plagioclase mantles on sanidine in silicic lavas clear lake california implications for the origin of rapakivi texture at clear lake california mixed dacite lavas contain sanidine mantled by oligoclase that closely resemble rapakivi feldspars in granites resorption and mantling of sanidine by plagioclase is one of many disequilibrium textures in these lavas resulting from maficfelsic magma interaction mantling of sanidine by plagioclase may occur directly in mixed magmas due to shifts in composition and temperature or indirectly in crystal rich silicic magmas influenced by thermal under plating or mafic felsic hybridization in adjacent regions of the magmatic system other silicic laves containing mantled sanidine also show evidence for mafic felsic magma interaction textural and compositional similarities between rapakivi texture in extrusive and intrusive rocks suggest that they have a common origin moreover modification of early formed textures due to protracted crystallization subsolidus reactions and metasomatic hydrothermal alteration in the plutonic environment accounts for most of the observed differences between extrusive and intrusive examples the association of coeval mafic rocks and evidence for mafic felsic magma interaction in many plutons containing rapakivi exture confirm that magma mixing plays a key role in its formation in some intrusive texamples evidence for a compositional control and multiple episodes of mantle formation are also compatible with repeated cycles of recharge and mixing regardless of the exact cause of k feldspar instability textural evidence from volcanic rocks and experiments indicates that development of rapakivi texture is controlled by cation diffusion in a dissolution boundary layer developed on k feldspar mantles appear to form in a two stage process that involves initial epitaxial nucleation of plagioclase on sanidine followed by simultaneous dissolution of sanidine and inward growth of plagioclase

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

fracturing and diking in incompletely crystallized granitic plutons abstract dikes in granitic plutons commonly have mineralogic and textural characteristics indicating a genetic relation to their host the contact between the dike and the host is marked signifcantly by interlocking unfractured crystals rather than by truncations and overgrowths although megascopically the contacts between dike and host pluton may be exceedingly sharp and planar an explanation of these relationships by fracturing an incompletely crystallized host rather than by entirely post magmatic fracturing with subsequent diking is postulated to be consistent with experimental date and certain petrologic observations published experimental research indicates that fracturing of crystal melt systems may occur if there is at least 70 crystals in the system at which point the system is capable of transmitting compressive and shear stresses via a crystalline framework dilatancy pumping of melt into fracture zones and subsequent hydraulic fracturing is thought to be one possible way late stage fluids of granitic systems evolve into dikes in granitic plutons such as leucogranites aplites and pegmatites interlocking textures between dike and host may also develop if magma from some distant source is interjected along the plane of fracturing in crystal melt systems

magma mingling and melt modification between granitic pipes and host diorite guernsey channel islands within the northern igneous complex of guernsey cylindrical pipe intrusions 20 40 cm in diameter developed by buoyant emplacement of granite magma into overlying denser diorite magma the high viscosity of the partially crystallized magmas and lack of mechanical stirring inhibited physical mixing and mesoscopically sharp well defined interfaces developed the granitic pipes are surrounded by aureoles up to a metre in diameter which exhibit changes in bulk chemical composition and partial mineralogical re equilibration these formed in response to the modification of interstitial melt in the partially crystallized host resulting from residual melt migration and or melt interdiffusion across the pipe host interface such processes between partially crystallized magmas may in part provide an explanation for textural mineralogical and chemical compositional features commonly exhibited by mafic enclaves within granites

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

melt segregation and magma interactions during crustal melting breaking out of the matrix abstract differentiation of the continental crust begins with its partial melting the products of crustal melting are silicic hydrous h2o undersaturated granitic liquids that are generated within matrices of residual crystals crustal differentiation requires that felsic magmas form and escape from these solid residua an important question is whether granitic magmas collect into large batches within or near their sources which then give rise to ascent or alternatively bleed out of the sources in smaller streams or pulses we demonstrate that the physical reality is closer to the second alternative and thus question the validity of the concepts of magma segregation and source fertility as they are sometimes visualised granitic plutons contain chemically distinct sub populations formed by source level entrainment of the peritectic assemblages into the melts rapid evacuation at source levels and high ascent rates protect the magmas from wall rock interactions during their tenure at source depths and during their ascent through cool upper crust the existence of different types of granites and hence of clearly defined chemically different magmas within plutons dictates that felsic magmas must separate efficiently from their anatectic sources and must ascend to the sites of their emplacement with minimal chemical interaction with crust through which the magma must move exposed deep crustal sections are typically lithologically diverse with the more fertile rocks commonly forming discrete layers surrounded by rocks with contrasting compositions if the melts were required to segregate and accumulate into large volumes within their hot sources especially by slow gravity driven melt percolation it is very likely that they would be substantially modified by reaction with diverse source rocks thus the processes mooted to occur in melting assimilation storage and homogenisation mash or deep crustal hot dch zones would act to erase original compositional heterogeneities and produce larger batches of more homogeneous magma perhaps carrying evidence of extensive magma mixing from various lines of evidence we conclude that mash and dch zones may not exist and even if they do they cannot form the sources of most granitic magmas the intrinsic heterogeneity in crustal source rocks the likely occurrence of peritectic assemblage entrainment and the inefficiency of magma mixing decree that granitic rocks will retain source inherited chemical and isotopic heterogeneities rapid semi continuous and disequilibrium withdrawal of small magma batches from source rocks means that elements of whole rock trace element chemistry and accessory mineral chemistry will be decoupled from major element variations this also means that a large source with low nominal fertility due to low hydrous mineral content for example could still produce a substantial granitic pluton by additions of individually small increments of magma

detection of wave groups in sar images and radar image sequences the properties of individual wave groups in space and time utilizing synthetic aperture radar sar images and nautical radar image sequences are studied this is possible by the quantitative measurement and analysis of wave groups both spatially and spatio temporally the sar with its high spatial resolution and large coverage offers a unique opportunity to study and derive wave groups in addition to sar images nautical radar image sequences allow the investigation of wave groups in space and time and therefore the measurement of parameters such as the group velocity the detection of wave groups is based on the determination of the envelope function which was first adopted for one dimensional 1 d time series by longuet higgins the method is extended from 1 d to spatial and spatio temporal dimensions to derive wave groups in images and image sequences to test the algorithm wave groups are derived from sar images and two radar image sequences recorded at locations in deep and shallow water it is demonstrated that the algorithm can be employed for the determination of both location and size of wave groups from radar images investigating the detected wave groups in radar image sequences additionally allows the measurement of the spatial and temporal development of wave groups and their extension and phase velocities comparison of measured wave group velocities in shallow and deep water gives a deviation of the average value from the group velocities resulting from linear wave theory and shows a clear oscillation of the group velocities in two dimensions

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

palaeoenvironmental and archaeological records for the reconstruction of the ancient landscape of the roman harbour of narbonne aude france abstract analysis of sediment records and ams radiocarbon dates are used to reconstruct quaternary landscapes and palaeoenvironments of the ancient roman harbour at narbonne capital of the roman province gallia narbonensis which extended from the pyrenees to the alps narbonne was one of the largest port cities in the northwest mediterranean during the first millennium ad yet the strategies deployed in managing the harbour particularly the management of natural processes are little understood a synthesis of archaeological geomorphological and geophysical data was made to assess the palaeoenvironmental constraints faced by residents of narbonne and what strategies they may have adopted in the management thereof harbour structures dating from the 1 st 5 th centuries ad discovered in castelou and mandirac were intended to canalize an aude river branch allowing transfer and unloading of trade goods these new insights about the harbour of narbonne provide a valuable comparison for other ancient mediterranean harbours such as ostia italy tell about hawam israel taposiris egypt

origin of sierra nevadan granite evidence from small scale composite dikes composite dikes at hell hole meadow in the central sierra nevada contain hybrids created by small scale mixing of andesitic and rhyolitic magmas early rhyolitic injections had partially solidified when subsequent andesitic magmas arrived and mixed with small increments of remnant rhyolitic magma in major element chemistry the hybrid rocks define linear mgo variation diagrams that closely resemble those for the half dome mt givens and eagle peak granodiorites the patterns suggest that mixing of mafic and felsic magmas has been important in the evolution of these plutons

granite magma generation ascent and emplacement within a transpressional orogen crustal thickening during transpressive orogenesis may produce anatectic granites which may then localize deformation leading to transcurrent movement granites may be transported from sites of generation through the mid crust in dyke like channelways within relatively narrow strike slip shear zones which link to major fault zones in the upper crust extensional jogs within fault systems provide developing sites for the assembly of plutons from magma arriving from below the model is based upon observations from the cadomian belt of nw france which exposes sections through middle and upper levels of the late precambrian crust within different elements of the orogen the mechanism provides a favourable alternative to diapirism and explains the common collocation of granites and shear zone fault systems within orogenic belts

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

magma mixing the marsco suite isle of skye scotland magma mixing has been proposed as a major mechanism for the origin of a wide variety of rock suites in mid ocean basalts there are few obstacles to mixing because of the similarities in chemical and physical properties of the proposed end members however in calc alkaline rocks the proposed end members have disparate properties and these present obstacles to mixing

the origin of small scale geochemical and mineralogic variations in a granite intrusion a crystallization and mixing model a post tectonic unzoned granite intrusion in the meatiq dome a late proterozoic metamorphic complex in the central eastern desert of egypt shows significant chemical and mineralogic heterogeneity on the scale of sampling 5 kg whole rock analyses of 21 samples indicate small variations in sio2 al2o3 na2o and k2o and larger systematic variations in the less abundant major elements such as feo tio2 cao mno and mgo and trace elements such as sc cr co rb sr zr la ce nd sm tb yb lu ta th and u these variations cannot be accounted for by processes such as marginal accretion assimilation alteration by late stage fluids or multiple intrusion instead we proposed a model involving 35 percent solidification of the granite magma followed by partial solid liquid segregation during emplacement resulting in rocks containing 7 71 volume percent early formed solids such randomly distributed local segregation could have been caused by filter pressing flow differentiation and possibly gravity segregation either singly or in combination thus each sample is interpreted as a mixture of two end members with nearly constant compositions an early formed solid assemblage of crystals and a complementary residual liquid early formed solids are enriched in tio2 feo cao p2o5 sc co cr sr la ce and depleted in sio2 rb yb lu ta th and u while the residual liquid has complementary enrichments and depletions this simple mixing model is consistent with field and petrographic observations experimental studies pertaining to the crystallization sequence in the system ab or qtz h2o at 1 kb and physical properties of silicic magmas furthermore it is quantitatively supported by trace element data for minerals computed endmember compositions at 35 crystallization using mineral analyses and reasonable kd values and internal consistency in the percent solid for each sample computed from each of 17 elements in the inferred end members we suggest that this model might also apply to other small epizonal granite intrusions that show small scale chemical heterogeneities

the significance of mafic microgranular enclaves in the petrogenesis of the dehno complex sanandaj sirjan belt iran abstract quartz monzodioritic and granodioritic enclaves occur in the upper cretaceous paleocene dehno complex nw of isfahan iran they are hosted by hornblende granodiorite and granodiorite monzogranite respectively the presence of xenocrystic plagioclase biotite quartz magnesio hornblende occasionally with relics of clinopyroxene in quartz monzodiorites minor k feldspar and the lack of peraluminous minerals dominate the mineralogy of these rocks and suggest a metaluminous source the plagioclase in the quartz monzodioritic enclaves has higher an content than that of the respective plagioclase of their host hornblende granodiorite indicating crystallization from more mafic magma the quartz monzodioritic enclaves generally contain higher values of fe 2 o 3 mgo cao mno na 2 o transition elements ni cr co v ree and lower values of sio 2 k 2 o p 2 o 5 and zr than their host which are in consistent with occurrence of abundant ferromagnesian minerals in these rocks compare to their host the granodioritic enclaves have higher amount of fe 2 o 3 mgo mno tio 2 p 2 o 5 rb zr y ni cr co and lower concentration of sio 2 k 2 o and ba aside from hornblende granodiorite and granodiorite monzogranite the dehno complex comprises leucogranodiorite and tourmaline leuco granites geochemically the rocks of the complex are metaluminous to strongly peraluminous and are enriched in lile e g rb k sr ba and depleted in hfse e g nb ta p ti zr hf with medium to high k calc alkaline nature these geochemical features are proposed for the volcanic arc granites emplaced in an active continental margin whole rock and quartz 18 o values for all rocks are high 9 7 14 4 and 10 1 14 9 respectively suggesting the interaction of magma with crustal derived components the strongly peraluminous composition can be interpreted in terms of this hypothesis all these mineralogical and geochemical features support the idea that the granitoid rocks of the dehno complex developed through variable degrees of mixing mingling between a basic magma and a supracrustal melt during subduction of the neotethys oceanic crust beneath central iranian microcontenent the quartz monzodioritic enclaves most likely represent the nearest composition to the original more mafic magma the granodioritic enclaves result from the mixing mingling of globules basic magma with host granitic magma

laboratory investigations of viscous effects in replenished magma chambers abstract some laboratory experiments are described which investigate the dynamical effects of replenishment of a magma chamber containing high viscosity magma by hotter denser and much more fluid magma in the experiments a layer of hot kno3 solution is emplaced beneath cold glycerine which has a viscosity 3000 times greater less dense fluid is released immediately and continuously from the interface as a result of crystallization in the lower layer and rises as plumes through the overlying glycerine further crystallization occurs in the plumes and the crystals fall out but there is little mixing between the two fluids and a layer of depleted kno3 solution forms at the top the experiments demonstrate that interfacial processes begin to dominate where there are large viscosity differences between adjacent fluid layers as would be the case in a rhyolitic magma chamber replenished by basaltic magma

extensional pluton emplacement models do they work for large plutonic complexes shallow crustal to mid crustal magma emplacement models commonly rely on local or regional extension to solve the room problem we argue that existing extensional models explain the emplacement of sheeted dike complexes or internally layered plutons but are not as easily reconciled with the emplacement of elliptically shaped plutons or batholiths for the following reasons 1 rock strengths and crustal stresses prevent large voids from existing at depth and therefore require wall rock extension to be balanced by magma influx 2 rates of extension are controlled by fault slip rates of millimetres to centimetres per year and thus require numerous small injections of magma and 3 because of their sheetlike shapes and small thicknesses these small magma injections will cool rapidly and form sheeted plutons or dike swarms extension may however facilitate emplacement of elliptically shaped plutons in concert with other mechanisms if certain kinematic constraints are satisfied

mixing between granitic and dioritic crystal mushes guernsey channel islands uk abstract the contact zone between the cobo granite and bordeaux diorite complex of guernsey channel islands uk displays numerous features which result from the interaction of these two penecontemporaneously emplaced intermediate to felsic magmas initial interaction resulted in the formation of chilled mafic enclaves in granite magma as thermal equilibrium was approached some physical mixing took place to produce a heterogeneous marginal facies continued interaction resulted in incorporation of previously mixed magma into intruding magma the early mixed material is locally preserved as enclaves but more commonly underwent disaggregation promoted by its incompletely crystallised nature the mineral components becoming distributed as xenocrysts and often as microenclaves or glomeroxenocrysts into surrounding magma further modification within the contact zone was brought about by the infiltration of melt through the interconnected pore space of the magma mushes on the scale of centimetres to hundreds of metres these processes produced geochemical profiles which do not exhibit perfect mixing trends the petrographic and geochemical features described not only demonstrate the efficacy of mixing between partially crystallised magma mushes of broadly similar composition but also provide criteria by which such interaction may be recognised elsewhere many features in particular mineral scale disequilibria and small scale modal heterogeneity bear striking similarities to those which occur widely in granite plutons where obvious evidence for magma mixing is absent as such it is possible that many granite bodies preserve a subtle record of hitherto overlooked mixing events

mixing basaltic and dacitic magmas by forced convection although magma mixing is an old concept which has been applied to many magma types recent petrographic studies have revived interest in the theory by suggesting that it may account for the origin of calk alkaline magma1 6 and mid ocean ridge basalt7 9 there has been no previous experimental investigation into how two magmas with different properties can mix to form a homogeneous magma of andesitic composition or to produce textures such as observed in banded dacite we present here the results of experiments demonstrating that basaltic and dacitic magmas can be easily mixed by forced convection to form both banded dacite and homogeneous andesite in less than a few hours

re examining pluton emplacement processes abstract previous pluton emplacement studies have attempted to explain how space is made during pluton emplacement in fact the only means of making space during emplacement of mantle derived magmas in the crust are 1 lowering the moho or 2 outward displacement of the earth s surface other pluton emplacement mechanisms are material transfer processes mtps that do not increase the volume of the crust one frequently cited mtp for emplacement of concentrically zoned and ballooning plutons is ductile flow of wall rocks around the plutons the expected structures and total strains near such plutons are dependent on the three dimensional pluton shape the width of the deforming aureole whether the pluton is a piercing or non piercing diapir and in the latter case the number of body radii the pluton travels we have re examined a few such plutons and calculated the amount of material transfer caused by ductile flow in no case is more than 40 and in most cases only 15 35 of the required material transfer accommodated by wall rock flow the contact aureoles around these plutons are too narrow and or strains too low indicating that the plutons are predominantly discordant bodies with narrow 0 1 0 4 pluton radii concordant aureoles a comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains we suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned plutons are superficial because the models are too simplistic instead we argue that the ascent and emplacement of magmas require multiple near field and far field mtps these mtps will show gradients with depth distance from the magma and with time rates of near field mtps must be rapid whereas far field rates are probably nearer to long term average rates of orogenic processes

microstructural evidence of orders of crystallization in granitoid rocks experimental melting studies of granitoid rocks have documented variations in the order of crystallization of minerals depending on the melt composition total pressure and the activity of water and other volatiles in the melt microstructural criteria for independent determination of the order of crystallization are needed to permit application of the experimental data to the evaluation of the conditions of crystallization unfortunately few criteria can be reliably applied to infer either the order of initial crystallization on the order in which minerals cease to crystallize in granitoid rocks most microstructures of granitoid rocks record simultaneous rather than sequential crystallization of minerals grain size criteria e g phenocrysts vs groundmass can be used to infer a partial order of crystallization in many volcanic rocks but the presence of extremely large phenocrysts of k feldspar that from experimental data must be the last mineral to crystallize highlights the dangers inherent in the use of grain size criteria providing it can be determined that included minerals did not form subsequently along cracks or from entrapped melt inclusions those inclusions that are demonstrably and consistently only near the centre of large grains must have ceased to crystallize before the host mineral where the host mineral occurs only as rims on the early formed mineral it is possible to infer both the order of cessation and initiation of crystallization common examples are provided by the rimming produced by a discontinuous reaction relationship most other examples of inclusion relationships could result from simultaneous crystallization microstructures involving moulding and impingement relationships are unreliable as the microstructure is produced only after the minerals have begun to crystallize in the melt or on the melt solid interface as most minerals continue to crystallize right to the solidus they cease to crystallize simultaneously new criteria perhaps involving detailed chemical zoning patterns need to be developed before the orders of crystallization can be reliably determined for granitoid rocks