magma mingling and hybridization in the kuh e dom pluton central iran abstract the upper eocene kuh e dom granitoids in central iran comprise mafic microgranular enclaves ranging from a few centimeters to meters in size the spherical to ellipsoidal enclaves consist of diorite quartz diorite monzodiorite and quartz monzodiorite whereas the more felsic host intrusions mainly comprise monzogranite and granodiorite most enclaves show sharp contacts with the host granites and distinct chilled margins in the small enclaves indicate rapid cooling after entering the felsic host magma disequilibrium textures include 1 poikilitic and antirapakivi textures in feldspar megacrysts 2 ocelli quartz rimmed by fine grained mineral aggregates 3 rounded and corroded plagioclase 4 patchy plagioclase 5 mafic clots 6 blade biotite 7 small lath shaped plagioclase in larger tabular plagioclase 8 acicular apatite and 9 crenulated and cuspate contacts between enclaves and host rocks these textures indicate mingling mixing of two different magmas microprobe data show variable plagioclase compositions ranging between oligoclase and andesine in granodiorite and between andesine to labradorite in the enclaves with normal zoning and oscillatory zoning geochemically the enclaves are na rich whereas the host rocks are k rich in addition the enclaves are depleted in lree and lile and enriched in hree and ti p nb and y relative to their host granodiorites average initial nd sr isotopic compositions for the host rocks are end 47 ma 5 09 and sri 0 7068 compared to enclave sri 0 7060 and end 47 ma 2 89 fractionation of both enclaves and host rocks from the same melt cannot explain these petrological geochemical and isotopic differences instead enclaves and host rocks more likely originated from two separate magmas which subsequently mingled and mixed the mafic enclaves are modified mantle derived melts while the granodioritic host rocks are partial melts of lower continental crust the mafic enclave magma was at near liquidus conditions when injected into the granitic host melt and the kuh e dom intrusion reflects a hybrid product from mingling and partial incomplete mixing of these two melts

copper mineralization prevented by arc root delamination during alpine himalayan collision in central iran contrasting geochemical signatures of copper ore hosting eocene and some barren undeformed miocene diorites to granites in central iran temporally overlap with the alpine himalayan collision and provide key implications on the existence and lack of cu mineralization during collisional magmatism high sr and low y and yb contents of eocene arc rocks in the natanz arc segment reflect thickened andean type orogenic arc crust 45 km whereas barren miocene natanz arc rocks 21 19 ma indicate thin arc crust similar to collisional volcanism in anatolia geochemical modeling indicates a change in the mineralogy of the melt residual from precollisional eocene basaltic garnet bearing 5 30 amphibolite to syn or postcollisional miocene metasomatized mantle peridotite which can be explained by collision induced delamination of the arc lithospheric root subsequent recharge of hot asthenosphere and melting of metasomatized mantle peridotite and lack of interaction with a garnet bearing arc crustal keel explain the low sr and high y and yb contents the relatively enriched initial sr isotope ratios of postcollisional miocene natanz rocks and the lack of copper mineralization in postcollisional miocene natanz arc rocks arc root delamination removes the copper and sulfur enriched metasomatized lithospheric arc root and hydrous cumulate reservoir required to form copper ore deposits lack of the dense melt residues also provides an alternative explanation for the elevated thin crustal iranian back arc plateau 38 km as a result of uplift by isostatic rebound rather than uplift by anomalous shortening miocene arc root delamination implies a minimum age of 21 ma for the alpine himalayan collision in central iran

role of subduction erosion in the generation of andean magmas subduction erosion or scraping off of the continental crust by subducting oceanic lithosphere is an important tectonic process along parts of the andean convergent plate boundary estimated rates of subduction erosion increase northward north of the southem andes due to decreasing subduction angle and decreasing sediment supply to the trench west of the central andes subduction erosion may remove as much as 535 km 3 of crust per 1 km of trench per 1 m y or 7 vol of the subducting oceanic lithosphere the higher 87 sr 86 sr ratios of mafic magmas erupted north of the southern andes may be explained by the higher rates of subduction erosion and increased amounts of contamination of the sub arc mantle magma source

mid neoproterozoic ridge subduction and magmatic evolution in the northeastern margin of the indochina block evidence from geochronology and geochemistry of calc alkaline plutons abstract the mid neoproterozoic medium to high k calc alkaline magmatic rocks in the northeastern margin of the indochina block sw china provide important insights into the relationship of the indochina block with the gondwana supercontinent here we report zircon la icp ms u pb data from the early and late stage plutons which yield weighted mean 206pb 238u ages of 765 ma and 732 739 ma suggesting mid neoproterozoic emplacement the zircon ehf t values show a range of 3 2 to 2 4 average 0 1 0 9 with tdmc of 1510 to 1870 ma for the early plutons and 5 4 to 5 1 average 2 1 to 3 9 with tdmc of 1366 to 1985 ma for late plutons both groups show similar geochemical characteristics including high mg enrichment of lile and lree slight negative eu anomalies and strongly negative nb ta and ti anomalies with all the samples falling within the continental island arc field in tectonic discrimination diagrams these features suggest that the early and late stage magmas were produced by the mixing of mantle derived magma and crust derived magma in different proportion within an active continental margin in subduction related continental arc tectonic setting the linear zoning and roughly parallel distribution of the two generations of intrusions with a hiatus of 20 ma might suggest an episode of ridge subduction with asthenosphere upwelling through the slab window that generated the second phase of plutons

how late are k feldspar megacrysts in granites abstract various petrologists have suggested that k feldspar megacrysts grow in granites that are extensively crystallized even at subsolidus conditions however experimental evidence indicates that though k feldspar nucleates relatively late in the crystallization history abundant liquid is available for development of large crystals a great deal of evidence involving many different factors favours a magmatic phenocrystic origin for k feldspar megacrysts in granites namely simple twinning oscillatory zoning euhedral plagioclase inclusions and concentric crystallographically controlled arrangements of inclusions in addition abundant evidence has been presented of 1 mechanical accumulation of k feldspar megacrysts in granites 2 alignment of megacrysts and megacryst concentrations in magmatic flow foliations 3 involvement of megacrysts in zones of magma mixing in granite plutons and 4 occurrence of megacrysts in some volcanic rocks implying that the megacrysts were suspended in enough liquid to be moved without fracturing or plastic deformation detailed trace element and isotopic data also indicate that megacrysts can move between coexisting felsic and more mafic magmas irregular overgrowths on megacrysts are consistent with continued magmatic growth after euhedral megacrystic growth ceased the overgrowths being impeded by simultaneously crystallizing quartz and feldspar grains

experimental interaction of granitic and basaltic magmas and implications for mafic enclaves we have performed time series experiments for periods ranging from 3 min to 44 h on the interaction of granite melt and partially molten basalt at 920 c and 10 kbar in the presence of 5 wt water with time the assemblage of the basalt domain changes from predominantly amphibole plagioclase to clinopyroxene garnet the melt fraction increases from 2 5 to 40 and between the two domains the melt compositions progressively equilibrate initially in each run melts of the basalt domain have uniform plateau concentrations for sio 2 al 2o 3 cao mgo and feo because the activities of these components are regulated by the mineral assemblage but at advanced stages of reaction no such control is evident we have derived analytical expressions to describe and simulate the diffusion profiles the concentration profiles for sio 2 al 2o 3 cao and na 2o in the granite emanating from the basalt granite interface have been used to estimate effective diffusivities the values from the shorter runs are compared with those of the experiment of longest duration for which we assumed finite couples in our calculations in the diffusion calculations for k2o the difference in melt fraction between the two domains is accounted for the resulting values in cm 2 s are d na 2o 6 10 7 d k 2o 3 10 7 d mgo 9 10 8 d cao 4 6 10 8 and d sio 2 and d al 2o 3 3 0 6 10 8 they are in reasonable agreement with values from other studies on the basis of our experiments we calculate that mafic enclaves of magmatic origin should equilibrate to a large degree with their host magma in slowly cooling non convecting granitic plutons enclaves approaching complete re equilibration retain distinctly higher modal amounts of mafic minerals they do not compositionally resemble binary magma mixtures but are more like host magma with accumulated crystals we show that the modal differences between enclave and host are indicative of the temperature of homogenization and that in principle this temperature can be deduced from equilibrium phase diagrams

geo fo 2 integrated software for analysis of magmatic oxygen fugacity oxygen fugacity fo 2 is a fundamental thermodynamic property governing redox potential in solid earth systems analysis of magmatic fo 2 aids our understanding of the valence state and solubility of multivalent elements during magma evolution specialized software geo fo 2 was developed for calculating magmatic fo 2 on the basis of oxybarometers and thermobarometers for common minerals amphibole zircon and biotite in intermediate silicic magmas with user friendly interfaces it is easy to input files csv or excel files output data in excel files and plot results as binary diagrams that can be saved as vector graphics and modified using image processing software

dissolution of tonalitic enclaves in ascending hydrous granitic magmas an experimental study dissolution of natural mafic magmatic enclaves in a hydrous leucogranitic synthetic melt has been tested experimentally results suggest that the mechanism of enclave dissolution is a potential hybridization process in granitic systems experiments performed in decompression simulating ascending magmas show interesting results from 10 kbar to 4 kbar for a given temperature enhanced dissolution of the tonalitic enclave into the melt has been observed compared with experiments at constant pressure furthermore the composition of the melt changed to higher cao feo and mgo contents dissolution textures on relict crystals from the tonalitic enclave were monitored these results have implications for the generation of peraluminous monzogranites and granodiorites and an example for the cabeza de araya caceres spain from the serie mixta of the iberian massif is given the tonalitic enclaves that are partially dissolved may be early or coeval intrusions into the granite magma or even into the source migmatitic area many mineralogical geochemical and isotopic features of monzogranites e g reverse zoning in plagioclase low sr isotopic ratios are accounted for by this mechanism of enclave dissolution during ascent and emplacement

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

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

a study of strontium diffusion in k feldspar na k feldspar and anorthite using rutherford backscattering spectroscopy abstract sr chemical diffusion has been measured in orthoclase anorthoclase and anorthite under dry 1 atm conditions a strontium oxide aluminosilicate powder mixture was used as the source material with rutherford backscattering spectroscopy rbs used to measure diffusion profiles over the temperature range 725 1075 c the following arrhenius relations were obtained orthoclase normal to 001 d 5 97 10 0 0060 0 0030exp 67900 1600rtcm 2 s 1 measurements of diffusion perpendicular to 010 and 100 indicate little diffusional anisotropy in orthoclase anorthoclase normal to 010 d 4 51 10 1 358 5 6exp 89100 4800rt cm 2 s 1 normal to 001 d 2 25 10 2 1615 31exp 89300 4600rt cm 2 s 1 anorthite normal to 010 d 3 85 10 2 0 380 0 0039 exp 78800 5400rt cm 2 s 1 the correlation of sr uptake with a reduction of k and ca in orthoclase and anorthite respectively indicates that sr is exchanging with these species nuclear reaction analysis nra measurements of al in orthoclase suggests that the coupled exchange sr 2 al 3 k 1 si 4 is taking place as expected sr closure temperatures for feldspars calculated with the above parameters are relatively high compared to those of some other minerals e g biotite muscovite apatite however closure temperatures of feldspars may be significantly depressed if they are exsolved or twinned leading to small effective diffusion lengths feldspar crystals of millimeter size should retain 87 sr 86 sr ratios except when subjected to thermal events of extreme temperature or duration

the cortlandt complex evidence for large scale liquid immiscibility involving granodiorite and diorite magmas abstract granodiorite and diorite plutons of the rosetown complex n y which are associated with the nearby cortlandt complex have chemical and textural characteristics indicating that large scale liquid immiscibility played a major role in their petrogenesis rare earth element zirconium niobium and phosphorus abundances are much greater in the diorite precluding the possibility that the rosetown diorite and granodiorite are related by fractional crystallization the trace element data also eliminate the possibility that the granodiorite represents 1 a partial melt of crustal rocks including basalt 2 a granitic cumulate or 3 a residue from an aqueous fluid derived either from a silicate melt or crustal rocks liquid immiscibility appears to be viable model for the origin of the rosetown granodiorite and iron rich diorite this model is supported by the following 1 the major element compositions occur in a two liquid field on a greig diagram 2 both bodies have similar sr isotope compositions 3 common phases in the two rock types have overlapping compositions 4 the major and trace element data of the diorite and granodiorite are similar to the experimentally determined partition data of immiscible liquid pairs and 5 possible ocelli of iron rich diorite are found in the granodiorite

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

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

southward extension of the bangonghu nujiang suture evidence from early cretaceous intermediate and felsic magmatism in the gaoligong orogen china abstract it remains debated as to whether the gaoligong orogen between the tengchong and baoshan blocks in yunnan china is the southward extension of the tibetan bangonghu nujiang suture bns here we present new geochronological and petrochemical data for early cretaceous magmatic rocks of the gaoligong orogen the la icp ms u pb dating of zircons from diorites granodiorites and granites yielded weighted mean 206pb 238u ages of 120 118 128 122 and 109 128 ma respectively for the diorites the ehf t values of zircons fall in a range of 1 2 to 5 4 with tdmc ages of 744 979 ma for the granodiorites they fall in a range of 9 8 to 2 9 with tdmc ages of 888 1564 ma and for the granites the range is 8 0 to 1 1 with tdmc ages of 1101 1488 ma they are magnsian calc alkaline enriched in liles and lrees and have strong negative nb ta p and ti anomalies and high values of mg all these features are indicative of continental arc affinities the data suggest that the dioritic and granitic magmas were produced by the mixing of variable proportions of mantle and crust derived magmas at an active continental margin the ages and tectonic settings of the diorites granodiorites and granites are similar to rocks found within the bns considering the ophiolitic melange belt the middle jurassic basaltic magmatism and the marine facies stratigraphic features of the gaoligong orogen are very similar to features in the bns we conclude that the gaoligong orogen represents the suture between the tengchong and baoshan blocks and is the southward extension of the bns

zircon u pb ages and emplacement history of the nodoushan plutonic complex in the central urumieh dokhtar magmatic belt central iran product of neotethyan subduction during the paleogene abstract the nodoushan plutonic complex is composed of a wide range of felsic and mafic rocks straddling several of the major orogenic zones in iran diorite porphyry diorite granodiorite and granite intrusives belong to the central part of the urumieh dokhtar magmatic belt which is part of the alpine himalayan orogenic belt monzogabbroic members of the complex are instead located within the bordering sanandaj sirjan magmatic metamorphic zone these plutons were emplaced into permian and lower cretaceous sedimentary units and eocene calc alkaline volcanic and subvolcanic rocks new u pb zircon ages reveal that the plutonic complex was assembled incrementally over ca 15 m y during three main episodes at 40 487 0 063 ma near the middle late eocene boundary at 30 52 0 11 ma and 30 06 0 10 ma in the early oligocene middle rupelian and at 24 994 0 037 and 24 13 0 19 ma in the late oligocene latest chattian the activity recorded in the nodoushan plutonic complex represents the final stages of subduction related magmatism prior to the eventual miocene collision between the arabian and eurasian blocks

some additional observations on inclusions in the granitic rocks of the sierra nevada microgranular quartz diorite and diorite inclusions are widespread in central sierra nevada granitoid rocks and are almost exclusively restricted to hornblende bearing rocks most commonly felsic tonalites and mafic granodiorites strontium 87 strontium 86 values of the inclusions and host granitoids from individual plutons generally plot on single isochrons that agree closely with previously determined ages neodymium 143 neodymium 144 values of five inclusions ranged from 0 51229 to 0 51248 and yield end values that correlate closely with values of their respective hosts the nd sm and rb sr systematics indicate that most inclusions were in isotopic equilibrium with enclosing materials at the time of formation silica contents of inclusions and granitoids are contiguous but inclusions generally contain less than and granitoids more than 60 sio2 linear continuity of the femic oxide and h2o trends relative to sio2 suggests many inclusions formed as concentrations of hydrous mafic minerals variation of other major element oxides and trace elements support this inference the aforementioned data are generally inconsistent with a direct genetic link between the mafic inclusions and the mantle derived basalt however many initial sierra nevada magmas were produced by mixing of mafic mantle derived melts and felsic crustal materials resulting in isotopically varied tonalitic and granodioritic magmas most inclusions thus represent fragmented crystal accumulations of early formed near liquidus minerals generated from these previously mixed magmas

late cretaceous and early miocene andean type plutonic activity in northern makran and central iran two calc alkaline plutonic complexes bazman and natanz intruded through the south eastern active and south western ancient continental margins of central iran have been dated by the rb sr whole rock isochron method at 74 2 and 24 4 5 ma respectively detailed trace element studies together with low 87 sr 86 sr initial ratios 87 sr 86 sr ratios and the gabbros at least were intruded some 10 ma earlier

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

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

plagioclase xenocrysts and mafic magmatic enclaves in some granitoids of the sierra nevada batholith california plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts an oscillatory locally patchy zoned andesine or more calcic core a ring with dusty calcic plagioclase and a normally zoned rim of sodic plagioclase although aspect of the calcic rings and width and zoning of the rims may slightly vary from the enclaves to the hosts cores of both phenocrysts and large plagioclase crystals show similar zoning and composition the andesine or more calcic cores are interpreted to have crystallized in the felsic or the mafic magma respectively and been incorporated into the coeval magma when the two magmas mixed introduction of the xenocrystic cores into a magma where they were not in equilibrium resulted in partial dissolution development of abundant patchy zoning and coating with dusty calcic plagioclase in both granitoids and mafic magmatic enclaves composition and zoning contrast between cores and rims of the plagioclase crystals reflect drastic changes in conditions of crystallization before and after the mechanical mixing event mixing of two magmas with contrasted compositions is suggested to be the major mechanism for generating complexly zoned plagioclase xenocrysts in granitoids and mafic magmatic enclaves this hypothesis is consistent with many recent models in which mixing of two contrasting components is proposed to play a fundamental part in the generation of calc alkaline granitoids and mafic magmatic enclaves of the sierra nevada batholith plagioclase xenocrysts may also provide information on the timing of the different mixing processes and on the magmatic evolution of the plutons

geochemical characteristics of the kuh e dom intrusion urumieh dokhtar magmatic arc iran implications for source regions and magmatic evolution abstract the kuh e dom pluton is located along the central northeastern margin of the urumieh dokhtar magmatic arc spanning a wide range of compositions from felsic rocks including granite granodiorite and quartz monzonite through to intermediate mafic rocks comprising monzonite monzodiorite diorite monzogabbro and gabbro the urumieh dokhtar magmatic arc forms a distinct linear magmatic complex that is aligned parallel with the orogenic suture of the zagros fold thrust belt most samples display characteristics of metaluminous high k calc alkaline i type granitoids the initial isotopic signatures range from end 47 ma 4 77 to 5 89 and 87 sr 86 sr i 0 7069 to 0 7074 for felsic rocks and end 47 ma 3 04 to 4 06 and 87 sr 86 sr i 0 7063 to 0 7067 for intermediate to mafic rocks this geochemical and isotopic evidence support a mixed origin for the kuh e dom hybrid granitoid with a range of contributions of both the crust and mantle most probably by the interaction between lower crust and mantle derived magmas it is seem the felsic rocks incorporate about 56 74 lower crust derived magma and about 26 44 of the enriched mantle derived mafic magma in contrast 66 84 of the enriched mantle derived mafic magma incorporates 16 34 of lower crust derived magma to generate the intermediate mafic rocks according to the differences in chemical composition the felsic rocks contain a higher proportion of crustal material than the intermediate to mafic ones enrichment in liles and depletion in hfses with marked negative nb ba and ti anomalies are consistent with subduction related magmatism in an active continental margin arc environment this suggestion is consistent with the interpretation of the urumieh dokhtar magmatic arc as an active continental margin during subduction of the neotethys oceanic crust beneath the central iranian microcontinent

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

eocene k rich adakitic rocks in the central iran implications for evaluating its cu au mo metallogenic potential abstract the kal e kafi intrusive complex is located in the central iran magmatic zone and includes a series of granitoid rocks ranging in composition from gabbro to granite these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y enrichment in lree and lile with no eu anomalies similar to products from all of which are compatible with derivation from slab melting however relatively their low end t values 0 21 to 2 35 and higher 87 sr 86 sr i 0 7041 0 7044 are inconsistent with an origin by slab melting with these rocks also showing shoshonitic affinities with high k 2 o na 2 o ratios geochemical characteristics indicate that the kal e kafi intrusive complex was probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thicknesses of 40 km generated near the boundary between garnet bearing amphibolite or amphibole bearing eclogite melting moreover the kal e kafi adakitic magmas must have interacted with the surrounding metasomatized mantle peridotite during their ascent which elevated not only their mgo cr and ni contents but also the oxygen fugacity o 2 of the magma the high o 2 could have induced oxidation of metallic sulfides in the mantle resulting in the mobilization of chalcophile elements which are required to produce porphyry cu au and mo mineralization

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

magma flow within the tavares pluton northeastern brazil compositional and thermal convection crystallization coupled with gravity removal of depleted interstitial melt has long been recognized as a mechanism of magma differentiation similarly heat released by synplutonic basaltic magma intrusions has long been recognized as capable of driving convection in granite chambers direct evidence of these processes has seldom been described in granites in the tavares pluton we mapped a number of melt extraction structures from pores of a crystal liquid mush an effectively solid magma where crystals form an interconnected skeleton and a variety of flow structures such as 1 meter scale tear or mushroom shaped blobs representing within chamber diapirs 2 meter scale ellipsoids representing frozen thermal plumes of granite driven by heat released from disrupted diorite intrusions and 3 ladder dikes and snail structures representing cross sections of several superposed cylindrical magma channels possibly feeders of diapirs and plume heads a fundamental feature of the structures in the tavares pluton is that they are well delineated by mafic schlieren developed at active channel margins we postulate a new model for the origin of marginal schlieren which combines shear flow sorting and melt escape from the flowing magma into an effectively solid surrounding mush extraction structures representing melt extraction from mush pores into melt pockets and schlieren representing regions where melt escaped into surrounding mush pores are both favored by magmas that form an interconnected solid framework at low crystal fractions 50 because these mushes are ductile and permeable favorable magmas are those with a high wetting angle between melt and solid 60 and a propitious crystal size and shape distribution we propose a model of compositional and thermal convection that accounts for all described structures

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

the nd and sr isotopic composition of i type microgranitoid enclaves and their host rocks from the swifts creek pluton southeast australia abstract initial nd and sr isotopic compositions have been determined for microgranitoid enclaves and their host rocks from the siluro devonian swifts creek pluton within the lachlan fold belt of southeastern australia enclaves are of quartz dioritic to tonalitic composition and their textures support an igneous origin host rocks range from tonalite to granite the isotopic data form an array in nd 87 sr 86 sr space with enclaves systematically displaced towards higher nd and lower 87 sr 86 sr values enclaves range in nd t 405 ma from 7 3 to 3 1 with a narrow range in 87 sr 86 sr from 0 70613 to 0 70718 whereas host rocks range from 9 0 to 6 4 and 0 70761 to 0 70946 in nd and 87 sr 86 sr respectively the isotopic relations rule out simple crystal liquid fractionation or restite unmixing alone as the major genetic link between enclaves and host rocks the data are also incompatible with an origin of the enclaves by crystal accumulation or liquid immiscibility instead mixing between a mafic mantle derived and a crustal derived end member to generate the host rock enclave spectrum is compatible with the data because the initial isotopic ratios of enclaves and host rocks are well within the range of crustal rocks we favour the alternative view that both enclave and host rock magmas are of crustal origin consequently we avoid extrapolations to hypothetical end members we suggest that the enclaves from the swifts creek pluton are derived by partial melting of a mafic lower crust and mixed at or near the site of magma generation with a chemically less primitive and isotopically more evolved component to generate the enclave and host rock spectrum the isotopic heterogeneities within the enclave and host rocks survived the superimposed effects of crystal liquid fractionation model ages tdm for enclaves and host rocks are almost identical averaging 1 7 and 1 6 ga respectively these model ages indicate that both the enclave and host rock protoliths were derived from a mantle reservoir during the proterozoic

numerical simulation of the atmospheric signature of artificial and natural seismic events the mechanical coupling between solid planets and their atmospheres enables seismically induced acoustic waves to propagate in the atmosphere we numerically simulate this coupled system for two application cases active seismic experiments ases and passive seismic experiments a recent ase krishnamoorthy et al 2018 https doi org 10 1002 2018gl077481 observed the infrasonic signals produced by a seismic hammer to measure the sensitivity of observations to seismic parameters we attempt to reproduce the results from this experiment at short range by considering a realistic unconsolidated subsurface and an idealized rock solid subsurface at long range we investigate the influence of the source by using two focal mechanisms we found surface waves generate an infrasonic plane head wave in the ase case of the rock solid material for the passive seismic experiments the amplitude of atmospheric infrasound generated by seismic surface waves is investigated in detail despite some limitations the simulations suggest that balloon measurement of seismically induced infrasound might help to constrain ground properties

the eocene bimodal piranshahr massif of the sanandaj sirjan zone nw iran a marker of the end of the collision in the zagros orogen abstract the bimodal piranshahr massif is composed of coeval but geochemically unrelated mafic 40 7 0 2 ma zircon u pb sensitive high resolution ion microprobe shrimp age and a type felsic rocks 41 0 5 ma rb sr and 41 3 0 8 ma zircon u pb shrimp age the mafic rocks consist of two geochemical types of gabbros that derived from different magmas the more abundant gabbros are moderately alkaline have ratios of large ion lithophile elements to ree and high field strength elements to ree similar to those of intraplate mantle magmas 87 sr 86 sr 41 ma 0 7036 and e nd 41 ma 7 2 the less abundant gabbros have calc alkaline affinities 87 sr 86 sr 41 ma 0 7043 and e nd 41 ma 4 78 felsic rocks are metaluminous a2 type annite fayalite hedenbergite hypersolvus leucocratic coarse grained agpaitic syenites pulaskites and granites with 87 sr 86 sr 41 ma 0 7048 and e nd 41 ma 3 6 4 5 syenites pulaskites and granites are genetically related pulaskites probably represent alkali enriched water rich residual melts from which an f rich vapour phase was later separated granites were probably generated during open system processes in which f rich hydrous alkaline fluids released from the syenites acted upon pre existing felsic rocks the c 41 ma age of the post collisional piranshahr massif indicates that the related collision probably occurred at 50 60 ma i e late palaeocene or early eocene thus resolving a much debated question

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

geochemical characteristics of igneous host rocks of lubin zardeh au cu deposit nw iran abstract the lubin zardeh au cu pb zn deposit is located in the azerbaijan western alborz zone 45 km ne of zanjan iran it is situated within the eocene oligocene volcanic plutonic belt of the tarom subzone of the alborz mountains range quartz monzonite and tuffs are the main host rock of the lubin zardeh au cu pb zn deposit granitoid rocks are predominantly high k calc alkaline with shoshonitic affinities they are i type metaluminous magnesian and are characterized by lile lree and th enrichment relative to hfse depletion in nb ta ti and weak depletion in hree and y these granitoids show some affinities with adakites e g high sr y and la yb ratios coupled with low yb and y and enrichment in lree and lile with weak eu anomalies their relatively low to moderate initial 87sr 86sr values 0 7047 0 7051 positive nd t 36 ma values 0 39 2 1 and tdm ages of 0 69 to 1 06 ga with pb isotopic ratios of initial 206pb 204pb 18 49 18 68 initial 207pb 204pb 15 58 15 61 and initial 208pb 204pb 38 33 38 77 are consistent with a phlogopite bearing amphibole rich and enriched lithospheric mantle source metasomatized by earlier subducted sediments the geochemical and isotopic compositions of the granitoids are similar to the host rocks of porphyry and epithermal deposits in the urumieh dokhtar zone

multiphase magma intrusion ore enhancement and hydrothermal carbonatisation in the siah kamar porphyry mo deposit urumieh dokhtar magmatic zone nw iran abstract the siah kamar mo deposit skmd is located at the northwestern termination of the urumieh dokhtar magmatic zone and it is the only porphyry mo ore reserve in iran the exploration program documented 39 2 mt proved reserves 539 ppm mo and 66 4 mt probable reserves 266 ppm mo in this study field and petrographic investigations integrated with geochemical fluid inclusion and quartz chemistry and geochronological u pb zircon re os molybdenite and rb sr multimineral isochron studies are used to propose a metallogenic model for the mo mineralisation in the skmd the geology of the skmd is characterized by the emplacement of a multiphase oligocene basic intermediate at ca 33 30 ma to acidic 29 28 ma magmatic suite which intruded the eocene volcanic country rocks the alteration zone about 4 3 km in size and with a general nw se trend is centered within the main basic porphyry stock grading from an inner potassic sodic zone to peripheral phyllic propylitic halos the late acidic magmatic products stocks and dykes intruded and post dated the main alteration zone two stage mo mineralisation is recognised including i stage 1 disseminated molybdenite coeval with the formation of potassic sodic alteration and minor microscale fsp bt qz po veinlets and ii stage 2 high grade molybdenite carbonate sericite structurally controlled stockwork veining fluid inclusion systematics combined with titaniq thermometry documents a mineralising fluid system compatible with a transition from high temperature up to ca 600 c magmatic to epithermal 250 c conditions during progressive cooling exhumation and mixing with meteoric sources at shallow crustal conditions ca 7 3 km the re os molybdenite dating constrains the high grade mo ore formation at ca 29 28 ma attesting for the intimate linkage between the main mo mineralisation and the acidic magmatic phase in the area the rb sr geochronology of the potassic sodic alteration zones confirms the two stage magmatic mineralisation scenarios overlapping within errors with the results obtained from the u pb zircon geochronology and constraining the formation of the potassic sodic and phyllic alteration at ca 33 and 28 ma respectively our results document an uncommon scenario of two stage porphyry mo mineralisation associated with intensive late stage carbonate precipitation and achieved during a long lasting and multiphase magmatic pulses of oligocene age we highlight the dominant role of acidic fluid neutralisation for further ore enrichment during polyphase magma intrusion as the dominant factor controlling the mo mineralisation in the skmd comparison at a regional scale indicates that parameters such as longevity of magma supply progressive magma crystallization differentiation and the presence of a possible pre enriched crustal material should be considered responsible for the mo endowment in the udmz

maximum and minimum water contents of granitic melts generated in the crust a reevaluation and implications abstract recent results of studies aimed to determine the water solubilities and the liquidus temperatures in synthetic and natural granitic systems are used to constrain the minimum water contents of granitic melts generated in the crust as a function of pressure temperature melt composition and water activity it is concluded that melts generated in the crust at high temperature and low water activities such as a type granites contain higher water contents than previously assumed up to 20 at 800 900 c and 3 7 kbar as a consequence the melt fraction produced at a given amount of available water can be up to 20 lower the minimum water content of melts generated by partial melting of crustal protoliths especially quartzofeldspathic rocks can be predicted adequately from the liquidus curves in granitic systems this water content can be higher if the melt composition departs from a minimum or eutectic quartzofeldspathic composition melts generated from quartzofeldspathic rocks at low temperature 750 c and below are necessarily water rich 5 wt h 2 o and have approximately the same viscosity or even slightly lower viscosities than melts generated at higher temperatures viscosities in the range 10 4 3 10 5 4 pa s recent experimental data also show that the value of the positive d p d t slope of the liquidus curves for fixed water contents above 800 c is lower than predicted by previous models thus adiabatic decompression produces a higher amount of melt than previously assumed at high temperature the formation of melt by adiabatic decompression can be up to 50 higher than assumed

noise and oscillatory zoning of minerals oscillatory mineral zonation is usually associated with crystal growth in an open system either a hydrothermal system or a melt after a period of magma mixing or degassing such systems may be driven sufficiently far from thermodynamic equilibrium to produce autonomous patterns by geochemical self organization the resulting zonation patterns will be the result of coupling between the generally nonlinear crystal growth dynamics and the boundary conditions imposed by externally controlled fluctuations we examine the effects of noisy boundary conditions on four different crystal growth models these are models for plagioclase growth in magmatic systems l heureux and fowler 1996 for carbonates in sedimentary systems wang and merino 1992 for garnets in hydrothermal systems jamtveit 1991 and for silicate growth from a melt wang and wu 1995 the plagioclase model is sensitive to noise even to low amplitude noise implying that an observed zonation pattern will be significantly affected by processes other than local growth and transport processes for the garnet model fluctuations in the external environment may cause synchronization so that different crystals develop similar zonation patterns even if the formation of zonation patterns is a consequence of nonlinear local dynamics this implies that similarity in intracrystalline zonation does not necessarily imply that the zonation pattern was produced by changes in the external environmental conditions the formation of a zonation pattern may be a consequence of local nonlinearities in the growth process but the pattern details may be strongly affected by subtle changes in the external environment copyright 2000 elsevier science ltd

the genesis of felsic mafic plutonic associations a sr and nd isotopic study of the hercynian braga granitoid massif northern portugal abstract the late tectonic braga plutonic complex in the centro iberian zone north portugal was emplaced during the hercynian orogeny within a silurian sedimentary sequence and displays an acid basic association which consists of three well defined intrusions the biotite dominant braga granite minor bodies of gabbro to granodiorite composition and the mildly peraluminous gonca leucogranite these three plutonic suites present field relationships indicating a synchronous magmatic emplacement for which a rb sr age of 310 10 ma is obtained the distribution of the three plutonic units along regular curves in major and trace element diagrams suggests that the different units can be genetically related however the rb sr and sm nd isotopic results do not indicate a unique homogeneous source and a simple fractional crystallization process the gabbros have chemical characters high k ba sr and light rare earth elements and low nb ti and zr contents and isotopic compositions sri 0 70497 and nd 2 5 which suggest an alkaline magmatic affinity of shoshonitic type they are probably derived from an enriched mantle source in contrast the peraluminous gonca leucogranite sri 0 70933 and nd 6 8 is more likely the result of crustal anatexis the braga granite and the evolved members of the basic series have an intermediate isotopic composition sri 0 70532 to 0 70733 and nd 3 0 to 6 2 which can be interpreted in terms of an hybridization process between the two previous end members the chemical and sr nd isotopic compositions of the braga plutonic series can be explained by an assimilation fractional crystallization afc model between a mantle derived magma equivalent to the gabbros and a crust derived magma the gonca granite

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

field evidence of magma mixing from microgranular enclaves hosted in palaeoproterozoic malanjkhand granitoids central india abstract the malanjkhand granitoids mg pluton about 1500 sq km occurs in the balaghat district of madhya pradesh the mg 2400 ma represent an episode of palaeoproterozoic felsic magmatism in central india and hosts potential cu mo au deposits the enclaves hosted in mg can be broadly classified into two categories microgranular enclaves dark coloured fine grained magmatic and xenoliths of country rocks the microgranular enclaves me may be rounded ellipsoidal discoid elongated lenticular or tabular and their size commonly reaches up to 2 metres across the me have sharp and in places diffuse contacts with their host granitoids the shape and size of me indicate contemporaneous flow and mingling of partly crystalline felsic mafic magmas some me exhibit dark crenulated margins giving them a pillow like form that has been attributed to undercooling of a me magma as globules intruded into a granitoid magma the presence of corroded felsic and mafic minerals xenocrysts in me is interpreted as the result of mechanical transfer during the mafic felsic magma interaction and mixing event mafic minerals biotite rim the quartz xenocrysts giving rise to ocellar texture which exhibit signatures of resorption under hybrid enclave magma conditions all these features suggest an origin for the calc alkaline intermediate granitoid magma in malanjkhand involving a magma mixing process

cascading breaching of the tangjiashan landslide dam and two smaller downstream landslide dams abstract the 2008 mw 7 9 wenchuan earthquake triggered at least 257 landslide dams most of which formed in series along rivers the failure of an upstream dam could cause the failure of dams downstream one after another the cascading dam breaching may result in a sharp increase in the flood and more serious damage downstream this paper aims to simulate the cascading breaching of landslide dams with a case study of the tangjiashan landslide dam and two smaller dams downstream a modified daba model is applied for this purpose in which the water soil interactions are simulated with erosion and shallow water flow theory this paper first introduces the methodology of the cascading dam breach simulation emphasizing modifications to the daba model then the cascading breaching of the tangjiashan landslide dam and two smaller downstream dams is simulated using the modified daba model finally the influences of several key factors e g dam height dam width dam erodibility on cascading dam breaching are analyzed to identify the critical conditions of overlapping effect in breaching floods the modified daba model is shown to be a reliable tool for simulating the cascading dam breaching the flood from the tangjiashan dam was not significantly amplified by the breaching of the two small dams downstream because the two smaller dams breached before the tangjiashan dam some parameters such as dam crest width and initiation water level may not influence the peak outflow rate and breach size of a single dam obviously but may influence the cascading breaching of several dams significantly through the amplification effect the cascading breaching of several dams is likely to generate multi peak floods a critical condition for the overlapping effects of cascading dam breaching is that large and increasing inflow erodes the dam breach downstream in the development phase if cascade breaching of several landslide dams is inevitable one principle to mitigate the risks is to lower the breach flood of the largest dam with engineering measures if significant overlapping effect is predicted engineering measures may also be taken to breach the smaller dams before the breaching of the large dam upstream or delay the breach of those downstream dams by reinforcement measures

apatite in igneous systems apatite is a minor but ubiquitous mineral in most igneous rocks although the modal proportion of apatite in common rocks is generally low it can reach high concentrations in enclaves cumulates and other rocks of low abundance i e rocks that constitute a small volume of the crust and mantle e g nelsonites the presence of apatite in most rocks is due not only to its low solubility in naturally occurring melts and aqueous solutions but also to the limited ability of common rock forming minerals to accept the amount of phosphorus that occurs in most rocks into their structure in this paper we will discuss some aspects of the occurrence texture composition physical chemistry and petrogenetic significance of apatite in felsic rocks i e andesite to rhyolite and their plutonic analogs in mafic i e basalts and related rocks and plutonic analogs and ultramafic rocks of the earth s crust and mantle fluorapatite is by far the most common member of apatite family found in igneous rocks however most natural fluorapatite contains some chlorine and hydroxyl as well and these constituents can attain high concentrations in some cases the other halogens bromine and iodine also occur in apatite but their concentrations are much lower than chlorine and fluorine many cations commonly substitute for calcium and phosphorus in apatite however they rarely reach concentrations that warrant the definition of a separate mineral species apatite can be described by the general formula a5 xo4 3z following sommerauer and katz lehnert 1985 the a site accommodates large cations e g ca2 sr2 pb2 ba2 mg2 mn2 fe2 ree3 eu2 cd2 na pan and fleet ch 2 in this volume and comprises two sites that exhibit vii fold