amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

crystallisation and zircon saturation of calc alkaline tonalite from the adamello batholith at upper crustal conditions an experimental study the understanding of the geochemical and petrophysical evolution of magmas forming intermediate calc alkaline batholiths at shallow crustal levels critically depends on knowledge of the phase equilibria relations along the liquid line of descent here we present experimental results for a tonalitic system at a pressure of 200 mpa and under water saturated conditions melting experiments were performed at temperatures between 700 and 1000 c in externally heated hcm pressure vessels with oxygen fugacity controlled close to the ni nio buffer equilibrium nno employing an argon methane mixture as pressure medium and co pd redox sensors to verify fo2 conditions natural rock powder of a medium k tonalite from the adamello batholith in northern italy served as experimental starting material based on compositional data of stable phases in the run products and images of entire run charges mass balance calculations as well as image processing were performed to investigate the evolution of the crystal melt ratio with respect to temperature furthermore compositional trends of minerals as well as the liquid line of descent of residual melts were obtained orthopyroxene clinopyroxene and plagioclase were identified as near liquidus phases below 990 c at 900 c amphibole joins the solid phase assemblage at the expense of clinopyroxene indicating the existence of a peritectic relationship after an initial near linear decrease with temperature residual melt fractions exhibit a plateau of 45 55 vol between 750 and 850 c followed by a rapid decrease coinciding with quartz saturation at 725 c compositions of residual liquids evolve along a typical calc alkaline differentiation trend with decreasing temperature increasing sio2 and decreasing tio2 al2o3 cao mgo and feo contents and become peraluminous below 900 c intermediate to acidic rocks from the adamello follow the experimental liquid line of descent indicating that the observed compositional spread of the natural intermediate composition rock record can be explained by low pressure magma differentiation and liquid extraction experimentally determined zircon saturation levels are at low temperatures distinctly lower compared to existing and often used zr saturation models but fully consistent with observed and modelled zr evolution trends from the natural rock record of the southern adamello batholith inferring that zircon saturation in these intermediate to felsic plutonic rocks occurred at 800 830 c corresponding to a melt fraction of about 50 vol

petrogenesis and assembly of the don manuel igneous complex miocene pliocene porphyry copper belt central chile the 4 0 3 6 ma don manuel igneous complex dmic central chile provides a window into igneous processes involved in magma genesis associated with porphyry style copper mineralization this study uses petrographic petrological geochemical and isotopic data to examine the evolution of magmas from the mid to lower crustal source region to shallow emplacement the data provide evidence for progressive oxidation of magma during differentiation and ascent fractionation of cl from s through degassing and the late stage near solidus removal of cl from the system magmas of basaltic andesite to rhyolite composition were produced by polybaric differentiation of hydrous parental mafic magmas variations in crustal differentiation depths led to variable suppression of plagioclase saturation that is recorded in distinctive strontium versus anorthite evolution patterns hydrous derivative magmas generated over a wide range of pressures were episodically emplaced into the shallow crust at depths between 3 5 and 5 km intermediate porphyry dikes closely associated with copper mineralization contain diverse crystal cargoes indicating significant magma mixing these crystal cargoes represent samples of crystal mush entrained from different depths as well as crystals originating in different magmas and crystals grown in situ from hybridized magmas mafic enclaves containing plagioclase and amphibole compositions that match those of the basaltic andesites occur within biotite tonalite testifying to magma mingling during ascent sulfur and chlorine contents of apatite within the different dmic units record variable degassing and decoupling of volatile components with sulfur showing variations of three orders of magnitude compared with one order of magnitude for chlorine the hypabyssal nature of the dmic affords a detailed integrated record of magmatic differentiation processes occurring within trans crustal magmatic systems of the sort thought to characterize many crustal arc settings and play a fundamental role in driving porphyry style copper mineralization

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

granitic magmas with i type affinities from mainly metasedimentary sources the harcourt batholith of southeastern australia the high k calcalkaline granitic rocks of the 370 ma post orogenic harcourt batholith in southeastern australia have i type affinities but are mildly peraluminous and have remarkably radiogenic isotope characteristics with 87sr 86srt in the range 0 70807 to 0 714121 and endt in the range 5 6 to 4 3 this batholith appears to be a good example of magmas that were derived through partial melting of distinctly heterogeneous source rocks that vary from intermediate meta igneous to mildly aluminous metasedimentary rocks with the balance between the two rock types on the metasedimentary side such transitional s i type magmas formed from mainly metasedimentary source rocks may be more common than is generally realised the harcourt batholith also contains mainly granodioritic igneous microgranular enclaves imes like their host rocks the imes are peraluminous and have rather radiogenic isotope signatures 87sr 86srt of 0 71257 0 71435 and endt of 7 3 to 4 3 though some are hornblende bearing origins of these imes by mixing a putative mantle end member with the host granitic magma can be excluded because of the variability in whole rock isotope ratios and for the same reason the ime magmas cannot represent quench cumulates autoliths from the host magmas less abundant monzonitic to monzosyenitic imes cannot represent accumulations of magmatic biotite and or alkali feldspar because k feldspar is absent and there is no co enrichment of k2o and feo mgo nor can they be mixtures of anything plausible with the host rock magma the granodioritic imes probably originated through high degrees of assimilation of a range of crustal materials partial melts by basaltic magmas in the deep crust and the monzonitic imes as melts of enriched subcontinental mantle such enclave suites provide little or no information on the chemical evolution of their host granitic rocks

effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels we numerically define the thermochemical evolution of a subduction related crystal bearing magmatic mass at mid crustal levels 0 7 gpa 20 25 km two main dynamic mechanisms are considered 1 a pure buoyancy driven system where the convective flow is induced by density changes during magma cooling 2 a buoyancy driven convective system governed by chaotic advection the non newtonian rheology of natural magmas is taken into account linking the herschel bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system the latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy driven convective system nearly 2 times faster our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems in particular 1 a time dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch 2 at the attainment of the maximum packing fraction i e just before the jamming condition homogeneous andesitic melts can be potentially extracted from the system and 3 the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy dominated system

geothermometry using minor and trace elements in igneous and hydrothermal magnetite abstract the temperature t and oxygen fugacity fo2 dependence of minor and trace elements mg al mn cr ni in magnetite mag in equilibrium with water bearing silicate liquids varying in composition from basalt to rhyolite 49 77 wt sio2 is examined in a compilation of experimental data n 299 from 700 to 1050 c 50 900 mpa and five order of magnitude range in fo2 the xmg mg mg fetot of mag is strongly dependent on t and can be formulated into an empirical geothermometer tmg mag c 8344 320 lnxmg 4 1 0 28 273 r2 0 83 that reproduces 72 of the experimentas to 50 c and conventional fe ti oxide thermometry in tuffs and vitrophyres to better than 60 c for 85 of the samples the tmg mag thermometer may have potential application in igneous or hydrothermally altered rocks where conventional thermometry or oxybarometry is not possible application to natural mag n 476 compiled from several settings shows igneous rocks mostly record 700 c but with some lower temperatures in plutonic rocks due to slow cooling hydrothermal samples skarns porphyry deposits show consistently subsolidus conditions tmg mag of 700 350 c consistent with other mineral and o isotopic equilibria the element correlations in natural mag from various settings are explored using multivariate statistical analysis to identify which minor or trace elements most critically depend on t fo2 or fluid composition

pre eruptive storage evolution and ascent timescales of a high mg basaltic andesite in the southern cascade arc crustal storage and transit play a critical role in the compositional evolution of arc magmas however the enigmatic nature of lower crustal magma storage and early differentiation limit our understanding of the connections between the physical processes of subduction zones and the architecture of the arc crust we present new geochemical data and applications of existing barometric and chronometric tools to interrogate the mantle source compositions crustal storage depths and ascent timescales of a primitive high mg clinopyroxene bearing cinder cone the basaltic andesite of box canyon located in the vicinity of lassen volcanic national park ca in the southern cascades petrographic examination in addition to bulk and in situ geochemical analyses xrf la icp ms and epma of tephra and lava derived samples reveals co crystallization of clinopyroxene and olivine as phenocrysts and glomerocrysts with mg 80 and fo85 respectively phase equilibria experiments of analogous cascade arc magma compositions estimate crustal storage of the observed phase assemblage at pressures in the lower crust 700 mpa reverse zonation in olivine and clinopyroxene phenocryst interiors from core rim analytical profiles record a lower crustal mafic mixing event results from one dimensional multi elemental olivine and clinopyroxene diffusion models fit to these interior mixing zones provide an assessment of available trace element ti la yb ce and nd diffusion chronometers in clinopyroxene by considering multiple element profiles within two phases that experienced the same pre eruptive conditions while multi elemental and multi phase diffusion timescales span two to three orders of magnitude ni in olivine profiles provide the most robust estimate of 19 1 8 6 years from mixing to eruption our results provide new constraints on arc crustal differentiation processes indicate rapid crustal transit timescales in agreement with a growing database of diffusion based ascent timescales of basaltic magmas and demonstrate significant systematic deviation of diffusion timescales calculated from natural zonation of rare earth elements in clinopyroxene and ti in clinopyroxene and olivine

granitic magma transport by fracture propagation granitic magmas commonly ascend tens of kilometres from their source terranes to upper crustal emplacement levels or to the earth s surface apart from its obvious bearing on the interpretation of the geology and geochemistry of felsic igneous rocks the magma ascent mechanism critically affects any modelling of the metamorphic evolution of the upper lithosphere as well as its rheology we propose that in general granitic magmas ascend via propagating fractures as dykes in extremely short time periods long distance diapiric transport of granitoid magmas through crustal sections is not viable on thermal or mechanical grounds and there is an apparent total absence of field evidence for diapiric rise of such magmas even in supposed type localities neither the shapes nor internal or external characteristics of granitic plutons necessarily reveal anything about the transport of their precursor magmas these are purely arrival phenomena dictated by local structure kinematics and stress states based on existing numerical treatments of the problem we show that granitic magmas are apparently sufficiently inviscid to travel through fractures to high crustal levels without suffering thermal death by freezing for example a 2000 km3 granitic batholith can be inflated by a 1 km 3m 20 km deep dyke system in less than 900 years the model proposed has numerous far reaching petrological and rheological consequences some of which are outlined

interpreting magmatic fabric patterns in plutons abstract most plutons have widespread magmatic fabrics the interpretation of which remains controversial we propose a method to constrain likely causes of fabric patterns the application of which indicates the following 1 preserved fabric patterns often form after chamber construction and only rarely provide information about ascent or emplacement 2 fabrics are poor recorders of total strain and are easily reset preserving only the last increment of strain during crystallization 3 in magmatic systems mechanically decoupled from host rocks patterns may result from strain during internally driven flow filter pressing or porous flow in relatively static chambers or by final increments of strain during emplacement 4 with greater emplacement depths fabric patterns increasingly reflect strain caused by regional deformation and 5 given that magmatic fabrics are easily reset and reflect only the last increment of strain of comparatively weak materials they may provide a relatively direct record of paleostress in orogenic belts

the influence of water on the petrogenesis of subductionrelated igneous rocks the presence of dissolved water can significantly change the sequence in which different minerals crystallize from a silicate magma1 3 this will alter the compositional path followed by residual liquids the liquid line of descent and modify the types and compositions of crystals that accumulate at the site of cooling the sharp decrease in the solubility of water in silicate melts with decreasing pressure makes direct measurements of pre eruptive concentrations in magmas difficult because much of the dissolved water boils off before eruption here we report experimental results on the crystallization of basalts that contain substantial dissolved water up to 6 wt and show how the results can be used to infer the amount of dissolved h2o involved in the petrogenesis of lavas that preserve a record of their liquid lines of descent or the accumulated minerals left behind after solidification the presence of abundant magmatic water is a signature of subduction zone volcanism4 and can be used to associate a suite of magmas or igneous cumulates with a convergent margin back arc or interarc tectonic setting

experimentally derived high pressure cumulates from hydrous arc magmas and consequences for the seismic velocity structure of lower arc crust 1 this contribution explores the consequences of experimentally derived ultramafic plutonic rocks for estimates of continental crust composition the formation of high pressure cumulates from primitive to evolved hydrous arc magmas was investigated in the range 0 8 1 5 gpa and 1350 800 c to provide constraints on solid assemblages that form the roots of island arc crust at pressures exceeding 0 8 gpa 25km 40 60 of ultramafic cumulates are produced to obtain andesite to dacite compositions that are typical for evolved island arc volcanic and plutonic rocks calculated cumulate densities are comparable or higher than upper mantle values while seismic velocities vp vary continuously between 7 3 and 8 km s resulting in a broad crust mantle transition the moho represents a plagioclase saturation boundary our results are consistent with seismic imaging from continental margins and island arcs revealing that beneath an active volcanic front a sharp geophysical moho signature is sometimes absent

models for granitoid evolution and source compositions this paper critically examines the bases of various models for the chemical evolution of granitoid suites the proposed mineralogical textural and chemical criteria for the recognition of restite components are found to be equivocal and can be plausibly explained by crystal fractionation and accumulation as well as by magma mixing and assimilation of non restitic solids these processes demonstrably account for the bulk of the chemical variation in a variety of granitic suites although restite controlled variation may have played a role in some types of metasediment derived suites granitoid magmas with non minimum melt chemistry are probably rather common the petrographic geochemical and isotopic features of individual plutons should be assessed carefully to elucidate the relative importance of various mechanisms for chemical evolution conclusions as to the character of magma source materials and magma evolution paths that are based on the restite model should be treated with caution

on the occurrence and implications of jurassic primary continental boninite like melts in the zagros orogen ultramafic rocks ranging from pyroxenites to hornblendites are associated with granitoids of the aligoodarz intrusive complex in the central sanandaj sirjan zone representing the mesozoic continental arc segment of the zagros orogen as inferred from the ultramafic whole rock composition and the most primitive clinopyroxene composition in pyroxenites the geochemical signature of primary melt is significantly different from that of the continental arc basalts in particular primary melt is characterized by extremely low concentrations of incompatible elements and high concentrations of mg and refractory elements typical of boninites amphibole is a late crystallizing mineral in these rocks and is in textural and chemical disequilibrium with olivine orthopyroxene clinopyroxene amphibole crystallized from a liquid underwent differentiation through a process of melt rock reaction in particular early differentiated boninitic cumulates reacted with later melts with a strong crustal signature similar to aligoodarz granodiorite u pb zircon geochronology from ultramafic rocks and surrounding quartz diorite yield similar ages and indicate that they are coeval with aligoodarz granitoids ca 165 170 ma however the occurrence of a marked negative eu anomaly in zircon from the ultramafic rocks which is absent in the boninitic primary melt indicates that zircons crystallized from the infiltrating melt and in turn date the timing of melt infiltration the interaction between ultramafic cumulates and infiltrated melt has generated a new liquid compositionally similar to high mg andesites and to the quartz diorites hosting the ultramafic cumulates the scenario that better account for the genesis of boninitic melts in the sanandaj sirjan zone is partial melting of a depleted mantle wedge in response to the onset of neotethys subduction according to this hypothesis middle jurassic calc alkaline magmatism in the sanandaj sirjan zone represents the mature stage of arc magmatism postdating boninite generation by about 10 ma

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

oxygen isotope trajectories of crystallizing melts insights from modeling and the plutonic record elevated oxygen isotope values in igneous rocks are often used to fingerprint supracrustal alteration or assimilation of material that once resided near the surface of the earth the 18 o value of a melt however can also increase through closed system fractional crystallization in order to quantify the change in melt 18 o due to crystallization we develop a detailed closed system fractional crystallization mass balance model and apply it to six experimentally and naturally determined liquid lines of descent llds which cover nearly complete crystallization intervals melt fractions of 1 to 0 1 the studied llds vary from anhydrous tholeiitic basalts to hydrous high k and calc alkaline basalts and are characterized by distinct melt temperature sio 2 trajectories as well as crystallizing phase relationships our model results demonstrate that melt fraction temperature sio 2 relationships of crystallizing melts which are strongly a function of magmatic water content will control the specific 18 o path of a crystallizing melt hydrous melts typical of subduction zones undergo larger increases in 18 o during early stages of crystallization due to their lower magmatic temperatures greater initial increases in sio 2 content and high temperature stability of low 18 o phases such as oxides amphibole and anorthitic plagioclase versus albite conversely relatively dry tholeiitic melts only experience significant increases in 18 o at degrees of crystallization greater than 80 total calculated increases in melt 18 o of 1 0 to 1 5 can be attributed to crystallization from 50 to 70 wt sio 2 for modeled closed system crystallizing melt compositions as an example application we compare our closed system model results to oxygen isotope mineral data from two natural plutonic sequences a relatively dry tholeiitic sequence from the upper and upper main zones uumz of the bushveld complex south africa and a high k hydrous sequence from the arc related dariv igneous complex mongolia these two sequences were chosen as their major and trace element compositions appear to have been predominantly controlled by closed system fractional crystallization and their llds have been modeled in detail we calculated equilibrium melt 18 o values using the measured mineral 18 o values and calculated mineral melt fractionation factors increases of 2 3 and 1 1 5 in the equilibrium melts are observed for the dariv igneous complex and the uumz of the bushveld complex respectively closed system fractional crystallization model results reproduce the 1 increase observed in the equilibrium melt 18 o for the bushveld uumz whereas for the dariv igneous complex assimilation of high 18 o material is necessary to account for the increase in melt 18 o values assimilation of evolved supracrustal material is also confirmed with sr and nd isotope analyses of clinopyroxene from the sequence beginning with a range of mantle derived basalt 18 o values of 5 7 pristine mantle to 7 0 heavily subduction influenced mantle our model results demonstrated that high silica melts i e granites with 18 o of up to 8 5 can be produced through fractional crystallization alone lastly we model the zircon melt 18 o fractionations of different llds emphasizing their dependence on the specific sio 2 t relationships of a given crystallizing melt wet relatively cool granitic melts will have larger zircon melt fractionations potentially by 1 5 compared to hot dry granites therefore it is critical to constrain zircon melt fractionations specific to a system of interest when using zircon 18 o values to calculate melt 18 o

critical role of water in the formation of continental crust continental arcs are the sites of production of continental crust but the origin of these magmatic systems is not well understood although a number of processes have been suggested to be important the role of water migrating from slab to surface during subduction has been underappreciated directly below the moho hot approximately 1 100 c hydrous basaltic magmas fractionate as they cool to the regional geotherm at 750 to 800 c ultimately solidifying as mafic underplates cooling and fractionation cause water to exsolve and ascend triggering fluid fluxed melting of overlying mafic underplates and other crust melting of prior mafic underplates buffers temperatures and generates the voluminous juvenile low k magmas of cordilleran batholiths these granitoid magmas comprise a low temperature slurry of melt and residue and recrystallize into silicic mush during adiabatic ascent such hydrous mushes are intermittently infused by hotter more mafic magmas which hybridize and facilitate ascent and potentially eruption fluid fluxed melting overcomes many of the general petrological and geochemical problems associated with models dominated by fractional crystallization the role of water during repeated episodes of mafic underplating is critical to generate the juvenile granitoid infrastructure of the continents migration of water from the slab to the surface during subduction is highlighted as a key process in the formation of continental crust

phase relationships of gabbro tonalite granite water at 15 kbar with applications to differentiation and anatexis phase relationships have been determined at 15 kbar with variable h 2o contents for three rocks a gabbro a tonalite and a muscovite granite representing the compositional trend of the calc alkaline rock series experiments were conducted in 0 5 in piston cylinder apparatus using ag pd or pt capsules the results obtained are acceptable representations of the phase relationships for elucidation of petrological processes selected runs with 5 h 2o were completed using au capsules to overcome the problem of iron loss up to the temperature limit of au for reliable electron microprobe analyses of glass garnet clinopyroxene amphibole and plagioclase no glasses could be analyzed in the gabbro the data provide k d values as a function of temperature for pairs of coexisting minerals and liquid the chemical variations are used to evaluate 1 the fractionation trends in hydrous magmas at 55 km in thickened continental crust or uppermost mantle and 2 the products of anatexis of the thickened crust at this depth fractionation of hydrous basalt or anatexis of gabbro and tonalite or their metamorphosed equivalents appears to produce liquids diverging from the calc alkaline trend anatexis of granite produces a liquid less siliceous than itself with some chemical characteristics of syenite

trace element composition of amphibole and petrogenesis of hornblendites and plutonic suites of cretaceous magmatic arcs developed in the fuegian andes southernmost south america abstract the evolution of continental crust in convergent margins can be explored in southernmost south america 54 56 s plutonic rocks of the fuegian batholith and the rear arc satellite ushuaia pluton were emplaced within the magmatic arc and the fuegian fold and thrust belt respectively they record subduction zone processes in two distinct tectonic settings during the evolution of the rocas verdes basin we report new u pb zircon geochronology bulk rock chemistry sr nd isotope data and epma and in situ la icp ms analyses of amphibole from hornblendites and gabbroic granitoid suites in order to evaluate the origin and evolution of the magmatic plumbing systems in the upper plate of the subduction zone textural relationships and amphibole compositions in hornblendite indicate crystallization at lower crustal depths with pressures of 7 8 kbar in the fuegian batholith and of 5 6 kbar in the ushuaia pluton lower cretaceous suites of hornblendite and calc alkaline hornblende gabbro diorite and tonalite in the fuegian batholith have endt values ranging between 2 and 4 they were emplaced within an island arc coeval with mid oceanic type spreading in the rocas verdes back arc basin isotope ratios and amphibole compositions in hornblendite indicate crystallization from primitive and hydrous sub alkaline basaltic melts with relatively low lree hree and low alkali contents the late cretaceous plutons in the fold and thrust belt were emplaced after the tectonic juxtaposition of rocas verdes ophiolitic complexes the ushuaia pluton consisting of clinopyroxene hornblende cumulates hornblende gabbro diorite and monzodiorite was emplaced during the waning stage of late cretaceous magmatism in this case hornblendite amphiboles show high contents of alkalis lree and incompatible elements with a strong crustal affinity th ba rb the enriched incompatible trace element patterns indicate their derivation from k rich transitional magmas formed in supra subduction settings chemical variations in amphibole from hornblendites and spatially related plutonic rocks are evaluated in terms of fluid flux from the subducted slab and partial melting of the sub arc mantle ultimately controlled by the thermal state of the subducted slab and convergence rates

redox controlled generation of the giant porphyry cu au deposit at pulang southwest china some porphyry cu au deposits with relatively reduced ore assemblages characterized by high hydrothermal pyrrhotite contents and a lack of primary hematite and magnetite are generally considered to be associated with reduced i type granitoids however the role of magmatic oxygen fugacity fo2 in controlling cu au mineralization in such reduced porphyry deposits is poorly understood the giant late triassic ca 216 ma pulang porphyry cu au deposit of southwest china shows typical reduced ore assemblages this study reported the systematical variation of upper crustal magmatic fo2 of pulang deposit based on detailed investigations of mineral crystallization sequences and compositional features of the mineralization related porphyries early p1 and late p2 porphyry results indicate that magma of the mineralization related porphyries experienced complex fo2 fluctuations during its upper crustal evolution the early primary magma had very high initial fo2 with fmq 3 0 at depths of 12 km fmq is the deviation of logfo2 from the fayalite magnetite quartz fmq buffer the fo2 of evolved parental magma subsequently decreased with fmq 1 9 due to injection of relatively reduced dioritic magmas fmq 1 4 to 2 3 from a deeper chamber 17 21 km depth into the primary magma chamber at 10 12 km depth magma mixing had largely ceased at 6 10 km depth the parental magma then ponded within the reduced tumugou formation at a depth of 3 7 km where magmatic fo2 decreased to a moderately oxidized state fmq 1 6 and finally to a moderately reduced state reflected by log fe2o3 feo ratios of 0 5 for p2 porphyry results of this study of magmatic fo2 indicate that porphyry magmas associated with reduced pulang ore assemblages were initially generated as highly oxidized magma which was subsequently reduced through magma mixing and contamination by reduced sedimentary rocks of the tumugou formation the sharp fo2 decrease at very shallow depth prevented the early loss of cu and au because the magma remained oxidized until it was emplaced at 3 7 km depth moderately reduced magmas may thus have a genetic association with porphyry cu au mineralization

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

the genesis of arc dacites the case of mount st helens wa throughout the last 35 ka mount st helens has been the most active volcano in the cascade arc but the origin of its voluminous dacites remains controversial these dacites were traditionally interpreted as a result of melting metabasaltic lower crust yet recent studies have challenged this view and suggested an origin dominated by differentiation of mafic magmas through assimilation fractional crystallization afc processes to address this discrepancy on the origin of dacites at mount st helens we conduct an interdisciplinary study using a combination of thermal and geochemical modeling our results show that 45 crystallization of a basaltic andesite parent reproduces the compositions of the dacites with a maximum of 20 30 assimilation of lower crustal lithologies amphibole textures and compositions support such a differentiation trend in a polybaric mush system combined with recent geophysical imaging and experimental data we suggest that mount st helens dacites are generated by 1 mantle derived arc magma evolving by afc to intermediate compositions in a lower crustal magma reservoir and 2 ascent of these magmas to a mid to upper crustal reservoir where they reach high crystallinity without significant further chemical differentiation and are subject to frequent recharge that leave a clear mixing mingling overprint

the tynong pluton its mafic synplutonic sheets and igneous microgranular enclaves the nature of the mantle connection in i type granitic magmas in the lachlan orogen of south eastern australia the high level postorogenic 368 ma i type tynong pluton contains granitic to granodioritic rocks that crystallised from a variety of mainly crustally derived magmas emplaced in the shallow crust in an extensional regime the isotopic characteristics of the main plutonic rocks are relatively unevolved 87sr 86srt 0 705 0 706 and endt 0 4 to 0 6 suggesting source rocks not long separated from the mantle we infer that arc mafic to intermediate rocks and associated immature greywackes formed the main crustal source rocks and that these are located in the largely unexposed neoproterozoic cambrian selwyn block that forms the basement as exposed near its southern margin the pluton also contains minor pillowed sheet like intrusions of quartz dioritic rock that show mainly mingling structures with the enclosing granodiorites as well as some hybrid pods and fairly abundant igneous microgranular enclaves that we infer to have been derived from the quartz dioritic sheets despite this evidence of direct mantle input into the tynong magma system the main granodioritic series do not appear to have been formed by magma mixing processes of any i type granite in the region the tynong pluton has perhaps the most direct connection with mantle magmas nevertheless the main mantle connection here is probably in the mantle derived protolith for these crustal magmas and in the mantle thermal event that gave rise to melting of the deep crust in the selwyn block this degree of mantle connectedness seems typical for i type granitic rocks worldwide

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

the role of clinopyroxene in amphibole fractionation of arc magmas evidence from mafic intrusive rocks within the gangdese arc southern tibet abstract amphibole is thought to be a key control on the differentiation of arc magmas but the fractionation of this mineral remains enigmatic because it is rarely present in erupted lavas this study presents detailed petrological mineralogical and geochronological data for newly identified late triassic 217 215 ma mafic intrusive rocks from the gangdese arc of southern tibet these gabbros host an amphibole rich cumulate enclave and clinopyroxene crystal clots including two mineral assemblages in chemical disequilibrium 1 amphibole and type 1 clinopyroxene within the enclave and clots and 2 small crystals of type 2 clinopyroxene plagioclase and biotite within the host textural and geochemical evidence indicate that the enclave and clots represent captured fragments of amphibole and clinopyroxene dominated lower crustal crystal mushes respectively whereas small host crystals formed by the shallow crystallization of evolved melts extracted from these crystal mushes the compositional variations between the two types of clinopyroxene also reveal this melt segregation process amphibole with similar rare earth element patterns to associated type 1 clinopyroxene inclusions suggest that the former formed through peritectic reactions consuming clinopyroxene enhanced amphibole fractionation may also have occurred as a result of the presence of high density clinopyroxene inclusions this indicates that the fractionation of amphibole together with precursory clinopyroxene inclusions within the deep crust controls the early chemical evolution of mafic arc magmas a process that is consistent with the geochemical variations in lavas from three other active arc volcanoes the associated cumulates can efficiently delaminate back into the mantle ultimately leading to the generation of sio2 rich continental crustal material

experimental determination of the partitioning behavior of rare earth and high field strength elements between pargasitic amphibole and natural silicate melts abstract the primary goal of this investigation was to derive a set of expressions that can be used to calculate the amphibole melt partitioning behavior of the rare earth elements ree and the high field strength elements hfse in natural systems to supplement the existing data set on basaltic systems we conducted experiments on systems where amphibole was in equilibrium with dacitic tonalitic and low si rhyolitic melts these experiments doped with la sm gd lu ta nb y zr and hf were run at pressures of 2 and 5 kbar temperatures between 900 c and 945 c and oxidation conditions ranging from qfm 1 to ninio 1 the partitioning data obtained in this study were combined with published data to calculate two sets of expressions describing trace element partitioning the first set models the partitioning of trace elements into amphibole using temperature pressure and several compositional parameters including the compositionally compensated partition coefficients of ti al caand sio2 and the exchange of fe and mg between the crystal and the melt dmg dfe the second set of expressions are slightly less precise but require no specific knowledge of p t or fo2 and for application to natural systems can be constructed solely on the basis of information available from standard electron microprobe analyses these expressions predict amphibole melt partition coefficients for ree and hfse within an internal precision of 14 40 relative for alkali basalt to low si rhyolite from 850 c to 1100 c 2 20 kbar and oxygen fugacity from qfm 1 to ninio 1 partition coefficients calculated from the expressions derived in this study were used to model the partial melting and fractional crystallization of a hypothetical amphibolite and hydrous melt respectively fractionation and or melting in amphibole bearing systems produces a magma with a convex upward ree pattern a characteristic common to many hornblende bearing dacites however the removal or addition of an amphibole component cannot produce the strong hfse depletion relative to the ree observed in many arc magmas

petrochronology of zircon and baddeleyite in igneous rocks reconstructing magmatic processes at high temporal resolution zircon zrsio4 and baddeleyite zro2 are common accessory minerals in igneous rocks of felsic to mafic composition both minerals host trace elements substituting for zr among them hf th u y rees and many more the excellent chemical and physical resistivity of zircon makes this mineral a perfect archive of chemical and temporal information to trace geological processes in the past utilizing the outstanding power and temporal resolution of the u pb decay schemes baddeleyite is a chemically and physically much more fragile mineral it preserves similar information only where it is shielded from dissolution and physical fragmentation as an inclusion in other minerals or in a fine grained or non reactive rock matrix it offers the potential for dating the solidification of mafic rocks with high precision through its crystallization in small pockets of zr enriched melt after extensive olivine and pyroxene fractionation zircon and baddelelyite u pb dates are for an overwhelming majority of cases and where we can assume a closed system considered to reflect the time of crystallization the development of the u pb dating tool ca id tims chemical abrasion isotope dilution thermal ionization mass spectrometry since 2005 has led to unprecedented precision of better than 0 1 in 206pb 238u dates bowring et al 2005 increased sensitivity of mass spectrometers and low laboratory blanks due to reduction of acid volumes allow routine u pb age determinations of micrograms of material at sufficiently high radiogenic common lead ratios see schoene and baxter 2017 this volume in situ u pb age analysis using laser ablation or primary ion beam sputtering allows analysis of sub microgram quantities of zircon material from polished internal sections or zircon surfaces with spot diameters ranging from 30 m for laser ablation inductively coupled plasma mass spectrometry la icp ms to 10 m for secondary ion mass spectrometry sims lateral resolutions of 2 5 m for nanosims

giant magmatic water reservoirs at mid crustal depth inferred from electrical conductivity and the growth of the continental crust the formation of the continental crust at subduction zones involves the differentiation of hydrous mantle derived magmas through a combination of crystallization and crustal melting however understanding the mechanisms by which differentiation occurs at depth is hampered by the inaccessibility of the deep crust in active continental arcs here we report new high pressure electrical conductivity and petrological experiments on hydrated andesitic melt from uturuncu volcano on the bolivian altiplano by applying our results to regional magnetotelluric data we show that giant conductive anomalies at mid crustal levels in several arcs are characterized by relatively low amounts of intergranular andesitic partial melts with unusually high dissolved water contents 8 wt h2o below uturuncu the altiplano puna magma body apmb displays an electrical conductivity that requires high water content up to 10 wt dissolved in the melt based on crystal liquid equilibria and melt h2o solubility experiments such a super hydrous andesitic melt must constitute about 10 of the apmb the remaining 90 being a combination of magmatic cumulates and older crustal rocks the crustal ponding level of these andesites at around 6 kbar pressure implies that on ascent through the crust hydrous magmas reach their water saturation pressure in the mid crust resulting in decompression induced crystallization that increases magma viscosity and in turn leads to preferential stalling and differentiation similar high conductivity features are observed beneath the cascades volcanic arc and taupo volcanic zone this suggests that large amounts of water in super hydrous andesitic magmas could be a common feature of active continental arcs and may illustrate a key step in the structure and growth of the continental crust one sentence summary geophysical laboratory conductivity and petrological experiments reveal that deep electrical conductivity anomalies beneath the central andes cascades and taupo volcanic zone image the ponding of super hydrous andesitic melts which contributes to the growth of continental crust

the stability of amphibole in andesite and basalt at high pressures reinvestigation of earlier work on mt hood andesite and kilauea olivine tholeiite under n no conditions and with silver capsules the revised curve for the appearance of garnet is significantly lower in pressure no orthopyroxene appeared in the run products in contrast to the results of the earlier work the high temperature segment of the amphibole out curve for the tholeiite is at least as high as 1040 degrees c at 13 kbar and 1050 degrees c at 16 kbar and the high pressure part of this curve is at about 27 kbars about 6 kbar higher than in the earlier work amphibole is the sole silicate phase on the vapor saturated liquidus in the andesite at pressures below the garnet in curve 15 5 kbar revised phase relationships are consistent with the derivation of andesite by amphibole liquid equilibria in basaltic magma and reveal stability to depths of nearly 100 km the great depths to which amphiboles are stable make it probable that they are a source of h 2 o for martial melting in deeply subducted oceanic crust modified journal abstract

copper partitioning between silicate melts and amphibole experimental insight into magma evolution leading to porphyry copper ore formation abstract a series of piston cylinder experiments were conducted to determine the partition coefficient of cu between amphibole and andesitic to rhyolitic silicate melts the experiments were run at t 740 990 c p 0 7 gpa oxygen fugacity f o 2 ranging from that of the ni nio buffer nno to 2 3 log units higher nno 2 3 and dissolved water in variable concentrations under saturated to saturated conditions fixed metal activities were imposed by using au 97 cu 3 and au 92 cu 8 alloy capsules which allowed simultaneously determination of cu solubility our data demonstrate that cu solubilities in both the silicate melt and amphibole decrease with decreasing temperature the solubility of cu decreases by a factor of 6 from 990 to 740 c in equilibrium with andesitic to rhyolitic melt compositions the average amphibole silicate melt partition coefficient of cu d cu amph melt is 0 066 0 006 and is essentially constant without showing any correlation with silicate melt composition dissolved water concentration temperature or f o 2 the low d cu amph melt value suggests that amphibole crystallizing at any stage of calc alkaline magma evolution is unable to scavenge a significant fraction of the initially available cu from the melt however d cu amph melt is high enough to yield precisely measurable cu concentrations in natural amphiboles as d cu amph melt remains constant along the liquid line of descent of calc alkaline magmas amphibole compositions may thus be used as a proxy to monitor the evolution of the cu concentration in the silicate melt not the bulk magma if sulfide is present this may be useful for understanding the metallogenic evolution of intrusive rocks in which silicate melt inclusions in minerals are generally absent as most porphyry type cu ore deposits are associated with upper crustal intrusions in situ microanalysis of inclusion free amphiboles in such rocks may help understand ore genesis and might also be used in mineral exploration to assess the fertility of prospective magmatic systems

paleoclimatic changes during the last 2 5 myr recorded in the kathmandu basin central nepal himalayas abstract palynological and sedimentological studies of a series of slimes collected from a 284 m long drill well from the kathmandu basin reveal paleoclimatic records and environmental changes within the kathmandu valley during the last 2 5 myr the slimes are composed of fluvio deltaic and lacustrine sediments comprising sand beds of 66 3 m and mud beds of 218 m in length pollen analyses show quercus and cyclobalanopsis are predominant with frequencies exceeding 70 pinus alnus and gramineae are the next dominant taxa three fossil pollen zones were discriminated each zone reflects major climatic change zone i the oldest stage indicates a cool and rather wet climate during 400 kyr from ca 2 5 to 2 1 ma zone ii the middle stage reflects a warm and relatively dry climate without remarkable fluctuation zone iii is characterized by seven cycles of warm and wet and cold and dry climate which reflect the alternation of glacial and interglacial periods the last cold maximum 11 m deep corresponds to the last glacial age around 20 kyr bp judging from the 14 c dating of the uppermost part of the lacustrine sediments the paleo kathmandu lake is likely to have been initiated at around 2 1 ma and to have been filled with black organic mud the kalimati clay the top of the kalimati clay is eroded and was overlain by fluvial sand after the last glacial age the abrupt appearance of a 4 m thick fossiliferous sand bed at the top of the middle member suggests a lowering of water level at around 1 ma

compositional changes of granitoids from the menglian batholith in sw china at ca 122 ma implications for the origin of decoupled nd hf isotopic compositions and crust generation in collision zones abstract determining the origin and related mantle dynamics responsible for the generation of giant granitic batholiths in convergent margins is critical to unravel the formation mechanism of the silica rich continental crust this paper reports the whole rock major element trace element sr nd isotopic and zircon u pb age and hf isotope data of samples from the menglian batholith in the eastern tengchong terrane of southwest yunnan these samples consist of two groups including the group i rocks that are mostly granitic with zircon u pb ages of 132 122 ma and the group ii rocks that display varying compositions from gabbroic to granitic with zircon u pb ages of 122 112 ma the group i samples have zircon ehf t of 11 7 to 4 2 and whole rock end t of 10 1 to 8 9 whereas the group ii samples show elevated zircon ehf t of 7 8 to 7 1 and whole rock end t of 9 0 to 6 9 and ehf t of 3 1 to 1 0 the nd hf isotopic compositions of the group i rocks are coupled likely resulting from the partial melting of an ancient lower crust however the nd hf isotopic compositions of the group ii rocks are decoupled likely inheriting from the mantle derived material with decoupled nd hf isotopic compositions regional geological correlation and compositional transition documented by the group i and group ii samples collectively indicate that the slab rollback and subsequent breakoff of the subducting bangong nujiang ocean lithosphere during the tengchong baoshan collision can be invoked to explain the generation of the menglian batholith the similarity of average compositions between the group ii samples and the bulk continental crust suggests that the addition of mantle derived material to the ancient crust derived melts seems to be an efficient process for crustal growth during continental collisions

collision vs subduction related magmatism two contrasting ways of granite formation and implications for crustal growth earth s continental crust is dominantly made of buoyant felsic igneous material granitoids that were ultimately extracted from the mantle as a result of earth s differentiation since felsic melts are not in chemical equilibrium with the mantle they can originate either from melting of older crustal lithologies or from differentiation of a primitive mantle melt only the latter case will contribute to crustal growth to understand the mechanisms of continental crust growth and differentiation through time it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites in modern earth granitoids are chiefly generated in convergent plate boundaries subduction and collision this paper examines the granitic suites in a late collision environment the variscan french massif central fmc and compares them with the suites found in an oceanic arc we therefore describe and compare two end members sites of granite generation in the fmc several main types of granites are described muscovite and cordierite bearing peraluminous granites resp mpg and cpg contain large amounts of inherited zircons and their chemistry demonstrates that their sources were older crustal material resp metasediments and metaigneous on the other hand potassic calc alkaline granites kcg associated to potassic diorites vaugnerites do not contain inherited zircons and ultimately derive from the vaugnerites the vaugnerites in turns form by partial melting of a mantle contaminated by the regional crust therefore although they are isotopically similar to the crust the kcg are net contributors to crustal growth thus we conclude that although late orogenic settings are dominated by crustal melting and recycling they may be sites of net crustal growth even though this is not visible from isotopes only in contrast arc granitoids are purely or almost purely mantle derived however the preservation potential of arcs is much smaller than the preservation of late orogenic domains such that at the scale of a whole orogenic belt late orogenic magmatism is probably as important as arc magmatism finally we speculate that the situation may have been similar in the archaean or even more skewed towards late orogenic sites or similar environments dominated by melting of a altered mafic protocrust owing to the hotter mantle and less stable subductions during that period

late cretaceous infant intra oceanic arc volcanism the central pontides turkey petrogenetic and tectonic implications abstract a tectonic slice of an arc sequence consisting of low grade metavolcanic rocks and overlying metasedimentary succession is exposed in the central pontides north of the izmir ankara erzincan suture separating laurasia from gondwana derived terranes the metavolcanic rocks mainly consist of basaltic andesite andesite and mafic cognate xenolith bearing rhyolite with their pyroclastic equivalents which are interbedded with recrystallized pelagic limestone and chert the metasedimentary succession comprises recrystallized micritic limestone with rare volcanogenic metaclastic rocks and stratigraphically overlies the metavolcanic rocks the geochemistry of the metavolcanic rocks indicates an arc setting evidenced by depletion of hfse ti p and nb and enrichment of fluid mobile lile identical trace and rare earth elements compositions of basaltic andesites andesites and rhyolites suggest that they are cogenetic and derived from a common parental magma the arc sequence crops out between an albian turonian subduction accretionary complex representing the laurasian active margin and an ophiolitic melange absence of continent derived detritus in the arc sequence and its tectonic setting in a wide cretaceous accretionary complex suggest that the kosdag arc was intra oceanic zircons from two metarhyolite samples give late cretaceous 93 8 1 9 and 94 4 1 9 ma u pb ages these ages are the same as the age of the supra subduction ophiolites in western turkey which implies that that the kosdag arc may represent part of the incipient arc formed during the generation of the supra subduction ophiolites the low grade regional metamorphism in the kosdag arc is constrained to 69 9 0 4 ma by 40 ar 39 ar muscovite dating indicating that the arc sequence became part of a wide tethyan cretaceous accretionary complex by the latest cretaceous non collisional cessation of the arc volcanism is possibly associated with southward migration of the magmatism as in the izu bonin mariana arc system

the temporal evolution of chemical and physical properties of magmatic systems exactly 100 years ago the great canadian born petrologist n l bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physico chemical understanding of the fractionation of crystals from melts in molten rock a subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution the image of sub volcanic magmatic systems has evolved greatly in that time from a simple boiling vat concept of molten rock in which bubbles crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten or mushy state real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma and heat at different fluxes magma fluxes between the different portions of this plumbing system and the variation of the chemical and physical properties of magma as it rises through the crust exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products this book presents a collection of contributions that use petrology geochemistry geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them

primary magmatic biotite in granitoid intrusions associated with late mesozoic jinchanggouliang erdaogou lode gold deposits north china craton linkage to gold mineralization abstract the late mesozoic jinchanggouliang and erdaogou lode gold deposits in the central segment of the northern north china craton are mainly hosted in late archaean metamorphic rocks of the jianping formation and jurassic volcanic sedimentary rocks these deposits are spatially and temporally associated with a series of i type granitoid intrusions i e the 128 136 ma duimiangou granodiorite complex with a massive margin and a porphyritic center at jinchanggouliang the 161 4 1 1 ma loushang quartz diorite intrusion and numerous syenite porphyry dykes 160 9 1 0 ma at erdaogou and the 227 217 ma xitaizi monzogranite batholith compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism all primary magmatic biotite grains are mg rich in composition xmg mg mg fe 0 41 0 69 the cl contents of biotite 0 09 0 42 wt in the loushang quartz diorite and the duimiangou massive granodiorite correlate negatively with xmg and are consistent with the mg cl avoidance rule the cl contents of biotite 0 01 0 14 wt in the duimiangou porphyritic granodiorite syenite porphyry and xitaizi monzogranite on the other hand remain relatively constant and may be affected by multiple variables such as cl rich fluids and subtle changes in temperature halogen fugacity of the parental magma calculated from biotite shows that the duimiangou granodiorite complex at jinchanggouliang and syenite porphyry dykes at erdaogou have the log fhf fhcl ranges of 0 71 to 0 27 and 2 16 to 1 08 respectively and have similar log fh2o fhcl values from 3 53 to 4 23 oxygen fugacities logfo2 calculated from biotite equilibria for the duimiangou granodiorite complex and syenite porphyry dykes are 13 7 to 7 2 straddling on the nickel nickel oxide and hematite magnetite buffers the xitaizi monzogranite and the loushang quartz diorite have lower log fo2 values from 14 9 to 12 4 between the nickel nickel oxide and hematite magnetite buffers the duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry cu mo au deposits these results suggest that multiple episodes of i type granitoid magmas in the study area were rich in cl and high in oxygen fugacity especially those associated with the duimiangou granodiorite complex and syenite porphyry dykes the i type melts represented by the duimiangou granodiorite complex and syenite porphyry dykes as well as their related cl rich oxidizing fluids were likely efficient in dissolving transporting and precipitating gold for the formation of the jinchanggouliang and erdaogou lode gold deposits

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

species diffusion in clinopyroxene solid solution in the diopside anorthite system the coupled multicomponent diffusion of the species ca2si2o6 caal2sio6 and mg2si2o6 was determined in diopside crystals in the diopside anorthite di an system at temperatures t of 1110 1260 c and oxygen fugacities fo2 between 1 0 log unit below and above the fayalite magnetite quartz equilibrium fmq 1 diffusion couples were prepared by the seed overgrowth technique element concentration profiles were measured perpendicular to the rim core interface by step scanning profiling with a field emission gun scanning electron microscope feg sem the multicomponent diffusion matrix was solved by fitting its eigenvalues and eigenvectors v to the measured concentration profiles the full diffusion matrix d can be recovered by using the formula d p varlambda p 1 resulting in the following equation d text di an left begin array 20 c 1 00 0 67 0 38 1 00 end array right left begin array 20 c lambda 1 left t right 0 0 lambda 2 left t right end array right left begin array 20 c 1 00 0 67 0 38 1 00 end array right 1 the eigenvalues 1 and 2 represent upper limit values and are described by the following arrhenius type equations lambda 1 left text di an right 10 15 98 pm 1 17 times exp left frac 114 4 pm 32 8 text kj mol rt right lambda 2 left text di an right 10 16 23 pm 1 17 times exp left frac 114 4 pm 32 8 text kj mol rt right where 1 and 2 are the first and second eigenvalue of the diffusion matrix in m2 s 1 r is the gas constant and t is the temperature in k the dominant eigenvalue 1 is one quarter order of magnitude larger than the second eigenvalue 2 the eigenvectors are constant for all experiments inferring that the entire d matrix can be described with the eigenvalues as the only t dependent parameter additionally the derived diffusion data and modeling approach were applied to constrain the duration of magmatic processes recorded in zoned clinopyroxene cpx phenocrysts from a basaltic post plutonic dyke of the tertiary adamello batholiths n italy the results reveal residence times of the overgrown cpx prior to final emplacement in the range of 0 25 1 7 years lower limit values testifying that the data and method can be applied to model cpx diffusion profiles in complex natural cpx

nd sr isotopic and geochemical characteristics of the southern adamello northern italy intrusives implications for crustal versus mantle origin among the periadriatic tertiary calc alkaline intrusions in northern italy the adamello batholith displays the most convincing evidence for a mafic parentage this is particularly the case for the southern adamello where minor ultramafic to gabbroic bodies form the margins of several distinct and dominantly tonalitic plutons isotopic analyses are presented for the val fredda and blumone ultramafic gabbroic to tonalitic leucoquartzdioritic suites for the more felsic rock types of the spatially predominant re di castello group as well as for a lamprophyre this dike of picrobasaltic composition is thought to represent the parental magma field relations and a large body of petrographic geochemical and mineral chemical data point to a cogenetic origin for all of these rocks and to magmatic differentiation with fractional crystallization and accumulation as the main evolutionary mechanism this is compatible with the isotopic results for the blumone series and the mafic rocks of val fredda with end 3 8 to 1 5 and esr 9 1 to 4 6 a common parental magma similar to the lamprophyre end 3 1 esr 4 4 also seems plausible the isotopically homogeneous felsic lithologies of val fredda end 0 1 to 0 3 esr 2 9 to 0 7 structurally intimately associated with their mafic counterpart indicate crustal contamination incurred prior to their differentiation for the re di castello group progressing crustal affinity of isotopic compositions end of 1 9 to 4 9 and esr of 16 5 to 40 9 with chemical differentiation implies large scale interaction with a granitoid crustal component attempts at quantifying this process reveal individual characteristics and evolution for each pluton the data indicate extraction of this component from a source in the lower crust with time integrated low rb sr esr approximating 50 and en close to 6 corresponding to a 1000 ma crustal residence age if a two stage evolution is assumed formation of a gabbroic reservoir from the above parental melt would require uptake of some 4 12 wt of granitoid component by combined assimilation fractional crystallization whereas subsequent evolution to tonalitic compositions would necessitate admixing of 40 70 wt of granitoid partial melt assimilation thus mainly occurs during evolution from gabbroic to tonalitic compositions when the mafic magma is ponded near the mantle crust boundary and where homogenization prior to resuming buoyant ascent is assured precise locations and more detailed petrography of the samples is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document 91b 002 2 50 payment must accompany order

a two state integral balance model for soil moisture and groundwater dynamics in complex terrain a dynamical model is devised for a hydrologic system where unsaturated and saturated storage serve as the principal control on rainfall runoff and where complex topography drainage area and variable depth of moisture penetration describe the flow geometry the model is formed by direct integration of the local conservation equation with respect to the partial volumes occupied by unsaturated and saturated moisture storage respectively this yields an integral balance model in just two state variables the relationship of the dynamical model to field data in complex terrain is found through a joint probability density for terrain features this serves as a volume weighting function to construct conditional averages for the state variables and fluxes over a specified range of terrain features the scale of averaging could range from hillslopes to river basins two examples of the joint probability of terrain features altitude and aspect are demonstrated for valley ridge and appalachian plateau digital elevation models the strategy of a dynamical model formed by conditional averages of state variables with respect to terrain features is proposed as a way of simplifying the dynamics while preserving the natural spatial and temporal scales contributing to runoff response the parametric form of the storage flux or constitutive relationships for the proposed model is determined from numerical experiments in a simple hillslope flow geometry the results show that a competitive relation exists between unsaturated and saturated storage except for the lowest precipitation rates saturation overland flow is proposed to be a storage feedback relation solutions to the integral balance model are presented in terms of the phase portrait which represents all possible solution trajectories in state space the timing and magnitude of peaks in the runoff hydrograph from pulse type input events demonstrate quick flow from near stream saturated storage saturation overland flow including rejected rainfall storage feedback and late time infiltration from upslope subsurface flow

can crystallization of olivine tholeiite give rise to potassic rhyolites an experimental investigation experiments were conducted to determine whether the rhyolites and basalts of the intraplate silica saturated potassic suites could be genetically related through crystallization extreme crystallization 96 97 of a high mgo 10 62 wt olivine tholeiite from the snake river plain with an initial bulk water content of 0 4 wt at a mid crustal pressure of 4 3 kbar generated potassic rhyolitic liquids similar in major element chemistry to those found in the quaternary rhyolite domes of the snake river plain and their plutonic equivalents in the proterozoic laramie anorthosite complex residual liquids comparable in composition to the bulk rock compositions of intermediate rocks found at the craters of the moon and cedar butte eruptive centers in the snake river plain are also generated along this crystallization path