fluid absent melting of a layered crustal protolith implications for the generation of anatectic granites we report the result of h2o undersaturated melting experiments on charges consisting of a layer of powdered sillimanite bearing metapelite hq36 and a layer of powdered tonalitic gneiss agc150 experiments were conducted at 10 kbar at 900 925 and 950 c when run alone the pelite yielded 40 vol strongly peraluminous granitic melt at 900 c while the tonalite produced only 5 vol weakly peraluminous granitic melt at 950 c the pelite and the tonalite yielded 50 vol and 7 vol granitic melt respectively when run side by side the abundance of melt in the tonalite was 10 times higher at all temperatures than when it was run alone in the pelite the melt abundance increased by 25 vol when run alone biotite dehydration melting in the tonalite yielded orthopyroxene and garnet in addition to granitic melt when run side by side only garnet was produced in addition to granitic melt experiments of relatively short duration however also contained al rich orthopyroxene we suggest that the large increase in melt fraction in the tonalite is mainly a result of increased activity of al2o3 in the melt which lowers the temperature of the biotite dehydration melting reaction in the pelite the increase in the abundance of melt is caused by transport of plagioclase component in the melt from the tonalite layer to the pelite layer this has the effect of changing the bulk composition of this layer in the direction of minimum temperature granitic liquids our results show that rocks which are poor melt producers on their own can become very fertile if they occur in contact with rocks that contain components that destabilize the hydrous phase s and facilitate dehydration melting because of this effect the continental crust may have an even greater potential for granitoid melt production than previously thought our results also suggest that many anatectic granites most likely contain contributions from two or more different source rocks which will be reflected in their isotopic and geochemical compositions

experimental melting of biotite plagioclase quartz muscovite assemblages and implications for crustal melting abstract in order to understand the role of mica rich rocks as a source of granite magmas a series of melting experiments was performed on two different starting materials the first composition is a model biotite gneiss consisting of 30 wt biotite 30 wt plagioclase and 40 wt quartz the second composition is a model two mica pelites consisting of 15 wt biotite 15 wt muscovite 30 wt plagioclase and 40 wt quartz experiments were performed under vapor absent conditions at 1 0 gpa and between 750 o and 950oc with only biotite in the starting material the volume of melt is always less than 15 vol below 900oc and reaches 25 vol at 950oc in experiments that involve both biotite and muscovite in the starting material the melt proportion increases up to 28 vol at 825oc and reaches 60 vol at 950oc for the biotite plagioclase quartz bpq assemblage the solidus is located at 800oc at 1 0 gpa the melting reaction produces a metaluminous granitic liquid and leaves a residuum consisting of garnet biotite orthopyroxene plagioclase quartz in addition the experiments show that at 1 0 gpa biotite can be stable above 950oc with both micas in the starting material bpqm the solidus at 1 0 gpa is located at 750oc the melting reactions produce a peraluminous granitic liquid and leave a residuum of garnet sillimanite biotite quartz plagioclase kfeldspar in experiments below 900oc at 950oc the residuum consists of garnet orthopyroxene biotite plagioclase the melt fraction is determined by the proportions of the hydrous phases and of the amount of feldspar relative to quartz mineral modes of the source rocks particularly the amount of quartz are at least as important as the amount of available h20 in controlling the melt fraction generated during crustal anatexis

magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

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

partial melting of metagreywackes part ii compositions of minerals and melts a series of experiments on the fluid absent melting of a quartz rich aluminous metagreywacke has been carried out in this paper we report the chemical composition of the phases present in the experimental charges as determined by electron microprobe this analytical work includes biotite plagioclase orthopyroxene garnet cordierite hercynite staurolite gedrite oxide and glass over the range 100 1000 mpa 780 1025 c biotites are na and mg rich with ti contents increasing with temperature the compositions of plagioclase range from an17 to an35 with a significant orthoclase component and are always different from the starting minerals at high temperature plagioclase crystals correspond to ternary feldspars with or contents in the range 11 20 mol garnets are almandine pyrope grossular spessartine solid solutions with a regular and significant increase of the grossular content with pressure all glasses are silicic sio2 67 6 74 4 wt peraluminous and leucocratic feo mgo 0 9 2 9 wt with a bulk composition close to that of peraluminous leucogranites even for degrees of melting as high as 60 vol with increasing pressure sio2 contents decrease while k2o increases at any pressure the melt compositions are more potassic than the water saturated granitic minima the h2o contents estimated by mass balance are in the range 2 5 5 6 wt these values are higher than those predicted by thermodynamic models modal compositions were estimated by mass balance calculations and by image processing of the sem photographs the positions of the 20 to 70 isotects curves of equal proportion of melt have been located in the pressure temperature space between 100 mpa and 1000 mpa with increasing pressure the isotects shift toward lower temperature between 100 and 200 mpa then bend back toward higher temperature the melting interval increases with pressure the difference in temperature between the 20 and the 70 isotects is 40 c at 100 mpa and 150 c at 800 mpa the position of the isotects is interpreted in terms of both the solubility of water in the melt and the nature of the reactions involved in the melting process a comparison with other partial melting experiments suggests that pelites are the most fertile source rocks above 800 mpa the difference in fertility between pelites and greywackes decreases with decreasing pressure a review of the glass compositions obtained in experimental studies demonstrates that partial melting of fertile rock types in the crust greywackes pelites or orthogneisses produces only peraluminous leucogranites more mafic granitic compositions such as the various types of calk alkaline rocks or mafic s type rocks have never been obtained during partial melting experiments thus only peraluminous leucogranites may correspond to liquids directly formed by partial melting of metasediments other types of granites involve other components or processes such as restite unmixing from the source region and or interaction with mafic mantle derived materials

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

case study numerical modeling of the tidal bore on the qiantang river china the tidal bore at the estuary of the qiantang river in china is one of the most spectacular bores in the world although it is a famous scenic spot it may cause disasters due to its destructive power in this paper a new numerical model based on a godunov type scheme with the water level bottom topography formulation combined with the improved wet dry techniques is constructed to numeri cally simulate the tidal bore on the qiantang river the simulated results using the model agree well with observed data which shows that the model can reproduce the formation evolution and dissipation of the tidal bore on the qiantang river

geochemistry of tuscan archipelago granitoids central italy the role of hybridization processes in their genesis this paper reports major trace and rare earth element data for selected samples from the elba giglio and monte cristo plutons which lie in the tuscan archipelago italy on the basis of field and petrologic constraints all the rocks can be divided into five facies and range in composition from granodioritic to alkali granitic with a strong predominance of monzogranites tuscan archipelago granitoids are clearly collision related rocks and they straddle the i and s types of chappell and white however mineralogical and chemical characteristics indicate that the more basic rocks are broadly i type while the high silica rocks are s type genetic models that relate these magmas through the segregation of their major and accessory mineral phases are inconsistent with major trace and ree element abundant data geological petrographical and geochemical constraints show that the microgranular mafic enclaves found within the rocks are blobs of mafic high temperature magma chilled within a cooler m

i type plutonism in a continental back arc setting miocene granitoids and monzonites from the central aegean sea greece miocene extension in the aegean sea was accompanied by the intrusion of granitoid and monzonitic magmas at upper crustal levels with increasing distance from the trench the metaluminous to slightly peraluminous i type intrusives show a systematic regional variation in their compositions medium to high k granodiorites in the wsw high k low silica granites in the central region and high k high silica granites monzonites monzogranites and composite lamprophyric monzonitic dikes in the ene the granodioritic and low silica granitic plutons comprise similar ranges of sio2 63 5 71 6 wt and initial nd sr and o isotopic values end i 7 0 to 9 8 87sr 86sr i 0 7092 0 7115 18o 9 7 11 5 but display significant differences in their chemical compositions compared with the granodiorites the low silica granites have higher abundances of large ion lithophile light rare earth and some high field strength elements initial isotopic signatures of the high silica granites in the ene end i 9 0 to 9 6 87sr 86sr i 0 7128 0 7144 18o 10 8 12 0 are slightly more crust like than those of the low silica granites in chemical variation diagrams samples from the high silica granites continue the trends defined by those from the low silica granites it is suggested that all granitoid magmas originated by dehydration melting of metaluminous older crustal sources most probably metagreywackes u pb systematics of zircon populations in conjunction with zr sio2 systematics and zircon saturation temperatures suggest a high proportion of restitic or assimilated crustal material in these magmas monzonitic to monzogranitic rocks show chemical and isotopic characteristics end i 0 8 to 3 6 87sr 86sr i 0 7059 0 7071 18o 9 4 10 6 that are significantly different from those of the granitoids a small portion of an older crustal component in these magmas is indicated by u pb systematics of zircon populations lamprophyric dikes display chemical and isotopic signatures end i 0 5 87sr 86sr i 0 7044 18o 8 9 that are compatible with an origin from either a mantle source previously enriched by slab derived hydrous fluids melts as suggested by negative nb ta anomalies or a new k rich basaltic underplate abundant composite dikes indicate the coexistence of and mingling mixing between lamprophyric melts and monzonitic magmas

cooling history of nested plutons from the variscan tichka plutonic complex morocco four imbricated mafic to felsic plutons of variscan age from morocco have been investigated for their cooling history and geochemical interactions with surrounding continental rocks oxygen isotope compositions of whole rocks and minerals have been used to model the cooling rates of these kilometer sized intrusions by combining both the knowledge of oxygen self diffusion data of rock forming minerals and the determination by ir spectroscopy of the water content of quartz the cooling times are estimated ranging from 10 to 5 10 years in agreement with the shallow emplacement 4 6 km depth of these intrusions into the continental crust such fast cooling rates could explain why after assimilation of the various country rocks heterogeneities of both neodymium and strontium isotope ratios were still preserved a progressive o increase from the mafic to felsic terms of the plutonic suite which does not excess 1 to 1 5 could be explained by the assimilation of metamorphosed pelitic and volcanic rocks that constitute the basement of the tichka plutonic complex

partial melting of apatite bearing charnockite granulite and diorite melt compositions restite mineralogy and petrologic implications melting experiments p 6 9 kbar t 850 950 c nno 02 hm were done on mafic to felsic charnockites a dioritic gneiss and a felsic garnet granulite all common rock types in the grenville basement of eastern north america a graphite bearing granulite gneiss did not melt water h2o 0 60 to 2 0 wt is bound in low grade retrograde metamorphic minerals and is consumed during the earliest stages of melting most melts are water undersaturated melt compositions range from metaluminous silicic granodiorite diorite starting composition to peraluminous or weakly metaluminous granites all others in general liquids become more feldspathic less silicic and less peraluminous and are enriched in feo mgo and tio2 with increasing temperature residual feldspar mineralogy controls the cao k2o and na2o contents of the partial melts and the behavior of these elements can be used particularly if the degree of source melting can be ascertained to infer some aspects of the feldspar mineralogy of the source k feldspar a common restite phase in the charnockite and granulite but not the diorite should control the behavior of ba and possibly eu in these systems and yield signatures of these elements that can distinguish source regions and in some cases bulk versus melt assimilation apatite a common restite phase is enriched in rare earth elements ree especially middle ree retention of apatite in the restite will result in steep light ree enriched patterns for melts derived from the diorite and charnockites

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

generation of metaluminous a type granites by low pressure melting of calc alkaline granitoids melting experiments on two calc alkaline rocks a tonalite and a granodiorite demonstrate that shallow dehydration melting of hornblende and biotite bearing granitoids generates metaluminous a type granitic melts profuse crystallization of calcic plagioclase orthopyroxene during low pressure p 4 kbar incongruent melting explains all of the major and trace element characteristics of a type granites e g their low al ca mg sr and eu contents and high ga al and k na ratios as well as their common association with anorthositic and mangeritic rocks the residual assemblage produced during melting of the same rocks in the deep crust p 8 kbar is dominated by clinopyroxene and as a consequence most of the chemical features diagnostic of a type granites are lost the high temperatures 900 c and low h 2 o contents 4 wt that are characteristic of a type magmas are adequately explained by the h 2 o poor nature of the granitoid source materials and require neither a granulitic nor a f rich source previous attempts to explain the origin of a type granites have focused on the nature of the source material these experiments show that pressure of melting is at least as important as source composition in engendering a type melts

vertical displacements induced by quasi stationary waves in the southern hemisphere stratosphere during spring abstract vertical displacements induced by the quasi stationary wave with wavenumber 1 qsw1 in the southern hemisphere stratosphere during spring are studied the displacement exhibits two amplitude maxima located in the upper and lower stratosphere with a phase change of 180 between the two regions ozone mixing ratio and temperature wave signatures are explained by the wave induced displacement in the presence of mean vertical gradients the qsw1 induces radiative diabatic forcing in the upper stratosphere that results in a cross isentropic ozone transport correlation between vertical displacement at different levels and total ozone indicates that total ozone is directly connected to the displacement in the lower stratosphere the displacement extends to the tropopause and results in a correlation between total ozone and the tropopause height but with smaller values relative deviation between reconstructed potential vorticity pv by using a high resolution model and pv from observations indicates

a fore arc origin for the thrace basin nw turkey hydrocarbon bearing thrace basin occupies much of the european part of turkey the middle eocene to oligocene sequence in the centre of the basin exceeds 9 km in thickness based on the stratigraphy structure and the regional context of this basin we propose that it developed as a fore arc basin between the medial eocene and the oligocene above the northward subducting intra pontide ocean its post miocene history has been dominated mainly by wrench tectonics resulting from the activity of the now deactivated northwestern strand of the present day north anatolian fault zone

comparison of element and isotope diffusion of k and ca in multicomponent silicate melts recent experimental work has shown that the homogenization of elemental concentrations can be much slower than that of isotopic ratios when there are strong concentration gradients in sio 2 and al 2o 3 the ramifications of this result for magma homogenization and other petrological problems related to diffusion are significant we report here a comparison of experimental profiles of elemental concentrations and isotopic fractions of k and ca in rhyolite andesite large concentration gradients and rhyolite rhyolite small concentration gradients melt couples when the concentration profile and the isotopic profile of the same element in a single couple are compared the former is much shorter than the latter in the rhyolite andesite couple consistent with other recent studies however the lengths of both concentration and isotopic profiles are similar in the rhyolite rhyolite couple therefore diffusion of an element or oxide may be decoupled from or coupled with isotopic diffusion depending on whether large concentration gradients of major components are present when the two couples are compared the intrinsic effective binary diffusivities obtained from isotopic profiles are similar for each element in the two couples whereas the effective binary diffusivity of k obtained from the concentration profile in the rhyolite rhyolite couple is 37 times that in the rhyolite andesite couple therefore isotopic homogenization is roughly independent of elemental homogenization and the presence of sio 2 al 2o 3 and other concentration gradients whereas elemental homogenization is strongly affected by concentration gradients our experimental data isotopic and concentration profiles including uphill diffusion profiles can be modeled quantitatively to a good approximation using a modified effective binary diffusion model in which the flux of a component is assumed to be proportional to its activity gradient instead of its concentration gradient therefore the multicomponent diffusion effect in the silicate systems of our experiments seems to be largely due to contributions of non ideal mixing to the cross terms of the diffusivity matrix

amphibole out phase boundary in partially melted metabasalt its control over liquid fraction and composition and source permeability a number of experimental studies in recent years have demonstrated that partial melting of hydrated basalt at lower crustal to upper mantle pressures is capable of generating up to 40 high sio2 liquids closely comparable in many geochemical respects to tonalitic trondhjemitic granitoids ttg from these studies it is apparent that the initiation of melting coincides with the beginning of amphibole dehydration but that a broad reaction interval over which amphibole coexists with high sio2 liquids is defined by the wet basalt solidus on one side and the amphibole out phase boundary on the other the phase relations of an alkali rich tholeiitic metabasalt have been examined in the outer half of this region up to and beyond the amphibole out phase boundary results indicate that amphibole exerts a strong control over the amount and composition of coexisting liquid over this interval melt fraction increases slowly and gradually from 0 up to 20 30 between the wet basalt solidus and up to amphibole out but increases substantially from 30 to 50 across and immediately beyond it liquids are strongly to moderately peraluminous molar al2o3 cao na2o k2o a cnk 1 0 up to amphibole out neutral at the boundary a cnk 1 0 and increasingly metaluminous a cnk 1 0 beyond it up to amphibole out potassium is strongly partitioned into liquid relative to amphibole i e mineral melt kd 0 2 0 3 whereas titanium is strongly partitioned into liquid kd 2 0 6 0 physical and chemical criteria suggest that efficient melt segregation leading to ttg plutonism requires more than 20 30 batch melting of a garnet bearing basaltic protolith near or beyond the amphibole out phase boundary leaving dry residues of eclogite or garnet granulite and producing metaluminous liquids that are strongly depleted in heavy rare earth elements hrees and yttrium y lower degrees of melting may involve critical melting where melt is squeezed out of the residue by deformation of the crystalline matrix resulting in disequilibrium melt compositions

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

a geochemical and experimental study of the role of k feldspar during water undersaturated melting of metapelites abstract the production of s type granites has been related to the extraction of melts during water undersaturated melting of metasediments in the lower continental crust if this mechanism is of widespread applicability a chemically distinctive granulitic restite must be left behind with a positive eu anomaly and depleted incompatible element concentrations however little geochemical evidence has been found in support of this hypothesis the rare earth element geochemistry of lower crustal granulites and associated melts will depend on the behaviour of the phases in which ree and trace elements are concentrated i e zircon monazite and k rich feldspar new experimental data on synthetic metapelites show that k feldspar can be a product or a reactant during water undersaturated melting of biotite depending on the h2o k2o of the melt relative to biotite past confusion over the role of k feldspar during melting is due to the reaction being close to degeneracy and changing its stoichiometry in response to only small changes in bulk composition coherent interpretation of the role of k feldspar in different experimental studies requires a better knowledge of phase water contents than has commonly been available the leucosomes formed in some antarctic granulite facies migmatites are likely to have had low h2o k2o ratios which suggests that k feldspar would have been a reactant during melting this could cause the positive eu anomalies observed in the leucosomes through the disequilibrium melting of k feldspar during water undersaturated melting the undersaturation of trace elements and ree in the leucosomes strongly suggests that disequilibrium melting took place caused by the incomplete dissolution of accessory phases monazite and zircon these phenomena give the melts a distinctive geochemical character which has also been seen in the other granulite facies leucosomes analysed to date this geochemical character contrasts with that of s type granites and therefore the production of granulites in the lower crust may not necessarily be associated with this type of magmatism if lower crustal granulite facies migmatites are the source region for peraluminous s type granites then the melts generated must undergo considerable modification during ascent

geology and geochronology of the arnea sithonia and ouranopolis intrusions chalkidiki peninsula northern greece abstract the chalkidiki peninsula comprises the greek geotectonic units of the vardar axios zone and the serbo macedonian massif several granitic bodies of various ages intrude this area and many of them are of unknown or disputed age the ages of the arnea sithonia and ouranopolis granitoids are investigated using 40 ar 39 ar stepheated mineral and rb sr whole rock analyses the arnea granite has experienced intense but variable deformation recrystallization and retrogression in general it lacks easily datable minerals because of it s highly evolved silica rich composition however coarse grained phlogopitic mica separated from a minor less evolved porphyritic part of the intrusion yields an excellent 40 ar 39 ar plateau age of 136 1 ma rb sr whole rock samples give a regression line of age 155 11ma and an initial 87 sr 86 sr ratio of 0 7174 0 0017 mswd 280 the scatter may reflect the widespread recrystallization and deformation of the arnea granite the arnea granite is at least late jurassic in age and has undergone regional greenschist metamorphism during the early cretaceous biotite from the sithonia granitoid yields a plateau age of 43 0 6 ma muscovites from crosscutting pegmatites within the granitoid give slightly saddle shaped age spectra with minimum ages of 49 ma and 50 ma suggesting argon 40 excess biotite and muscovite from the ouranopolis granitoid yield plateau ages of 44 1 1 ma and 47 0 7 ma respectively it is suggested that this granitoid is coeval and cogenetic with the sithonia granitoid both intrusions are eocene in age rb sr whole rock samples from the sithonia and ouranopolis granitoids failed to provide any isochrons this is interpreted to be due to inhomogeneities in these young intrusions the age data strongly suggest that the sithonia and ouranopolis granitoids are unrelated to the arnea granite coupled with geochemical and petrographic data these results clarify the relationships between some of the granitic intrusions and have important regional implications

magma mixing in the genesis of hercynian calc alkaline granitoids an integrated petrographic and geochemical study of the sazava intrusion central bohemian pluton czech republic the devonian early carboniferous 354 1 3 5 ma conventional zircon u pb age sazava intrusion biotite amphibole quartz diorite tonalite and granodiorite of the central bohemian pluton cbp associated with bodies of olivine pyroxene amphibole gabbro gabbrodiorite quartz diorite and rare hornblendite gives an opportunity for a comparative study of a rather shallow calc alkaline magma mixing zone at two levels separated by a vertical difference of approximately 1 km the deeper section p ibram displays the direct evidence for the existence of a long lived periodically tapped and replenished floored magma chamber masli the contacts between the subhorizontal sheet like basic bodies and the surrounding commonly cumulus rich sazava granitoid are arcuate and cut by a series of veins and ascending pipes shallow dipping swarms of strongly elongated and flow aligned mafic microgranular enclaves mme concordant with the contacts of the basic bodies are commonplace the higher level teletin section shows relatively independent basic intrusions some of them distinctly hybrid in character and mainly of quartz dioritic composition surrounded by relatively homogeneous nearly cumulus free sazava tonalite rich in texturally variable mme larger quartz microdiorite bodies and the mme both interpreted as hybrids contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning particularly well shown by cathodoluminescence cl most often the megacrysts have cores of labradorite anorthite partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth also characteristic are long prisms of apatite oikocrysts of quartz and k feldspar and zoned amphibole the latter has brown pargasite and magnesiohastingsite cores resorbed and overgrown by magnesiohornblende compositionally similar to the amphibole in the sazava tonalite the brown cores are probably relics of a higher p t stage with temperature exceeding 900 c plots of major element analyses of the teletin quartz microdiorite and the mme fall close to the line joining the compositions of the evolved sazava granodiorite tonalite and the associated gabbros the estimated minimal proportions of the acidic end member range from ca 15 to 20 for the quartz microdiorite and ca 40 to 60 for the enclaves field relationships macroscopic and mineralogical features and whole rock geochemistry are consistent with a hybrid origin of the quartz microdiorite masses and enclaves unzoned calcic plagioclase cores are interpreted as having crystallized from a basic magma prior to its injection into a high level acidic magma chamber the sudden decrease in ca activity and introduction of water due to magma mixing with tonalitic melt led to their resorption and brecciation quartz ocelli that are abundant locally in some basic bodies are most likely xenocrysts introduced from the felsic magma in the basic melt they were resorbed and became a substrate for heterogeneous nucleation of the amphibole or pyroxene coronas strong undercooling of the basic magma resulted in the growth of long prismatic apatite together with dendritic boxy cellular plagioclase both types of plagioclase cores were subsequently overgrown by more sodic mantles at the same time small unzoned plagioclase crystals nucleated in the groundmass following thermal re adjustment crystallization of the hybrid magma ended with considerably slower growth of quartz and k feldspar oikocrysts

interplay between geochemistry and magma dynamics during magma interaction an example from the sithonia plutonic complex ne greece orogenic granitoids often display mineralogical and geochemical features suggesting that open system magmatic processes played a key role in their evolution this is testified by the presence of enclaves of more mafic magmas dispersed into the granitoid mass the occurrence of strong disequilibrium textures in mineralogical phases and or extreme geochemical and isotopic variability in this contribution intrusive rocks constituting the sithonia plutonic complex northern greece are studied on the basis of mineral chemistry whole rock major trace element geochemistry and sr and nd isotopic composition sithonia rocks can be divided into a basic group bearing macroscopic mafic enclaves microscopic disequilibrium textures geochemical and isotopic evidence of magma interaction and an acid group in which most geochemical and isotopic features are consistent with a magma mixing process but macroscopic and microscopic features are lacking a two step mixing plus fractional crystallization mfc process is considered responsible for the evolution of the basic group the firststepexplainsthechemicalvariationinthemaficenclavegroup abasicmagma representedbytheleastevolvedenclaves interacted

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

multistage crystallization of tonalitic enclaves in granitoid rocks hercynian belt spain implications for magma mixing the crystallization sequence nucleation density and crystal index n nucleation density mode of tonalitic enclaves from different granitoids of the hercynian orogeny indicate that they are pieces of magma partially crystallized in the interior of synplutonic bodies of basic magma which was injected into a silicic magma chamber a rapid cooling stage can be identified from the high nucleation density and high n values of minerals a final stage of slow cooling is identified by a low nucleation density and low n values at this stage a residual melt crystallized in thermal equilibrium to the cooling rate of the whole magma chamber thermal equilibrium and convection are necessary conditions for mixing enclaves can be interpreted as the remaining non disaggregated portions of an early injected mafic magma which in turn underwent hybridization during injection their presence indicates the existence of magma mixing processes and the possibility that the host granitoid was a hybrid rock

trace element variations in atlantic ocean basalts and proterozoic dykes from northwest scotland their bearing upon the nature and geochemical evolution of the upper mantle abstract trace element data on ocean floor and ocean island basalts from the atlantic and from early proterozoic dyke swarms are considered in relation to the nature and causes of upper mantle heterogeneity studies of dredged and drilled basalts from the north atlantic have enabled the compositions of erupted ridge basalts to be monitored in space and time and have revealed the following features a that while melting processes may give rise to appreciable ree variation at a particular site ratios of the more incompatible elements remain remarkably consistent in basalts erupted at a particular ridge segment for tens of millions of years and b that there are major differences in incompatible element ratios in basalts erupted at different ridge segments the relationships suggest that the volumes of mantle with these characteristic incompatible element ratios must be large but that the processes associated with basalt generation are not capable of significantly changing incompatible element ratios nevertheless the processes which have produced these incompatible element variations must be incorporated into any model for mantle evolution our preferred model invokes both crustal extraction and incipient mantle melting as the major mechanisms for changing incompatible element mantle source regions both represent very small degrees of mantle melting a depleted upper mantle variably veined with incompatible element enriched liquids or fluids derived through incipient melting at greater depths is most consistent with the trace element and isotopic compositions of north atlantic basalts many of which are not normal mid ocean ridge basalts n type morb ocean island basalts may represent more intensely veined and in some cases at least more refractory sources sampled at lower degrees of partial melting mantle from which incipient melts have been removed probably represents the n type morb source extraction of crustal material having high contents of the large ion lithophile elements but low contents of the high field strength ions ie ta and nb from a veined metasomatized mantle source leaves the upper mantle residue enriched in ta and nb relative to the large ion lithophile elements this might explain the enrichment of ta and nb in most mantle sources of continental and ocean island basic lavas mantle sources enriched by incipient melting processes are continually dissipated by mantle convection but may be preserved for a significant time beneath stable continents trace element data on early proterozoic tholeiitic to picritic dyke swarms from scotland suggest that short term mantle heterogeneities may have existed beneath the region at that time and could have been related to the processes of crustal generation 600 m y earlier

geochemical modeling of acid basic magma interaction in the sardinia corsica batholith the case study of sarrabus southeastern sardinia italy abstract the hercynian intrusive rocks outcropping in the sarrabus area southeastern sardinia italy consist of microgranular mafic enclave mme bearing granites 95 associated with coeval stratified gabbroic complexes and basic septa bs

geologie und bau des sithonia ophioliths chalkidiki ne griechenland anmerkungen zur bildung ozeanischer krusten der oberjurassische sithonia ophiolith der chalkidiki ne griechenland bietet die moglichkeit die an der bildung fossiler ozeanischer krusten beteiligten prozesse ausfuhrlich zu untersuchen

origin of microgranular enclaves in granitoids equivocal sr nd evidence from hercynian rocks in the massif central france we examined the rb sr and sm nd systematics of three different high level to subvolcanic granitoid plutons and their microgranular enclaves the host granitoids are adamellites and grano diorites while the enclaves are mostly microtonalites with igneous textures the enclaves are rounded in shape and vary from 1 m across contacts with the enclosing granitoids are sharp and mostly nonlobate the microtonalitic enclaves are similar in mineralogy to their hosts initial 87sr 86sr are all 0 7070 and initial end is 3 0 to 6 6 for both the enclaves and their hosts this precludes a major input of an unmodified mantle derived component at the time of magma genesis nd isotopic contrasts between enclaves and hosts are 1 e nd unit at most these data indicate broadly cogenetic origins for enclave host systems though some enclaves have slightly less crustal signatures than the enclosing granitoids there are several possible interpretations 1 there may have been nearly complete isotopic homogenization between enclaves and host magmas derived from different starting parents 2 the enclaves and granitoids could all have purely crustal origins enclaves might represent magmas derived from slightly less evolved protoliths or parental magma or they could be concentrations of early formed crystals with interstitial melt 3 basaltic magma from the depleted mantle could have thoroughly mixed with a large volume of crustal melt in the lower crust 4 there could have been a significant input of melt derived from an enriched mantle source several of these mechanisms may have played roles in the genesis of the granitoids and their enclaves nd isotopes do not always allow unequivocal recognition of mantle components in granitoid magmatism we argue that enclaves of this type are probably not products of major mixing processes relevant to granitoid protoliths and large scale crustal evolution they commonly result from second order mingling of broadly cogenetic magma fractions that may have a variety of different origins

evolution of magmatic afm mineral assemblages in granitoid rocks the hornblende melt biotite reaction in the liberty hill pluton south carolina

fluid absent melting behavior of a two mica metapelite experimental constraints on the origin of black hills granite we have studied experimentally the vapor absent melting behavior introduction of a proterozoic metapelite hp 60 1 from the black hills south peraluminous leucogranites such as the miocene granites dakota to assess whether the high do tourmaline bearing granites of the himalaya and tourmaline granites of the harney of the harney peak suite resulted from muscovite dominated depeak suite in south dakota are widely considered to be hydration melting at 10 kbar samples were sealed with no added the product of muscovite dehydration melting yet few h2o in gold capsules then run in a 0 5 inch 1 27 cm pistonexperimental studies of muscovite dehydration melting cylinder apparatus over the temperature interval 812 975 c reactions have been performed because the low temexperiments were conducted at 10 kbar to allow comparison with peratures of the reactions hinder the approach to equiother metapelite melting studies mass balance calculations imply librium in addition melt fractions generated are typically the melting reaction muscovite biotite plagioclase quartz low resulting in small melt pockets which are very difficult melt alkali feldspar aluminosilicate garnet until to analyze with the electron microprobe in this study muscovite is exhausted 812 c then the reaction biotite we assess the possible genetic relationship between the plagioclase quartz alkali feldspar aluminosilicate tourmaline bearing granites of the harney peak suite melt garnet the inferred muscovite reaction is completed below and the aluminous metasediments these granites intrude 812 c and produces 1 2 wt melt melt production of the although the attempt to investigate the muscovite decontinuous biotite reaction increases steadily with rising temperature hydration melting reaction was hindered by the surto 32 wt in our highest temperature run the low melt prisingly low melt productivity we were able to infer a productivity of the muscovite reaction at 10 kbar suggests that balanced reaction illuminating the dominantly peritectic melting at lower pressures may be necessary to generate mobile melt nature of fluid absent muscovite breakdown under the fractions by muscovite dominated reactions in our starting material conditions investigated in addition melts of hp 60 1 are considerably more mafic than isotopic and trace element studies indicate a genetic the tourmaline bearing granites with average combined tio2 relationship between s type granites and aluminous metamgo feo contents of 1 85 wt and 0 84 wt respectively sediments in the black hills of south dakota where the in particular melts of hp 60 1 are enriched in ti and would harney peak granite hpg intruded proterozoic and probably stabilize biotite rather than tourmaline upon cooling archean schists and metagreywackes undergoing regional arguing against hp 60 1 as a potential source rock for the metamorphism the timing and mode of emplacement of tourmaline granites the hpg and the deformation and regional metamorphic