the apparent effects of the mt pinatubo eruption on the greenland ice sheet melt extent the indirect climatological effects of major volcanic eruptions can be of great importance because of the complex feedbacks that exist in the global climate system one such effect is the melt area reduction on the greenland ice sheet using passive microwave satellite data for the period 1979 1995 the melt conditions of the ice sheet before and after the 1991 mt pinatubo eruptions are examined statistical tests indicate that an observed drop following the eruptions has a 97 to 99 probability of being outside the limits of undisturbed variability furthermore this anomaly diminishes as the time from the eruption increases these characteristics in conjunction with an observed increasing melt trend prior to the eruptions indicate that mt pinatubo has had a significant effect on the melt conditions and consequently the energy balance characteristics of the greenland ice sheet

prolonged residence times for the youngest rhyolites associated with long valley caldera 230th 238u ion microprobe dating of young zircons abstract we describe a new ion microprobe method for dating magmatic zircon growth that is based on in situ measurement of the magnitude of238u 230th disequilibrium our results support independent inferences that zircon can remain suspended for long periods 100 ka in the convecting potions of the magma from which it crystallizes because the crystallization ages date when the magma cooled to its zircon saturation temperature even when the zircons have long magmatic residence times 238u 230th zircon dating can be used to constrain the thermochemical evolution of silicic magmas 238u 230th ages have been determined for individual zircons from rhyolites associated with the long valley magmatic system of eastern california the samples are from deer mountain an 115 3 ka low silica moat rhyolite and from the coarsely porphyritic low silica rhyolite of south deadman dome one of the 0 6 ka inyo domes previous investigations have suggested that the two lavas were derived from the same magma reservoir a few of the zircon model ages calculated with respect to the isotopic characteristics of the whole rocks are within error of that for eruption of the deer mountain rhyolite however the majority of zircons from both lavas cluster around an age of 230 ka this common interval of zircon nucleation and growth for petrologically similar lavas suggests that the younger inyo dome lava may have tapped the same magma body from which the deer mountain rhyolite erupted more than 100 ka before on the other hand most of the zircon model ages are younger than previous episodes of silicic volcanism in the long valley caldera suggesting that the rhyolites may have been generated during development of a silicic upper crustal magma chamber in the western portion of long valley caldera zircon saturation temperatures for the rhyolites studied 795 810 c are the same as those obtained from coexisting fe ti oxides 809 4 c showing that the magma cooled to

incremental growth of an upper crustal a type pluton argentina evidence of a re used magma pathway abstract carboniferous igneous activity in the sierra de velasco nw argentina led to the emplacement of several magmas bodies at shallow levels t 5 8 and ehf t in zircon 2 9 to 4 5 the second group comprises the metaluminous to peraluminous granitic rocks of the youngest units san blas and hualco which were formed by a heterogeneous mixture between mantle and crustal sources end t 0 6 to 4 8 and ehf t in zircon 3 to 6 our results provide a comprehensive view of the evolution of an intrusive complex formed from multiple non consanguineous magma intrusions that utilized the same magmatic plumbing system during downward transfer of host materials as the plutonic system matures the ascent of magmas is governed by the visco elastic flow of host rock that for younger batches include older hot magma mush the latter results in ductile downward flow of older during rise of younger magma such complexes may reflect the plutonic portion of volcanic centers where chemically distinct magmas are erupted

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

petrochronology and tims thermal ionization mass spectrometers or tims were developed by the pioneers of mass spectrometry in the mid 20th century and have since been workhorses for generating isotopic data for a wide range of elements later developed mass spectrometric techniques have many advantages over tims including higher spatial resolution with in situ techniques such as secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icpms and greater versatility in terms the elements that can be easily and well measured the reason tims persists as an important method for geochronology is that for some key parent daughter systems e g u pb sm nd it can produce isotopic data and resultant dates with 10 100 times higher precision and more quantifiable accuracy than in situ techniques even when sample sizes are very small such as those that might result from single crystals or even small portions of zoned crystals for many questions in the geosciences the highest achievable precision and accuracy are required to resolve the timescales of processes and or correlate events globally as an example modern tims u pb geochronology is capable of producing dates with precision and accuracy better than 0 1 of the age for single crystals with only a few picograms pg of pb therefore it is possible to constrain the durations of single zircon crystal growth in magmatic systems over tens to hundreds of kyr in mesozoic and younger rocks if these dates and rates can be connected with other igneous processes such as magma transfer emplacement and crystallization then it becomes possible to calibrate thermal and mass budgets in magmatic systems and evaluate competing models for pluton assembly and subvolcanic magma storage as another example sm nd geochronology of garnet permits dates with precision better than 1 million years for garnets of any age including multiple concentric growth zones in single crystals such

late pleistocene granodiorite beneath crater lake caldera oregon dated by ion microprobe variably melted granodiorite blocks ejected during the holocene caldera forming eruption of mount mazama were plucked from the walls of the climactic magma chamber at 5 km depth ion microprobe u pb dating of zircons from two unmelted granodiorite blocks with shrimp rg sensitive high resolution ion microprobe reverse geometry gives a nominal 238 u 206 pb age of 100 78 80 ka or 174 89 115 ka when adjusted for an initial 230 th deficit shrimp rg u th measurements on a subset of the zircons yield a 230 th 238 u isochron age of 112 24 ka considered to be the best estimate of the time of solidification of the pluton these results suggest that the granodiorite is related to andesite and dacite of mount mazama and not to magmas of the climactic eruption the unexposed granodiorite has an area of at least 28 km 2 this young shallow pluton was emplaced in virtually the same location where a similarly large magma body accumulated and powered violent explosive eruptions 7700 yr ago resulting in collapse of crater lake caldera

phase equilibrium constraints on the viscosity of silicic magmas 1 volcanic plutonic comparison by using recently determined experimental phase equilibria we show that the viscosity of granitic magmas emplaced at upper crustal levels is approximately constant at 104 5 pa s irrespective of their temperature and level of emplacement magmas crystallizing as granitic plutons are not water poor and thus not more viscous than their extrusive equivalents instead comparison between pre eruption magma viscosities of extrusive silicic intermediate and intrusive granitic magmas shows that the former are on average slightly more viscous given the typical strain rates in silicic magma chambers magma rheological behavior is expected to be dominantly newtonian bubbles having a minor rheological influence at depth although exceptions can exist thus whether a silicic intermediate magma is erupted or frozen at depth depends primarily on the rheological properties of surrounding terranes or on external tectonic factors but not on the rheology of the magma itself however preemptive viscosities of extrusive magmas rarely exceed 106 pa s which suggests that crystal melt mushes with higher viscosities cannot leave the magma storage regions beneath volcanoes the narrow range of viscosities displayed by silicic intermediate magmas results from both the strong control that pressure exerts on volatile solubilities in silicate melts and thermal limitations required to produce acid magmas considerations of the relationships between magma crystallinities bulk sio2 and preemptive melt h2o contents show that the higher the melt h2o content is the higher the maximum crystallinity that a given magma will be while still being potentially erupted an empirical correlation is proposed that enables us to estimate preemptive melt h2o contents of erupted magmas by knowing their crystallinity and bulk sio2

geodynamic controls on tertiary arc magmatism in ecuador constraints from u pb zircon geochronology of oligocene miocene intrusions and regional age distribution trends abstract we obtained u pb zircon ages of late tertiary intrusions in the northern andes to provide robust time calibration points for the intrusive geochronologic framework of ecuador which is mostly based on k ar data magmatism associated with intrusion emplacement ranges from 31 to 7 ma with ages mainly pooling in the late oligocene early miocene where both k ar and u pb data exist for a given intrusive system ages obtained by the different methods are usually concordant within 1 4 m y suggesting that k ar ages are accurate indicators for the timing of tertiary arc magmatism on a regional multi m y scale except for a single sample the investigated intrusions completely lack externally inherited zircons in agreement with dominantly zircon poor oceanic crustal basement domains spatio temporal distribution trends of tertiary arc magmatism inferred from screened u pb k ar and zircon fission track geochronologic data allow tracking of the progressive along arc broadening of a flat slab segment below southernmost ecuador in the mid to late miocene and of moderate slab shallowing in northern central ecuador in the late miocene these regional arc migration patterns correlate in time with the subduction of the buoyant inca plateau and the carnegie ridge seamount chain the temporal distribution of tertiary ecuadorian arc magmatism indicates a late oligocene early miocene arc magmatic flare up event comprising widespread ignimbrite eruption and batholith construction initiation of the flare up event coincides in time with accelerating less oblique farallon nazca south america plate convergence suggesting a positive feedback between convergence rates asthenospheric melt production mantle crust melt flux and upper crustal arc magmatic productivity in ecuador

depositional features and stratigraphic sections in granitic plutons implications for the emplacement and crystallization of granitic magma abstract many granitic plutons contain sheet like masses of dioritic to gabbroic rocks or swarms of mafic to intermediate enclaves which represent the input of higher temperature more mafic magma during crystallization of the granitic plutons small scale structures associated with these bodies e g load cast and compaction features silicic pipes extending from granitic layers into adjacent gabbroic sheets indicate that the sheets and enclave swarms were deposited on a floor of the magma chamber on granitic crystal mush and beneath crystal poor magma while the mafic magma was incompletely crystallized these structures indicate way up typically toward the interior of the intrusions and appear to indicate that packages of mafic sheets and enclave concentrations in these plutons are a record of sequential deposition hence these plutons preserve a stratigraphic history of events involved in the construction filling replenishment and crystallization of the magma chamber the distinctive features of these depositional portions of plutons allow them to be distinguished from sheeted intrusions which usually preserve mutual intrusive contacts and dike sill relations of different magma types the considerable thickness of material that can be interpreted as depositional and the evidence for replenishment suggest that magma chamber volumes at any one time were probably much less than the final size of the pluton thus magma chambers may be constructed much more slowly than presently envisaged the present steep attitudes of these structures in many plutons may have developed gradually as the floor of the chamber along with the underlying solidified granite and country rock sank during continuing episodes of magma chamber replenishment these internal magmatic structures support recent suggestions that the room problem for granites could be largely accommodated by downward movement of country rock beneath the magma chamber

dissecting complex magmatic processes an in depth u pb study of the pavia pluton ossa morena zone portugal the build up of large magmatic complexes can proceed piecemeal over periods of several million years through sequences of complex processes of magma production differentiation assimilation final crystallization and subsequent metasomatic modification all these stages can produce or modify minerals used as geochronometers such as zircon monazite and titanite the present study exemplifies such complex relationships also demonstrating how a systematic approach with comprehensive sampling and careful high resolution u pb analyses can yield a coherent picture of the entire magmatic process the study was conducted on the pavia pluton an elongated variscan intrusion in the ossa morena zone of portugal the geochronological data show that the pavia pluton was emplaced by the amalgamation of multiple magma pulses into the crust over a period of c 11 myr an early event at 340 ma revealed by xenocrystic zircon preceded the magmatic activity at the exposed level of the pluton but is recognized as the main magmatic event elsewhere in the ossa morena zone a second event at 328 ma formed tonalite trondhjemite and granodiorite and subordinate differentiates in the central domains of the pluton units i and ii a third event at c 324 ma emplaced granodiorite in the flanking domains iii v and the contemporaneous and widespread two mica granite in domainvi together with late rhyodacite porphyries microgranodiorites aplite pegmatite and pegmatite dikes a fourth event at 319 317 ma was characterized by the emplacement of some microgranites and pegmatite dikes these two last magmatic events also had an effect on the previously emplaced rocks causing local overgrowths and isotopic resetting of minerals the occurrence of a fifth magmatic event at depth at 313 ma is the inferred cause of the hydrothermal activity responsible for local zircon monazite and titanite resorption and or recrystallization and for some of the textures exhibited by the main rock forming minerals the magmatic episodes were interspersed with periods of quiescence this cyclicity presumably reflects an external control by the transtensional tectonic regime of the ossa morena zone

late pleistocene granodiorite source for recycled zircon and phenocrysts in rhyodacite lava at crater lake oregon abstract rhyodacite tephra and three lavas erupted 27 ka interpreted to be early leaks from the climactic magma chamber of mount mazama contain ubiquitous resorbed crystals antecrysts that were recycled from young granodiorite and related plutonic rocks of the same magmatic system the shallow composite pluton is represented by blocks ejected in the 7 7 ka climactic eruption that formed crater lake caldera plagioclase crystals in both rhyodacite and granodiorites commonly have cores with crystallographically oriented fe oxide needles exsolved at subsolidus conditions at least 80 of plagioclase crystals in the rhyodacite are antecrysts derived from plutonic rocks other crystals in the rhyodacite notably zircon also were recycled sims 238 u 230 th dating indicates that zircons in 4 granodiorite blocks crystallized at various times between 20 ka and 300 ka with concentrations of analyses near 50 70 110 and 200 ka that correspond to periods of dacitic volcanism dated by k ar u th ages of zircon from a rhyodacite sample yield similar results no analyzed zircons from the granodiorite or rhyodacite are pre quaternary zircon minimum ages in blocks from different locations around the caldera reflect ages of nearby volcanic vents and may map the distribution of intrusions within a composite pluton survival of zircon in zircon undersaturated hydrous magma and of fe oxide needles in plagioclase suggests that little time elapsed from entrainment of antecrysts to the 27 ka eruption of the rhyodacite the 27 ka rhyodacite is an example of young silicic magma that preserved unstable antecrysts from a known source early during growth of a large high level magma chamber in contrast the voluminous 7 7 ka climactic rhyodacite pumice is virtually lacking in zircon indicating dissolution of any granodioritic debris in the intervening period mineralogical evidence of assimilation may be destroyed in hot vigorously growing silicic magma bodies such as ultimately produced the climactic eruption of mount mazama

hydrothermal alteration and mineralization of the galore creek alkalic cu au porphyry deposit northwestern british columbia canada the late triassic galore creek porphyry district is the largest accumulation of cu au prospects in british columbia canada in terms of contained metal the principal economic resource is the central zone deposit it comprises three high grade centers the au rich north and south gold lenses and the cu dominated central replacement zone alteration footprints ore shells and porphyry intrusions in these centers dip 45 to 60 to the west in the north gold lens and southwest in the south gold lens and central replacement zone indicative of significant postmineral tilting this inclination created an oblique vertical expression of the central zone at surface and at depth providing a 700 m depth profile through the deposit galore creek is considered to be the end member of the silica undersaturated class of alkalic porphyry cu au deposits it displays a unique hydrothermal alteration footprint generally devoid of quartz veining despite the lack of crosscutting veins a paragenetic sequence of several discrete potassic and calcic alteration events has been established during main stage alteration two mineralization events occurred that formed the economic resource in the central zone highly oxidizing fluids derived from porphyritic syenite to monzonite intrusions produced initial potassic alteration and sulfide mineralization in the north gold lens and south gold lens cu au ore shells are characterized by a gold rich core dominated by bornite associated with hematite dusted orthoclase specular hematite and anhydrite the second period of hydrothermal activity caused brecciation and calcic alteration in the central replacement zone the calcic fluids formed hydrothermal cement grading from ti rich andraditic to grossularitic garnet in the core of the breccia to a diopside and magnetite dominated assemblage at the margins calcic alteration also formed in the surrounding host rock this alteration event was followed by potassic alteration and mineralization characterized by biotite anhydrite and chalcopyrite in the cu rich ore shell of the central replacement zone most of the au is hosted in bornite that is spatially associated with oxidized reddened rock units dominated by an alteration assemblage of orthoclase hematite specular hematite garnet anhydrite high grade cu in the central zone is related to abundant chalcopyrite that has commonly replaced an assemblage of biotite magnetite diopside this distinct spatial separation strongly suggests that the local redox environment within the wall rocks governed sulfide and gold distributions the switch from early au rich mineralization to late stage cu dominated mineralization appears to have been controlled by varying redox conditions within the magma the change from more oxidized alteration assemblages fe3 fe2 to more reduced assemblages fe3 fe2 is indicative of a change in oxidation potential that may have propelled sulfide saturation in the magma and thus the subsequent depletion of most of the au

probing the accumulation history of the voluminous toba magma the age and compositional zonation in crystals from the youngest toba tuff record the prelude to earth9s largest quaternary eruption we used allanite crystals to date and decipher this zoning and found that the crystals retain a record of at least 150 000 years of magma storage and evolution the dominant subvolcanic magma was relatively homogeneous and thermally stagnant for 110 000 years in the 35 000 years before eruption the diversity of melts increased substantially as the system grew in size before erupting 75 000 years ago

observations and controls on the occurrence of inherited zircon in concord type granitoids new hampshire u pb analyses of zircons separated from two concord type plutons near sunapee and dixville notch new hampshire reveal differences in the pattern and magnitude of zircon inheritance which are related to differences in melt chemistry the sunapee pluton contains only slightly more zr than required to saturate the melt at the peak temperature of 700 30 sup 0 c traces of inherited zircon in this separate are inferred to be present as small largely resorbed grains in contrast the long mountain pluton near dixville notch contains about 240 more zr than required to saturate the melt thus more than half of the zr existed as stable inherited zircon crystals during the partial fusion event consistent with the observation of substantial inheritance in all grain size fractions ion probe intra grain analyses of zircon from the long mountain pluton indicate a complex pattern of inheritance with contributions from at least two proterozoic terranes and caution against simple interpretations of upper and lower intercepts of chords containing an inherited component ion probe analyses of zircons from the sunapee pluton reveal clear evidence of u loss which results in incorrect apparent conventional u pb ages ages of crystallization for the long mountain and sunapee pluton are approx more 350 and 354 5 ma respectively a sm nd measurement for the long mountain pluton yields a depleted mantle model age of 1 5 ga consistent with the observed inheritance pattern in contrast a sm nd model age for the sunapee pluton is improbably old due to minor monazite fractionation less

characteristics of internal contacts in the tuolumne batholith central sierra nevada california usa implications for episodic emplacement and physical processes in a continental arc magma chamber internal contacts along the eastern margin of the tuolumne batholith central sierra nevada california and structures preserved along these contacts are highly variable the contacts range from relatively sharp to gradational boundaries to sheeted zones to very complex boundaries formed by multiple processes fractional crystallization kilometer scale mixing within broad transition zones voluminous magmatic stoping along sharp contacts and downward return flow and or margin collapse of older magma units were important large scale processes along these contacts during chamber construction in contrast sheeting extensional cracking and diking represent only second order small scale complexities formation of the most complex zones along internal contacts resulted from the interaction of the sequential emplacement of different units with the irregular geometry of these contacts which often resulted from removal of earlier phases by stoping our results indicate that multiple processes are likely during emplacement of large magma bodies within one another and that it is unlikely that evidence for all internal processes during batholith construction are preserved we also argue that fairly large magma chambers existed in this batholith and thus that large accumulations of magma may exist in upper crustal chambers for significant periods of time

imbricate architecture of the upper paleozoic to jurassic oceanic cache creek terrane central british columbia upper paleozoic to lower jurassic oceanic rocks of the cache creek terrane near fort st james in central british columbia form a stack of thrust sheets cut by steeply dipping strike slip faults paleontologically dated upper paleozoic strata include bioclastic shallow water limestone and ribbon chert isotopically dated permian rocks consist of tonalite sills and stocks and rhyolite flows intercalated with basalt flows paleontologically dated lower mesozoic rocks include greywacke sandstone siltstone argillite ribbon chert conglomerate limestone and basalt tuff trembleur ultramafite unit of the cache creek complex in places part of an ophiolite suite forms thrust sheets and klippen that overlie lower mesozoic sedimentary rocks sedimentological lithochemical paleontological petrological and textural comparisons with other areas and established models demonstrate that cache creek terrane is an accretionary complex a structurally stacked assemblage of rocks that originated in diverse and

melts mush and more evidence for the state of intermediate to silicic arc magmatic systems understanding the physical state of intermediate to silicic arc magmatic systems is necessary for our petrologic models of these systems researchers have generated a plethora of data geophysical geochronological petrological theoretical over the past few decades these data have changed how we view arc magmatic systems leading to a model of crystal mush that is rejuvenated repeatedly over the lifespan of the magmatic system however much data are either circumstantial or incomplete paterson et al 2016 october issue use a combined set of textural geochemical and temporal data to demonstrate the changing physical state of the tuolumne intrusive complex in california over its 10 million year history they offer evidence for magmatic erosion and recycling along with the potential for a surge growth of the batholith that allows for significant volumes of magma to exist ephemerally under arc volcanoes most intermediate to silicic arc magmas henceforth arc magma are stored 3 km depth so direct observation is impossible instead this question has been approached in four main ways 1 geophysical inspections of active arcs 2 mineral geochronology 3 field observations of plutons and 4 thermal and physical modeling of magmatic systems each of these four avenues has their own strengths and shortcomings many times the interpretation of these data appears to be at odds some overarching observations can be made about what we know of the state of active intermediate to silicic arc magmatic systems geophysical observations such as seismic tomography have yielded little evidence for large bodies of fully molten magma persistently underneath arc volcanoes if anything only small lenses of partial melt are observed at

zircon crystallization and the lifetimes of ore forming magmatic hydrothermal systems magmatic hydrothermal copper ore formation involves multiple pulses of subvolcanic porphyry intrusion vein opening and hydrothermal ore deposition it is driven by larger subjacent magma reservoirs acting as the source of fluid and ore forming components high precision u pb ages of individual zircon crystals from porphyries immediately predating and postdating cu au mineralization at bingham canyon utah united states and bajo de la alumbrera northwestern argentina show a significant spread of reliably concordant ages this demonstrates zircon crystal formation over a protracted period of 1 m y which is interpreted to record the lifetime of the magma reservoir from which porphyries and ore fluids were extracted the youngest zircons in all pre ore and post ore intrusions overlap within a much shorter time interval of 0 32 m y at bingham canyon and 0 090 m y at alumbrera these youngest zircons of each intrusion are interpreted to bracket the maximum duration of porphyry emplacement and ore formation to short periods consistent with thermal constraints this study illustrates that age brackets based on individual magmatic zircon grains are geologically more informative than the calculation of means and standard deviations based on apparently normal age distributions in zircon populations

rayleigh taylor instability of a particle packed viscous fluid implications for a solidifying magma 1 we performed laboratory experiments of rayleigh taylor instability of superposed viscous fluids where the upper layer contains denser spherical solid particles a series of experiments are made by varying the viscosity and the particle diameter and we measure the growth rate and the wave length of the instability the instability consists of fine scaled plumes which coalesce as they descend plumes are observed to form intermittently and the particle layer thins with time which finally descend as blobs we find that the growth rate can be explained by using the linear stability analysis for rayleigh taylor instability of viscous fluids by taking the effective viscosity of particle bed to be 20 times that of the fluid and scale the thickness of the upper layer by twice the particle diameter using this scaling we find that a partially solidified layer beneath the surface of a lava lake may become unstable by this mechanism

comparison of mount pinatubo and el chichon volcanic events lidar observations at 10 6 and 0 69 μm analyses of a dense set of lidar observations of the volcanic clouds from mount pinatubo and el chichon primarily over boulder colorado and at a wavelength of 10 59 m reveal notable similarities and differences the importance of tropopause folding events for purging stratospheric debris into the troposphere is confirmed as well as the role of gravitational settling to bring debris into the grasp of the folding mechanism seasonal influences appear more important than time after eruption in both poleward transport and in purging stratospheric material downward we discuss the lengthening of the decay process for the mount pinatubo clouds by either an equatorial reservoir of debris or by eruptions of mount spurr simultaneous observations at 0 69 and 10 59 m help monitor aerosol effective radii versus altitude with good temporal and vertical resolution

development of igneous layering during growth of pluton the tarcouate laccolith morocco abstract we discuss the significance of igneous layering with respect to pluton growth processes the case study is the tarcouate laccolith morocco whose core consists of modally layered hornblende granodiorites with high amount of monzodioritic enclaves contrasting with peripheral non layered biotite granodiorites with low amount of enclaves rhythmic layering with modal grading cross stratification and trough layering is associated with monzodioritic layers and wraps around mafic enclaves its steep dips 45 result from tilting that occurred above solidus conditions as indicated by sub vertical and synmagmatic granite aplite and monzodiorite dykes cutting across the layering the systematic association of igneous layering with mafic enclaves in calc alkaline plutons suggests that layering originates from recurrent injection of mafic magma viscosity calculations suggest that the physicochemical properties of magma alone cannot account for the presence of layering in the central hornblende granodiorite and its coeval absence in the peripheral biotite granodiorite of the tarcouate laccolith intermittent pulses of hot mafic magma into crystallizing granodiorite likely produced thermal perturbations able to trigger local convection formation of mafic enclaves and development of igneous layering through protracted crystallization

cache creek terrane entrapment oroclinal paradox within the canadian cordillera exotic and far traveled oceanic crustal rocks of the cache creek terrane cc are bordered by less exotic quesnel qn and stikine st arc terranes to the east north and west all of these terranes are enveloped by an arcuate belt of displaced continental margin rocks the kootenay ko nisling ns and parts of the yukon tanana ytt terranes that have indirect ties to ancestral north america na initial 87sr 86sr isopleths conform to this arcuate pattern such a pattern of concentric belts presents a geological conundrum how did the qn st and cc come to be virtually enveloped by terranes with ties to na past and current models that explain assembly of the canadian cordillera are deficient in their treatment of this problem we propose that early mesozoic qn and st were joined through their northern ends as two adjacent arc festoons that faced south toward the cache creek ocean panthalassa oceanic plateau remnants within the cc today were transported from the tethyan realm and collided with these arcs during subduction of the cache creek ocean counterclockwise oroclinal rotation of st and ns terranes in the late triassic to early jurassic caused enclosure of the cc rotation continued until these terranes collided with qn in the middle jurassic paleomagnetic declination data provide support for this model in the form of large average anticlockwise rotations for permian to early jurassic sites in st but moderate clockwise rotations for sites in qn specific modern analogues for the cordilleran orocline include the yap trench where the caroline rise is colliding end on with the mariana arc and the banda arc located on the southeastern tail of the asian plate which is being deformed into a tight loop by interactions with the australian and pacific plates

geology and district scale setting of tilted alkalic porphyry cu au mineralization at the lorraine deposit british columbia lorraine is a copper gold porphyry deposit 6 4 mt indicated resource at 0 61 copper and 0 23 g t gold and 28 8 mt inferred resource at 0 45 copper and 0 19 g t gold in north central british columbia one of the youngest known alkalic porphyry deposits within the triassic jurassic quesnel arc the deposit is hosted by the early jurassic duckling creek syenite complex an alkalic multiphase intrusive dike complex of pyroxenite syenite and monzonite composition the southern part of the complex hosts numerous copper gold porphyry prospects in addition to lorraine together they constitute the duckling creek district main stage cu au porphyry mineralization at lorraine is hosted by phase 1 of the duckling creek syenite complex an sw dipping early intrusive suite of silica undersaturated pyroxenites and syenites mineralized zones are up to 2 5 km long by 500 m wide in the form of northwesterly elongate sw dipping panels that generally parallel the phase 1 intrusive contacts mineralization is attributed to blind porphyries within the phase 1 sequence which was tilted after main stage mineralization copper sulfides define deposit scale zonation patterns of bornite chalcocite cores rimmed by chalcopyrite rich and outer weakly developed pyrite dominated domains alteration patterns and intensity are consistent across mineralized zones strong pervasive k feldspar biotite potassic core zones are rimmed by albite diopside magnetite calc potassic alteration that is pervasive near the center of the zones but varies laterally outward to vein style alteration pervasive albite alteration sodic is locally present and is interpreted to be an early alteration event mineralization at lorraine has been cut by later phases of the duckling creek syenite complex a second cycle of pyroxenite syenite monzonite intrusion phase 2 is mineralogically similar to phase 1 but is unmineralized and has vertical intrusive contacts that strike northwest a change to late silica saturated intrusions is marked by subvertical phase 3 silica saturated leucosyenite and pegmatite dikes u pb zircon and ar ar geochronology constrain the timing of main stage mineralization at lorraine to an approximately 1 5 m y interval between 180 ma and 178 5 ma phase 1 intrusions are as old as 181 68 0 95 ma based on an ar ar age on biotite from pyroxenite but may range to as young as 180 2 0 28 ma based on a u pb zircon age from a mineralized phase 1 syenite the upper age limit for mineralization is 178 75 0 21 ma based on u pb data for a postmineral phase 2 syenite an alternate interpretation considers the presence of zircon antecrysts in an analyzed phase 1 rock which leads to a more narrow time window of 0 31 m y that includes phase 1 intrusion main stage porphyry mineralization and structural tilting which was followed by phase 2 intrusion magmatic and hydrothermal activity in the lorraine area persisted until at least 176 ma based on the u pb zircon age of 176 77 0 36 ma from a phase 3 leucosyenite dike and a late biotite albite apatite vein with an ar ar biotite age of 175 21 0 91 ma several intrusive hosted porphyry prospects within the duckling creek district share mineralogical and alteration characteristics as well as relative igneous paragenesis with lorraine the model for magmatic and hydrothermal development at lorraine may broadly be applied to the district as a whole providing a geologic framework upon which to base future exploration in the district

mineralization u pb geochronology and stable isotope geochemistry of the lower main zone of the lorraine deposit north central british columbia a replacement style alkalic cu au porphyry the lower main zone of the lorraine alkalic porphyry cu au district bc canada is hosted in an intrusive complex that comprises pre and late mineral biotite pyroxenites monzonites and syenites some of the biotite pyroxenites have interstitial sulfides which appear similar to net textured sulfides in magmatic ore deposits however the pyroxenites have undergone several stages of hydrothermal alteration main stage mineralization produced sulfide zonation patterns consisting of a bornite chalcocite or bornite chalcopyrite core grading outward to domains of chalcopyrite chalcopyrite pyrite and a peripheral domain of pyrite with minor chalcopyrite syenite in the inner bornite chalcopyrite zone typically contains abundant turbid k feldspar 70 whereas syenite marginal to the bornite chalcopyrite core contains less k feldspar 50 70 indicating an increase in k metasomatism of syenites toward the core of the deposit main stage mineralization predominantly occurs as fine grained disseminated sulfides in syenite biotite pyroxenite and fine grained k feldspar biotite rock textural analyses have shown that 1 primary magmatic diopside in contact with sulfides has corroded and actinolite altered margins suggesting alteration of primary minerals 2 scalloped relicts of biotite and diopside occur as inclusions in sulfides implying that sulfides have replaced primary minerals and 3 the deposit scale sulfide zonation patterns overprinted numerous rock types including the biotite pyroxenites that contain interstitial sulfides these results provide evidence for replacement style mineralization at lorraine where primary magmatic biotite and diopside were totally or partially replaced by sulfide minerals during main stage alteration u pb zircon dates from pre and late mineral syenite dikes show that the timing of main stage mineralization occurred between 178 8 and 176 0 ma lorraine is hosted within the quesnel island arc terrane and mineralization and magmatism at lorraine postdate accretion of the quesnel terrane to ancestral north america by approximately 7 to 10 m y the lorraine deposit represents the youngest known alkalic cu au porphyry deposit within the quesnel terrane and appears to coincide with the last gasp of alkalic magmatism within the quesnel terrane during the mesozoic

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

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

sheeted intrusion of the synkinematic mcdoogle pluton sierra nevada california field microstructural and geochronologic evidence indicates that the late cretaceous mcdoogle pluton located near the eastern margin of the sierra nevada batholith was emplaced as a subvertically sheeted complex into a steep reverse sense shear zone evidence of internal subvertical sheeting includes abundant concordant wall rock inclusions and screens that separate the pluton from adjacent jurassic plutons preservation of a ghost tectonostratigraphy in the distribution of the inclusions and rare interphase contacts the solid state tectonic fabric in the wall rocks and the magmatic submagmatic and weak solid state fabrics in the mcdoogle pluton all are concordant and record northeast southwest horizontal shortening subvertical extension and a significant component of northeast side up simple shear intrusive contacts generally are concordant with the fabrics but where discordances occur the wall rock fabric invariably is truncated by the contact however late synkinematic emplacement of the mcdoogle pluton is indicated by synintrusive boudinage of apophyses of the pluton and by the overall concordance of pluton fabrics including magmatic lineation zircon u pb isotope dates were obtained from the quartz monzodiorite central phase of the mcdoogle pluton 94 4 ma the mafic granodiorite border phase 94 8 0 6 ma and an older hornblende granodiorite included in the central phase 97 6 0 4 ma granodiorite orthogneiss in the wall rock yielded a u pb zircon date of 164 2 1 6 8 ma which we interpret to be the crystallization age and which is indistinguishable from a new age of 164 5 2 3 ma for the twin lakes pluton a u pb titanite date of 94 4 0 9 ma from the 164 ma orthogneiss sample may reflect thermal effects of the intruding mcdoogle pluton synkinematic growth of titanite in the shear zone or perhaps both the age of the sawmill lake shear zone that hosts the mcdoogle pluton is bracketed between 148 ma the age of the independence dike swarm and 92 ma the age of the lamarck pluton that crosscuts both the mcdoogle pluton and the shear zone fabrics regional evidence suggests a shear zone age younger than 110 ma but older deformation is possible the predominance of horizontal shortening over transcurrent motion and an age older than 90 ma exclude a direct relationship to the dextral sierra crest shear system which has been proposed to pass near the study area the location age constraints and kinematics of the shear zone are consistent with both the later stages of movement in the east sierran thrust system and isostatic sinking of the arc magmatic complex into its substrate

multistage emplacement of the mount givens pluton central sierra nevada batholith california the ca 90 ma mount givens pluton is one of the largest granodioritic to granitic intrusions in the sierra nevada batholith of california emplacement of the pluton occurred during a critical time in the tectonic evolution of the central sierra nevada magmatic arc marked by a transition from regional contraction to dextral transcurrent shear a model for the emplacement of the intrusion is developed based on detailed mapping of the pluton and its wall rocks and characterization of its internal structure by measurements of the anisotropy of magnetic susceptibility ams at 351 stations one of the key results of the study is documentation of a strong correlation between petrologic and structural fabrics in the pluton and determination that these fabrics reflect internal magma chamber dynamics more than regional tectonic strain the 80 km long 15 30 km wide pluton crystallized from a multiphase three segment magma chamber marked by a bulbous northern lobe and linear central and southern segments the pluton is interpreted to be tabular in shape with a thickness of 5 km most of the space for the pluton was created by piecemeal block downdrop of the magma chamber floor along three principal fracture sets the most important of which were steeply dipping northwest trending fractures formed parallel to the structural grain of the arc and vertical north trending extension fractures formed in response to a component of arc parallel dextral shear some of these fractures acted as magma conduits episodically filling the pluton as source rocks became depleted in melt an initial voluminous intrusive event stage 1 quickly filled the southern chamber with granodiorite magma but only partially filled the northern and central chambers stage 2 magmatism involved underplating of megacrystic granite in the northern chamber and lateral flow of a large batch of this magma from the northern to the central chamber the latter delineated by a 20 km long belt of megacrystic granite containing subhorizontal magnetic lineations that connects the pluton segments floor downdrop eventually ceased to be an effective space making process in the northern lobe and renewed magmatism stage 3 led to expansion and doming of the chamber as the northern lobe cooled a ring fault ruptured within the viscoelastic stage 1 2 carapace allowing ring dike intrusion stage 4 and sinking of a central flap of consolidated material the temporal and spatial variations in emplacement mechanisms demonstrated for the mount givens pluton i e fracture generation floor downdrop underplating inflation ring diking suggest that end member models e g fracture vs diapir are oversimplifications of the pluton assembly process

greenland ice sheet melt extent 1979 1999 analysis of melt extent on the greenland ice sheet is updated to span the time period 1979 1999 and examined along with its spatial and temporal variability using passive microwave satellite data to acquire the full record the issue of continuity between the previous passive microwave sensors smmr ssm i f 8 and ssm i f 11 and the most recent ssm i f 13 sensor is addressed the f 13 cross polarized gradient ratio melt classification threshold is determined to be 0 0154 results show that for the 21 year record a positive melt trend of nearly 1 yr is observed but this trend falls just below the 90 significance level the observed melt increase does appear to be driven by conditions in the western portion of the ice sheet rather than the east where melt appears to have decreased slightly moreover the eruption of mount pinatubo in 1991 is likely to have had some impact on the melt but not so much as previously suspected the 1992 melt anomaly is 1 7 standard deviations from the mean finally the relationship between coastal temperatures and melt extent suggests an increase in surface runoff contribution to sea level of 0 31 mm yr for a 1 c temperature rise

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

steep schlieren and associated enclaves in the vinalhaven granite maine possible indicators for granite rheology schlieren that form above the solidus are potentially diagnostic of the rheology of crystallizing granitic magmas and could provide insights into magma chamber structure here we focus on steep schlieren associated with comagmatic enclaves in the vinalhaven granite steep schlieren extend 1 3 m upward from the sides of enclaves and appear to have steep cylindrical shapes in 3d analyses of schlieren widths and the sizes of associated enclaves suggest that granitic crystal mush in which they occur had a plastic rheology probably characterized by a yield strength the enclaves now enclosed in coarse grained granite must have existed at higher levels in a crystal poor part of a magma chamber and settled downward until reaching material with a yield strength exceeding the buoyancy of the enclaves in addition to constraining the local rheology of the granite their relative positions may indicate vertical rheological variations and possibly the chamber floor

interpreting noble gas concentrations as proxies for salinity and temperature in the world s largest soda lake lake van turkey in this work we present noble gas concentration profiles measured in the water column and in the sediment pore water of the earth s largest soda lake lake van eastern anatolia turkey the concentrations of noble gases in particular ar kr and xe in the water body deviate significantly from the expected equilibrium concentrations calculated from the in situ temperature and salinity using existing solubility functions for seawater the specific chemical composition of the water of the soda lake seems to be responsible for the observed deviations our measurements allow the identification and quantification of salinity factors that can be applied to correctly calculate the noble gas equilibrium concentrations for the lake these salinity factors provide a solid and robust empirical basis for the interpretation of noble gas concentration signals measured in the sediment pore water of lake van in terms of palaeosalinity and palaeotemperature

assembly of a dike fed magma chamber the jackass lakes pluton central sierra nevada california the mechanisms of ascent assembly and emplacement of granitic magma in the crust are critical to understanding the dynamics of continental margin growth yet these mechanisms remain controversial and poorly understood detailed study of structural and petrologic fabrics in the middle cretaceous jackass lakes pluton wall rock system central sierra nevada california coupled with u pb geochronology indicates that the pluton formed via sheet like assembly of a dike fed magma chamber final emplacement of the pluton was facilitated by multiple brittle and ductile mechanisms that were active at different times and places within the system this supports hybrid viscoelastic emplacement models as realistic alternatives to end member models i e dike versus diapir fracture propagation which initiated 40 of the space required for emplacement may have been facilitated by a small component of arc parallel dextral shear that produced north northwest striking tension gashes a combination of ductile wall rock shortening during lateral expansion of sheets and return flow of elongate strongly deformed wall rock septa produced an additional 25 of the space required other mechanisms including coeval formation of the overlying minarets caldera and stoping in the subvolcanic part of the magma chamber must account for the remaining 35 space implying that vertical transfer of material is an important emplacement mechanism at shallow crustal levels

residence resorption and recycling of zircons in devils kitchen rhyolite coso volcanic field california zircons from the devils kitchen rhyolite in the pleistocene coso volcanic field california have been analyzed by in situ pb u ion microprobe shrimp rg and by detailed cathodoluminescence imaging the zircons yield common pb corrected and disequilibrium corrected pb u ages that predate a previously reported k ar sanidine age by up to 200 kyr and the range of ages exhibited by the zircons is also approximately 200 kyr cathodoluminescence imaging indicates that zircons formed in contrasting environments most zircons are euhedral and a majority of the zircons are weakly zoned but many also have anhedral embayed cores with euhedral overgrowths and multiple internal surfaces that are truncated by later crystal zones concentrations of u and th vary by two orders of magnitude within the zircon population and by 10 20 times between zones within some zircon crystals indicating that zircons were transferred between contrasting chemical environments a zircon saturation temperature of 750 c overlaps within error a previously reported phenocryst equilibration temperature of 740 25 c textures in zircons indicative of repeated dissolution and subsequent regrowth are probably caused by punctuated heating by mafic magma input into rhyolite the overall span of ages and large variation in u and th concentrations combined with calculated zircon saturation temperatures and resorption times are most compatible with crystallization in magma bodies that were emplaced piecemeal in the crust at coso over 200 kyr prior to eruption and that were periodically rejuvenated or melted by subsequent basaltic injections

co2 dynamics in the amargosa desert fluxes and isotopic speciation in a deep unsaturated zone 1 natural unsaturated zone gas profiles at the u s geological survey s amargosa desert research site near beatty nevada reveal the presence of two physically and isotopically distinct co2 sources one shallow and one deep the shallow source derives from seasonally variable autotrophic and heterotrophic respiration in the root zone scanning electron micrograph results indicate that at least part of the deep co2 source is associated with calcite precipitation at the 110 m deep water table we use a geochemical gas diffusion model to explore processes of co2 production and behavior in the unsaturated zone the individual isotopic species 12co2 13co2 and 14co2 are treated as separate chemical components that diffuse and react independently steady state model solutions constrained by the measured 13c in co2 and 14c in co2 profiles indicate that the shallow co2 source from root and microbial respiration composes 97 of the annual average total co2 production at this arid site despite the small contribution from deep co2 production amounting to 0 1 mol m 2 yr 1 upward diffusion from depth strongly influences the distribution of co2 and carbon isotopes in the deep unsaturated zone in addition to diffusion from deep co2 production 14c exchange with a sorbed co2 phase is indicated by the modeled 14c profiles confirming previous work the new model of carbon isotopic profiles provides a quantitative approach for evaluating fluxes of carbon under natural conditions in deep unsaturated zones

age and timing of the permian mass extinctions u pb dating of closed system zircons the age and timing of the permian triassic mass extinction have been difficult to determine because zircon populations from the type sections are typically affected by pervasive lead loss and contamination by indistinguishable older xenocrysts zircons from nine ash beds within the shangsi and meishan sections china pretreated by annealing followed by partial attack with hydrofluoric acid result in suites of consistent and concordant uranium lead u pb ages eliminating the effects of lead loss the u pb age of the main pulse of the extinction is 252 6 0 2 million years synchronous with the siberian flood volcanism and it occurred within the quoted uncertainty

zircon crystallization and recycling in the magma chamber of the rhyolitic kos plateau tuff aegean arc in contrast to most large volume silicic magmas in continental arcs which are thought to evolve as open systems with significant assimilation of preexisting crust the kos plateau tuff magma formed dominantly by crystal fractionation of mafic parents deposits from this 60 km3 pyroclastic eruption the largest known in the aegean arc lack xenocrystic zircons secondary ion mass spectrometry sims u pb ages on zircon cores never older than 500 ka and display sr nd whole rock isotopic ratios within the range of european mantle in an area with exposed paleozoic and tertiary continental crust this evidence implies a nearly closed system chemical differentiation consequently the age range provided by zircon sims u th pb dating is a reliable indicator of the duration of assembly and longevity of the silicic magma body above its solidus the age distribution from 160 ka age of eruption by sanidine 40ar 39ar dating smith et al 1996 1 to ca 500 ka combined with textural characteristics high crystal content corrosion of most anhydrous phenocrysts but stability of hydrous phases suggest 1 a protracted residence in the crust as a crystal mush and 2 rejuvenation reduced crystallization and even partial resorption of minerals prior to eruption probably induced by new influx of heat and volatiles this extended evolution chemically isolated from the surrounding crust is a likely consequence of the regional geodynamics because the thinned aegean microplate acts as a refractory container for magmas in the dying aegean subduction zone continent continent subduction 1 ref 32

syenitic group intrusions of the archean kurnalpi terrane yilgarn craton hosts to ancient alkali porphyry gold deposits abstract archean alkali rich syenitic group intrusions in the eastern goldfields superterrane yilgarn craton are chemically similar to intrusions associated with phanerozoic alkali porphyry systems high temperature potassic and ferruginous alteration associated with the yilgarn intrusions are also similar to those in phanerozoic counterparts but these are generally not well mineralized disseminated and fracture controlled gold mineralization associated with syenitic group intrusions is commonly hosted by mesothermal albite carbonate pyrite assemblages the origin of which is ambiguous this communication aims to stimulate discussion on the origin of gold in and around syenitic group intrusions and the apparent absence of significant gold or copper mineralization in associated high temperature alteration gold associated with syenitic group intrusions in the yilgarn craton has many similar characteristics to disseminated gold deposits associated with syenitic intrusions in the abitibi greenstone belt canada and may be present in other archean greenstone belts

geochronological constraints on post extinction recovery of the ammonoids and carbon cycle perturbations during the early jurassic abstract this paper presents the first quantitative study of the early jurassic recovery of ammonoids after the end triassic mass extinction based on detailed u pb id tims isotope dilution thermal ionization mass spectrometry geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level this study was triggered by the discovery of a rich peruvian succession of ammonites deposited concomitantly with an unusually large number of ash beds two major phases of rediversification are observed during the psiloceras spelae and angulaticeras zones that correspond to positive peaks in the 13corg curve providing a possible link between biodiversity and the global carbon cycle in the case of the post extinction recovery the development of the earliest hettangian ammonites occurs within the genus psiloceras which begins with the occurrence of p spelae and then explodes into worldwide development of smooth psiloceratids of the psiloceras planorbis group s l this rapid biodiversification likely occurred less than 100 ka after the end triassic crisis the genus psiloceras occupied all the possible ecological niches worldwide from the pacific deep waters to the nw european shallow deposits and also in some rare tethyan occurrences like at germig in tibet this global dispersion allowed the differentiation of the group in several major phyla the schlotheimiidae discamphiceratinae arietitidae and lytocerataceae which were the roots of all other jurassic and cretaceous ammonites

rejuvenation of crustal magma mush a tale of multiply nested processes and timescales some relatively crystal rich silicic volcanic deposits including large volume ignimbrites preserve evidence of a history where a rheologically locked high crystallinity magma was rejuvenated unlocked through enthalpy mass exchange with newly injected recharge magma of higher specific enthalpy this is one event in a possible complex history that is the volcanic product of an eruption reflects an array of sequential and nested processes including melt formation and segregation ascent cooling crystallization crustal assimilation magma recharge unlocking shallow ascent fluid exsolution and eruption deconvolution of these these nested processes and concomitant timescales is complicated and relies on a multidisciplinary approach studies that do not clearly associate process and correlated timescale have the potential to provide misleading timescale information we report the results of thermodynamic and heat transfer calculations that document mass energy and phase equilibria constraints for the unlocking of near solidus rhyolite mush via magma mingling heat exchange only with basaltic recharge magma of higher specific enthalpy to achieve unlocking defined as the transition from near solidus to 50 percent melt of the host silicic magma phase equilibria computations provide 1 the enthalpy required to unlock mush 2 the mass ratio of recharge magma to mush mr mm when the two magmas achieve thermal equilibrium and 3 the changes in melt mineral and fluid phase masses compositions and temperatures during the approach to unlocking the behavior of trace elements is computed with knowledge of mineral fluid and melt proportions and solid fluid and solid melt partition coefficients evaluation of unlocking for relatively dry 0 5 wt h2o and wet 3 9 wt h2o rhyolitic mushy locked magma by basaltic recharge at upper crustal pressures indicates minimum values of mr mm can be significantly less than 1 assuming the mingling process is isenthalpic with no waste heat for active volcanic systems estimates of mr may be tested using geodetic data wet mush has lower energy requirements for unlocking and thus requires lower mr mm than dry mush wet rejuvenated magmas therefore may be more abundant in the volcanic rock record and unlocked dry mushes may be restricted to extensional tectonic settings with high recharge flux temperature changes in dry mush as it unlocks are pronounced greater than 150 c compared to those in wet mush which are smaller than the resolution of classical geothermometry 15 c phase equilibria calculations show that as required the net volume of crystals decreases during unlocking interestingly calculations also indicate reactive crystal growth by chemical re equilibration at the crystal size scale during unlocking may also take place in either dissolution by unidirectional resorption or reactive dissolution new growth the chemical signatures of unlocking potentially preserved in crystals or parts of crystals for example rims are predictable and hence testable independent of unlocking thermodynamics the phase equilibria and elemental consequences of isentropic magma ascent a transport event that follows unlocking can also be predicted detailed examination of several canonical cases reveals a marked contrast with isenthalpic unlocking thereby providing a means of process deconvolution unlocking timescales are estimated by two methods one that calculates the time to reach thermal equilibrium for recharge magma dispersed in mush as clumps of fixed size and the second where the required volume of recharge magma is initially a single clump and evolves to smaller size through clump stretching and folding for a range of magma volumes from 0 1 to 5000 km3 unlocking times range from 10 2 to 106 years the shorter timescales for any magma volume requires a large number of relatively small clumps n 106 which implies that large volumes of mush purported to unlock over short timescales 102 103 years and less should preserve and exhibit evidence of intimate magma mingling the key result of our analysis is that multiple timescales are operative during the potentially long and complex history of silicic mush formation rejuvenation and ascent to correctly ascribe timescales to unlocking requires a holistic understanding of the myriad processes that affect the magma before during and after enthalpy exchange in the absence of this context unlocking timescales may be incorrectly constrained which in turn may hinder eruption forecasting and associated hazard mitigation

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

shrimp u pb dating of the preeruption growth history of zircons from the 340 ka whakamaru ignimbrite new zealand evidence for 250 k y magma residence times the whakamaru group ignimbrites are products of one of the largest caldera forming eruptions from the central taupo volcanic zone new zealand ca 340 ka imaging of zircons separated from low silica rhyolite pumice from whakamaru group ignimbrite reveals a complex magmatic crystallization history some grains contain resorbed cores cores and rims of individual zircons were dated using the sensitive high resolution ion microprobe due to the high u contents of the zircons 206 pb count rates were sufficiently high to obtain 206 pb 238 u ages with precisions of 5 10 1 s using longer than usual 206 pb count times and this has allowed zircon core and rim ages to be distinguished zircon rim and outer growth zone ages range from within 1 s error of the eruption age to 449 20 ka whereas zircon cores produced ages to 608 20 ka indicating magmatic residence times exceeding 250 k y for some zircons the data are consistent with a prolonged evolution of the magma system over hundreds of thousands of years involving magma replenishment and mixing with residual phases of older silicic magma chambers in addition to crystal fractionation processes prior to eruption the study has shown that 206 pb 238 u dating using high resolution ion microprobe can be used to determine zircon preeruptive growth histories in quaternary lavas and pyroclastic rocks

fractional crystallization in granites of the sierra nevada how important is it although compositional variation in zoned calc alkalic plutons is often ascribed to crystal fractionation diagnostic large scale field evidence of crystal accumulation in these slowly cooled bodies is generally missing in many plutons however small scale crystal cumulates have been preserved as layered schlieren and in microcosm may allow an assessment of the importance of crystal fractionation in their host pluton9s development small widely separated patches of schlieren in the tuolumne intrusive series yosemite national park california formed as cumulates their darkest layers show high concentrations of magnetite sphene biotite horn blende and zircon and have unusually fractionated major and trace element compositions feo 33 al 2 o 3 in chondrites 750 zr 2000 ppm the layers define smooth trends on major and trace element al 2 o 3 variation diagrams that diverge strongly from patterns for the main sequence rocks of the tuolumne series and granitoids throughout the sierra nevada removal of such cumulates from any main sequence magma would produce al rich evolved rocks not the al poor felsic rocks of the pluton the findings suggest that fractional crystallization did not produce the dominant chemical patterns seen in the tuolumne and similar sierra nevada granites

a two stage thermal evolution model of magmas in continental crust when a basaltic magma is emplaced in a continental crust a introduction silicic magma is generated by melting of the crust the light silicic when magma is emplaced into continental crust it is magma forms a separate magma layer with little chemical interaction believed to be stored in a magma chamber for a certain with the underlying dense basaltic magma layer extensive melting period extensive studies have revealed how petrological occurs at the boundary between the silicic magma and the crust and geochemical features of magmas are controlled by while the basalt acts a heat source the mass and heat transfer at processes in magma chambers such as crystallization of the boundary between the silicic magma and the crust controls the magma melting of crustal materials and mixing of thermal evolution of the silicic magma the thermal evolution of magmas e g mcbirney 1980 huppert turner 1981 the silicic magma after the basalt emplacement is divided into two sparks et al 1984 koyaguchi blake 1991 this paper stages in the first stage the temperature in the silicic magma rises discusses how petrologic processes such as assimilation above and then decays back to the melting temperature of the crust and fractional crystallization affect the thermal evolution on a short timescale 10 years the results of fluid dynamics and the residence times of magmas in magma chambers experiments suggest that the silicic magma generally has a lower in continental crust melting temperature than the crust because of fractional crystallization some exploratory models for the residence time of a and mixing of partial melts during the first stage and that it can magma chamber in continental crust have been proposed be effectively liquid at the end of the first stage in the second stage on the basis of the physics of heat and mass transfer the silicic magma cools slowly by heat conduction on a much longer spera 1979 huppert sparks 1988a marsh 1989 timescale 10 years petrological features of the magma in the to formulate the present problem it is helpful to introduce second stage are strongly constrained by petrological features of the the model by huppert sparks 1988a in which the surrounding crust as well as those of the supplied magma itself its physics of crystallization and melting at the chamber roof temperature remains at or just below the melting temperature of the as well as the effects of thermal convection in the magma crust for a long time because of the slow cooling rate its phenocryst are taken into account according to their model a content reflects the difference in the melt fraction vs temperature basalt emplaced into continental crust results in extensive relationships between the magma and the crust judging from the melting of the crustal materials at the chamber roof to distinct cooling rate between the two stages erupted magmas are form a silicic magma the temperature in the silicic statistically more likely to reflect the characteristics of magmas in magma rises above and then decays back to the fusion the second stage temperature of the crust in general the effective fusion

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

chronological and geochemical constraints on the pre variscan tectonic history of the erzgebirge saxothuringian zone abstract a combined u pb zircon geochronological and whole rock isotopic and geochemical study has been carried out on high grade orthogneiss meta basite and meta sediments from the erzgebirge the results indicate multiple pulses of ediacaran ordovician magmatism in a transitional volcanic arc to rift basin setting orthogneiss from high pressure nappes exhibit a step like pattern of inherited zircon ages and emplacement ages of 500 475 ma in contrast granite gneiss from the medium pressure core of the erzgebirge is characterised by three pulses of magmatism in the early cambrian late cambrian and early ordovician a trend of decreasing th u ratios in zircon is observed to c 500 ma after which significant increases in the trend and variability of the data is inferred to mark the transition from arc related to rift related magmatism sediments deposited in the early cambrian have continental island arc affinity major detrital peaks in the ediacaran and subordinate tonian palaeoproterozoic and neoarchaean data are consistent with an avalonian cadomian arc and west african craton derivation the early cambrian sediments were locally reworked by a thermal event in the ordovician resulting in leucocratic banding and recorded in ordovician zircon rims characterised by systematically lower th u ratios ptygmatically folded leucocratic bands containing ordovician zircon rims associated with low th u ratios are further observed in the granite gneiss core of the erzgebirge variscan ages are rare except in a fine grained high pressure micaschist which contains exclusively small structure less zircon with a weighted mean age of 350 2 ma these data along with a re evaluation of previously published data have been interpreted as the product of flattening subduction during the early cambrian followed by the opening of slab windows in the late cambrian and finally delamination in the early ordovician delamination of the orphaned slab led to asthenospheric upwellings triggering extension bimodal magmatic pulses recycling of fertile crust high temperature metamorphism and cratonisation of relatively young crust

isotope geochemistry of the northeast zone mount polley alkalic cu au ag porphyry deposit british columbia a case for carbonate assimilation mount polley is a late triassic 205 ma alkalic porphyry cu au ag deposit 226 3 thousand tonnes t cu 21 5 t au and 65 1 t ag hosted by silica undersaturated to silica saturated monzonitic intrusions of the mount polley complex located in british columbia canada the northeast ore zone at mount polley is hosted by magmatic hydrothermal breccia copper and precious metals occur in sulfide minerals primarily as coarse to fine grained breccia cement local wall rocks include equigranular to porphyritic diorite monzodiorite and monzonite alteration breccia cement and veins of the northeast ore zone formed in five paragenetic stages prebreccia stage 1 brecciation and main stage mineralization stage 2 late stage mineralization stage 3 unmineralized postbreccia dikes and veins stage 4 and epithermal style veins stage 5 intense pervasive k and fe metasomatism calcite and calc silicate alteration occurred prior to brecciation caused by the intrusion of megacrystic k feldspar phyric monzonite stage 2 fluids were silica undersaturated high temperature 350 c co2 enriched and of near neutral to alkaline ph potassic sodic and calc potassic assemblages precipitated with mineralization during stage 2 with moderate temperatures at the deposit periphery and in stages 3 and 4 evidence for more acidic and lower temperature conditions is preserved in stage 5 veins the 34ssulfide isotope compositions of stages 2 and 3 chalcopyrite pyrite and bornite range from 7 1 to 1 4 sulfur isotope compositions of anhydrite and gypsum are mostly between 6 2 and 9 8 these values together with the presence of hematite are consistent with deposition from an oxidized sulfate dominant high temperature magmatic hydrothermal fluid limited sulfur isotope geothermometry indicates that cu sulfides precipitated at temperatures from 480 to 250 c hydrothermal calcite occurs in all paragenetic stages at mount polley calcite 13c values range from 0 2 to 10 5 and 18o values from 4 0 to 20 9 the enriched c o isotope values are not consistent with simple precipitation from an entirely magmatic source of hydrothermal fluid interaction of the fluid and or magma with limestone is considered a likely process to explain the c and o isotope signature lead isotope data suggest mixing of mantle and crustal sources during mineralization main stage chalcopyrite and pyrite as well as late stage galena have 206 204pb values of 18 77 to 18 92 207 204pb of 15 56 to 15 59 and 208 204pb of 38 22 to 38 32 strontium isotope data 0 70331 0 70371 provide evidence of a strongly depleted mantle source of sr with minor crustal input epsilon nd values for main stage apatite range between 5 9 and 6 5 also indicating a depleted mantle source stage 5 carbonate 206 204pb values of 18 96 to 19 04 207 204pb of 15 57 to 15 59 and 208 204pb of 38 26 to 38 36 suggest superposition of an epithermal system onto the northeast ore zone potentially as late as 100 m y after breccia formation the data presented are consistent with the hypothesis that the silica undersaturated alkalic mount polley complex formed due to carbonate assimilation prior to mineralization this process can explain the 13c 18o isotope data calcite precipitation concurrent with cu au mineralization and silica undersaturation of the magma the co2 released during assimilation of carbonate also could have promoted magmatic hydrothermal brecciation silica undersaturated alkalic porphyry systems may preferentially form in arc terranes built on a carbonate bearing substrate

isotopic zonations in silicic magma chambers many ash flow tuffs are zoned in radiogenic isotope ratios indicating that roofward assimilation of crust occurs in ash flow magma chambers prior to eruption cases where relatively well constrained calculations may be made regarding the percentage of assimilation in the roof zone indicate that the percentage of assimilation often exceeds the percentage of phenocrysts in the tuffs this relation in addition to the fact that assimilation gradients are opposite to that of the percentage of phenocrysts suggests that assimilation and crystallization in the silicic roof zones of crustal magma chambers are separated in time and space and that these processes are best modeled as two component mixing true assimilation fractional crystallization is probably restricted to the lower mafic parts most phenocrysts in the silicic upper parts of magma chambers crystallized after assimilation providing minimum estimates of time between assimilation and eruption 1 100 yr preservation of monotonic isotopic gradients suggests that convection is minor in the upper parts of silicic magma chambers during the late stages of evolution

the ridgeway gold copper deposit a high grade alkalic porphyry deposit in the lachlan fold belt new south wales australia ridgeway is a high grade gold copper porphyry deposit 54 mt at 2 5 g t au and 0 77 cu related to an alkalic intrusive complex of monzonitic composition the deposit occurs within the cadia district of new south wales australia which consists of a cluster of four late ordovician gold copper porphyry deposits and two iron copper gold skarn deposits with a combined gold resource in excess of 574 metric tonnes t the deposits lie on a 7 km long northwest oriented corridor of alteration and mineralization transverse to the axis of the postulated volcanic arc alteration and mineralization at ridgeway are zoned around a vertically attenuated intrusive complex of monzodioritic to quartz monzonitic composition distinct styles of veining and alteration are related to different intrusive phases of the monzonite complex with the intensity of alteration and grade of mineralization decreasing from early to late mineral intrusions early mineral intrusions are associated with intense actinolite magnetite biotite calc potassic alteration and up to four stages of high grade quartz magnetite sulfide veining bornite is the most abundant sulfide formed during early stage alteration and correlates well with gold moderate to weak intensity orthoclase biotite plus or minus magnetite potassic alteration accompanies the inter and late mineral intrusions this alteration being associated with chalcopyrite and pyrite rich quartz orthoclase veins propylitic and sodic albite pyrite alteration assemblages are peripheral to and locally overprint the potassic alteration phyllic alteration is restricted to the margins of late stage faults the fluid inclusion assemblage comprises one and two salt bearing brine inclusions in addition to aqueous liquid vapor inclusions of low to moderate salinity no low density vapor rich inclusions are present indicating that the fluids from which the quartz veins precipitated did not enter the liquid vapor field of the h2o nacl system the brine inclusions undergo final homogenization to liquid via halite dissolution this phenomenon in addition to the absence of low density vapor inclusions suggests that the mineralizing fluids at ridgeway were nonboiling hypersaline brines that exsolved directly from the crystallizing magma the presence of mineralized aplitic vein dikes and comb quartz layering are interpreted to indicate that the early and transitional stages of mineralization at ridgeway formed at the transition between magmatic and hydrothermal conditions

temporal and genetic link between incremental pluton assembly and pulsed porphyry cu mo formation in accretionary orogens economically important porphyry cu mo deposits pcds are generally hosted by upper crustal plutons of variable chemical compositions related to distinct geodynamic settings the absolute timing and duration of pluton assembly and pcd formation are critical to understanding the genetic relationship between these interrelated processes here we present new comprehensive zircon u pb and molybdenite re os ages that tightly constrain the timing and duration of pluton assembly and the age of mineralization in one of the largest ore bearing plutons of the central tethyan metallogenic belt the meghri ordubad pluton southern armenia and nakhitchevan lesser caucasus this composite pluton was incrementally assembled during three compositionally distinct magmatic episodes over 30 m y comprising middle eocene 48 9 43 1 ma calc alkaline subduction related magmatism lasting 5 8 0 8 m y followed by postsubduction late eocene middle oligocene 37 8 28 1 ma shoshonitic magmatism over 9 7 0 9 m y and late oligocene early miocene 26 6 21 2 ma adakitic magmatism consisting of shoshonitic dikes and high k calc alkaline granodioritic magmas emplaced over 5 4 0 4 m y despite the distinct geodynamic settings and magma compositions each intrusive suite culminated in the formation of variably sized pcds including the giant oligocene kadjaran porphyry cu mo deposit associated with high sr y shoshonitic magmas complementary in situ zircon hafnium ehfzircon 8 to 11 3 and oxygen 18ozircon 4 6 to 6 0 isotope data support a mantle dominated magma source with limited crustal contribution and or cannibalization of young and juvenile lower crustal cumulates we conclude that independent of geodynamic setting and magma composition long lived 5 10 m y incremental mantle derived magmatism is a prerequisite to form fertile magmatic hydrothermal systems and especially giant pcds

thermal fractionation of air in polar firn by seasonal temperature gradients 1 air withdrawn from the top 5 15 m of the polar snowpack firn shows anomalous enrichment of heavy gases during summer including inert gases following earlier work we ascribe this to thermal diffusion the tendency of a gas mixture to separate in a temperature gradient with heavier molecules migrating toward colder regions summer warmth creates a temperature gradient in the top few meters of the firn due to the thermal inertia of the underlying firn and causes gas fractionation by thermal diffusion here we explore and quantify this process further in order to 1 correct for bias caused by thermal diffusion in firn air and ice core air isotope records 2 help calibrate a new technique for measuring temperature change in ice core gas records based on thermal diffusion severinghaus et al 1998 and 3 address whether air in polar snow convects during winter and if so whether it creates a rectification of seasonality that could bias the ice core record we sampled air at 2 m depth intervals from the top 15 m of the firn at two antarctic sites siple dome and south pole including a winter sampling at the pole we analyzed 15n 14n 40ar 36ar 40ar 38ar 18o 16o of o2 o2 n2 84kr 36ar and 132xe 36ar the results show the expected pattern of fractionation and match a gas diffusion model based on first principles to within 30 although absolute values of thermal diffusion sensitivities cannot be determined from the data with precision relative values of different gas pairs may at siple dome 40ar 4 is 66 2 as sensitive to thermal diffusion as 15n in agreement with laboratory calibration 18o 2 is 83 3 and 84kr 48 is 33 3 as sensitive as 15n the corresponding figures for summer south pole are 64 2 81 3 and 34 3 accounting for atmospheric change the figure for o2 n2 4 is 90 3 at siple dome winter south pole shows a strong depletion of heavy gases as expected however the data do not fit the model well in the deeper part of the profile and yield a systematic drift with depth in relative thermal diffusion sensitivities except for kr constant at 34 4 suggesting the action of some other process that is not currently understood no evidence for wintertime convection or a rectifier effect is seen

chronological link between deep seated processes in magma chambers and eruptions permo carboniferous magmatism in the core of pangaea southern pyrenees abstract in the southern pyrenees there are upper carboniferous lower permian sedimentary basins with a significant volume of volcanic material derived from explosive eruptions rhyolitic ignimbrites and andesitic flows these basins are spatially associated with granodiorites and dacitic dykes emplaced in variscan basement rocks u pb shrimp dating of zircons extracted from three granodiorites an andesitic flow a dacitic dyke and six ignimbrites revealed that magmatism occurred over an extended period of thirty eight million years from ca 304 ma to ca 266 ma upper carboniferous middle permian a scattering of zircon ages in each sample shows that the history of melt crystallization was complex with more than one zircon forming event in each magma chamber the prolonged crystallization history was transferred to the product of the eruptions a chronological link between the deep seated magma chambers and processes in eruptions was identified on the basis of four overlapping intervals at ca 309 307 ma upper carboniferous ca 304 296 ma upper carboniferous lower permian ca 294 282 ma lower permian and ca 276 ma lower permian the variation of zircon u th ratios exposes a tendency for an increase in mafic sources as crystallization advances in the permian zircons probably crystallized from melt phases related to both a felsic intermediate metaluminous source from ca 310 293 ma mostly 0 1

on curved laminae graded layers convection currents and dynamic crystal sorting in the ploumanac h brittany subalkaline granite curved layered objects in a subalkaline potassic intrusive granite are analyzed biotite laminae and cyclic reverse size and modal layers are encountered in an annular zone both cyclic and intermittent layers are observed in rhythmic arrangement truncation the bifurcation curvature of layers with ladle shape represents the action of magmatic currents as would convection cells or fluid dynamic fingers emphasis is put on the bagnold effect related to such currents which would explain the reverse size grading of layers this kind of size sorting hydrodynamic occurs in highly viscous granitic magma simple convection seems more likely than diffusive convection

vertical and lateral variation of mineralogy and chemistry in the early jurassic mt milligan alkalic porphyry au cu deposit british columbia canada the moderately tilted and faulted early jurassic mt milligan au cu deposit provides a cross section view of the hydrothermal alteration sulfide mineralogy and geochemical zonation of a silica saturated alkalic porphyry system over a vertical distance approaching 700 m magnetite bearing potassic alteration and associated au cu form a core to the system in the central monzonitic stock and adjacent basaltic trachyandesite host rock lateral to the high temperature core are sodic calcic and inner and outer propylitic alteration assemblages chalcopyrite dominates the high temperature potassic core whereas pyrite is the predominant sulfide within and outboard from the sodic calcic assemblage a funnel shaped remnant of carbonate rich phyllic alteration of the host supracrustal rocks in the fault bounded 66 zone represents the upper auriferous alteration in the alkalic porphyry au cu system alteration mineral assemblage s isotope ranging from 34s 5 relative to canon diablo troilite in the core to 34s 0 5 in the periphery and limited fluid inclusion data suggest mineralization at the au cu alkalic porphyry system was derived from an oxidized co2 bearing magmatic fluid that rose upward along the margins and through the magnetite breccia stock laterally from the au cu mineralized potassic core magmatic fluid evolved through water rock interaction mixing with an external fluid as shown by a shift in calculated 87sr 86sr for alteration minerals to values higher than magmatic values declining temperature or some combination of all variations in trace element concentrations of epidote v mn sb zr as and bi and pyrite mn as zr pb and bi across the deposit show a local high degree of variability but general increases or decreases in overall trends in their median values are inferred to reflect the hydrothermal evolution of the system pistachite ratios of epidote show an outward decrease in ferric iron as recorded in the pistachite ratio changing from ps36 to ps25 suggesting less oxidizing conditions on the system periphery additionally light rare earth elements in epidote fractionate toward the core of the deposit and the height of positive eu anomalies also appears to have a similar spatial trend in pyrite there is a general increase in trace element concentration toward the epidote pyrite rich outer propylitic assemblage forming the system periphery alteration mineralogy and trace element signatures indicate the southeastern portion of the deposit the 66 zone is a down dropped segment from higher in the paleohydrothermal system s isotope signatures of sulfides within and surrounding the stratiform upper trachyte unit in the 66 zone indicate structural channeling of oxidizing fluids that likely were the distal and cooler expression of more oxidizing magmatic derived hydrothermal fluids responsible for potassic alteration and au cu in the subjacent magnetite breccia zone the main orebody

setting new constrains on the age of crustal scale extensional shear zone vivero fault implications for the evolution of variscan orogeny in the iberian massif the vivero fault is crustal scale extensional shear zone parallel to the variscan orogen in the iberian massif belt with an associated dip slip movement toward the hinterland to constrain the timing of the extension accommodated by this structure we performed zircon u pb la icp ms geochronology in several deformed plutons some of them emplaced syntectonically the different crystallization ages obtained indicate that the fault was active at least between 303 2 and 287 3 ma implying a minimum tectonic activity of 16 5 ma along the fault the onset of the faulting is established to have occurred later than 314 2 ma the geochronological data confirm that the vivero fault postdates the main variscan deformation events in the nw of the iberian massif and that the extension direction of the late carboniferous early permian crustal scale extensional shear zones along the ibero armorican arc was consistently perpendicular to the general arcuate trend of the belt in sw europe

genesis of the late triassic southwest zone breccia hosted alkalic porphyry cu au deposit galore creek british columbia canada the late triassic southwest zone alkalic porphyry cu au deposit in the galore creek district northwestern british columbia is hosted in hydrothermally cemented breccias that overprinted older matrix rich breccia and megacrystic orthoclase phyric syenite and monzonite dikes synmineralization cemented breccias and biotite phyric monzodiorite dikes are localized at the contact of the matrix rich breccia and host syenite and monzonite dikes as well as in crosscutting faults regional shortening tilted the southwest zone deposit so that the cemented breccias now dip 50 to 60 southwest four paragenetic stages formed the deposit a premineralization stage 1 consists of the emplacement of coherent syenite and monzonite host rocks that are cut by a matrix rich breccia the synmineralization stage 2 produced potassic altered rocks and phlogopite magnetite k feldspar cemented breccia and veins and most of the cu fe sulfides a halo of stage 2 diopside magnetite grandite phlogopite calcic potassic veins and altered rocks formed around the potassic domains and cu ore zones alteration during stage 2 probably formed at temperatures of about 500 to 425 c from oxidized saline magmatic hydrothermal fluids contemporaneous high aca2 ah 2 conditions peripheral to the potassic domains are required to form the marginal calcic potassic and calcic assemblages the potassic and calcic potassic alteration domains were overprinted by propylitic and calcic alteration assemblages due to the retrograde influx of an admixture of cooler magmatic and nonmagmatic fluids sphene from a stage 2 calcic potassic vein yielded a 202 8 2 1 ma age u pb shrimp rg that is interpreted to reflect the approximate time of hydrothermal alteration late mineralization stage 3 alteration overprinted the cemented breccias and comprises sericite anhydrite sericitic grandite calcic and chlorite epidote carbonate pyrite propylitic assemblages localized late mineralization and cu poor stage 4 k feldspar fe carbonate specularite carbonate potassic and quartz pyrite veins quartz veins cut stage 2 and 3 assemblages chalcopyrite and bornite dominate the core of the deposit and grade outward to chalcopyrite pyrite and to pyrite chalcopyrite flanked by a pyrite only halo the core of the system is cu au rich grading outward to an au enriched cu poor halo coincident with pyrite bearing propylitic alteration gold copper ratios increase upward within stage 2 potassic zones and outward from the core variations in ph redox and temperature along and across fluid flow paths best explain the change to higher au cu values upward and away from the cu rich potassic domains

lidar observations of a breaking mountain wave associated with extreme turbulence observations from a doppler lidar which are enhanced by stratospheric aerosols from mount pinatubo s eruption provide unique measurements of mountain waves over the rocky mountains including nearly instantaneous observations of wave breaking in the lower stratosphere the wave breaking is revealed by a flow reversal aloft that marks a localized critical layer created when the wave amplitude was great enough to cause overturning the altitude spatial scale and duration of this wave induced critical layer are documented the mountain waves led to turbulence affecting commercial aircraft including one accident in which a cargo jet lost an engine and part of a wing in extreme turbulence at the same time the lidar was making observations nearby although earlier observations of mountain wave drag assumed wave stationarity over 3 5 h significant changes over less than 2 h are documented here such nonstationarity could contribute to discrepancies remaining between observations and simulations of mountain wave drag

accessory mineral fractionation of rare earth element ree abundances in granitoid rocks abstract accessory minerals with large distribution coefficients k d s for the ree have the potential to strongly affect the evolution of ree abundances during igneous differentiation e g crystallization melting assimilation a cogenetic suite of lavas basaltic andesites through high silica rhyolites from the batopilas area of mexico which preserve petrographic evidence for apatite and zircon saturation is used to illustrate and confirm an inverse geochemical approach to recognizing early liquidus accessory mineral saturation the transition in behavior of zr from an incompatible trace element in basaltic andesites and dacites to an essential structural constituent esc in high silica rhyolites marks the onset of zircon crystallization a previously published zircon saturation model provides liquidus temperatures that support the interpretation that three high silica rhyolites represent zircon saturated melts while one has excess zircon these results contradict the previous study in which zircon fractionation had been argued against the potential effect of zircon fractionation and accumulation on ree abundances in the samples is evaluated and contributes to an improved petrogenetic interpretation a cogenetic suite of granitoid samples from the saganaga tonalite minnesota ontario north america is characterized by apparently strongly compatible behavior of the ree apatite zircon and sphene are the observed high ree k d accessory minerals forward and inverse modelling approaches provide no evidence that accessory mineral fractionation contributed to the behavior of the ree during differentiation of the samples the data instead suggest that the ree characteristics of the samples were already established by other petrogenetic processes prior to the samples becoming saturated with the observed accessory minerals

fractionation of gases in polar ice during bubble close off new constraints from firn air ne kr and xe observations gas ratios in air withdrawn from polar firn snowpack show systematic enrichments of ne n2 o 2 n2 and ar n2 in the firn ice transition region where bubbles are closing off air from the bubbles in polar ice is correspondingly depleted in these ratios after accounting for gravitational effects gas in the bubbles becomes fractionated during the process of bubble close off and fractionation may continue as ice cores are stored prior to analysis we present results from firn air studies at south pole and siple dome antarctica which add ne kr and xe measurements to the suite of observations ne o2 and ar appear to be preferentially excluded from the shrinking and occluding bubbles and these gases therefore accumulate in the residual firn air creating a progressive enrichment with time and depth in firn air early sealing of gases by thin horizontal impermeable layers into a nondiffusive zone or lock in zone greatly enhances this enrichment a simple model of the bubble close off fractionation and lock in zone enrichment fits the data adequately the model presumes that fractionation is caused by selective permeation of gas through the ice lattice from slightly overpressured bubbles the effect appears to be size dependent because ne o2 and ar have smaller effective molecular diameters than n2 and fractionation increases strongly with decreasing size ne is fractionated 34 2 times more than o2 in south pole firn air and reaches an enrichment of 90 in the deepest sample the large atoms kr and xe do not appear to be fractionated by this process despite the large size difference between the two gases suggesting a threshold atomic diameter of 3 6a above which the probability becomes very small that the gas will escape from the bubble these findings have implications for ice core and firn air studies that use gas ratios to infer paleotemperature chronology and past atmospheric composition

u th pb and 230th 238u disequilibrium isotope systematics precise accessory mineral chronology and melt evolution tracing in the alpine bergell intrusion in order to investigate the potential of combined th u pb isotope and 230th 238u disequilibrium systematics for tracing magmatic crystallization and melt evolution conventional high resolution single crystal tims techniques have been applied to zircon titanite and fragments of geochemically characterized growth zones of allanite these minerals were extracted from a single tonalite specimen collected from the feeder zone of the tertiary bergell pluton southern steep belt s switzerland n italy the isotopic results document an extended history of crystallization and melt evolution of at least 5 ma with well resolved zircon ages defining an early interval of 33 0 to 32 0 ma followed by crystallization of zoned allanite from 32 0 to 28 0 ma and formation of magmatic epidote possibly as late as 26 ma trace and major element patterns in zoned allanite closely mirror melt evolution characterized by increase of u concentration and sharp decrease of th and lree reflecting early crystallization of phases low in u and in particular the dominating control by allanite precipitation preservation of substantial quantities of excess 206pb derived from initial excess 230th in all analyzed allanite grains indicates that their isotopic systems have not been reset by loss of radiogenic pb during prolonged residence at magmatic conditions and regional metamorphic cooling and that the measured sequence of 208pb 232th dates translates into a real age sequence major loss of radiogenic pb from compositionally zoned allanite by volume diffusion would have resulted in a data pattern grossly different from the observed one as demonstrated by numerical modeling of 232th 208pb 238u 230th 206pb isotopic evolution the results therefore suggest closure temperatures 700 c for magmatic allanite quantification of 230th 238u disequilibrium relationships reveals a smooth initially steep decrease of th u in the magma from values of 2 9 at 32 0 ma to 0 1 at 28 0 ma in equilibrium with sequential allanite zoning comparison of calculated th u magma with measured total rock th u 0 79 requires fractional crystallization of allanite at an early stage this process of removal of allanite and thus th from the melt was operative at least until 31 5 ma providing an upper limit for the time of emplacement of the studied magma batch the fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep seated plutons with intrusion ages the persistence of magmatic conditions over a period of 5 ma concentrated in a narrow collision zone between the european and the african plate has been a major controlling factor for the oligocene evolution of the adjacent insubric fault the main tectonic lineament of the alps being active from late cretaceous to miocene times

construction of mid crustal sheeted plutons examples from the north cascades washington large parts of many orogenic belts consist of highly elongate plutons constructed by the injection of multiple sheets of magma we describe in detail two such intrusions the deep 20 25 km mid crustal cardinal peak and entiat plutons and emphasize the dynamic nature of these magma chambers these ca 72 73 ma plutons consist of heterogeneous mafic complexes in their margins and tips that give way inward to thicker but still abundant sheets of tonalite intrusive and petrologic relationships provide evidence for injection of early mafic mantle and crustal melts development of heated pathways utilized by larger batches of more felsic magma and potentially a filtering mechanism in which conduits represented by the plutons fed larger more homogenized magma bodies at shallower crustal levels well developed gently to moderately dipping magmatic and subsolidus foliations in these plutons are commonly discordant to sheet contacts internal layering and pluton contacts but are continuous with host rock foliation they define small to map scale magmatic folds which have orientations and geometries similar to those of regional host rock folds these magmatic structures thus primarily record regional contractional tectonism during chamber construction host rocks also record complex processes during chamber evolution with narrow structural aureoles displaying remarkable lateral variability deflection of gently to moderately dipping host rock markers toward parallelism with steep pluton contacts indicates vertical and largely downward ductile material transfer along sheet margins during emplacement several sharply discordant segments of pluton contacts imply late stoping regional ductile flow and folding also played a role but regional faulting did not further evidence for chamber construction is provided by host rock rafts which are abundant along sheet contacts in the cardinal peak pluton and particularly between marginal sheets of the entiat pluton but are sparse elsewhere in the latter pluton we interpret these relationships to indicate a temporal sequence in which magmatic sheets initially intruded host rock then wedged aside this rock and coalesced preserving pieces of the host along margins and eventually formed large relatively inclusion free chambers as host rock was detached and transported vertically downward through the chamber

observations of nonclassical frontal propagation and frontally forced gravity waves adjacent to steep topography through the integrated analysis of remote sensing and in situ data taken along the front range of colorado this study describes the interactions that occurred between a leeside arctic front and topographically modulated flows these interactions resulted in nonclassical frontal behavior and structure across northeastern colorado the shallow arctic front initially advanced southwestward toward the front range foothills before retreating eastward then a secondary surge of arctic air migrated westward into the foothills during its initial southwestward advance the front exhibited obstacle like density current characteristics its initial advance was interrupted by strong downslope northwesterly flow associated with a high amplitude mountain wave downstream of the continental divide and by a temporal decrease in the density contrast across the front due to diurnal heating in the cold air and weak cold advection in the warm air the direction and depth of flow within the arctic air also influenced the frontal propagation the shallow obstacle like front actively generated both vertically propagating and vertically trapped gravity waves as it advanced into the downslope northwesterly flow resulting in midtropospheric lenticular wave clouds aloft that tracked with the front because the front entered a region where strong downslope winds and mountain waves extended downstream over the high plains the wave field in northeastern colorado included both frontally forced and true mountain forced gravity waves a sequence of scorer parameter profiles calculated from hourly observations reveals a sharp contrast between the prefrontal and postfrontal wave environments consequently analytic resonant wave mode calculations based on the scorer parameter profiles reveal that the waves supported in the postfrontal regime differed markedly from those supported in the prefrontal environment this result is consistent with wind profiler observations that showed the amplitude of vertical motions decreasing substantially through 16 km above mean sea level msl after the shallow frontal passage

barometric pumping of a fractured porous medium barometric pumping plays a crucial role in the release of trace gases from fractured porous media to the atmosphere and it requires a rigorous and complete modeling in order to go beyond the approximate schemes available in the literature therefore a coupled set of convection and convection diffusion equations for a slightly compressible fluid in unsteady conditions should be solved the numerical methodology is presented and it is applied to conditions close to the ones of the roselend natural laboratory france the precision of the code is assessed and the mechanism of barometric pumping is explained the usual schematization by simple vertical fractures is shown to be only qualitative finally barometric pumping is shown to be efficient in a narrow range of parameter values its efficiency is a decreasing function of the matrix porosity and of the fracture density

atmospheric purging of el chichon debris a 3 year program for sensing the vertical profiles of debris from el chichon in the atmosphere over boulder colorado has measured purging time constants of 208 and 60 days for the stratosphere and troposphere respectively no appreciable removal occurred from the atmosphere until the cloud descended to 6 km altitude 420 days after the eruptions at a given altitude data are lognormally distributed in time and by assumption in space a simple theoretical model is offered in explanation

time scales of pluton construction at differing crustal levels examples from the mount stuart and tenpeak intrusions north cascades washington deciphering the magmatic history of continental magmatic arcs in general and the growth history of individual intrusions in particular is key to understanding the complex history of magma generation segregation and transport that define the dynamics of crustal growth we utilize high precision u pb geochronology to resolve a detailed magmatic history from two composite intrusions the 2 4 kbar mount stuart batholith and the 7 10 kbar tenpeak pluton emplaced in the cretaceous north cascades arc this temporal framework provides a way to evaluate models of pluton growth that explain common features of intrusions such as concentric compositional zoning and internal magmatic contacts u pb zircon crystallization ages were obtained from 12 samples of the mount stuart batholith and 8 samples of the tenpeak intrusion representing the range of compositional diversity and geographical extent these dates indicate that the mount stuart batholith was constructed over a 5 5 m y time period that was punctuated by four intervals of high magma flux the durations of the high flux periods are short a few hundred thousand years relative to the duration of the batholith the consistent pattern of magmatic fabrics and the lack of distinct contacts in the batholith may be explained by the juxtaposition of melt rich and mush zones with subtle contacts between mineralogically and texturally similar tonalite and time transgressive magma fabrics in contrast the tenpeak intrusion was constructed over a 2 6 m y time period with magma influx distributed throughout the intrusive history and texturally distinct magma bodies the tenpeak intrusion lacks distinct age domains which suggests that any magma reservoir was smaller in size and potentially more ephemeral although the distinct age domains and discrete compositional and textural phases indicate that pluton growth occurred incrementally neither pluton bears resemblance to a purely end member incremental growth model whereby a pluton is constructed from hundreds to thousands of discrete magma pulses that have little if any interaction in particular ages from the youngest domain of the mount stuart batholith indicate that a melt rich magma reservoir of 520 km 3 existed over a 170 90 k y time span

episodic and long lasting paleozoic felsic magmatism in the pre alpine basement of the suretta nappe eastern swiss alps the suretta nappe of eastern switzerland contains a series of meta igneous rocks with the rofna porphyry complex rpc being the most prominent member we present la icp ms u pb zircon data from 12 samples representing a broad spectrum of meta igneous rocks within the suretta nappe in order to unravel the pre alpine magmatic history of this basement unit fine grained porphyries and coarse grained augengneisses from the rpc give crystallization ages between 284 and 271 ma which either represent distinct magma pulses or long lasting magmatic activity in a complex magma chamber there is also evidence for an earlier variscan magmatic event at 320 310 ma mylonites at the base of the suretta nappe are probably derived from either the rpc augengneisses or another unknown carboniferous permian magmatic protolith with a crystallization age between 320 and 290 ma two polymetamorphic orthogneisses from the southern suretta nappe yield crystallization ages of 490 ma inherited zircon cores are mainly of late neoproterozoic age with minor neo to paleoproterozoic sources we interpret the suretta nappe as mainly representing a gondwana derived crustal unit which was subsequently intruded by minor cambrian ordovician and major carboniferous permian magmatic rocks finally the suretta nappe was thrust into its present position during the alpine orogeny which hardly affected the u pb system in zircon

precise determination of ar kr and xe isotopic fractionation due to diffusion and dissolution in fresh water abstract dissolved noble gases are ideal conservative tracers of physical processes in the earth system due to their chemical and biological inertness although bulk concentrations of dissolved ar kr and xe are commonly measured to constrain physical models of atmosphere ocean and terrestrial hydrosphere processes stable isotope ratios of these gases e g 136xe 129xe are seldom used because of low signal to noise ratios here we present the first results from a new method of dissolved gas sampling extraction and analysis that permits measurement of stable ar kr and xe isotope ratios at or below 5 per meg amu 1 precision 1 two orders of magnitude below conventional kr and xe isotopic measurements this gain in precision was achieved by quantitative extraction and subsequent purification of dissolved noble gases from 2 l water samples via helium sparging and viscous dual inlet isotope ratio mass spectrometry we have determined the solubility fractionation factors sol for stable ar kr and xe isotope ratios between 2 and 20 c via laboratory equilibration experiments we have also conducted temperature controlled air water gas exchange experiments to estimate the kinetic fractionation factors kin of these isotope ratios we find that both sol and kin normalized by isotopic mass difference m decrease in magnitude with atomic number but are proportional to m for isotope ratios of the same element with the new ability for high precision isotopic measurements we suggest that dissolved kr and xe isotope ratios in groundwater represent a promising novel geochemical tool with important applications for groundwater modeling water resource management and paleoclimate

introduction to the special issue devoted to alkalic porphyry cu au and epithermal au deposits this special issue is devoted to alkalic porphyry cu au and epithermal au deposits and focuses on two regions british columbia canada fig 1 and the southwest pacific region australia and papua new guinea fig 2 the special issue commences with a review of triassic to jurassic metallogeny of british columbia logan and mihalynuk 2014 then documents ore zones from several alkalic deposits central zone galore creek micko et al 2014 southwest zone galore creek byrne and tosdal 2014 northeast zone mt polley pass et al 2014 lower main zone lorraine bath et al 2014 mt milligan jago et al 2014 and provides a comprehensive overview of mineralization in the lorraine district devine et al 2014 four contributions document alkalic porphyry and epithermal deposits in new south wales northparkes harris and holcombe 2014 endeavour 41 zukowski et al 2014 endeavour 42 henry et al 2014 cadia harris et al 2014 the final contribution uses the results of mapping and core logging in order to resolve the physical volcanology and hydrothermal evolution of the giant ladolam alkalic epithermal gold deposit papua new guinea blackwell et al 2014 eight of these papers are the outcome of a collaborative project between the mineral deposit research unit mdru at the university of british columbia the australian research council s centre for excellence in ore deposits codes at the university of tasmania and industry partners the remaining are based on work by the british columbia geological survey logan and mihalynuk 2014 teck resources ltd devine et al 2014 a research collaboration between codes and newcrest mining ltd harris et al 2014 and the university of queensland harris and holcombe 2014 fig 1 terrane map and location of selected alkalic porphyry cu au deposits of british columbia deposits that are the subject of

mo rich source and protracted crystallization of late mesozoic granites in the east qinling porphyry mo belt central china constraints from zircon u pb ages and hf o isotopes abstract in the east qinling orogenic belt central china there are numerous mo deposits with over 6 mt mo metal the giant nannihu shangfanggou and yuchiling porphyry mo deposits are hosted in porphyry stocks associated with the heyu batholith whereas the giant donggou porphyry mo deposit is hosted in a stock associated with the taishanmiao batholith zircon grains from the heyu batholith have concordant 238u 206pb ages scattered from 150 3 to 130 2 ma with an age interval of nearly 20 m y whereas ore hosting granitic porphyry stocks from the nannihu shangfanggou and yuchiling deposits have 206pb 238u ages ranging from 151 1 to 135 1 ma 143 1 to 132 1 ma and 143 5 to 131 5 ma respectively it is likely that the heyu batholith has a prolonged history of incremental assembly and the ore bearing granitic porphyry stocks may have originated from the same magma reservoir and emplaced in different stages likewise zircon grains from the taishanmiao batholith have concordant 238u 206pb ages spanning in a period from 130 2 to 111 3 ma whereas those from the donggou granitic porphyry stock have 238u 206pb ages ranging from 125 2 to 110 3 ma nearly coeval with the taishanmiao batholith the molybdenite re os model ages for each deposit are coincident with relatively young zircon 238u 206pb ages of the host stock indicating that mo mineralization is likely related to late stage magmatism zircon grains from the batholiths and granitic porphyry stocks have ehf t ranging from 10 to 30 tdm2 ages from 1 6 to 2 5 ga and 18o from 5 0 to 8 7 which are taken to suggest the involvement of the subducted continental crust of the yangtze block in the source we thus propose that the extensive mo mineralization in the east qinling porphyry mo belt is genetically related to the prolonged granitic magmatism in the late mesozoic and a mo rich source that was related to the subducted continental crust of the yangtze block stagnating beneath the southern margin of the north china craton

rethinking the emplacement and evolution of zoned plutons geochronologic evidence for incremental assembly of the tuolumne intrusive suite california new u pb geochronologic data indicate that the tuolumne intrusive suite california was assembled over a period of at least 10 m y between 95 and 85 ma and that the half dome granodiorite intruded over a period approaching 4 m y simple thermal considerations preclude the possibility that a magma chamber the size of the half dome pluton could have existed as a liquid at shallow crustal depths for that long rather field evidence for sheeting along the margins of the suite the range of ages and the regular decrease of ages toward the center of the suite and within individual plutons suggest incremental assembly geochronologic evidence for incremental assembly is consistent with the failure of geophysical methods to detect large magma chambers with more than 20 melt even in active volcanic areas because it is unlikely that the individual plutons composing the tuolumne ever coexisted as liquid rich magmas the chemical evolution of the suite cannot be the result of simple fractionation and or mixing between exposed units but instead must reflect processes occurring during magma generation

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved