a markov model for beach changes on the holderness coast of england markov models offer an objective and quantitative method of assessing beach changes for a stretch of the holderness coast a beach classification scheme was devised and a probabilistic first order matrix model based on surveyed profile data was produced this could describe and predict transitions between beach types and between different time periods different profile types dominated different coastal locations and seasonal variations were seen in order to improve the accuracy of prediction throughout the year a second winter model was added to the original summer one although the models had been prepared independently of wave conditions a comparison of the wave record and beach transitions revealed that waves under 0 3 0 5 m high produced fairly static beaches when waves were between 0 5 and 1 0 m the beach was more dynamic and variable while waves over 1 0 m led to the depletion of the upper beach this was broadly in accordance with published theory markov models have the advantage that they can be adjusted periodically if conditions change and are thus useful for prediction on coasts for which no wave records exist

ambiguous isotopic and geochemical signatures resulting from limited melt interactions in a seemingly composite pluton a case study from the strzegom sobotka massif sudetes poland the western part of the late variscan strzegom sobotka massif exemplifies an intrusion that formed in a multi component system the system shows ambiguous isotopic and geochemical signatures and presents a seemingly composite character biotite granite with negligible amount of hornblende hbg and microgranular mafic enclaves mmes the melts responsible for forming granitic rock and its mmes were not derived from contrasting crustal and mantle sources but from different crustal domains these melts exhibit hybrid characteristics due to subsequent contamination processes the data suggest two different stages of hybridization of two geochemically distinct magmas corresponding to granite and enclaves the processes were temporally and spatially distinct heterogeneous protoliths and hybridization made these magma isotopic signatures and trace element patterns ambiguous the main mechanism involved in developing granitic rocks was fractional crystallization fc the mechanism responsible for mme composition was mixing but other local processes were also involved in rock formation generally the fc signature was not obscured by the hybrid mafic melt input this felsic mafic melt interaction was a limited one sided process granitic melt was changed by the presence of small mafic magma blobs but their influence on granite crystallization was negligible the massif is thus an ideal example of an environment where mmes coexist with a granitic body although mmes do not determine the actual composite character of the pluton the early stage of variscan pluton formation within the bohemian massif and adjacent areas was shaped by interacting mantle and crust derived melts the pluton described in this paper belongs to the late stage of variscan magmatism it is a multi component system shaped by the participation of melts derived from heterogeneous crustal domains the presence of enclaves does not explicitly indicate their dominant role in the formation of composite plutons of crust mantle origin it is decisive to determine whether the ambiguous signatures appearing in such cases truly indicate both of these sources

long term erosion of the tidal flats king sound north western australia abstract king sound in northwestern australia with a tropical semi arid climate is situated in a macrotidal tide dominated regime the shores of king sound are bordered by tidal flats that exhibit a considerable variation in geomorphology and stratigraphy erosion is the dominant geomorphic process forming the tidal flats today three types of erosion are important these are sheet cliff and tidal creek erosion tidal flat geomorphology at the local scale is an expression of which erosion type is dominant the geomorphology at regional scale is largely an expression of the extent that erosion has gone to completion in removing holocene pleistocene and bedrock stratigraphic units determination of erosion rates over the past few decades extrapolation of these rates into the past together with stratigraphic and diagenetic data point to a long term erosional history for king sound king sound itself appears to be formed largely as a result of long term lateral erosion

a numerical model for shore normal sediment size variation on a macrotidal beach this paper describes a computer simulation model which is designed to predict the selective shore normal sorting of grain sizes in the nearshore environment the model simulates wave shoaling wave height attenuation due to frictional losses and breaking using linear theory up to the break point and a breaker decay model in the surf zone peak horizontal orbital velocities at the bed are calculated from stokes second order wave theory the peak onshore and offshore velocities are used with the threshold expression of komar and miller 1975 to generate a spatial pattern of size variation of threshold grain diameter along a profile normal to the shore from deep water to the swash zone the predicted grain size is used in an hydraulic interpretation of grain size distribution on the intertidal profile based on the hydrodynamic variations over a tidal cycle on a macrotidal beach the model is successful in predicting the broad pattern of increasing grain size in the onshore direction which has been observed in nature comparisons between measured and predicted grain size distributions indicate that the predictions of the model are better than those of previous models but the model is more successful at predicting sediment size distributions than at predicting mean sizes on a beach profile

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

syn collisional felsic magmatism and continental crust growth a case study from the north qilian orogenic belt at the northern margin of the tibetan plateau abstract the abundant syn collisional granitoids produced and preserved at the northern tibetan plateau margin provide a prime case for studying the felsic magmatism as well as continental crust growth in response to continental collision here we present the results from a systematic study of the syn collisional granitoids and their mafic magmatic enclaves mmes in the laohushan lhs and machangshan mcs plutons from the north qilian orogenic belt nqob two types of mmes from the lhs pluton exhibit identical crystallization age 430 ma and bulk rock isotopic compositions to their host granitoids indicating their genetic link the phase equilibrium constraints and pressure estimates for amphiboles from the lhs pluton together with the whole rock data suggest that the two types of mmes represent two evolution products of the same hydrous andesitic magmas in combination with the data on nqob syn collisional granitoids elsewhere we suggest that the syn collisional granitoids in the nqob are material evidence of melting of ocean crust and sediment the remarkable compositional similarity between the lhs granitoids and the model bulk continental crust in terms of major elements trace elements and some key element ratios indicates that the syn collisional magmatism in the nqob contributes to net continental crust growth and that the way of continental crust growth in the phanerozoic through syn collisional felsic magmatism production and preservation is a straightforward process without the need of petrologically and physically complex processes

the influence of long waves on macrotidal beach morphology the aim of the following paper is to demonstrate that standing long waves can generate intertidal morphological features in a dissipative macrotidal setting in this environment the tidal excursion can exceed the length scales associated with long waves this extends the work of simmonds et al 1995 in which it was shown that monochromatic long waves could generate sediment convergence patterns that bore a good similarity to observed topographic features namely ridges and runnels from a field site on the belgian coast the simulation is modified to include a band of long waves and it is found that a good correspondence with real topography can still be achieved on a tidally averaged basis by allowing for a degree of uncertainty in the breaking criterion it is also argued why the observed scales are more likely to correspond with the shorter end of the long wave spectrum the simulation helps to shed light on the conditions in which such features are known to form

crystallization and hybridism in microgranitoid enclave magmas microstructural evidence microstructural evidence indicates that many microgranitoid enclaves mafic inclusions in granitoids crystallize from globules of magma that have undergone previous magma mixing hybridism the evidence includes 1 rounded xenocrysts ocelli of quartz rimmed with fine grained aggregates of early formed minerals especially mafic minerals 2 k feldspar megacrysts commonly rimmed with plagioclase rapakivi structure and 3 corroded cores dendritic overgrowths and calcic spikes in plagioclase initial quenching of a magma globule in felsic magma involves rapid temperature equilibration which causes a high rate of nucleation of minerals precipitating from the enclave magma at the time followed by a period of slow cooling during which the nucleation and growth rates of later crystallizing minerals are similar to the much slower rates prevailing in the granitic melt this may result in markedly poikilitic microstructures involving inclusion of the earlier formed finer grained minerals in quartz and or k feldspar which are common in microgranitoid enclaves

early paleozoic high mg diorite granodiorite in the eastern kunlun orogen western china response to continental collision and slab break off abstract phanerozoic high mg diorites and granodiorites are known to be related to diverse subduction styles at convergent margin settings but have not been linked to collision processes the santonggou complex in the eastern kunlun orogen is composed of a dominant granodiorite intruded by small stocks and dykes of porphyritic granodiorites and diorites which are all characterized by high mgo and ni but low yb and y contents mafic microgranular enclaves mmes occur in the granodiorite and the porphyritic granodiorites la icpms u pb analyses of zircon from the granodiorite porphyritic granodiorite and porphyritic diorite yield similar ages of 432 2 ma 432 2 ma and 427 3 ma respectively plagioclase in the granodiorite exhibits complex zonations with resorbed and patchy cores plagioclase and hornblende phenocrysts in the porphyritic granodiorites and diorites also show textural and compositional zonations the highest e nd t value of 0 6 in mmes suggests asthenosphere derived mafic magma these lines of mineralogical and geochemical evidence together with results from geochemical modeling suggest that the porphyritic diorites were derived from mantle metasomatized slab melts the porphyritic granodiorites and the granodiorite were generated by simultaneous assimilation and fractional crystallization of the magma approximated by the porphyritic diorites plus mixing of asthenosphere derived mafic and evolved granodioritic magmas pressure estimates from the al in hornblende geobarometer suggest that the granodiorite had been uplifted to near the surface before the emplacement of the porphyritic granodiorites partial melting of the slab upwelling of the asthenosphere and rapid orogenic uplift at 430 ma suggest that the cessation of subduction and the initiation of collision as well as slab break off occurred almost simultaneously in the eastern kunlun orogen

morphodynamics of a macrotidal beach abstract an intensive field investigation of hydrodynamic processes processes of sediment entrainment and suspension and morphologic change was carried out on an unprotected macrotidal beach near broome in northwestern australia the spring tide range was 9 5 m waves had heights of 0 5 1 2 m and periods of 9 13 s the beach had an overall concave upward profile with low gradient and dissipative subtidal and low tidal zones and steeper more reflective mid tidal and high tidal zones direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 1 2 w m 2 of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height time averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low tidal zone and over the lower part of the high tidal zone most of the work over the low and mid tidal zones was performed by unbroken shoaling waves rather than by surf zone processes surf zone processes only dominate over the high tidal zone the nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level the growth of standing waves and infragravity surf beat oscillations as identified from spectra and cross spectra of surface elevation and currents u and v was inhibited over most of the profile however well developed secondary standing wave energy particularly at infragravity frequencies was observed over the high tidal zone at spring high tide and over the mid tidal zone at neap high tide over the low tidal and subtidal zones strong shore parallel tidal currents were subordinate only to the orbital velocities of unbroken incident waves over the subtidal zone asymmetrical tidal currents skewed toward the north attained maximum speeds of 0 5 m s 1 just after high water field measurements of suspended sediment concentration profiles under broken and unbroken waves showed very good fit to a diffusion model for wave induced sediment suspension and suggested that sediment suspension was probably attributable largely to waves northerly advection of wave suspended sediment by asymmetrical tidal currents over the subtidal and low tidal zones accounted for a net northerly longshore transport the greatest morphologic mobility of the intertidal profile occurred over the lower high tidal and upper mid tidal zones corresponding to the position of the coarsest material and secondary maximum of time averaged wave work and to a beach state intermediate between the reflective and dissipative extremes temporally the greatest mobility of the profile as a whole was observed on the short within tidal cycle time scale net changes over the longest time scale of a lunar half cycle were negligible

syn collisional adakitic granodiorites formed by fractional crystallization insights from their enclosed mafic magmatic enclaves mmes in the qumushan pluton north qilian orogen at the northern margin of the tibetan plateau the qumushan qms syn collisional granodiorite which is located in the eastern section of the north qilian orogen at the northern margin of the greater tibetan plateau has typical adakitic characteristics and also contains abundant mafic magmatic enclaves mmes this recognition offers an unprecedented insight into the petrogenesis of both the adakitic host granodiorite and the enclosed mmes the mmes and their host granodiorites share many characteristics in common including identical crystallization age similar to 430 ma same mineralogy similar mineral chemistry and whole rock isotopic compositions indicating their genetic link the mmes are most consistent with being of cumulate origin formed at earlier stages of the same magmatic system that produced the qms adakitic granodiorite subsequent replenishment of adakitic magmas could have disturbed the cumulate piles as mmes dispersed in the adakitic granodiorite host during emplacement the geochemical data and petrogenetic modeling of trace elements suggest that the qms adakitic host granodiorite is most consistent with fractional crystallization dominated by the mineral assemblage of the mmes the parental magma for the qms granodiorite is best explained as resulting from partial melting of the ocean crust together with recycled terrigenous sediments during continental collision which may have also experienced interaction with mantle peridotite during ascent c 2016 elsevier b v all rights reserved

tidal asymmetry in sediment resuspension on a macrotidal beach in northwestern australia abstract a field experiment was conducted on a macrotidal beach in northwestern australia to investigate the relation between sediment resuspension and sea bed morphology continuous measurements of waves currents and suspended sediment concentrations were carried out over a period of several hours around high tide concurrent with half hourly visual observations of the sea bed morphology the incident waves had a significant wave height of 0 35 m and period 11 s most of the data were collected outside the surf zone where sediment resuspension was mainly by wave groups and suspended sediment transport was primarily accomplished by mean longshore and cross shore currents the sediment resuspension process was further characterised by a pronounced tidal asymmetry with suspended sediment concentrations and transport rates during the falling tide significantly larger than during the rising tide the asymmetry is attributed to the combined effects of a larger bed roughness and stronger mean nearshore flows during the falling tide the increase in bed roughness occurred during the rising tide under the influence of decreasing bed shear stresses when post vortex ripple morphology developed on a previously plane bed around high tide the ripples were fully developed and had attained a ripple height of approximately 0 005 m and a ripple length of 0 06 0 08 m application of the van rijn van rijn l c 1989 handbook sediment transport by currents and waves delft hydraulics report h461 sediment transport model further confirmed that enhanced sediment resuspension during the falling tide was primarily the result of the development of ripple morphology with increased mean current strengths playing a secondary role the results have major implications for modelling suspended sediment transport on macrotidal beaches

simulating the influence of groundwater seepage on sediment transported by the sweep of the swash zone across macro tidal beaches abstract a numerical model is developed to simulate the influence of groundwater seepage on swash zone sediment transport across macro tidal beaches the emergence of equilibrium profile morphology is examined in response to varying tide sediment and initial profile characteristics due to the unresolved complexities of boundary layer flow and corresponding shear stresses in the swash zone sediment transport across the beach face is modelled by incorporating an uprush phase described by the shallow water wave equations within an heuristic model of equilibrium beach face slope a new parameter termed the m net transport parameter is defined to parameterize the net flux of sediment per uprush backrush cycle the definition of differing equilibrium gradients across saturated versus unsaturated regions of the intertidal profile permits the saturation characteristics of the bed to be incorporated the dynamics of the watertable exit point on the beach face is central to the scheme as this defines the time varying extent of saturated and unsaturated regions of the intertidal profile the sensitivity of coastal seepage face development to tide profile and sediment characteristics is highlighted through the derivation of a new seepage face parameter the simulation model is found to successfully reproduce key aspects of observed profile adjustment and resulting equilibrium morphology complex morphodynamic feedback is observed between the tidal stage net transport per uprush backrush cycle profile slope and the dynamics of the watertable outcrop net upper profile steepening and lower profile lowering is simulated on beaches composed of medium to coarse sand this results in the emergence of a distinctive break in slope within the intertidal profile such morphology is commonly observed on macro tidal coasts

geochemistry and thermodynamics of an earthquake a case study of pseudotachylites within mylonitic granitoid abstract pseudotachylites are melts produced by frictional heating during seismic slip understanding their origin and their influence on slip behavior is critical to understanding the physics of earthquakes to provide insight into this topic we conducted a case study in the proto mylonitic to mylonitic asbestos mountain granitoid in the eastern peninsular ranges batholith california which records both ductile mylonites and brittle deformation features pseudotachylites and ultracataclasites u pb chronology and zr thermometry of titanite porphyroblasts in the mylonites indicate that mylonitization of the plutons occurred at near solidus conditions 750 c over a 10 ma interval from 89 to 78 ma mylonitization resulted in recrystallization of quartz plagioclase and biotite with the biotite concentrated into biotite rich foliation planes subsequent brittle deformation is superimposed on the ductile fabrics micro xrf elemental mapping and in situ la icp ms analyses on these brittle deformation products show that the pseudotachylites are more mafic lower si but higher fe and k rich than the host mylonite while the ultracataclasites are intermediate between the host and the pseudotachylites inverse mass balance calculations show that both brittle deformation products are depleted in quartz but enriched in biotite with the pseudotachylites showing the most significant enrichment in biotite indicating preferential involvement of biotite during brittle deformation we suggest that biotite rich layers generated during ductile deformation may have been the preferred locus of subsequent brittle deformation presumably because such layers represent zones of weakness frictional heating associated with slip along such planes results in melting which causes a decrease in viscosity in turn leading to further strain localization during the short time span of an earthquake frictional melting appears to be a disequilibrium process in which the minerals are melted in order of their melting points from biotite 800 c to plagioclase 1400 c and finally to quartz 1700 c rather than by equilibrium melting which results in silicic eutectoid melts at lower temperatures 650 c thus with progressive slip melt composition should evolve from mafic to felsic eventually approaching the bulk composition of the host rock the mafic composition of the pseudotachylites thus indicates that they formed between the melting point of biotite and plagioclase 800 1400 c our chemical and modeling analyses on the pseudotachylites suggest that the chemical composition of pseudotachylites can potentially be used to constrain the thermodynamic conditions in the shear zone as well as earthquake source mechanics

petrogenesis of the early cretaceous granitoids and its mafic enclaves in the northern tengchong terrane southern margin of the tibetan plateau and its tectonic implications abstract cretaceous granites are widely exposed in the tengchong terrane that is the southern extension of the tibetan plateau resulting from the evolution of the tethys they therefore play a critical role in deciphering the tethys evolution and the growth of the tibetan plateau in this paper we present new zircon u pb dating and hf isotopic results along with whole rock elemental and sr nd isotopic data of the granitoids from the lushui pianma lp batholith and its mafic enclaves and the strongly deformed granites from the gaoligong shear zone in the northern tengchong terrane the dating results show that both the lp granitic batholith and the strongly deformed granites in the gaoligong shear zone formed in the early cretaceous of 122 110 ma they are composed of granodiorite quartz monzodiorite and monzogranite with minor gabbroic enclaves mineralogically and geochemically the granitoids in the lp batholith particularly for the less evolved ones display a metaluminous nature and an affinity to i type granite all the granitoids are characterized by similar rare and trace patterns and whole rock nd and zircon hf isotopic compositions indicating a common origin the sodium rich feature for the less evolved dioritic rocks and the predominantly negative zircon ehf t and whole rock end t values for all the granitoids demonstrate that they were derived mainly from the partial melting of the mesoproterozoic metabasic rocks likely the basement rocks of the gaoligong group in the lower crust of the tengchong terrane in the case of the mafic enclaves they share similar mineralogical assemblages and nd hf isotopic compositions to its host granodiorite indicating a cognate origin with the latter in combination with previous data for the granitoids in the tengchong terrane our study further illustrates that the early cretaceous granitic rocks are dominated by metaluminous i type granites with minor highly fractionated peraluminous i type granites rather than the dominant s type granites as assumed before the new identification of the myitkyina meso tethys ophiolitic suite in eastern myanmar together with regional early cretaceous magmatic and sedimentation patterns indicate that these early cretaceous magmatic rocks were the products of the evolution of the myitkyina tethys ocean which was related to post collisional slab breakoff

reactive bulk assimilation a model for crust mantle mixing in silicic magmas bulk assimilation of small millimeters to 1 km fragments of crust driven and ultimately masked by reactions during xenolith melting and magma crystallization is an important mechanism for crust mantle mixing xenoliths containing mica or amphibole undergo dehydration melting when incorporated into a host magma yielding mainly plagioclase pyroxene fe ti oxides and hydrous melt the xenolith is physically compromised by partial melting and begins to disintegrate xenolithic melt and crystals are mixed into the host magma xenocrystic zircon is liberated at this stage the cryptic character of assimilation is greatly enhanced in any hydrous magma by hydration crystallization reactions the reverse of dehydration melting all pyroxenes and oxides phenocrysts xenocrysts or crystals having a hybrid signature will be subject to these reactions producing feldspars amphiboles and micas that incorporate material from several sources a particularly effective mixing mechanism implicit in the model is a reduced energy penalty for bulk assimilation much of the assimilant remains in solid form compared to melt assimilation models a large role for bulk assimilation supports stoping as a credible mechanism for the ascent of magmas while the assimilation of low density crust and concomitant fractionation provide the isostatic impetus for ascent the wholesale incorporation and processing of crustal rocks in the magma chamber helps create the room for ascent

the survival of mafic magmatic enclaves and the timing of magma recharge many intermediate to felsic intrusive and extrusive rocks contain mafic magmatic enclaves that are evidence for magma recharge and mixing whether enclaves represent records of pro longed mixing or

runup estimations on a macrotidal sandy beach abstract this paper presents a methodological approach to calculate runup from the analysis of morphodynamic conditions on a macrotidal sandy beach the method is based on measurements of the elevation of high tide deposits and on the analysis of morphological and hydrodynamic changes a series of measurements has been carried out on the beach of vougot brittany france under different wave conditions this allowed to assess runup formula effectiveness on a macrotidal sandy beach and to determine the best slope parameters to estimate runup the results suggest that on that macrotidal sandy beach the slope of the active section of the upper beach should be used instead of the entire slope of the foreshore the latter resulting in an underestimation of runup elevations when used in predictive equations from the literature results obtained with widely used equations are relatively well correlated with observed values r2 0 63 an analysis of the relationship between observed runup elevations and various variables has enabled the establishment of a runup estimation formula with a relatively good fit to the study site r2 0 86

interaction between mingling mafic and felsic magmas its roles in differentiation of a quartz monzonite and mmes from eastern south china abstract compositional profiles and mapping of selected mafic microgranular enclaves mmes in muchen quartz monzonite in eastern south china give constraints on the interaction between mingling mafic and felsic magmas the intrusion is a typical i type mme bearing magnetite series granitoid in western pacific the mmes and host quartz monzonite are not deformed and have similar magnetic fabrics which does not support the mmes are restites or earlier solidified mafic rocks but implies mafic magma globules flowed with felsic magma the two mmes represent mafic magma interacting with felsic magma at early and late stage respectively the late stage mme has a hbl bt kfs pl mag assemblage the early stage mme has a cpx bt kfs pl mag assemblage with a rim similar to the late stage mme acicular apatite implies rapid cooling of the mafic magmas however the similar isotopic ratios and mafic silicate compositions of the mme and quartz monzonite indicate partial equilibrium during magma interactions al in hornblende estimates the pluton emplacement at 3 1 3 6 km and therefore the magma mingling mixing still worked at shallow levels most trace element harker diagrams do not produce linear variation trends and magma mixing cannot solo explain such a pattern enrichments of na2o ree y nb ta ga fe3 and depletions of k2o rb ba sr in the mmes through diffusion caused noticeable chemical differentiation of both mafic and felsic magmas therefore mass transfer during magma mingling is an important mechanism influencing petrography and chemical compositions of i type granitoids such processes may also extensively occur in the deep hot zones of the continental arc environments

dynamics of a high energy dissipative surf zone vright l d guza r t and short a d 1982 dynamics of a high energy dissipative surf zone mar geol 45 41 62 pressure and horizontal current u v time series were measured at different positions across the inner 150 m of a wide 500 m surf zone of a microtidal high wave energy beach incident waves had average heights of 3 4 m with maxima of 5 m and periods of 12 to 15 sec bores of broken waves diminished in height at a nearly constant rate as they progressed across the surf zone the ratio of bore height h to local water depth h was everywhere less than 1 for even the highest bores and was on the order of 0 40 for the significant bores at incident wave frequencies rip circulation was weak or absent but a moderate longshore current was present shore normal flows were vertically segregated with strong net onshore flows prevailing just below the surface accompanied by weaker net seaward flows near the bed spectra of water surface oscillations as determined from pressure u and v reveal that most of the energy in the inner surf zone was at infragravity frequencies periods greater than 30 sec shoreward decay of wave energy at incident wave frequencies was accompanied by shoreward growth of infragravity energy near the beach the infragravity oscillations had heights on the order of 1 m cross spectra show that the infragravity oscillations were standing in the shore normal direction from the relative magnitudes of infragravity versus incident wave currents it is inferred that the surf beat may be an order of magnitude more important than incident waves to the transport of sediment in the inner surf zone

mineral leucosome trace element partitioning in a peraluminous migmatite a laser ablation icp ms study abstract low pressure peraluminous migmatites from the pena negra complex central spain stayed partially molten for 5 10 ma until the latest hercynian deformations allowed the segregation of melt as discordant leucosome veins due to long residence within its source the melt had time enough to equilibrate with residual phases other than accessories included within major refractory minerals we estimated crystal melt partition coefficients as the concentration ratios between leucosome samples appearing to be pure melts and mesosome minerals which were analyzed for trace elements with a laser probe coupled to an icp mass spectrometer our data reveal that when biotite is stable li rb cs tl sc v cr ni nb and ta become strongly compatible the role of biotite in fractionating y th u and the ree is insignificant cordierite strongly fractionates li and be and also has some effect on the hree and u garnet produces extreme fractionation of sc y and the hree the ree partition coefficients for ferromagnesian silicates increase with the atomic number this effect being progressively more important through biotite cordierite and garnet k feldspar strongly fractionates ba and pb but plays a secondary role to biotite for rb and cs k feldspar fractionation does not change the lree hree ratio but plagioclase fractionation produces a significant decrease in the lree hree ratio both feldspars greatly fractionate sr and eu monazite fractionation produces a dramatic depletion in ree th and u as well as a decrease in the lree hree and th u ratios apatite also fractionates the ree although in contrast with monazite it increases the lree hree ratio and does not affect the th u ratio zircon fractionation like apatite and garnet produces a strong depletion in the hree and a concomitant increase in the lree hree ratio in contrast with monazite zircon fractionation causes the th u ratio to increase

enclaves in the cadillac mountain granite coastal maine samples of hybrid magma from the base of the chamber the cadillac mountain intrusive complex is dominated by the introduction cadillac mountain granite and a 2 3 km thick section of interlayered enclaves occur in nearly all granites and have recently gabbroic dioritic and granitic rocks which occurs near the base of been the focus of many studies see reviews by vernon the granite the layered rocks record hundreds of injections of basaltic 1983 and didier barbarin 1991 although enclaves magma that ponded on the chamber floor and variably interacted may have originated in many different ways and from with the overlying silicic magma magmatic enclaves ranging in different sources there has been a growing consensus composition from 55 to 78 wt sio2 are abundant in granite that there are textural criteria to recognize a class of above the layered mafic rocks the most mafic enclaves are highly enclaves that formed from different magmas that were enriched in incompatible elements and depleted in compatible elemingled into the granitic magma while it was still mobile ments their compositions can be best explained by periodic vernon 1984 1990 these can appropriately be termed replenishment mixing and fractional crystallization of basaltic magmatic enclaves their compositions are commonly magma at the base of the chamber the intermediate to silicic intermediate but can vary from basaltic to highly silicic enclaves formed by hybridization between the evolved basaltic magma magmatic enclaves occur in all types of granite and are and resident silicic magma there is little evidence for significant probably the dominant type of enclave in most calcexchange between enclaves and the enclosing granite instead alkaline i type granites in spite of partial reequilibration hybridization apparently occurred between stratified mafic and silicic enclaves of this type commonly have nd isotopic commagmas at the base of the chamber enclaves in a restricted area positions that are distinct from the enclosing granite and commonly show distinctive compositional characteristics suggesting support their formation from mantle derived magmas they were derived from a discrete batch of hybrid magma enclaves holden et al 1987 were probably dispersed into a localized portion of the granitic the compositions of magmatic enclaves can vary magma when replenishment or eruption disrupted the intermediate widely even within a single pluton and they can only layer rarely be interpreted as simple mixtures between an original basaltic magma and the host granitic magma there is ample petrographic and chemical evidence in many enclaves for hybridization mixing of liquids and

neo tethyan evolution in southeastern extension of tibet constraints from early paleocene to early eocene granitic rocks with associated enclaves in tengchong block abstract the granite is one of most widely distribution rocks in crust and its petrogenesis is crucial to advance our knowledge of thermal condition in continental crust the long time tectonic evolution of crust in the active continental margin could be recorded by multi stages of granitic assemblage in order to reveal the subduction of neo tethys and initial collision of indian asian continents in eastern tibetan plateau we selected the early paleocene to early eocene granitic rocks with associated enclaves in tengchong block southeastern extension of gangdese magmatic belt to clarify their different derivation regimes using geochemical and isotopic compositions mineral compositional variation the zircon data show that early paleocene granites formed at 64 ma and early eocene granitic rocks formed at 54 ma combing with the field contact relationship the similar and enriched sr nd pb and zircon hf isotopic compositions indicate that the two stages of granitic rocks have a common and ancient lower crustal source the enclaves in early paleocene granites could represent crystallization of coeval and cognate magmas at margin of magmatic conduit but the enclaves in early eocene granitic rocks are products of magma mixing between mafic and felsic magma according to rock assemblages and geochemical signatures of granitic rocks during early paleocene to early eocene in tengchong block we propose that early paleocene granitic rocks are derived from partial melting of lower crustal rocks induced by long lived heat accumulation with no or minimal basalt flux during the neo tethyan subduction whereas early eocene granitic rocks are derived from melting of crustal materials resulted from high mafic magma flux during indian asian continental collision the initial collision occurred at ca 55 ma

petrogenesis of late triassic mafic enclaves and host granodiorite in the eastern kunlun orogenic belt china implications for the reworking of juvenile crust by delamination induced asthenosphere upwelling abstract late triassic granitoids containing abundant mafic microgranular enclaves mmes occur widely in the eastern kunlun orogenic belt ekob in this work we present mineral chemistry zircon u pb ages and l hf isotopes whole rock chemistry and s nd isotope compositions of the mmes and host granodiorite from the huda pluton in the elashan area within the easternmost domain of the ekob these rocks contain inherited meso to neoproterozoic and xenocrystic ca 240 ma zircon grains that yield apparent older ages whereas the magmatic zircons from mmes and granodiorite yield similar weighted mean ages around 224 ma which are interpreted as their crystallization ages the mmes have low sio2 but high tio2 tfe2o3 cao mgo and mno concentrations with relatively high mg values 48 54 and 100mno mno mgo tfe2o3 ratios 1 2 1 6 they display identical sr nd hf isotope compositions to the host granite combined with petrological evidence we suggest that the mmes are cognate cumulates that formed by pressure quenching during the late stage of magma evolution from the same parental magma of the host granodiorite rather than a magma mixing origin the granodiorite is calc alkaline to high k calc alkaline metaluminous i type granite they show relatively low sio2 and mno but high mgo al2o3 cao and tfe2o3 contents with mg values of 45 50 they are enriched in light rare earth elements lrees and large ion lithophile elements liles such as rb th k and pb and are depleted in p and high field strength elements hfse including nb ta and ti these rocks display slightly negative eu anomalies and low sr y and la yb ratios together with the rim ward chemically evolved nature of some phenocrysts the comparatively high initial sr isotope 0 70888 0 70912 low whole rock end t 5 6 to 6 0 and zircon ehf t 3 3 to 0 1 values and low nb th 0 11 0 26 and ta u 0 53 0 68 ratios we suggest that the granodiorite magma was sourced from the lower crust considering their comparatively young two stage nd and hf model ages 1 42 1 49 ga and 1 13 1 42 ga respectively and same trace element character with the juvenile crust beneath the ekob we interpret the juvenile lower crust as the dominant source rocks for the granodiorite based on our data and regional geological evidence we suggest that the partial melting of juvenile crust resulted from delamination related asthenosphere mantle upwelling the latter process resulted in extensive melting of the lower crust producing a major late triassic magmatic flare up event in the ekob

morphodynamics of intertidal bars in wave dominated coastal settings a review abstract intertidal bar systems are ubiquitous features on wave dominated beaches in coastal settings with a significant 1 m tidal range depending primarily on the wave conditions and the tidal range and to a lesser extent on the nearshore gradient they can assume a variety of forms slip face bars represent the most pronounced and dynamic intertidal bar morphology and are generally found on their own around the mean high tide level they usually form low on the intertidal beach after storm induced beach erosion and develop into a berm under prolonged calm wave conditions low amplitude ridges and sand waves represent multiple bar morphologies the bars occur across the entire intertidal profile and they remain present throughout the year multiple intertidal bars tend to be rather subdued and relatively static especially sand waves and their origin remains unclear the morphological response of intertidal bars to changing wave conditions is largely forced bars build up and migrate onshore under calm waves and are flattened and may migrate offshore during storms the morphological response is however significantly affected by relaxation time effects and morphological feedback particularly on beaches with multiple intertidal bars despite their morphological differences the intertidal bar types exhibit pronounced similarities in their morphodynamics sediment transport processes and morphological response are principally controlled by the tidal water levels on the beach because these together with the offshore wave energy level and the beach morphology determine the type intensity and duration of the wave processes operating on the cross shore profile it is the dominant importance of tidal water level variations and wave processes in shallow water depths swash and surf zone bores rather than wave height variability and deeper water wave processes breaking and shoaling waves that constitutes the main difference between intertidal and subtidal bar morphodynamics

dynamics of multiple intertidal bars over semi diurnal and lunar tidal cycles north lincolnshire england multiple intertidal bars are common features of wave dominated sandy beaches yet their short term 1 month and small scale 1 km morphology and dynamics remain poorly understood this study describes the morphodynamics of multiple intertidal bars in north lincolnshire england during single and lunar tidal cycles under two contrasting conditions first when significant wave height was 0 5 m and second when significant wave height frequently exceeded 1 m the relative importance of swash surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model the beach featured four intertidal bars and both cross shore and longshore bar morphology evolved during the field investigation particularly under medium to high wave energy conditions numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions hs 0 5 m and that surf zone processes become more common during neap tides and under more energetic hs 0 5 m conditions surf processes dominate the inner two bars though swash influence increases in a landward direction the numerical modelling results combined with low tide survey data and high resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes this is because shoaling waves do not induce significant sediment transport to have any morphological effect whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone it was found however that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar making this process important for bar morphodynamics copyright 2007 john wiley sons ltd

microgranitoid enclaves in granites globules of hybrid magma quenched in a plutonic environment microgranitoid enclaves autoliths cognate xenoliths mafic inclusions are common in high level granitoid plutons they have relatively fine grained igneous microgranitoid microstructures1 and many show evidence of having flowed in a magmatic condition2 these features counter interpretations that the enclaves represent transformed solid fragments of diverse wall rocks3 5 or restite6 11 an alternative interpretation is that the enclaves represent globules of mafic magma that have mingled commingled and quenched in the granitoid host magma12 16 a detailed review of the literature occurrence morphology and composition of micro granitoid enclaves strongly supports this view hut indicates that the enclave magmas range in composition from mafic to felsic and that magma mixing may be involved in their formation17 i summarize here the main features of microgranitoid enclaves and briefly outline the possible processes leading to their incorporation as magma globules in the host granitoid

gas driven filter pressing in magmas most silicic and some mafic magmas expand via second boiling if they crystallize at depths of about 10 km or less the buildup of gas pressure due to second boiling can be relieved by expulsion of melt out of the region of crystallization and this process of gas driven filter pressing assists the crystallization differentiation of magmas for gas driven filter pressing to be effective the region of crystallization must inflate slowly relative to buildup of pressure and expulsion of melt these conditions are satisfied in undercooled magmatic inclusions and in thin sheets of primitive magma underplating cooler magma reservoirs gas driven filter pressing thereby adds fractionated melt to magma bodies gas driven filter pressing is probably the dominant process by which highly evolved melts segregate from crystal mush to form aplitic dikes in granitic plutons this process could also account for the production of voluminous crystal poor rhyolites

characteristics and dynamics of multiple intertidal bars north lincolnshire england multiple intertidal bars and troughs often referred to as ridges and runnels are significant features on many macrotidal sandy beaches along the coastline of england and wales they are particularly prevalent in the vicinity of estuaries where the nearshore gradient is gentle and a large surplus of sediment is generally present this paper examines the dynamics of such bar systems along the north lincolnshire coast a digital elevation model of the intertidal morphology obtained using lidar demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m the largest and most pronounced bars height 0 5 0 8 m are found around mean sea level whereas the least developed bars height 0 2 0 5 m occur in the lower intertidal zone annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates however there is little resemblance between concurrent photographs and resetting of the intertidal profile occurs on an annual basis three dimensional beach surveys were conducted monthly at three locations along the north lincolnshire coast over a one year period the intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions and bars are least numerous and flattest during the more energetic winter months morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month the behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors e g incident wave energy different types of wave processes longshore and cross shore sediment transport relaxation time and morphodynamic feedback copyright 2005 john wiley sons ltd

seasonal changes and morphodynamic behavior of a high energy mesotidal beach case study of charf el akab beach on the north atlantic coast of morocco the morphodynamic behavior of a mesotidal sandy beach was monitored during both calm and energetic conditions two years of seasonal surveys were carried out on charf el akab a gently sloped beach in the north atlantic coast of morocco the method of survey consisted of a 3d study of the beach morphological changes and provided 2 cm vertical accuracy during the surveyed period charf el akab beach underwent very energetic wave conditions and the breaking wave height was of h b 1 5 m the beach is characterized by a nonpermanent swash bar and composed of well sorted medium sand the application of environmental parameters revealed a dissipative state with very low beach gradient which did not vary significantly over the studied period morphological changes consist of beach erosion and bar decay under high energy waves whereas the intertidal bar re established and the beach recorded an accentuated accretion due to relatively fair weather conditions the beach volume reveals a seasonal behavior the sand accumulated during summer is dramatically removed during winter season the range in beach sand volume from the most accreted to the most eroded conditions observed is about 5 493 m3 the average sand volume flux between surveys reaches 1 and 0 4 m2 day during peak erosion and accretion periods the relationships between the wave forcing and the sand volume adjustments were examined the sand volume change was found to be highly correlated 0 91 with the wave energy flux the highest correspondence 0 95 was found between the sand flux rate and the wave energy flux the wave forcing is expected to be the main factor governing beach morphodynamics at charf el akab site

mafic felsic magma mixing limited by reactive processes a case study of biotite rich rinds on mafic enclaves article history mafic enclaves in felsic plutons are often used to argue that intermediate magmas are formed by mafic felsic magma mixing but the extent and nature of mixing remains unclear here we examine biotite rich rinds on mafic enclaves from the cretaceous bernasconi hills pluton in the peninsular ranges batholith of southern california to gain insight into magma mixing processes rinds differ from the enclave interior and the host monzogranite in being more fine grained and more mafic and potassic rinds are also 2 5 times more enriched in rare earth elements than the host monzogranite and up to 3 times more enriched than enclave interiors these observations indicate that the rinds were not generated by isochemical quenching binary mixing between enclave and host monzogranite or in situ magmatic differentiation instead rinds appear to have been formed by chemical reaction between the solidified enclave and a hydrous k rich residual melt or fluid formed after progressive crystallization and cooling of the host magma body transforming amphibole in the enclave into biotite rich rinds field observations show snapshots of biotite rich rinds being eroded away and new rinds simultaneously forming on freshly eroded surfaces of enclaves consistent with rinds being formed by chemical reaction instead of as quenching products deformation of enclaves is accommodated primarily by ductile attenuation of the thin rind while the enclave as a whole tends to rotate as a rigid body with minimal internal deformation other than localized brittle failure a comparison of the aspect ratios and cross sectional areas of mafic bodies in the pluton shows that those with high aspect ratios indicating greater accumulated strain are systematically more biotite rich and have smaller cross sectional areas than those with lower aspect ratios which are amphibole rich these relationships not only confirm that biotite rich lithologies are more deformable but also indicate that the high aspect ratio biotite rich bodies also known as schlieren derive from small parent bodies consistent with a derivation from eroding enclave rinds rather than from the enclave itself finally geochemical and thermodynamic modeling indicates that the biotite rich rinds formed when the host felsic magma had cooled to a low melt fraction state f 0 15 0 3 700 760 c suggesting that such reactions occur late in the lifespan of a magma body thus mafic felsic mixing may not be an efficient process for making intermediate magmas unless the magma body can reside at this low temperature range long enough to permit rind formation and subsequent deformation

petrogenesis and ni cu co sulfide formation of mafic enclaves in tulaergen mafic ultramafic intrusive rocks eastern tianshan northwest china implications for liquid immiscibility and hydrothermal remobilization of platinum group elements

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

boundary roughness and bedforms in the surf zone hydrodynamical models of the nearshore system frequently assume that a single friction coefficient is sufficient to represent flow conditions at a point in the surf zone furthermore models attempting to relate bed configuration to surf zone flows have relied primarily upon the wave orbital velocity as an indicator of potential bedforms and thus as the control on boundary roughness the data presented here point out potential errors arising from either of these approaches the results of a field experiment conducted at wendake beach ontario show that at a single location in an active surf zone the darcy weisbach friction coefficient f varied by approximately 250 in this case between 0 016 and 0 041 it is also shown that existing bedform models based upon primary wave motions alone do not accurately predict conditions at this study site for a relatively constant wave orbital velocity and velocity asymmetry it is found that changes in bed roughness as a result of bedform development are reflected mainly in the vertical profile of the longshore current velocity a sequence of bedforms from oscillatory ripples through flat bed is inferred from the data and found to be supported by diver observations and preserved primary sedimentary structures

a new workflow to assess emplacement duration and melt residence time of compositionally diverse magmas emplaced in a sub volcanic reservoir construction durations of magma reservoirs are commonly inferred from u pb zircon geochronology using various statistical methods to interpret zircon u pb age spectra e g weighted mean ages of concordant zircon populations however in compositionally different magmas zircon saturation and crystallization are predicted to occur at different times relative to other mineral phases and the geological event of interest for instance magma emplacement the timescales of these processes can be predicted by numerical modeling and measured using u pb zircon thermal ionization mass spectrometry tims geochronology therefore creating an opportunity to quantify magma emplacement in space and time to constrain the size and longevity of magma reservoirs during pluton construction the jurassic tilted bimodal gabbroic and granitic guadalupe igneous complex gic in the sierra nevada arc presents an exceptional opportunity to study the construction duration of a shallow 1 10 km magma reservoir comprising multiple magma batches we present a new workflow to constrain emplacement ages from zircon geochronology of compositionally different magma batches and evaluate melt present timescales high precision u pb chemical ablation isotope dilution ca id tims zircon ages are combined with melts modeling to calculate zircon saturation ages for each dated sample bayesian statistics are then used to compare calculated zircon saturation distributions with zircon age distributions from tims data to predict time temperature and melt fraction at zircon saturation and solidus in addition we use mineral thermometry and cooling rate calculations to relate zircon saturation ages to emplacement ages for felsic and mafic rocks resulting in a best estimate for the total construction duration of 295 110 kyr for the gic rhyolites exposed at the top of the gic are 2 3 myr older and thus not part of the same magmatic system the good agreement between ti in zircon crystallization temperatures and calculated zircon saturation temperatures by melts implies that bulk rock compositions of both mafic and felsic rocks are close to liquid compositions mafic and felsic magmas experienced extensive mingling at the emplacement level in a magma chamber which as defined here has temperatures above the solidus of the respective rock composition encompassing 60 of the exposed map area of the complex shortly after construction melt was present within the system for a total duration of 550 kyr as constrained by two dimensional thermal finite difference modeling using an incremental growth and sill emplacement model the construction and melt present timescales calculated in this study for the shallow gic have implications for the potential of in situ differentiation mixing and mingling timescales and eruption in shallow magmatic systems

magma recharge and reactive bulk assimilation in enclave bearing granitoids tonglu south china national nature science foundation of china 41530211 mlr special funds for public welfare projects 201211013 2 state administration of foreign expert affairs of china b07039 most special funds of the state key laboratory of geological processes and mineral resources msfgpmr01

beach groundwater dynamics abstract an understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level swl but the exact nature of the relationship between swash flows beach watertable flow and cross shore sediment transport is not fully understood this paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled after defining the principal terms relating to beach groundwater the behavior measurement and modelling of beach groundwater dynamics is described research questions related to the mechanisms of surface subsurface flow interaction are reviewed particularly infiltration exfiltration and fluidisation the implications of these mechanisms for sediment transport are discussed

magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of california effects of assimilation crustal thickness and depth of crystallization in order to better understand geologic fac tors controlling pronounced regional variations in whole rock chemistry mineralogy and mineral chemistry in the batholiths of california we calculate the magmatic intensive variables f hf f h 2 o f hf f hcl and f o 2 regional scale west to east increases in f oh in mafic silicates corresponding to the systematic i wc to i mc and i sc progression reflect orders of magnitude increase in f hf f h 2 o attending pluton crystallization low f hf f h 2 o of formation of western i wc types is consistent with their derivation from low fluorine source rocks in subducted oceanic slabs or the upper mantle in contrast higher f hf f h 2 o of crystallization of i mc and i sc types to the east implies the involvement of 1 progressively greater amounts of continental crustal source material such as biotite bearing metamorphic rocks their unweathered sedimentary derivatives retaining f rich mafic minerals or their fusion products and or 2 source materials which become more f rich toward the continental interior the regional distribution of i mc and i sc types suggests that the precambrian craton of western north america or derivative sediments may extend farther north in california and be morphologically more complex than previously thought from seemingly out of place occurrences of i wc plutons on the eastern slopes of the sierra nevada batholith we infer the existence of regions where precambrian basement was thin or absent in mesozoic time which prevented extensive cratonal contamination of subducted slab or upper mantle derived magmas new methods for estimating t f o 2 relations in the magmas demonstrate that i scr granites crystallize at oxygen fugacities as much as five orders of magnitude lower than those of i wc i mc and i sc types under conditions at or below the maximum stability limit of graphite in equilibrium with a c o h s gas phase the local scale formation of i scr granites in plutonic belts within specific wall rock terranes containing highly reducing sediments or metasediments may occur by contamination of i types with graphitic pelite or in some cases by the direct fusion of this reducing pelitic wall rock the spatial distribution of i scr granite provinces therefore is controlled simply by wall rock lithology amphibole geobarometry demonstrates a general west to east decrease in crystallization pressure across the sierra nevada batholith in contrast the peninsular ranges batholith displays a west to east crystallization pressure increase the bulk of the california batholiths crystallized at pressures less than 4 5 kb and depths less than about 15 19 km in the southern sierra nevada batholith the san gabriels and the eastern peninsular ranges however plutons crystallized at pressures exceeding 6 kb at deep crustal levels 23 km reconstruction of the pre erosion top of the batholith shows that in an east west cross section the central sierra nevada batholith was a horizontal tabular body with an aspect ratio of at least five to one

morphodynamic zone variability on a microtidal barred beach abstract this paper builds on the work of masselink masselink g 1993 simulating the effects of tides on beach morphodynamics j coast res si 15 180 197 on the use of the residence times of shoaling waves breaking waves and swash backwash motions across a cross shore profile to qualitatively understand temporal beach behaviour we use a data set of in situ measurements of wave parameters height and period and water depth and time exposure video images overlooking our single barred intertidal measurement array at egmond aan zee netherlands to derive boundaries between the shoaling zone the surf zone and the swash zone we find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness this contrasts with the use of constant relative wave heights or water levels in earlier work we use the obtained boundaries and a standard cross shore wave transformation model coupled to an inner surf zone bore model to show that large 5 relative tide ranges rtr defined as the ratio tide range wave height indicate shoaling wave processes across almost the entire intertidal profile with surf processes dominating on the beach face when the rtr is between 2 and 5 surf processes dominate over the intertidal bar and the lower part of the beach face while swash has the largest residence times on the upper beach face such conditions associated with surf zone bores propagating across the bar around low tide were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen for rtr values less than about 2 surf zone processes dominate across the intertidal bar while the dominance of swash processes now extends across most of the beach face the surf zone processes were now observed to lead to offshore bar migration while the swash eroded the upper beach face

contribution of enclave studies to the understanding of origin and evolution of granitic magmas enclaves give important information on the origin and evolution of granitic magmas the presence in a granite of surmicaceous enclaves restites is good evidence of continental crust contribution to magma genesis the presence of dark microgranular enclaves is an indication of mantle contribution the joint presence in the same granite of the two types of enclaves indicates that its magma has probably more than one source dark microgranular enclaves and their host granites as well are hybridized rocks resulting from incomplete mixing or mingling of more acidic and basic components enclave studies allow one to specify mixing conditions when mixing occurs relatively early with respect to granite crystallization only earlier formed granitic minerals zircon apatite may be incorporated in the basic magma when mixing occurs later all granitic minerals may be involved when all the dark microgranular enclaves of a granite are similar the intervention of a single mixing event can be assumed on the contrary when several chemically and mineralogically contrasted varieties occur several mixing events can be assumed the order of these events may be deduced from the nature of the granitic minerals present in the enclaves early of late minerals or sometimes by observation of double enclaves enclave shapes bring information on the distance between the place of mixing and the place of observation enclaves with irregular or crenulated margins or with chilled margins as well always occur near mixing places the enclave transport in the magma makes these characteristics disappear in spite of hybridization processes the primitive composition of the basic component of the mixture may sometimes be recognized a systematic identification of this component in the different granites from the same orogen should allow to understand the space and time evolution of basic magmatism in an orogen magma mixing is a cause of heterogeneity in granites but it is also an important factor of homogenization as the thermal contribution of the basic magma produces new mingling of the components and sometimes new intrusive processes

interaction between two contrasting magmas in the albtal pluton schwarzwald sw germany textural and mineral chemical evidence the magmatic evolution of the variscan albtal pluton schwarzwald sw germany is explored using detailed textural observations and the chemical composition of plagioclase and biotite in both granite and its mafic magmatic enclaves mmes mmes probably formed in a two step process first mafic magma intruded a granitic magma chamber and created a boundary layer which received thermal and compositional input from the mafic magma this is indicated by corroded granitic quartz crystals and by large granitic plagioclase xenocrysts which contain zones of higher anorthite and partly crystallized from a melt of higher sr content texturally different plagioclase types e g zoned and inclusion rich types correspond to different degrees of overprint most likely caused by a thermal and compositional gradient in the boundary layer the intrusion of a second mafic magma batch into the boundary layer is recorded by a thin an50 zone along plagioclase rims that crystallized from a melt enriched in sr most probably the second mafic intrusion caused disruption of the boundary layer dispersal of the hybrid magma in the granite magma and formation of the enclaves rapid thermal quenching of the mmes in the granite magma is manifested by an30 overgrowths on large plagioclase grains that contain needle apatites our results demonstrate the importance of microtextural investigations for the reconstruction of possible mixing end members in the formation of granites

chemical modification of enclave magma by post emplacement crystal fractionation diffusion and metasomatism hornblende bearing microgranitoid enclaves from the swifts creek pluton scp se australia display mineralogical and textural variations from their margins to their centers margins are fine grained and display quench textures and are enriched in amphibole biotite and in some cases magnetite relative to their coarser grained centers enclaves of this type and their adjacent granitoid host rocks have been sectioned into 0 3 to 1 cm thick slabs in order to determine the chemical variations associated with these mineralogical changes the fine grained margins are variably enriched in ti al mg fe mg k rb ba nb y sc v ni and the ree up to a factor of three relative to the enclave centers this enrichment is compensated by a depletion of si and zr elements like ca na and sr show less coherent variation from margin to center host rocks in immediate contact with these enclaves are depleted in mg na k rb and ba relative to host rocks that are not exposed to enclaves no one single process can account for all the variations instead we propose that the chemical variations are related to a combination of in situ crystal fractionation of isolated magma globules mass transfer by diffusion and metasomatic exchange

nearshore wave height variation in unsaturated surf the nearshore evolution of wave height is presented from field observations during unsaturated surf conditions from 10 different beaches characterized by microtidal conditions and predominantly swell dominated wave climates wave evolution is presented in terms of wave height to water depth ratio gamma for comparison with previous data from saturated surf both conventional time averaged gamma rms and a new wave by wave analysis gamma w are performed values of gamma increase with increasing offshore wave height indicating unsaturated surf the observations show a variation in gamma values from near constant values in the mid surf zone to rapidly and asymptotically increasing gamma values in the inner surf zone in contrast to previous data from saturated surf gamma shows no dependence on either the absolute beach slope or the relative beach slope beta k h over bar the skewness of the distributions of gamma w is consistent with waves that are not depth limited the inner surf zone wave heights are approximately equally dependent on the water depth and offshore wave height the previous observations of gamma from saturated surf are shown to be consistent with a terminal bore height at the shoreline which is in excellent agreement with a previously derived value for the miche parameter in contrast for the present unsaturated surf conditions the terminal bore height at the shoreline can be approximated by h b approximate to 0 12h o which is consistent with recent laboratory data sets

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

monsoon influenced variations in morphology and sediment of a mesotidal beach on the mekong river delta coast abstract a mesotidal beach on the mekong river delta coast exhibits unique patterns of river sediment discharge and experiences reversals of ocean wave directions in response to the summer and winter monsoons we analyzed long term changes of the shoreline since 1936 from past topographic maps and satellite images and short term changes in geomorphology and sedimentology by undertaking repeated field surveys between november 2005 and february 2008 along six shore normal beach transects the shoreline of the mekong river delta coast has changed asymmetrically over the last 70 years in response to net southwestward sediment transport related to dry northeasterly winter monsoons during the summer rainy season large volumes of sediments are discharged from the river at this time wave direction is reversed in response to the relatively weak southwesterly summer monsoon mud and very fine sand in the surface sediments of the northeastern updrift beach transects tend to be removed during winter suggesting that the sediment supplied from the river during summer is temporarily deposited near the river mouth and later transported southwestward during the winter monsoon the relief of intertidal bars on the beach increased during winter in response to higher waves however previous studies have suggested that higher waves flatten bars we hypothesize that the increase in relief that we observed is related to a wide and shallow subtidal delta front platform that attenuates ocean waves at all times other than at high tide the beach profile varies longshore the accreting to stable beach dips seaward at a gradient of about 1 80 with up to three longshore intertidal bars classified here as either slip face bars or low amplitude ridges in contrast the eroding beach profile is much steeper 1 20 1 40 and linear without intertidal bars and is similar in form to a low tide terrace because there is little variation of wave size and grain size within the study area we consider that the spatial variation of the beach profile is related to the availability of sediment accumulated on the beach

field observations of surf beat 1 progressive edge waves nineteen biaxial electromagnetic current meters have been used to determine the longshore and on offshore structure of currents at surf beat periods 1 4 min the sensors formed two linear arrays a long shore array within the surf zone and an on offshore array stretching from the shoreline to well beyond the breaker line analysis of the longshore current components yields a clear picture of progressive low mode edge waves with frequency wave number dispersion relations which are in remarkably good agreement with predictions some separation of edge wave modes is found with mode zero energy dominating in the frequency band 0 006 and 0 011 hz and mode one between 0 015 and 0 025 hz on offshore currents present a rather different picture which while not inconsistent with the longshore currents suggests that other sources of energy are also important to the on offshore currents these include standing edge waves probably formed by reflections at nearby scripps canyon and motions which are nonresonantly forced by incoming wave groups

magma mixing in the kalaqin core complex northern north china craton linking deep lithospheric destruction and shallow extension abstract the widespread mesozoic magmatism in the north china craton ncc has received considerable attention as a trigger for large scale lithospheric destruction here we investigate the early cretaceous jiguanzi adamellite from the northern part of the ncc which is contemporaneous with shallow extensional deformation and deep lithospheric destruction this intrusion emplaced at ca 133 ma is located in the foot wall of the kalaqin metamorphic core complex mcc and occurs as a synextensional ring complex with numerous magmatic equigranular group 1 and porphyritic group 2 enclaves hornblende and plagioclase from the host adamellite and xenocrysts of group 2 enclaves show distinct inverse zoning with mg and ca rich mantle the group 2 enclaves are characterized by plagioclase xenocrysts hosting hornblende biotite and apatite inclusions quartz ocelli with fine grained rim enriched in biotite and hornblende and poikilitic biotite surrounded by hornblende geochemically the host intrusion is calc alkaline to alkaline and metaluminous with variable contents of sio 2 60 70 72 20 wt al 2 o 3 14 19 17 22 wt na 2 o k 2 o 6 16 9 42 wt and mg values 28 0 47 7 whereas the group 2 enclaves exhibit low sio 2 54 05 55 55 wt high fe 2 o 3 8 18 8 64 wt and tio 2 2 08 2 28 wt and moderate mg 44 0 44 1 both the host intrusion and group 2 enclaves are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements and heavy rare earth elements except that the latter has lower ba and high nb ta and ti contents the major and trace element contents of the group 1 enclaves are broadly similar to those of the host intrusion analyses of sr nd hf isotopes in the host intrusion and in group 1 and group 2 enclaves show 87 sr 86 sr i host 0 70600 0 70618 e nd t host 8 2 to 9 6 t 2dm nd host 1592 1706 ma e hf t host 9 2 to 12 0 87 sr 86 sr i group 1 0 70590 0 70635 e nd t group 1 9 6 to 10 4 t 2dm nd group 1 1705 1775 ma 87 sr 86 sr i group 2 0 70586 0 70587 e nd t group 2 0 6 to 0 7 t 2dm nd group 2 971 978 ma and e hf t group 2 4 5 to 10 0 the mineralogical and geochemical features suggest that the host jiguanzi adamellite and group 2 enclaves were generated through synchronous mixing and fractional crystallization accompanied by mechanical and chemical exchanges the group 1 enclaves showing cogenetic affinity with their felsic host represent the mechanical concentrations of mafic minerals and accessory phases from evolved hybrid host magma magma sources of the host jiguanzi adamellite and its group 1 enclaves are dominated by lower crust lcc components whereas those for the group 2 enclaves are dominated by metasomatized lithospheric mantle the magma genesis involved complex multi stage crust mantle interaction processes including 1 lithospheric mantle modification induced by triassic subduction of the paleo asian ocean slab and or triassic cretaceous asthenospheric melt underplating and 2 melting of the ancient lcc and lithospheric mantle and hybridization of mantle and crust derived melts in conjunction with regional geological and geochemical data we argue that the late jurassic early cretaceous shallow extension events represented by the kalaqin mcc triggered deep seated multi stage magmatism and lithospheric destruction and the continuous generation of magma further strengthened the extension and result in more extensive lithospheric thinning

geochemistry and mineralogy of early archean spherule beds barberton mountain land south africa evidence for origin by impact doubtful abstract spherule layers in the 3 4 ga barberton greenstone belt south africa have been interpreted as being the result of large asteroid or comet impacts on the early earth this interpretation was based among other arguments on the enrichment of siderophile elements especially the platinum group elements we made a detailed mineralogical petrological and geochemical study of spherule bed samples taken from drill cores and underground exposures at the princeton mt morgan and sheba gold mines as well as surface localities the macrostructure of each sample from within different spherule layer units shows evidence for multiple more than five events over about 30 cm this would require multiple impacts within a few million years which is unlikely the mineral phases are almost exclusively of secondary origin the mineralogy provides evidence for extensive hydrothermal and metasomatic alterations of the spherule beds geochemical analyses of alternating spherule shale and chert layers show no correlation between the siderophile elements e g ir co ni and au contrary to that which would be expected if the siderophile elements had an extraterrestrial source furthermore no significant variation in the content of the siderophile elements was detected between spherule layers and shale layers however siderophile element contents are high only in layers containing abundant sulphide minerals and having high as sb se and cr contents we suggest that complex mineralizations similar to those that have formed the barberton archean gold deposits or the bon accord deposit were responsible for the siderophile element enrichments in the spherule beds the mineralogical and geochemical data provide no direct evidence in favour of their initial origin by impact nowhere else in the world have such multiple or even single spherule beds been observed and none of the numerous known impact crates or the cretaceous tertiary boundary is associated with comparable spherule beds known impact debris usually contains

suspended sediment reference concentration under waves field observations and critical analysis of two predictive models two commonly adopted but fundamentally different approaches for predicting time averaged suspended sediment reference concentration cref under waves are tested against field measurements and compared with each other the first model relates cref to the cube of the non dimensional skin friction whereas the second model adopts a more complex function of excess skin friction incorporating the empirical constant 0 the dataset is from the zone of wave shoaling seaward of an open coast surfzone and includes measurements of waves currents suspended sediment and bedforms estimates of cref are derived from acoustic backscatter data and the seabed and suspension process are described from video footage when waves were energetic the bed was deformed into large hummocks during less energetic conditions the bed was rippled the time averaged concentration profiles over the ripples were consistent with settling flux balanced by pure gradient diffusion and a sediment diffusivity that is constant with elevation above the bed cref in that case is shown to apply at z 0 where z is the elevation above the bed over the hummocks there was a sheet flow at the base of the suspension and cref is shown to apply at z 1 cm the concentration profiles over the hummocks implied sediment diffusivity that varied linearly with elevation within 10 cm of the bed and constant sediment diffusivity above that level for both rippled and hummocky beds 0 derived from the field data was found to be sensitive to the value assumed for critical stress for initiation of sediment motion which could explain the range of values reported in the literature for 0 0 was also found to vary in a complex way with skin friction which suggests that the reference concentration model based on excess skin friction is not correctly formulated nevertheless two functions for 0 one applying to rippled beds and the other to hummocky beds were contrived to make the model fit the data the model based on non dimensional skin friction was found to be a good predictor of cref when a correction was made for flow contraction over ripples the correction was not required for the hummocky bed where sediment was being entrained in a thin sheet flow layer the model based on non dimensional skin friction correctly portrayed the relationship between flow and sediment response without contrivance and therefore should be the favoured approach in predicting reference concentration

a morphological model of the beach profile integrating wave and tidal influences abstract meso and macrotidal beaches constitute a significant proportion of the world s beaches however by far they have been less studied and understood than tideless beaches even though in recent times several local studies have addressed this problem few attempts to model tidal beaches exist a morphological model capable of predicting the beach profile behaviour under different wave and tide conditions is proposed it is based on the concept of the two section equilibrium beach profile and has been validated with field and laboratory data this is achieved by means of two parameters the modal tidal range and the dimensionless fall velocity tide is considered a local variable whose principal effect is the lengthening of the intertidal profile the greater the tidal range the wider the intertidal profile here defined as the surf profile the dimensionless fall velocity defines the transition from dissipative to reflective situations in beaches of any given tidal range wave height is the controlling parameter in seasonal beach changes as the wave height decreases the beach profile changes from erosive to accumulative these morphological changes in the surf and shoaling sections of the profile occur in the opposite direction whilst in the surf profile the slope of the upper part of this section becomes steeper and the concavity of whole section increases in the shoaling profile the upper part flattens resulting in a less concave section in this transition the slope break between surf and shoaling profiles here defined as the discontinuity point becomes smoother and difficult to identify the main morphological parameter of the model xo describes the length of the surf profile this parameter is capable of expressing slightly different variability in micro meso and macrotidal beaches in microtidal beaches the length of the surf profile decreases proportionally to the dimensionless fall velocity in meso and macrotidal beaches xo decreases from the dissipative to the intermediate state but increases from intermediate to reflective this results from the flattening of the lower part of the surf profile in the reflective case where a small change in tidal range generates a high stretching of the surf profile this beach morphological model is presented as a framework to understand the first order behaviour of beaches under the action of waves and tides this becomes a useful and easy to apply tool in coastal management and prediction of equilibrium beach profile under diverse conditions

compositional variations of granitic rocks in continental margin arc constraints from the petrogenesis of eocene granitic rocks in the tengchong block sw china abstract in order to address the causes of compositional variations of crust derived granitic rocks in continental margin arc we focused on the petrogenesis of eocene granitic host rocks with enclosed mmes associated metagabbro fine grained quartz diorite in xima tongbiguan area the tengchong block which is a continental margin arc related to the subduction of neo tethys both the eocene granitic and mafic rocks are characterized by gradual increment in enriched compositions such as k rb th lree initial 87sr 86sr end t and ehf t but decreasing pb isotopic ratios from the west to the east of the tengchong block zircon u pb age data of granitic host rocks mmes metagabbro and fine grained quartz diorite reveal a similar age range of 55 50 ma the lithologies zircon hf compositions geochemical and isotopic signatures of host granitic rocks show that the origin of these host rocks are mainly controlled by magma mixing between felsic and mafic magma the products of the mafic magma are dominated by metagabbro fine grained quartz diorite and mmes enclosed in granitic rocks which are all resulted from the reaction and mixture between different mafic magmatic products and felsic magma the metagabbros could be the products of felsic magma mixing with early crystallized mafic magma and the fine grained quartz diorites could be the products of felsic magma mixing with crystal rich mafic magma and the mmes could be the products of felsic magma mixing with crystal poor mafic magma or melt the metagabbro has positive ehf t values of 1 8 to 10 9 which could provide the relative primitive lu hf isotopic compositions of mafic magma indicating that the mafic magma is derived from a depleted mantle the host granitic rocks have negative end t values of 5 2 to 6 5 indicating that the felsic magma is derived from partial melting of an ancient mafic lower crust furthermore there are excess reactions after magma mixing between the mafic and felsic magma such as multi stage reactions between solidified mmes and felsic magma and the disaggregation of mmes finally resulting in the basification of felsic magma magma mixing is therefore the main mechanism of the formation of granitic rocks in the tengchong block the compositional variation of intermediate to acid igneous rock in a continental margin arc is likely dominated by the characteristics of mafic magma because the intermediate to acid igneous rock is derived from mixing of crust derived granitic and different mantle sources derived mafic magma

early silurian granitic rocks and associated enclaves as evidence of rapid cooling in a cognate magma system the case of the xuehuading panshanchong pluton south china block

segregation vesicles gas filter pressing and igneous differentiation some vesicles in certain subaerial flows of basalt and basaltic andesite are partially filled with dark partly glassy segregation material the segregation material has about three times the concentration of k o tio and p o as the associated host rock therefore the segregation materials are inferred to be frozen residual liquids that migrated into the vesicles several possible processes for filling the vesicles are examined within the context of the cooling time implied by heat conduction the preferred process is one in which the residual liquid migrates through a porous and permeable but rigid network of interlocking crystals in response to a pressure gradient generated by vapor saturated crystallization as crystallization proceeds h o is concentrated in the residual liquid and gas this produces a higher pressure in the gas poor matrix than in the vesicles and forces liquid to migrate into the vesicles textural features suggestive of or consistent with the process include 1 vesiculation

field chemical and physical constraints on mafic felsic magma interaction in the lamarck granodiorite sierra nevada california evidence of magma interactions resulting in both hybridization and mingling are preserved in a diverse suite of gabbroic to intermediate rocks associated with the compositionally zoned hornblende biotite lamarck granodiorite of the eastern sierra nevada california ellipsoidal mafic enclaves were formed by quenching of small amounts of high alumina basaltic magma upon injection into and dispersal through granodiorite magma early in its crystallization synplutonic intrusions of hornblende gabbro through hybridized mafic granodiorite represent injection of mafic magma at a later stage of crystallization of the granodiorite as they crosscut regional trends in foliation and compositional zoning in the host pluton where compositional contrasts between intrusion and host granodiorite are large contacts are sharp and abundant enclaves derived from the mafic intrusion are present in the granodiorite where the host is relatively mafic or where the local scale proportion of mafic magma is large contacts are zones of extensive hybridization that contain both enclaves and hybrid schlieren uncontaminated mafic intrusions have high alumina basaltic compositions whereas hybridized intrusions have silica contents as high as 63 5 mafic intrusions locally contain coarse grained cumulus gabbro inclusions mafic schlieren in granodiorite far from mafic intrusions represent localized accumulations of hornblende fe ti oxides and biotite from the granodiorite intrusion of late mafic dikes mobilized and entrained granitic residue from the granodiorite and formed composite dikes of aplite and pillowed diorite whether interacting magmas mix or mingle is a function of the heat contents and mass fractions of the end members calculations that account for compositions heats of fusion heat capacities of liquids and crystals and a range of initial temperatures crystallinities crystal sizes and magma water contents indicate that in most circumstances the basalt end member quenches the resulting large viscosity contrast between the end members prevents hybridization homogenization is likely only if the compositional difference between host and injected mafic magma is less than 10 sio2 or if the mass fraction of mafic magma is greater than 0 5 resulting mixtures have the composition of tonalite or mafic granodiorite thus the more silicic rocks of the granodiorite pluton must represent differentiation products rather than direct hybrids of mafic or intermediate magma and felsic magma

generation of continental adakitic rocks crystallization modeling with variable bulk partition coefficients abstract the geochemical signatures i e high sr y and la yb ratios of adakitic rocks in continental settings which are derived from the continental lower crust rather than from subducted slabs may reflect high pressure melting in the lower crust or may be inherited from their sources the north china craton ncc is an ideal place for investigation of this type of adakites due to its ubiquitous distribution as an example we explore the petrogenesis of the jurassic 163 ma adakitic rocks in western liaoning in the ne part of the ncc using elemental and sr nd isotopic analysis and crystallization modeling based on rhyolite melts the modeling demonstrates that adakitic signatures can be generated by fractional crystallization of magmas within crust of normal thickness i e 33 km partial melting modeling based on the composition of the lower continental crust shows that only the adakitic rocks from orogenic belts require a thickened crust i e 45 km we suggest that continental adakitic rocks are not necessarily linked to high pressure processes and their use as an indicator of thickened delaminated continental crust should be regarded with caution

field and model constraints on silicic melt segregation by compaction hindered settling the role of water and its effect on latent heat release to investigate how large volumes of silicic melts segregate to form granitic plutons we conducted a case study of a zoned pluton in which sio 2 increases from intermediate 69 wt to highly silicic compositions 74 wt toward the contact with metasedimentary wallrock in the outer 25 m of the pluton all other major minor and trace elements vary systematically with sio 2 and indicate that outward increasing sio 2 is due to a decrease in mafic elements and minerals whole rock oxygen isotopes and elemental variation diagrams do not support mixing with wallrock as an explanation for the si rich boundary layer instead mafic enclaves which are common in the pluton also decrease in abundance in the outer 25 m of the pluton suggesting a mechanical origin for the si rich boundary layer the coupling of mechanical and geochemical boundary layers combined with geochemical modeling indicate that the silica rich enclave poor boundary layer formed by hindered settling or compaction of a crystal rich crystal fractions 60 magmatic mush segregation of melts at high crystal fraction is known to be a slow process however petrography and zr based thermometry indicate that the residual si rich liquids were water saturated water decreases melt viscosity which helps expulsion but equally importantly water also delays much of the latent heat release to late in the thermal and crystallization history of a cooling magma we show that the higher the water content the longer the time interval over which a magma chamber resides at the stage when water saturated high silica liquids form allowing sufficient time for exfiltration of silicic liquids before the magma body freezes

swash zone sediment transport modes abstract the result of field experiments designed to investigate the relative proportions of bedload and suspended load are described the ratio of bedload to suspended sediment load in the swash zone is examined in both swash and backwash on four beaches by measuring the amounts collected in a sediment trap bedload transport is found to dominate the backwash the relative proportions of bedload and suspended load change over the tidal cycle with increasing bedload dominance at low tide the total amount of sediment transported as swash and backwash is noticeably greater at high tide than at low tide more sediment is transported on the flood tide than on the ebb

the significance of microgranitoid enclave shapes and orientations abstract enclaves are often incorrectly used to measure magmatic strains in plutons we emphasize that microgranitoid enclaves are not like other ellipsoidal markers used to determine strain for the following reasons 1 adjacent enclaves may form at different times and different places and initially have non spherical shapes with axial ratios up to 2 7 2 the final shapes and orientations of enclaves are a complex function of a initial shape and temperature of enclaves b subtle changes in composition melt percents volatiles grain sizes and thus temporally variable viscosity contrasts between the enclave and magma c a competition between strain and interfacial energies and d deformation path which may include internal strain and rigid rotations caused by magma flow during ascent convection expansion chamber boundary processes and tectonism 3 enclaves spend much of their time in magma as relatively rigid objects and thus rigidly rotate and potentially break apart rather than strain at matrix strain rates 4 in some instances enclaves do not record or track finite strain because of the above final enclave populations are heterogeneous and the use of single enclaves or enclave populations as strain markers violates many assumptions needed to complete strain analyses on the other hand a comparison of the preserved characteristics of igneous layering mineral fabrics and carefully evaluated enclave fabrics including internal mineral alignment in enclaves may provide qualitative data on the changing magnitude and kinematics of magmatic strains

short term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach abstract this paper describes the morphological and sedimentological evolution of amacrotidal beach over a 20 day period under varying hydrodynamicconditions signi cant breaker heights of 0ae3 2 m and tidal ranges of 2 5 m during the eld campaign an intertidal bar developed around the mid tidelevel migrated onshore welded to the upper beach and was then attenedunder energetic wave conditions the bar had a wave breakpoint origin and itsformation was triggered by a reduction in tidal range causing more stationarywater level conditions rather than an increase in wave height most of theonshore bar migration took place while the bar was positioned in the inner tomid surf zone position such that the bar moved away from the breakpoint andexhibited divergent behaviour the depth of disturbance over individual tidalcycles was 10 20 of the breaker height such values are more typical of steepre ective beaches than gently sloping dissipative beaches and are consideredto re ect the maximum height of wave generated ripples the grain sizedistribution of sur cial sediments did not vary consistently across the beachpro le and temporal changes in the sedimentology were mostly unrelated tothe morphological response the lack of clear links between beach morphologyand sedimentology may be in part due to shortcomings in the samplingmethodology which ignored the vertical variability in the sediment sizecharacteristics across the active layer keywords beach sediment depth of disturbance intertidal bar macrotidalbeach morphology introductionbeaches respond rapidly to changing wave andtide conditions through the redistribution of theirsediments by oscillatory and quasi steady cur rents resulting in spatial patterns of erosion sediment divergence and accretion sedimentconvergence given suf cient time these bed level changes modify the beach shape by theformation modi cation destruction and ormigration of secondary morphological features such as berms beach cusps swash bars ripchannels and nearshore bars the dynamics ofthese secondary morphological features and theirrole in affecting beach stability has been a majorfocus of beach research over the last few decades e g komar 1998 short 1999 most short term days to weeks eld investi gations addressing the morphological response ofsandy beaches to wave and tide forcing have beenconducted in microtidal or mesotidal settings beaches in macrotidal settings have on the otherhand only received limited attention despitetheir common occurrence short 1991 a mainreason for this imbalance is that macrotidalbeaches are often planar and lack pronouncedsecondary morphological features indeed theonly type of macrotidal beach that does featureprominently in the coastal literature is the ridgeand runnel beach which is characterized bysedimentology 2007 54 39 53

role of viscous folding in magma mixing abstract magma mixing is a complex phenomenon and occurs through the interplay of a number of processes recent developments in microfluidics and chaotic mixing experiments have enabled us to better understand the complex processes associated with magma mixing from the hybrid rocks of the ghansura rhyolite dome grd of proterozoic chotanagpur granite gneiss complex cggc eastern india the hybrid rocks of grd have preserved amphibole rich microzones arm and microfolded mineral veins resulting from the mixing of felsic rhyolitic and mafic basaltic melts based on textural features and mineral chemical data interpretations we infer that viscous folding can be an important mechanism to obtain chemical equilibrium in a magma mixing scenario magma mixing is a chaotic process brought about by the interplay of advection i e stretching and folding and diffusion in our scenario stretching and folding of the mineral veins or filaments were achieved through viscous folding followed by chemical diffusion between the contrasting magmas to enhance magma mixing our findings reveal that when mafic magma carrying phenocrysts of augite came in contact with the felsic magma there was diffusion of heat from the hotter mafic phase to the colder felsic phase followed by diffusion of elemental components diffusion of elements like h al3 and other cations from the felsic phase to the mafic phase converted clinopyroxene phenocrysts in the mafic system into aggregates of small amphibole crystals the formation of abundant amphibole microcrysts greatly increased the viscosity of the mafic system allowing the amphibole rich magma to venture into the surrounding felsic melt as veins and undergo viscous folding to facilitate mixing