the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

the dynamics of magma mixing in a rising magma batch the conditions under which two magmas can become mixed within a rising magma batch are investigated by scaling analyses and fluid dynamical experiments the results of scaling analyses show that the fluid behaviours in a squeezed conduit are determined mainly by the dimensionless number i mu 1 u g delta rho r 2 where 1 is the viscosity of the fluid u is the velocity g is the acceleration due to gravity is the density difference between the two fluids and r is the radius of the tube the parameter i represents a balance between the viscous effects in the uppermost magma which prevent it from being moved off the conduit walls and the buoyancy forces which tend to keep the interface horizontal the experiments are carried out using fluid pairs of various density and viscosity contrasts in a squeezed vinyl tube they show that overturning of the initial density stratification and mixing occur when i order 10 1 the two fluids remain stratified when i order 10 3 transitional states are observed when 10 3 i 10 1 these results are nearly independent of reynolds number re 1 rho 1 ur mu 1 and viscosity ratio mu 1 mu 2 in the range of 10 2 mu 1 mu 2 10 3 and re 1 300 applying these results to magmas shows that silicic to intermediate magmas overlying mafic magma will be prone to mixing in a rising magma batch this mechanism can explain some occurrences of small volume mixed lava flows

petrogenetic evolution of arc magmatism associated with late oligocene to late miocene porphyry related ore deposits in ecuador we present a data set on the geochemical and isotopic composition of mineralized porphyry intrusions se riate intrusions and arc volcanic formations spatially associated with late oligocene to late miocene porphyry related ore deposits in ecuador our aim is to constrain the petrogenetic evolution of these arc magmas to evaluate geodynamic and tectonic impact factors on arc magmatism and to explore the metallogenic signifi cance of these parameters we distinguish four petrogenetic groups associated with the investigated magmatic centers indicating dif ferent paths of low and high pressure crustal magma evolution tertiary ecuadorian arc magmas which dif ferentiated at higher crustal pressures are commonly characterized by adakite like compositions related to fractionation and or restite equilibration effects of amphibole garnet titanite particularly in hydrous silicic melts without concomitant or subsequent major plagioclase fractionation trace element distribution patterns of arc magmas through time are broadly systematic and indicate that crustal magma differentiation progres sively extends to higher pressures from the late oligocene to the late miocene possibly related to crustal thick ening locally adakite like features possibly related to high melt h2o contents or accessory phase fractiona tion are already observed in the early miocene in a regional setting otherwise dominated by low pressure magma evolution compositional differences between mineralized porphyry intrusions and spatially associated seriate precur sor intrusions in ecuador mostly reflect regional scale changes in magma composition through time and are not observed if the relative emplacement age difference is small where porphyry intrusions are associated with shallow crustal batholith systems in northern central ecuador their emplacement is commonly late with re spect to batholith magmatism intrusive compositions indicate that porphyry parental melts mostly evolved at higher crustal pressures where metallogenically favorable melt preconditioning might possibly occur

interfacial turbulent mixing in stratified magma reservoirs abstract we analyse the interfacial turbulent mixing of molten magmas in a two layer stratified convecting magma chamber we examine situations where convection is driven by the heat and or compositional flux associated with the melting of a solid boundary the model applies to the case in which the rayleigh number is sufficiently large that the effect of a viscosity difference on turbulent entrainment is negligible and so the model predictions represent an upper bound for interfacial mixing our results suggest that the extent of mixing induced by the thermal buoyancy flux is relatively small however the compositional buoyancy fluxes associated with phase change may be much larger and the mixing they induce may significantly affect the evolution of the reservoir our analysis of the melting of the floor of a two layer stratified magma chamber shows that turbulent mixing at the interface between the two magmas may suppress the melting and decrease the final amount of melt produced when the system reaches thermal equilibrium it is also shown that although floor melting tends to decrease the density of the lower layer of magma somewhat counterintuitively turbulent interfacial mixing with the overlying layer of smaller density may inhibit large scale overturn and preserve the stratified state of the chamber in the case in which both the floor and roof of a chamber melt turbulent mixing at the interface between the newly formed light melt at the roof and the lower layer of dense magma induces a shift of the melting process from the floor to the roof for typical parameter values in a basaltic magma chamber we estimate that under conditions of very large rayleigh number the amount of crustal melt produced at the roof may be as high as 50 of that produced at the floor

some effects of viscosity on the dynamics of replenished magma chambers some aspects of the dynamical behavior of magma chambers replenished from below with hotter but denser magma have been modeled in a series of laboratory experiments in previously reported work the fluids used were aqueous solutions of comparable viscosity and thus the results should be applicable to basaltic magma chambers in which the magmas do not vary greatly in viscosity in that case the lower layer cools by convective heat transfer to the fluid above and crystallization causes the density of the residual liquid in the lower layer to decrease when the density becomes equal to that in the upper layer sudden overturning and intimate mixing take place the present paper reports experimental results that allow us to extend the application to systems in which there is a large viscosity ratio between the resident and the injected fluid for example to calcalkaline magmas where magma viscosity can vary by as much as 5 orders of magnitude the largest viscosity ratio in our experiments about 3000 was achieved using cold glycerine for the upper layer above a hot denser kno3 solution the most striking new feature with the very viscous upper layer is that now less dense fluid is released immediately and continuously from the interface and rises as plumes through the upper layer further crystallization occurs in the plumes and the crystals fall out but there is little mixing and a layer of depleted kno3 solution is eventually deposited at the top the transfer process between the layers is dominated by interfacial effects with the high viscosity upper layer acting as a nearly rigid lid that allows buoyant fluid to accumulate just below the interface and then rise in localized plumes across the interface into the viscous layer this physical picture is supported by a series of experiments in which the viscosity ratio is varied systematically the mixing behavior changes gradually between that described above for a large viscosity ratio and the sudden over turning characteristic of layers with comparable viscosity the importance of the viscosity ratio rather than just an increase in viscosity is confirmed by experiments in which both viscosities are increased by the same factor the overturning process is then slower but symmetrical other variations suggested by previous experiments are also described the release of gas by a chemical reaction to model the release of volatiles following an overturning event in a magma chamber the effect of a cold immiscible layer above the cooling crystallizing fluid the influence of two viscous layers with a density step between them and the constraining effects of a density with corresponding viscosity gradient in the upper region the experiments indicate that whatever the stratification whether it be in layers or continuous the form of the initial motion in the upper fluid is determined by the viscosity ratio between the two fluids immediately adjacent to the interface geological applications are not examined in detail in this paper but the experiments suggest that both sudden overturning characteristic of magmas of nearly equal viscosity and continuous release when the upper layer is much more viscous are viable mechanisms for magma mixing in the appropriate circumstances

reply to comment by aftabi and atapour on arc magmatism and subduction history beneath the zagros mountains iran a new report of adakites and geodynamic consequences we herein answer the comments by aftabi and atapour to our paper entitled arc magmatism and subduction history beneath the zagros mountains iran a new report of adakites and geodynamic consequences we show that their criticism rests on rather weak grounds and numerous contradictions we reassess the validity of our analytical results and stress the lack of alteration in our adakitic samples we further discuss the interpretation of our findings in particular the fact that the distribution of these adakites is not random in the urumieh dokhtar magmatic arc neither in space nor time being restricted to the central part and to upper miocene to younger rocks finally we point out that aftabi and atapour even somewhat support our model when they suggest slab break off as a cause for the miocene pliocene adakitic rocks

metallogeny of structural zones grenville province northeastern north america abstract recent subdivision of the grenville province into northwestern central and southeastern tectonic zones provides a convenient basis for describing the tectonic affiliation of the contained mineral deposits the northwestern zone consists of reworked foreland lithologies southeast of the grenville front major deposits of metamorphosed superior type iron formations are present in metamorphosed kaniapiscau supergroup equivalents exposed at lower metamorphic grades in the labrador trough occurrences of volcanogenic massive sulphides abitibi group equivalents ni cu quartzite hosted u au and alkaline intrusion hosted ree s are of only mineralogical importance the central zone contains polydeformed gneisses that have been intruded by three ages of anorogenic anorthosite massifs circa 1 64 1 36 and 1 14 ga and associated charnockite magnerite complexes major magmatic ti fe lac allard and large low grade ni cu mcnickel deposits are associated with the younger anorthosite suite magmatic ni cu also occurs in differentiated metapyroxenite metaperidotite of uncertain age pegmatites are widespread but not commercially important the southeastern zone consists of the rocks of the central metasedimentary belt cmb and central granulite terrane cgt as well as rocks of the relatively unmetamorphosed wakeham supergroup initial deposition of volcanic and carbonate rocks occurred in the cmb between 1 28 and 1 24 ga and was followed by deposition of the flinton group 1 15 ga the rocks are overprinted by the elzeviran and ottawan orogenies 1 25 and 1 08 ga respectively volcanogenic zn pb ag au deposits and sedex marble hosted zn deposits occur widely in the layered rocks of the central metasedimentary belt deposition 1 28 ga small massive sulphide and shale hosted base metal occurrences and both oxide and sulphide iron formations are widespread near volcanic lithologies but are generally small or very low grade syngenetic magmatic deposits include subeconomic fe ti and ni cu deposits that are syntectonic with respect to the ottawan orogeny but others may be as old as elzeviran small magnetite rich skarn deposits are widespread with 2 major past producing deposits and are related to magmatic events accompanying the elzeviran orogeny gold and gold sulphosalt occurrences in grenville volcanic and carbonate lithologies and flinton group rocks of various types are not well constrained in age some are spatially associated with older elzeviran intrusions and have been genetically related to them others exhibit metamorphic textures but cut younger flinton group rocks while others appear to be completely post metamorphic extensive pegmatitic and related skarn and carbonate vein u mo ree occurrences may relate either to metamorphic or intrusive processes related to the ottawan orogeny in the cgt fe ti and ni cu occurrences associated with the younger anorogenic anorthosite massifs are similar to occurrences in the central zone large fluorite bearing magnetite iron deposits associated with alaskitic gneisses are interpreted as similar to the swedish kiruna type deposits following stabilization of the grenville craton rifting associated with the opening of iapetus in the latest proterozoic cambrian and again in the cretaceous resulted in the regional intrusion of alkaline complexes which included large nb and ree rich carbonatite intrusions in the cretaceous rift related faults became the sites of small fluorite barite galenastrontianite deposits over a wide area in the elzevir and frontenac terranes and in the charlevoix saguenay area of the central zone

generation of metal rich felsic magmas during crustal anatexis we show that partial melting of a preexisting mineral deposit during regional anatexis is likely to lead to incorporation of sulfide melt into silicate melt simple dissolution of metals in silicate melt during anatexis leads to minor metal addition to escaping magma but physical entrainment of sulfide melt can lead to extreme enrichment and higher total metal incorporation metal enrichment is enhanced if melt segregation is structurally driven only dissolved metal is incorporated if initial segregation is driven by buoyancy alone however once encapsulated within a larger volume of silicate melt immiscible globules of sulfide melt are physically carried by buoyantly rising magma gradual dissolution of entrained sulfide melt globules is expected as the silicate magma migrates from the lower crust this process may lead to significant variations in metal contents of silicate magmas above regions that underwent anatexis

petrogenesis of the squirrel hills granite and associated magnetite rich sill and vein complex lightning creek prospect cloncurry district northwest queensland the lightning creek fe oxide cu au prospect is hosted within a mesoproterozoic granitoid batholith composed dominantly of high k calc alkaline porphyritic quartz monzodiorite the quartz monzodiorite contains enclaves of quartz diorite and has been intruded by more felsic granitoids monzogranite and alkali feldspar granite and a series of subhorizontal sills the quartz monzodiorite crystallised at crustal depths in excess of 10 km pnot vert similar4 kb t 800 850 c melt xh2o 4 wt fo2not vert similarnno buffer and was probably fluid saturated xh2o xco2 of 0 5 as might be expected the more fractionated granitoids crystallised at progressively lower temperatures quartz monzonite not vert similar800 c alkali feldspar granite 2 5 kb and temperatures greater than 500 c phase separation occurred in the fluid phase producing in a co2 rich vapour and a metal rich fe cu brine

reply to discussion on giant versus small porphyry copper deposits of cenozoic age in northern chile adakitic versus normal calc alkaline magmatism by oyarzun r marquez a lillo j lopez i rivera s mineralium deposita 36 794 798 2001

mixing of stratified liquids by the motion of gas bubbles application to magma mixing mafic magma underlying more silicic magma in a reservoir can exsolve volatiles as it crystallizes forming bubbles that segregate upwards to the interface with the overlying silicic magma we describe laboratory experiments designed to investigate how gas bubbles migrate into the more viscous upper layer in one regime bubbles move individually across the interface entraining a small quantity of lower layer fluid and the two layers become progressively stirred into a homogeneous mixture in a second regime bubbles form a thin foam layer at the interface which becomes gravitationally unstable giving rise to two phase plumes which rise and produce a coarse mixture of the liquids for a given viscosity ratio the transition between these regimes occurs when the gas flux is greater than a critical value which we found to decrease with increasing viscosity ratio we estimate the critical gas flux for magmatic conditions and how vesiculation may vary with pressure degree of crystallization and the composition of volatile components mafic inclusions which are often found in silicic to intermediate lavas can form in the plume regime analysis of the instability of the foam predicts wavelengths of between 1 cm and 1 m which is consistent with the observed sizes of inclusions volatiles from the mafic magma may be efficiently transported by this mechanism into the viscous silicic magma as bubble plumes despite low stokes velocities for individual vesicles at small viscosity ratios or low gas fluxes the bubbling regime can produce hybrid magmas

origin of the badaguan porphyry cumo deposit inner mongolia northeast china constraints from geology isotope geochemistry and geochronology abstract the badaguan porphyry cu mo deposit is located in the derbugan metallogenic belt of northeastern inner mongolia china the host granodioritic porphyry and the wall rock granitic porphyry were emplaced at 230 ma and 238 ma respectively the granodioritic porphyry has 87 sr 86 sr i values of 0 70535 0 70549 e nd t values of 0 41 1 17 e hf t values of 1 30 6 51 and two stage model ages t dm2 of 1131 848 ma in contrast the granitic porphyry is characterized by e hf t values from 0 75 to 7 28 that yield t dm2 model ages of 1355 816 ma the geochemical and sr nd hf isotopic data for the magmatic rocks associated with the badaguan porphyry cu mo deposit indicate that these intrusions were generated by the partial melting of juvenile lower crust the 18 o values of ore fluids from different mineralizing stages are between 6 0 and 1 5 and the fluid d water values vary from 119 3 to 140 0 indicating a mixed fluid of magmatic and meteoric water the s pb isotopes show that the metal was mostly derived from a deep seated magma that involved some crustal materials with a narrow 34 s range 2 4 to 3 5 we infer that the badaguan porphyry cu mo deposit formed during a period of southeast directed subduction of the mongol okhotsk oceanic plate beneath the erguna block

contrasting geochemical signatures between upper triassic mo hosting and barren granitoids in the central segment of the south qinling orogenic belt central china implications for mo exploration abstract as a world class molybdenum province the qinling orogenic belt is characterized by voluminous mesozoic granitoids which are attributed to the closure processes of the paleo tethys and the collision between the south china and north china blocks the middle segment of the south qinling orogenic belt is marked by widespread triassic granitoids several small intrusions occurring as porphyry stocks or apophyses are associated with mo mineralization that occurred at ca 200 ma as constrained by molybdenite re os dating to delineate the differences between ore hosting and barren granitic intrusions in this contribution we report new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages and element and sr nd hf isotope data the granitoids were emplaced episodically from 215 to 203 ma with the lithologies evolving from quartz diorites through granodiorites to monzogranites they are metaluminous to peraluminous high k calc alkaline rocks transitional to shoshonites showing arc affinity geochemical traits such as enrichment in liles and depletion in nb ta and ti the ore hosting intrusions are monzogranites with high sio2 contents 68 wt whereas the barren ones are quartz diorites and granodiorites with low sio2 contents 60 7 64 6 wt compared to the barren quartz diorites and granodiorites the ore hosting monzogranites show much lower mg lower contents of transition metals e g sc ti co and v and much stronger depletion of sr ba eu ti and p the isotopic ratios of the ore hosting monzogranites isr 0 7012 0 7060 end t 3 32 4 58 ehf t 0 81 2 30 and the barren granitoids isr 0 7058 0 7060 end t 1 24 5 80 ehf t 3 47 5 24 are similar but the former show slightly lower isr higher end t and higher ehf t this suggests that the ore hosting magmas originated from a slightly more juvenile source but were much more fractionated which is also supported by their younger ages compared to the barrens therefore the prolonged fractional crystallization is a feasible mechanism for the formation of the ore hosting monzogranites in addition the u th correlation and zr hf ratios indicate that the fluid process was responsible for the formation of quartz veins in both the barren and ore hosting intrusions consequently a combination of fractional crystallization and fluid action may have played a crucial role in the development of the mo mineralization

controls on gold solubility in arc magmas an experimental study at 1000 c and 4 kbar in order to 1 explain the worldwide association between epithermal gold copper molybdenum deposits and arc magmas and 2 test the hypothesis that adakitic magmas would be au specialized we have determined the solubility of au at 4 kbar and 1000 c for three intermediate magmas two adakites and one calc alkaline composition from the philippines the experiments were performed over a fo2 range corresponding to reducing not vert similarnno 1 moderately oxidizing not vert similarnno 1 5 and strongly oxidizing not vert similarnno 3 conditions as measured by solid ni pd o sensors they were carried out in gold containers the latter serving also as the source of gold in presence of variable amounts of h2o and in a few additional experiments of s concentrations of au in glasses were determined by la icpms gold solubility in melt is very low 30 240 ppb but increases with fo2 in a way consistent with the dissolution of gold as both au1 and au3 species in the s bearing experiments performed at not vert similarnno 1 gold solubility reaches much higher values from not vert similar1200 to 4300 ppb and seems to correlate with melt s content no systematic difference in gold solubility is observed between the adakitic and non adakitic compositions investigated oxygen fugacity and the sulfur concentration in melt are the main parameters controlling the incorporation and concentration of gold in magmas certain adakitic and non adakitic magmas have high fo2 and magmatic s concentrations favorable to the incorporation and transport of gold therefore the cause of a particular association between some arc magmas and au cu mo deposits needs to be searched in the origin of those specialized magmas by involvement of au and s rich protoliths the subducted slab which contains metal rich massive sulfides may constitute a potentially favorable protolith for the genesis of magmas specialized with respect to gold

simultaneous crystallization and melting at both the roof and floor of crustal magma chambers experimental study using nh4cl h2o binary eutectic system abstract thermal and compositional evolution of magmas after emplacement of basalt into continental crust has been investigated by means of fluid dynamic experiments using a cold solid mixture with eutectic composition and a hot liquid with higher salinity in the nh 4 cl h 2 o binary eutectic system the experiments were designed to simulate cases where crystallization of a basalt magma is accompanied by melting at both the roof and floor of a crustal magma chamber the results show that thermal and compositional convection occur simultaneously in the solution the thermal convection is driven by cooling at the roof and the compositional convection is driven by melting and crystallization at the floor the roof was rapidly melted by the convective heat flux which resulted in formation of a separate eutectic melt layer the upper liquid layer with negligible mixing of the underlying liquid the lower liquid layer on the other hand a mushy layer formed at the floor the compositional convection at the floor carried a low heat flux so that the heat transfer at the floor was basically explained by simple heat conduction the thermal boundary layer in the lower liquid layer at the interface with the upper liquid layer became thicker with time and subsequently temperature decreased upward throughout the lower liquid layer compositional gradient with nh 4 cl content decreasing upward formed by compositional convection in the lower liquid layer the formation of these gradients resulted in formation of double diffusive convecting layers in the lower liquid layer the upward heat transfer was suppressed when compared with the case where the liquid region is homogenized by vigorous convection these experimental results imply that when a basalt magma is emplaced in continental crust floor melting does not always enhance the cooling of the magma but it may even reduce the total heat loss from the magma to the crusts due to suppression of convection by formation of a stabilizing compositional gradient

trace element discrimination of arc slab failure and a type granitic rocks abstract although widely used classification schemes for granitic rocks have until now failed to separate slab failure from arc magmatism in collisional orogens our previous work showed that cretaceous cordilleran type batholiths are composed of a pre collisional belt of mesozonal to epizonal arc plutons commonly emplaced into their own cover and a post accretion tract of what we interpret as slab failure plutons emplaced into the tectonically thickened collisional hinterland histograms based on new geochemical compilations of pre and post collisional igneous rocks were employed to derive trace element criterion to distinguish between these two plutonic types using rocks over the sio2 range of 55 70 wt and aluminum saturation index of 20 nb y 0 4 ta yb 0 3 la yb 10 gd yb 2 and sm yb 2 5 also we found that a type magmas can be distinguished from other post collisional igneous rocks based on ta yb 6 ppm and nb y 60 ppm these trace element differences between our pre collisional arc and post collisional slab failure plus a type groups allowed us to build composite discrimination diagrams for destructive margin igneous rocks although most s type granites are also post collisional they should not be plotted on our diagrams for some of their geochemical features overlap those of our slab failure group unlike our arc and slab failure groups a type granites are formed in diverse tectonic settings such that their classification is more related to geochemical signature and magma sources than to tectonic setting lastly we show how our discrimination diagrams delineate examples of slab failure magmatism through time and suggest links with porphyry cu au deposits

discrimination of productive and nonproductive porphyritic intrusions in the chilean andes a geochemical comparison between productive intrusions those associated with mineralization and nonproductive intrusions those unrelated to mineralization has been made on the basis of over 100 fresh granitoid rocks from the chilean porphyry copper belt the study was carried out on the scale of a mining district el salvador potrerillos then on the scale of a single traverse el salvador chilean coast and finally on the scale of the andes itself the productive intrusions are best characterized by large negative anomalies in y mn th and the heavy rare earth elements a discriminant diagram of y against mno is recommended for predicting whether an apparently fresh intrusion has associated peripheral mineralization the low values of y and mn in productive intrusions can be partly explained by the early crystallization of y and mn rich hydrous phases such as hornblende and by the loss of mn rich fluids from the magma the same elements make useful discriminants in other porphyry copper provinces although the exact position of the discriminant boundary varies from island arcs through continental margin to continental settings

the origin of contractional structures in extensional gneiss domes the juxtaposition of domains of shortening and extension at different scales in orogens has fueled many debates about driving forces and tectonic interpretations including timing of deformation at the orogen scale gravitational collapse and mass transfer from orogenic plateaux to forelands explain some of these juxtapositions at a regional scale structures in gneiss domes are commonly contractional yet are coeval with regional extension and denudation here we use three dimensional numerical experiments to show that crustal flow in orogenic domains does not necessarily conform to plate motion we document contractional crustal flow associated with the formation of a gneiss dome in an orogenic pull apart setting where localized extension and crustal thinning focus the exhumation of deep crust we show that the flow field results in a complex strain pattern in which an extensional strain regime that is collinear with the direction of plate motion is partitioned into the shallow crust whereas contractional structures and fabrics at a high angle to the direction of imposed transport develop in the deep crust advective mass transfer across regions of contrasting yet coeval strain regimes leads to a polyphase tectonic history we observe structural features remarkably similar to those documented in some natural gneiss domes such as the montagne noire which developed in a dextral pull apart domain at the southern margin of the french massif central

geochemical differences between subduction and collision related copper bearing porphyries and implications for metallogenesis abstract porphyry cu mo au deposits occur not only in continental margin arc settings subduction related porphyry cu deposits such as those along the eastern pacific rim eprim but also in continent continent collisional orogenic belts collision related porphyry cu deposits such as those in southern tibet these cu mineralized porphyries which develop in contrasting tectonic settings are characterized by some different trace element e g th and y concentrations and their ratios e g sr y and la yb suggesting that their source magmas probably developed by different processes subduction related porphyry cu mineralization on the eprim is associated with intermediate to felsic calc alkaline magmas derived from primitive basaltic magmas that pooled beneath the lower crust and underwent melting assimilation storage and homogenization mash whereas k enriched collision related porphyry cu mineralization was associated with underplating of subduction modified basaltic materials beneath the lower crust with subsequent transformation into amphibolites and eclogite amphibolites and resulted from partial melting of the newly formed thickened lower crust these different processes led to the collision related porphyry cu deposits associated with adakitic magmas enriched by the addition of melts and the subduction related porphyry cu deposits associated with magmas comprising all compositions between normal arc rocks and adakitic rocks all of which were associated with fluid dominated enrichment process in subduction related cu porphyry magmas the oxidation state fo2 the concentrations of chalcophile metals and other volatiles e g s and cl and the abundance of water were directly controlled by the composition of the primary arc basaltic magma in contrast the high cu concentrations and fo2 values of collision related cu porphyry magmas were indirectly derived from subduction modified magmas and the large amount of water and other volatiles in these magmas were controlled in part by partial melting of amphibolite derived from arc basalts that were underplated beneath the lower crust and in part by the contribution from the rising potassic and ultrapotassic magmas both subduction and collision related porphyries are enriched in potassium and were associated with crustal thickening their high k2o contents were primarily as a result of the inheritance of enriched mantle components and or mixing with contemporaneous ultrapotassic magmas

the red chris porphyry copper gold deposit northern british columbia canada igneous phases alteration and controls of mineralization red chris is a late triassic porphyry cu au mo deposit in the stikinia island arc terrane in northern b c late triassic sedimentary and volcanic rocks of the stuhini group host a series of late triassic to early jurassic 204 198 ma diorite to quartz monzonite stocks and dikes the red chris deposit is hosted in the 204 ma red stock the largest 6 5 1 5 km and most altered intrusion in the area volcanic rocks approximately time equivalent with the stock are exposed 2 km to the southwest and west postmineral early and middle jurassic sedimentary rocks unconformably overlie the stuhini group and red stock to the south and southeast the composite red stock consists of multiple phases of crowded porphyries 30 65 plagioclase hornblende biotite phenocrysts including abundant premineral p1 leucodiorite multiple subphases of synmineral p2 quartz monzonite porphyries and volumetrically minor late mineral monzonite p3 and monzodiorite p4 porphyries the stock evolved from subalkaline to silica saturated alkalic composition with the mineral related p2 porphyries being high k calcalkalic and high sr y common septa of stuhini biotitic hornfels are entrapped within the stock minor postmineral weakly altered mafic dikes cut the stock the zone of 0 25 cu equiv cu au is 2 km long wsw ene and up to 650 m wide early a type quartz veins with disseminated bornite accompanied biotitic and k feldspar magnetite alteration which was coeval with p2 porphyries higher cu and au grades correlate in a general way with zones of more abundant a veins chlorite carbonate epidote actinolite replaced hornblende peripheral to biotitic alteration and chlorite overprinted much of the secondary biotite late alteration affected all porphyry phases and is subdivided into earlier sericite clay pyrite and later low sulfide carbonate clay hematite late sericite clay pyrite alteration sulfidized much of the primary bornite to chalcopyrite with or without pyrite and carbonate clay hematite alteration converted most magnetite to hematite highest cu au grades 2 cu equiv occur in and around the early and intermediate stage p2 porphyries zoning of cu au au cu ratios sulfides and quartz veins is centered and mostly symmetrical around a core of high grade cu au within and surrounding apices of p2 porphyry contact relationships confirm the close association of p2 porphyry phases with cu au zones of 50 ppm mo surround the highest grade cu au zone at depth west northwest and east northeast strike slip to oblique slip faults offset sulfide cu au and mo patterns several lines of evidence indicate 15 to 20 of southward tilt since the system formed due to glaciation oxidation is very thin and supergene enrichment negligible red chris was previously considered by most workers as an alkalic or hybrid alkalic deposit new chemical data on synmineral porphyry phases instead suggest high k calc alkalic composition similar to the monzonitic cu mo au class of porphyry deposits which includes bingham and bajo de la alumbrera red chris is also classified as an a vein type deposit due to strong control of higher grade cu au by a vein stockworks with abundant disseminated cu sulfides

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

petrogenesis of cambro ordovician subduction related granitic magmas of the quebec appalachians canada abstract in the quebec appalachians cambro ordovician subduction related granitic rocks are found as intrusive bodies aci in the ascot complex volcanic arc and as eroded fragments mgc in the adjacent magog group sedimentary basin major and trace element geochemistry indicates that aci and mgc rocks are typical peraluminous granitoids both suites are lree enriched with minor negative eu anomalies aci granitoids displaying higher mree and hree abundances than mgc ree and trace element data indicate that aci and mgc granitoids are chemically similar but differences in their respective fractionation trends and trace element ratios demonstrate a significant petrological decoupling 143 nd 144 nd are higher in the mgc granitoids than in the aci both suites display negative nd ratios 10 to 3 implying limited juvenile material input sm nd isotopes from both suites suggest that they originated from the anatectic partial melting of a compositionally zoned grenville like continental crust

geochemistry of igneous rocks associated with mineral deposits in the tarom hashtjin metallogenic province nw iran an analysis of the controls on epithermal and related porphyry style mineralization abstract cenozoic magmatism in iran is associated with many epithermal porphyry cu au ore systems which mainly occur within the alborz magmatic arc and urumieh dokhtar magmatic arc systems the tarom hashtjin metallogenic province in the nw part of iran is located in the western alborz magmatic arc and is host to numerous ls is and hs type epithermal deposits within eocene volcano plutonic rocks whole rock geochemical data indicate that volcanic rocks vary extensively and continuously from subalkaline basaltic to rhyolitic compositions granitoid rocks are characterized by subalkaline metaluminous to peraluminous i to a type magmatism geochemical and geochronological studies of the igneous rocks associated with epithermal deposits particularly the enrichment of large ion lithophile elements depletion of high field strength elements including nb ta depletion and their eocene ages are consistent with extensional back arc tectonic settings suggesting that primary source magmas were generated by partial melting of the mantle wedge garnet bearing depleted lithospheric upper mantle and were subsequently affected by both fractional crystallization and crustal assimilation during their magmatic evolution the regional magmatism likely contributed to the heat advection and composition of metal bearing hydrothermal fluids in the formation of the epithermal deposits considering strong plagioclase fractionation relative to hornblende fractionation an extensional back arc tectonic setting the lack of any skarn mineralization and a considerably shallower depth of magma generation the tarom hashtjin metallogenic province is proposed to be prospective for precious metal epithermal mineralization by contrast the urumieh dokhtar magmatic arc and ahar arasbaran zone systems are probably more eroded and thus more prospective for porphyry cu au exploration

on convection and mixing driven by sedimentation the sedimentation of small particles from a suspension and the concomitant release of light interstitial fluid may constitute a buoyancy source for the development of convective motions when the dense suspension is emplaced beneath a stratified fluid an intermediate convecting layer between the sedimenting front and the density gradient above gradually grows in depth by erosion of the overlying stratified fluid novel laboratory experiments involving sedimentation below a two layer stratified region show that turbulent mixing and entrainment across the top density interface is significant for a broad range of the richardson number a simple theoretical model predicting the rate of erosion of the stratification above the convecting layer agrees well with these experiments the model is then extended to include the case of an overlying continuous density gradient and compared successfully with both new experimental data and the original data of kerr 1991 owing to the effects of dispersion of grain sizes small particles in the convecting fluid may lower the efficiency of the interfacial mixing by the turbulent eddies our model calculations suggest that turbulent mixing and entrainment driven by sedimentation may be significant in the atmospheric and oceanic contexts in both of which stratification is weak such mixing may also occur in molten magma chambers following the sedimentation of suspended crystals and in this case it may suppress large scale overturning events

mechanisms for the generation of compositional heterogeneities in magma chambers although there is general agreement that systematic variations of composition temperature and crystallinity in pyroclastic deposits provide strong evidence for chemical heterogeneities inside of magma chambers no hypothesis for the origin of these heterogeneities is widely accepted the chemical boundary layer flow hypothesis receives the most attention in the literature but other potentially valuable hypotheses are ignored in this paper we review the representative hypotheses and attempt to quantitatively evaluate their potential for producing compositional heterogeneities our conclusions can be summarized as follows based on volcanological data for compositionally zoned eruptions evolved magma is generated at a rate between 10 2 and 10 4 km3 a with a typical value of 10 3 km3 a melting of silicic country rock by intrusion of basaltic magma is a viable hypothesis because evolved melt is produced at a rate consistent with the volcanological observations some systems however do not show the extensive isotopic contamination predicted by this model mechanisms which involve porous media flow separation of partial melts from the source region and boundary layers in a magma chamber s marginal liquid crystal mush are unlikely due to low permeability of the porous media diffusion limited chemical boundary layers are capable of transporting significant quantities of h2o rich melt to the roof of a magma chamber components which diffuse more slowly for example sio2 are transported in sufficient quantities only if diffusively coupled to more mobile species in the melt cross coupling effects will be important if the off diagonal diffusion coefficients are 10 of the on diagonal coefficients or larger

the pleasant bay layered gabbro diorite coastal maine ponding and crystallization of basaltic injections into a silicic magma chamber

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

recycling of orogenic arc crust triggers porphyry cu mineralization in kerman cenozoic arc rocks southeastern iran pre collisional eocene oligocene arc diorites quartzdiorites granodiorites and volcanic equivalents in the kerman arc segment in central iran lack porphyry cu mineralization and ore deposits whereas collisional middle late miocene adakite like porphyritic granodiorites without volcanic equivalents host some of the world s largest cu ore deposits petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment ore hosting kuh panj porphyry intrusions exhibit high sr 400 ppm low y 20 no negative eu anomalies eu eu 1 and relatively non radiogenic sr isotope signatures 87sr 86sr 0 7042 0 7047 relative to eocene oligocene granitoids mainly sr 12 la yb 15 eu eu 1 87sr 86sr 0 7053 0 7068 trace element modeling indicates peridotite melting for the barren eocene oligocene intrusions and a hydrous garnet bearing amphibolite source for middle late miocene ore hosting intrusions the presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30 35 to 40 45 km or 12 kbar the changes in residual mineralogy in the source of eocene to miocene rocks in the kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel underplating of cu and sulfur rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust mantle boundary and dehydration melting under oxidizing conditions produced syn and post collisional ore hosting intrusions while the lack of post collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur rich and oxidized adakitic magmas

effects of volatiles on mixing in calc alkaline magma systems the intimate mixing between different magmas of disparate densities characteristic of some calc alkaline magma systems is explained by a new mechanism involving the emplacement of a layer of wet undersaturated mafic magma at the base of a magma chamber containing more differentiated magma turbulent transfer of heat between the mafic magma and the overlying magma leads to crystallization and exsolution of volatiles in the lower layer for an initial water content of a few per cent the bulk density of the mafic magma can become equal to that of the overlying magma causing overturning and intimate mixing of the magmas the mechanism is most probable in the low pressure environment of a high level magma chamber

comments on arc magmatism and subduction history beneath the zagros mountains iran a new report of adakites and geodynamic consequences by j omrani p agard h whitechurch m bennoit g prouteau l jolivet abstract based on the imprecise geochemical data for 62 samples from qom anar and baft regions in central iranian magmatic arc omrani et al omrani j agard p witechurch h benoit m prouteau g jolivet l 2008 arc magmatism and subduction history beneath the zagsros mountains iran a new report of adakites and geodynamic consequences lithos 106 380 398 suggested that all studied magmatic rocks display the geochemical affinity of subduction related calc alkalic rock suites here we demonstrate that the incorrect altered and variable geochemical data e g al 2 o 3 sr y ni cr sio 2 na 2 o la yb and th ce show that most of the samples actually display calc alkaline shoshonitic and calc alkalic adakitic affinities furthermore as a result of alteration rock samples of similar age e g qom indicate both adakitic and non adakitic compositional signatures which is misleading on the basis of more than 400 previously published geochemical analyses we suggest that after eliminating the false geochemical signatures the calc alkaline and adakitic affinities of the central iranian magmatic arc are due to flat subduction and might be related to a second phase of miocene pliocene porphyry copper mineralization which is a considerable exploration target and thus merits further investigation

density changes during the fractional crystallization of basaltic magmas fluid dynamic implications the dynamical behaviour of basaltic magma chambers is fundamentally controlled by the changes that occur in the density of magma as it crystallizes in this paper the term fractionation density is introduced and defined as the ratio of the gram formula weight to molar volume of the chemical components in the liquid phase that are being removed by fractional crystallization removal of olivine and pyroxene whose values of fractionation density are larger than the density of the magma causes the density of residual liquid to decrease removal of plagioclase with fractionation density less than the magma density can cause the density of residual liquid to increase during the progressive differentiation of basaltic magma density decreases during fractionation of olivine olivine pyroxene and pyroxene assemblages when plagioclase joins these mafic phases magma density can sometimes increase leading to a density minimum calculations of melt density changes during fractionation show that compositional effects on density are usually greater than associated thermal effects in the closed system evolution of basaltic magma several stages of distinctive fluid dynamical behaviour can be recognised that depend on the density changes which accompany crystallization as well as on the geometry of the chamber in an early stage of the evolution where olivine and or pyroxenes are the fractionating phases compositional stratification can occur due to side wall crystallization and replenishment by new magma with the most differentiated magma tending to accumulate at the roof of the chamber when plagioclase becomes a fractionating phase a zone of well mixed magma with a composition close to the density minimum of the system can form in the chamber the growth of a zone of constant composition destroys the stratification in the chamber a chamber of well mixed magma is maintained while further differentiation occurs unless the walls of the chamber slope inwards in which case dense boundary layer flows can lead to stable stratification of cool differentiated magma at the floor of the chamber in a basaltic magma chamber replenished by primitive magma the new magma ponds at the base and evolves until it reaches the same density and composition as overlying magma successive cycles of replenishment of primitive magma can also form compositional zonation if successive cycles occur before internal thermal equilibrium is reached in a chamber in a chamber containing well mixed plagioclase saturated magma the primitive magma can be either denser or lighter than the resident magma in the first case the new magma ponds at the base and fractionates until it reaches the same density as the evolved magma mixing then occurs between magmas of different temperatures and compositions in the second case a turbulent plume is generated that causes the new magma to mix immediately with the resident magma

convection and particle entrainment driven by differential sedimentation when a suspension of small particles is overlain by a clear fluid whose density is greater than that of the interstitial fluid but less than that of the bulk suspension the settling of the dense suspended particles can lead to vigorous convection in the overlying fluid this novel situation is investigated experimentally and theoretically a sharp interface is observed between the convecting upper region and a stagnant lower region in which there is unimpeded sedimentation at low reynolds number there is no transport of fluid from the upper region into the lower though there is mixing of both buoyant fluid and entrained particles from the lower region into the upper the interface between the two regions is found to descend at a constant velocity systematic laboratory measurements have determined how this velocity depends on the densities of the layers and the distributions of settling velocities of the particles a theoretical description is developed which calculates the evolution of the density of the lower region due to differential sedimentation of polydisperse particles buoyancy arguments based on the calculated density profile are used to placc upper and lower bounds on the amount of particle entrainment into the upper layer and on the rate of fall of the interface between the convecting and sedimenting regions the theoretical predictions are in good agreement with the experimental observations the analysis of the interaction between convection and sedimentation in the system considered here may be particularly relevant to the description of evolving crystal rich layers in magma chambers and of silt laden outflow from rivers and has a wide range of other industrial environmental and geological applications

high sr y arc magmas and porphyry cu mo au deposits just add water porphyry cu mo au deposits are commonly associated with intermediate composition arc related igneous rocks with high sr y and la yb ratios and such rocks are equated by some researchers with melts derived from subducted oceanic crust undergoing eclogite facies metamorphism adakites however similar geochemical characteristics are readily developed in normal asthenospheric mantle wedge derived magmas by fractionation of amphibole and or garnet and or by interaction with crustal materials during ascent through the upper plate lithosphere while there is widespread evidence for such fractionation and contamination processes in porphyry magmas there is little direct evidence for an origin by slab melting the enhanced fertility of arc magmas relates primarily to their high water content which is required for the formation of magmatic hydrothermal systems upon shallow crustal emplacement magmatic water contents 4 wt percent h 2 o cause abundant amphibole garnet fractionation but suppression of plagioclase crystallization at deep crustal levels resulting in increasing sr y and la yb ratios with differentiation commonly into adakitic ranges but not reflecting slab melting additional factors that affect arc magma fertility are relatively high oxidation states and sulfur content but these are secondary to the requirement for sufficient water thus arc magmatic suites with high sr y ratios and evidence for the presence of hydrous phenocryst phases hornblende and or biotite are indeed prospective for porphyry cu mo au deposits but only because these parameters indicate high magmatic water content