 6 of the terrain induced rotor experiment t rex in which intense mountain wave activity was observed all of the models use an identical horizontal resolution of 1 km and the same vertical resolution the six simulated test cases use various terrain heights a 100 m bell shaped hill a 1000 m idealized ridge that is steeper on the lee slope a 2500 m ridge with the same terrain shape and a cross sierra terrain profile the models are tested with both free slip and no slip lower boundary conditions the results indicate a surprisingly diverse spectrum of simulated mountain wave characteristics including lee waves hydraulic like jump features and gravity wave breaking the vertical v

assembly of the lhasa and qiangtang terranes in central tibet by divergent double subduction abstract integration of lithostratigraphic magmatic and metamorphic data from the lhasa qiangtang collision zone in central tibet including the bangong suture zone and adjacent regions of the lhasa and qiangtang terranes indicates assembly through divergent double sided subduction this collision zone is characterized by the absence of early cretaceous high grade metamorphic rocks and the presence of extensive magmatism with enhanced mantle contributions at ca 120 110 ma two jurassic cretaceous magmatic arcs are identified from the caima duobuza rongma kangqiong amdo magmatic belt in the western qiangtang terrane and from the along tso yanhu daguo baingoin daru tso magmatic belt in the northern lhasa terrane these two magmatic arcs reflect northward and southward subduction of the bangong ocean lithosphere respectively available multidisciplinary data reconcile that the bangong ocean may have closed during the late jurassic early cretaceous most likely ca 140 130 ma through arc arc soft collision rather than continent continent hard collision subduction zone retreat associated with convergence beneath the lhasa terrane may have driven its rifting and separation from the northern margin of gondwana leading to its accretion within asia

structural criteria for identifying granitic cumulates abstractcumulates are igneous rocks that reflect relative concentration of crystals and or loss of melt and that therefore did not crystallize entirely from a magma of their current whole rock composition however this definition does not help to identify cumulates and so the problem is to determine whether the current whole rock composition reflects cumulate processes which is where structural criteria can be useful identification of cumulates in granitoids can be difficult especially in the absence of major whole rock compositional differences between cumulate and host structural and structural mineralogical criteria diagnostic of or at least consistent with granitic cumulates include 1 locally high concentrations of particular minerals relative to concentrations in the bulk of the intrusion 2 abundant euhedral crystals in contact at least with regard to cores that touched before any overgrowths and consequent molding of minerals about each other occurred 3 abundant antecrysts or mantle

trace element indicators of crystal accumulation in silicic igneous rocks abstract if fractional crystallization coupled with some crustal assimilation afc is the dominant process for generating evolved magmas in the earth s crust large quantities of igneous cumulates must be present in the rock record however despite some reported occurrences intermediate to silicic rocks characterized by an unambiguous crystal accumulation signature have remained elusive the signature is expected to be subtle in viscous silicic magmas and sensitive criteria need to be developed to test whether these cumulates are truly rare or simply difficult to discern we propose models that use specific trace element concentrations and ratios zr ba eu eu and zr hf within a well constrained framework for the physical extraction of liquid from crystals mostly occurring between 50 and 70 vol crystals to identify silicic cumulates the results of these models indicate that crystal accumulation or melt extraction has occurred in multiple natural examples around the world both in plutonic and volcanic realms however these examples were selected because they represent conditions that are most favorable high amount of melt extraction well constrained initial liquid compositions for unambiguously identifying cumulate residue in many cases we show that the trace element signature for crystal accumulation will remain largely concealed in addition the different liquid lines of descent related to the various tectonic settings on earth dry reduced in hot spots divergent margins and wetter more oxidizing in arc environments will lead to different trace element evolution and each criterion must be applied on a case by case basis despite these limitations the undeniable but subtle presence of silicic cumulates in the mid to upper crust lends support to the idea that igneous differentiation is dominantly driven by melt extraction from partially crystalline reservoirs

age and petrogenesis of a type granites in the middle segment of the bangonghu nujiang suture tibetan plateau abstract during geological investigations conducted over the past several years the authors found a group of a type granites in the middle segment of the bangonghu nujiang suture on the tibetan plateau these granitic plutons occur as stocks with exposed areas of less than 1 km 2 and lithologically include biotite granite and granodiorite porphyry which had intruded into cretaceous sedimentary rocks petrogeochemically the a type granites contain high sio 2 levels varying from 68 62 75 36 wt moreover they contain relatively high fe 2 o 3 t 0 86 5 39 wt and low al 2 o 3 12 76 15 54 wt levels and are weak peraluminous to metaluminous a trace element n morb normalized spider diagram showed apparent enrichment of the large ion lithophile elements lile rb th u k and pb with marked depletions of ba and sr the high field strength elements hfse nb ta and ti were sharply depleted with relative enrichment of zr and hf these signatures are characteristic of a type granite the granite samples had high rare earth element ree contents with ree 122 37 291 19 ppm light ree were rich relative to heavy ree with lree hree 4 89 9 58 and negative eu anomalies were sharp with eu varying from 0 14 0 5 and a mean value of 0 34 their chondrite normalized rare earth element distribution patterns appear as gently right dipping v types zircon u pb laicpms dating for three granitic plutons yielded weighted mean ages of 109 6 1 4 ma mswd 3 7 112 3 0 51 ma mswd 0 21 and 113 73 0 5 ma mswd 0 21 indicating that they formed in the late stage of the early cretaceous epoch the nd sr and pb isotopic results showed that the granites were rich in radiogenic isotopes the 87 sr 86 sr and i sr ratios varied from 0 719842 0 786395 and 0 706900 0 710378 respectively the 143 nd 144 nd ratios were from 0 512123 0 512392 with relatively large negative e nd values 3 37 to 10 34 the 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios ranged from 18 703 19 070 15 680 15 732 and 39 121 39 576 respectively exhibiting isotopic signatures typical of crustal sources all of the data demonstrated unanimously that these granites were derived from partial melting of arc basaltic rocks underplated in the lower crust during oceanic crust subduction the high temperature heat source for melting of anhydrous basaltic rocks of the lower crust was from upwelling asthenosphere through slab windows formed as a result of slab break off during post collisional extension of the orogenic zone

trace element and isotopic evidence for two types of crustal melting beneath a high cascade volcanic center mt jefferson oregon mt jefferson is an andesite dacite composite volcano in the cascade range the locus of andesite and dacite dominated volcanism for at least 1 million years a large trace element data set for mt jefferson and its surrounding mafic volcanic platform effectively rules out any fractionation based model fc or afc for the generation of mt jefferson andesites several incompatible element zr nb y concentrations decrease in the range from basalt to andesite and then increase in the range from andesite to rhyodacite others ba rb la th remain constant or show a slight increase in the basalt to andesite range with modest increases from andesite to rhyodacite systematic variations in highly incompatible element ratios such as ba la and rb th suggest magma mixing dominates the trace element signatures rhyodacites are isotopically uniform 87sr 86sr 0 70325 0 70343 206pb 204pb 18 75 18 85 18o 6 3 0 3 whereas andesite and dacite are more variable 87sr 86sr 0 70291 0 70353 206pb 204pb 18 59 18 86 18o 6 0 0 6 typical basaltic andesite has 87sr 86sr 0 70326 0 70358 206pb 204pb 18 78 18 85 and 18o 5 9 0 4 sr rich 1 000 ppm basaltic andesite is more variable 87sr 86sr 0 70300 0 70360 206pb 204pb 18 70 18 89 18o 5 9 0 4 the data define mixing arrays with one end member at 87sr 86sr 0 7029 206pb 204pb 18 59 another at rhyodacite and a third at 87sr 86sr 0 7036 206pb 204pb 18 89 the first end member is defined by sr rich 800 1 200 ppm andesite with high al2o3 and low k2o ba and rb th the third one by k2o and very sr rich 2 000 ppm shoshonite isotopic data for basalts in northern oregon preclude any fractionation relationship between basalt and either rhyodacite or sr rich andesite e g the minimum 206pb 204pb ratio in basalt is 18 83 considered in light of geophysical models for the cascades these data suggest two types of crustal melting beneath the arc rhyodacite may be generated at 25 30 km depth by partial melting of arc basalt like amphibolite at 850 900 c sr rich andesite may be formed by partial melting of depleted morb like mafic granulite at 35 45 km depth at 1 000 1 100 c experimental and ree evidence supports these interpretations as does the restriction of sr rich andesite in the cascades to the area south of the 100 mw m2 heat flow contour between mt jefferson and mt hood thick crust and high heat flow are necessary to produce such andesite

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

hybridization between felsic and mafic magmas in calc alkaline granitoids a case study in northern sardinia italy abstract two examples of felsic mafic association resulting from a magma mingling mechanism have been studied in carboniferous calc alkaline granitoids from sardinia using mineralogical and geochemical techniques 1 the centimetric to decimetric magmatic mafic enclaves from the reversely zoned tonalitic santa restituta pluton this type of enclave which is common in calc alkaline granitoids represents blobs of mafic magma incorporated into a silicic host magma 2 the osidda mafic complex about one kilometre in diameter enclosed in the benettuti granodiorite this study intends to compare these two types of felsic mafic association in order 1 to clarify the nature of the interaction processes which occurred between the two magmatic components 2 to test the influence of the degree of fragmentation of the mafic component into the felsic matrix on the intensity of such processes the santa restituta enclaves sre and the osidda mafic complex omc exhibit the same general mineral assemblage plagioclase biotite hornblende quartz this assemblage is similar to that of the corresponding host granitoids however the sre and the omc are characterized by a greater abundance of biotite and hornblende the mineralogical study reveals the presence of two types of crystals the first type corresponds to minerals typical of the mafic or the felsic component in the mafic magma they are represented by remnants of an rich plagioclase by hornblende clots presumably pyroxene relicts and by orthopyroxene observed only in one facies of the omc these crystals represent remnants of phenocrysts present in the mafic component prior to the mingling event in the felsic component the first type of crystals is represented by quartz ocelli which are sometimes incorporated in the mafic magma as xenocrysts surrounded by a reaction rim of biotite and hornblende the second type comprises minerals which are found indiscriminantly in both magmatic components and which formed during the mingling event mingling minerals they include plagioclase an52 35 biotite hornblende quartz mineralogical data indicate that thermal equilibrium occurred between the mafic magma and the felsic matrix that equilibration was reached in the sre is shown by the compositional similarity of the mingling minerals of the enclaves and their host rocks however due to a lesser degree of fragmentation thermal equilibration was not reached in the omc geochemical data however do reveal close relationships between the two magmas which appear therefore to have both been hybridized by mutual chemical interaction a chemical comparison between the sre and the omc shows that in both cases the same qualitative interaction mechanisms operated between the host granitoids and either a voluminous mafic body osidda or a highly fragmented mafic component santa restituta enclaves however the intensity of hybridization is minor in the omc as compared with the sre it is suggested that hybridization of the host granitoids involves 1 mass to mass mixing due to disaggregation and dispersal of the mafic magma in the host granitoid resulting from mechanical stirring during the pluton s genesis from the initial meeting of the two magmas to the pluton s final emplacement 2 loss of certain elements si k rb ba li zr p nb ree which migrated towards the mafic magma through diffusion due to compositional gradients fluid transfer as a consequence the composition of the host granitoids is linked to that of their magmatic enclaves the enclaves with the lowest feo tot mgo ratios are enclosed in the least felsic granitoids and vice versa hybridization of the mafic component involves 1 mechanical transfer of crystals quartz from the host granitoid 2 enrichment in numerous elements migrating from the felsic component this is expressed mineralogically by the crystallization of numerous anhedral phases such as quartz sio2 biotite k rb h2o hornblende h2o apatite p and zircon zr 3 loss of ca and sr by the mafic component the nature of the processes of chemical migration are discussed the importance of the continuous renewal of the contact surface between the two components is emphasized the original compositions of the interacting mafic and granitic components become therefore highly modified this phenomenon can probably be generalized to apply to calc alkaline granitoids as a whole which are in fact characterized by the common occurrence of magma mingling

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

dehydration melting of a basaltic composition amphibolite at 1 5 and 2 0 gpa implications for the origin of adakites this study presents the results of dehydration melting experiments on a basaltic composition amphibolite under conditions appropriate to a hot slab geotherm 1 5 and 2 0 gpa and temperatures of 850 to 1150 c dehydration melting produces an omphacitic augite and garnet bearing residue coexisting with rhyolitic to andesitic composition melts at 1 5 gpa the amphibolite melts in two stages between 800 and 1025 c the 2 0 gpa data also define two melting stages at 2 0 gpa the first stage involves nearly modal melting of the original amphibolite minerals qtz pl amp to produce melt cpx grt during the second stage the eclogite restite melts non modally 0 86 cpx 0 14 grt 1 melt the experimental results were combined with data from the literature to generate a composite p t phase diagram for basaltic composition amphibolites over the 800 to 1100 c temperature range for pressures up to 2 0 gpa comparison of the major element compositions of the experimentally produced melts with compositions of presumed slab melts adakites shows that partial melting of amphibolite at conditions appropriate to a hot slab geotherm produces melts similar to andesitic and dacitic adakites except for significant mgo and cao depletions trace element modelling of amphibolite dehydration melting using the 2 0 gpa melting reactions produces ree abundances similar to those of adakites at 10 15 wt batch melting but the models do not reproduce the high sr y ratios characteristic of adakites taken together the major and trace element results are not consistent with the derivation of adakites by dehydration melting of the subducted slab with little or no interaction with the mantle wedge or crust if adakites are partial melts of the subducted slab they must undergo significant interaction with the mantle and or crust during which they acquire a number of their distinctive characteristics

observations and numerical simulations of subrotor vortices during t rex high resolution observations from scanning doppler and aerosol lidars wind profiler radars as well as surface and aircraft measurements during the terrain induced rotor experiment t rex provide the first comprehensive documentation of small scale intense vortices associated with atmospheric rotors that form in the lee of mountainous terrain although rotors are already recognized as potential hazards for aircraft it is proposed that these small scale vortices or subrotors are the most dangerous features because of strong wind shear and the transient nature of the vortices a life cycle of a subrotor event is captured by scanning doppler and aerosol lidars over a 5 min period the lidars depict an amplifying vortex with a characteristic length scale of 500 1000 m that overturns and intensifies to a maximum spanwise vorticity greater than 0 2 s 1 radar wind profiler observations document a series of vortices characterized by updraft downdraft couplets and regions of enhanced reversed flow that are generated in a layer of strong vertical wind shear and subcritical richardson number the observations and numerical simulations reveal that turbulent subrotors occur most frequently along the leading edge of an elevated sheet of horizontal vorticity that is a manifestation of boundary layer shear and separation along the lee slopes as the subrotors break from the vortex sheet intensification occurs through vortex stretching and in some cases tilting processes related to three dimensional turbulent mixing the subrotors and ambient vortex sheet are shown to intensify through a modest increase in the upstream inversion strength which illustrates the predictability challenges for the turbulent characterization of rotors

overlapping sr nd hf o isotopic compositions in permian mafic enclaves and host granitoids in alxa block nw china evidence for crust mantle interaction and implications for the generation of silicic igneous provinces abstract in general the mantle provides heat and or material for the generation of the silicic igneous provinces sips the rarity of mafic microgranular enclaves mmes however hampers understanding of the mantle s role in generating sips and the process of crust mantle interaction the widespread distributed mmes in the newly reported alxa sip provide an opportunity to study these processes this study integrates in situ zircon u pb age and hf o isotope analyses whole rock geochemistry and sr nd isotope results for the mmes and host granitoids in the alxa block sims zircon u pb dating reveals that there are two generations of mmes and host granitoids the mmes in the bayannuoergong batholith were formed at ca 278 ma similar to the age 280 ma of host granitoids and the mmes and host granitoids in the yamaitu pluton were formed at ca 272 270 ma all mmes have relatively low sio 2 50 7 61 4 wt and th 0 8 2 8 ppm but relatively high mgo 2 6 4 9 wt cr 23 146 ppm and ni 6 38 ppm contents compared to the host granitoids with sio 2 63 6 77 5 wt th 5 2 41 ppm mgo 0 23 2 1 wt cr 10 38 ppm and ni 5 14 ppm all mmes have whole rock sr nd and zircon hf o isotope compositions similar to their corresponding host granitoids the 280 ma mmes have lower whole rock e nd t 13 5 and higher initial 87 sr 86 sr values 0 7095 and zircon 18 o values 6 3 compared to the e nd t 11 5 initial 87 sr 86 sr values 0 7070 and zircon 18 o values 5 6 of the 270 ma mmes the occurrences of quartz xenocrysts k feldspar megacrysts corroded feldspars and acicular apatites indicate that the mmes are the products of the mixing between mantle and crust derived magmas the striking similarities in the zircon hf o isotopic compositions in both mme host granitoid pairs indicate that the granitoids and mmes have similar sources the granitoids are proposed to be mainly sourced from magmas generated by remelting of newly formed mafic rocks which were generated by earlier basaltic magmas underplating or injected into the mid to lower crust the continuing basaltic magma underplating and remelting of earlier formed mafic rocks in the mid to lower crust indicate that the mantle provided both heat and materials for the generation of the alxa sip the scenario also suggests that basaltic magma underplating may play a more important role in the crustal growth in the alxa sip than it is generally recognized in other sips

initial condition sensitivities and the predictability of downslope winds the sensitivity of downslope wind forecasts to small changes in initial conditions is explored by using 70 memberensemblesimulationsoftwoprototypicalwindstormsobservedduringtheterrain inducedrotor experiment t rex the10 weakestand 10 strongest ensemblemembersare compositedand compared for each event in the first case the 6 h ensemble mean forecast shows a large amplitude breaking mountain wave and severe downslope winds nevertheless the forecasts are very sensitive to the initial conditions because the difference in the downslope wind speeds predicted by the strong and weak member composites grows to larger than 28 m s 21 over the 6 h forecast the structure of the synoptic scale flow one hour prior to the windstorm and during the windstorm is very similar in both the weak and strong member composites wave breaking is not a significant factor in the second case in which the strong winds are generated by a layer of high static stability flowing beneath a layer of weaker mid and upper tropospheric stability in this case thesensitivitytoinitialconditionsisweakerbutstillsignificant thedifferenceindownslopewindspeeds between the weak and strong member composites grows to 22 m s 21 over 12 h during and one hour before the windstorm the synoptic scale flow exhibits appreciable differences between the strong and weakmember composites although this case appears to be more predictable than the wave breaking event neither case suggests that much confidence should be placed in the intensity of downslope winds forecast 12 or more hours in advance

petrogenesis of early cretaceous granites and associated microgranular enclaves in the xiabie co area central tibet crust derived magma mixing and melt extraction abstract multiple petrogenesis models have been proposed for granitic rocks and the mafic microgranular enclaves mmes hosted in them the mantle and crust derived magma mixing mingling process was widely suggested for the formation of mmes or the host granitoids however whether the mixing between magmas derived from different crustal sources may also form microgranular enclaves mes not restricted to mafic or the host granites remain unclear here we report petrological geochemical and zircon in situ hf o isotopic data for mes and their host granites in the northern nyima area southern qiangtang terrane sqt central tibet the host granitic rocks consist of amphibole bearing biotite granites and syenogranite minor granodiorite and aplite veins and mes comprising diorite and granodiorite host rocks and mes are contemporaneous and were generated in the early cretaceous 120 ma host granitoid samples are high k calc alkaline rocks and have high sio2 66 78 wt and low mgo 5 wt high zr 500 ppm with zr hf ratios 45 and high ba 400 ppm implying biotite and zircon concentrations combining this information with embayed feldspars curved biotites and closely spaced feldspar grains we suggest that liquid loss resulted from crystal compaction or filter pressing both the fine grained syenogranites and aplite veins exhibit high sio2 and rb sr ratios in addition to low zr hf ratios and zr and ba concentrations with remarkably negative eu anomalies indicating that they are highly differentiated melts extracted from felsic crystal mush such a crystal mush is possibly represented by the biotite granites gradual contact relationships between variable granitic phases indicate that melt extraction and crystal concentration were coeval residual melt extraction from the crystal mush was facilitated by mush remobilization resulting from magma replenishment we suggest that for the host rocks the biotite granites were mainly derived by partial melting of ancient crust and the granodiorites most likely resulted from the magma mixing mingling that might be accompanied with the loss of melts the fine grained syenogranites and aplites represent highly evolved residual melts mes are geochemically characterized by intermediate to felsic compositions sio2 56 3 67 8 wt with low mgo

influence of lee waves on the near surface flow downwind of the pennines the results of a recent field experiment focusing on the near surface pressure and flow fields downstream of the pennines in northern england are presented the main aim of the experiment is the improvement of wind forecasts downstream of orography trapped lee waves commonly occur in westerly flow in this region and during the experiment there were numerous instances of apparent flow separation indicating the formation of lee wave rotors the spatial variability of the near surface flow in these circumstances is closely linked to the positions of lee wave crests and troughs aloft and appears to be a response to pressure gradients induced by the lee waves for large amplitude waves it has been possible to demonstrate a correlation between the fractional change of the flow speed across the measurement array which if large enough may lead to flow separation and a normalized pressure perturbation amplitude for a group of lee wave cases during which the cross mountain flow is strong a rapid decrease in the scorer parameter within the lower portion of the troposphere appears to be a prerequisite for rotors to form however this does not guarantee their occurrence for a fixed scorer parameter profile idealized two dimensional simulations indicate that the lee wave induced pressure perturbation amplitude and hence the occurrence of rotors is controlled largely by the strength of the wind upstream close to the mountain top level it seems that the combination of a favourable scorer parameter profile and sufficiently strong low level winds is required for rotors to develop crown copyright 2007 reproduced with the permission of her majesty s stationery office published by john wiley sons ltd

u pb zircon geochemical and sr nd hf isotopic constraints on age and origin of jurassic i and a type granites from central guangdong se china a major igneous event in response to foundering of a subducted flat slab abstract the mesozoic geology of se china is characterized by widespread jurassic to cretaceous igneous rocks consisting predominantly of granites and rhyolites and subordinate mafic lithologies however the tectonic regime responsible for the inland jurassic granites remains controversial we report here u pb zircon ages geochemical and sr nd hf isotopic data for the nankunshan alkaline granite and the fogang granitic batholith in central guangdong mineralogical and geochemical features suggest that the fogang and nankunshan rocks are i and aluminous a type granites respectively shrimp u pb zircon analyses yield consistent ages ranging from 159 3 ma to 165 2 ma for four samples from the fogang batholith and an age of 158 5 ma for the nankunshan granite the fogang granites having i sr 0 7098 0 7136 e nd t 4 3 to 12 2 and e hf t 11 5 to 3 1 for the magmatic zircons were derived from paleoproterozoic mafic intermediate igneous protolith with minor addition of mantle derived magmas the nankunshan rocks have relatively lower i sr 0 706 0 708 higher e nd t 0 3 to 2 4 and e hf t 5 7 to 1 1 for the magmatic zircons and some oib like trace element ratios they were likely generated through extensive fractional crystallization of mantle derived alkaline parental magma associated with crustal assimilation these 160 ma i and a type granites in central guangdong were emplaced coeval with the widespread 165 155 ma i and a type granites and syenites following the initiation of intraplate basaltic and or bimodal igneous magmatism at 180 170 ma in the adjacent regions we interpret these jurassic igneous rocks as anorogenic magmatism formed during a major igneous event in response to foundering of an early mesozoic subducted flat slab beneath se china continent

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

trace element composition of igneous zircon a thermal and compositional record of the accumulation and evolution of a large silicic batholith spirit mountain nevada hafnium u th and ree content of zircons from the spirit mountain batholith in southern nevada correlate with calculated temperatures from the ti in zircon thermometer to support field and petrologic evidence of rejuvenation of crystal mush and melt extraction events during the 2 million year accumulation of the granitoid batholith marked variation in zircon composition from sample to sample from grain to grain within individual samples and from zone to zone within individual grains documents in detail a history of fluctuating conditions with repeated episodes of replenishment reheating crystal mush rejuvenation fractional crystallization and melt segregation the zircons exhibit compositional and thermal variability indicative of variations in host melt composition due to 1 melt rejuvenation mixing and fractionation 2 coeval growth of other ree rich accessory minerals and possibly 3 fluctuation in fo2