extreme climatic conditions recorded in santa barbara basin laminated sediments the 1835 1840macoma event abstract the santa barbara basin sbb record of laminated sediment well known for its excellent time resolution shows the presence of an unusual once in a millenium event in the period 1835 1840 at a depth of 55 57 cm below the surface of the seafloor this macoma event is the brief flourishing of a macrofaunal community in the deep center of the sbb from which large organisms are normally excluded by the lack of oxygen shells of the pelecypodmacoma leptonoidea dall and associated fossils which congregate in a thin layer dated at 1840 provide evidence for a sudden local extinction of macrobenthos by suffocation various stratigraphic evidence suggests thatm leptonoidea colonized the basin floor for a few years prior to 1840 as a result of temporarily decreased productivity and increased oxygen content in the water spilling over the sill into the basin historical eyewitness reports indicate unusually severe winter storms from southeasterly directions during the 1830s in the sbb we suggest that coastal upwelling was severely reduced during 1835 1839 with the effect of reducing the intensity of the oxygen minimum layer themacoma event apparently is one manifestation of large scale climatic anomalies felt throughout north america and which were possibly linked to the major volcanic eruption of cosiguina nicaragua in 1835

paleocene planktonic foraminifera from dsdp site 356 south atlantic paleoceanographic inferences abstract in the present study the planktonic foraminiferal distribution in a core section representing an interval between the cretaceous paleogene k pg boundary and the end of the paleocene danian selandian from dsdp site 356 sao paulo plateau south atlantic was analyzed the results point towards a gradual recovery of the marine pelagic ecosystem in the aftermath of the k pg mass extinction event the changes in distribution patterns and composition of the danian planktonic foraminiferal assemblages are primarily related to the instability and changing conditions of oceanic surface waters the quantitative analyses of the planktonic foraminifera showed that a series of speciation events took place in the danian immediately after the k pg boundary marking three distinct main intervals i in the p zone evidenced by the predominance of specimens that likely inhabited the most superficial portions of the water column mixed layer represented mainly by microperforated taxa globoconusa guembelitria parvularugoglobigerina and woodringina the occurrence of this group suggests poorly stratified water masses and a water column with meso eutrophic conditions in this interval the first appearance of spines in the planktonic foraminifera eoglobigerina of the family globigerinidae evidences the development of a carnivorous habit ii between zones p1a and p2 there is a continuous increase of species that inhabited the lower portion of the water column in the thermocline and sub thermocline suggesting the recovery of the pelagic ecosystem with the development of a more stratified water column in mesotrophic to oligotrophic conditions iii from zone p3 onwards most of the planktonic foraminifera inhabited the lowest portions of the water column together with the first occurrences of mixed layer endosymbiont bearing species such as morozovella acarinina and igorina

human responses to middle holocene climate change on california s channel islands abstract high resolution archaeological and paleoenvironmental records from california s channel islands provide a unique opportunity to examine potential relationships between climatically induced environmental changes and prehistoric human behavioral responses available climate records in western north america 7 3 8 ka indicate a severe dry interval between 6 3 and 4 8 ka embedded within a generally warm and dry middle holocene very dry conditions in western north america between 6 3 and 4 8 ka correlate with cold to moderate sea surface temperatures sst along the southern california coast evident in ocean drilling program odp core 893a b santa barbara basin an episode of inferred high marine productivity between 6 3 and 5 8 ka corresponds with the coldest estimated ssts of the middle holocene otherwise marked by warm low productivity marine conditions 7 5 3 8 ka the impact of this severe aridity on humans was different between the northern and southern channel islands apparently related to degree of island isolation size and productivity of islands relative to population fresh water availability and on going social relationships between island and continental populations northern channel islanders seem to have been largely unaffected by this severe arid phase in contrast cultural changes on the southern channel islands were likely influenced by the climatically induced environmental changes we suggest that productive marine conditions coupled with a dry terrestrial climate between 6 3 and 5 8 ka stimulated early village development and intensified fishing on the more remote southern islands contact with people on the adjacent southern california coast increased during this time with increased participation in a down the line trade network extending into the western great basin and central oregon genetic similarities between middle holocene burial populations on the southern channel islands and modern california uto aztecan populations suggest middle holocene movement of people at this time from southern california desert environs westward to the southern islands a migration perhaps stimulated by increased continental aridity

slow dense replenishments of a basic magma chamber the layered series of the newark island layered intrusion nain labrador the newark island layered intrusion is a composite layered intrusion within the nain anorthosite complex labrador the intrusion comprises a lower layered series ls dominated by troctolites olivine gabbros and oxide rich cumulates and an upper hybrid series hs characterized by a wide range of mafic granitic and hybrid cumulates and discontinuous layers of chilled mafic rocks wiebe 1988 the hs crystallized from a series of replenishments of both silicic and basic magmas the ls crystallized from periodically replenished basic magmas the ls has a lower zone that consists mainly of olivine plagioclase cumulates and contains minor cryptic reversals in mineral compositions that resulted from replenishments of relatively primitive magma an upper zone is dominated by olivine plagioclaseaugite ilmenite cumulates cumulus titanomagnetite and pyrrhotite occur within some oxide rich cumulates and the stratigraphically highest layers contain cumulus apatite at intermediate levels in the sequence cumulus inverted pigeonite occurs in place of olivine several prominent regressions in the stratigraphy of the upper zone are marked by fine grained troctolitic layers with much higher mg no 100 mgo mgo feo and anorthite than underlying cumulates these layers coarsen upward and grade back to oxide bearing olivine gabbros within thicknesses ranging from 10 cm to 15 m dikes that cut the ls have major and trace element compositions that strongly suggest that they are feeders for the replenishments in the lower zone when olivine and plagioclase were the only cumulus phases replenishments were less dense than the resident magma and rose as plumes and mixed with it precipitation of cumulus oxides in the upper zone lowered the density of resident magma so that subsequent replenishments were more dense than resident magma replenishments that occurred after oxides began to precipitate had small injection velocities these post oxide injections flowed along the interface between resident magma and the cumulate pile and precipitated flow banded fine grained troctolites

a rb sr and sm nd isotope geochronology and trace element study of lunar meteorite lapaz icefield 02205 abstract rubidium strontium and samarium neodymium isotopes of lunar meteorite lapaz icefield lap 02205 are consistent with derivation of the parent magma from a source region similar to that which produced the apollo 12 low ti olivine basalts followed by mixing of the magma with small amounts 1 2 wt of trace element enriched material similar to lunar kreep rich sample sau 169 the crystallization age of lap 02205 is most precisely dated by an internal rb sr isochron of 2991 14 ma with an initial 87sr 88sr at the time of crystallization of 0 699836 0 000010 leachable ree rich phosphate phases of lap 02205 do not plot on a sm nd mineral isochron indicating contamination or open system behavior of the phosphates excluding anomalous phases from the calculation of a sm nd isochron yields a crystallization age of 2992 85 initial e143nd 2 9 0 8 that is within error of the rb sr age and in agreement with other independent age determinations for lap 02205 from ar ar and u pb methods the calculated 147sm 144nd source ratios for lap 02205 various apollo 12 and 15 basalts and samples with strong affinities to kreep sau 169 nwa 773 15386 are uncorrelated with their crystallization ages this finding does not support the involvement of a common kreep component as a heat source for lunar melting events that occurred after crystallization of the lunar magma ocean

energy constrained open system magmatic processes iv geochemical thermal and mass consequences of energy constrained recharge assimilation and fractional crystallization ec rafc 1 a wealth of geochemical and petrological data provide evidence that the processes of fractional crystallization assimilation and magma recharge replenishment dominate the chemical signatures of many terrestrial igneous rocks previous work spera and bohrson 2001 bohrson and spera 2001 has established the importance of integrating energy species and mass conservation into simulations of complex magma chamber processes an extended version of the energy constrained formulation energy constrained recharge assimilation fractional crystallization ec rafc tracks mass and compositional variations of melt cumulates and enclaves in a magma body undergoing simultaneous recharge assimilation and fractional crystallization spera and bohrson 2002 because many ec rafc results are distinct from those predicted by extant rafc formulations the primary goal of this paper is to present a range of geochemical and mass relationships for selected cases that highlight issues relevant to modern petrology among the plethora of petrologic problems that have important well documented analogues in nature are the geochemical distinctions that arise when a magma body undergoes continuous versus episodic recharge the connection between erupted magmas and associated cumulate bodies the behavior of recharge fractionation dominated systems rfc thermodynamic conditions that promote the formation of enclaves versus cumulates and the conditions under which magma bodies may be described as chemically homogeneous investigation of the effects of continuous versus episodic recharge for mafic magma undergoing rafc in the lower crust indicates that the resulting geochemical trends for melt and solids are sensitive to the intensity and composition of recharge suggesting that ec rafc may be used as a tool to distinguish the nature of the recharge events compared to the record preserved in melts the geochemical and mass characteristics of solids associated with particular rafc events may record a more complete view of the physiochemical history of an open system magma body the capability of ec rafc to track melts and solids creates a genetic link that can be compared to natural analogues such as layered mafic intrusions and flood basalts or mafic enclaves and their intermediate composition volcanic or plutonic hosts the ability to quantify chemical and volume characteristics of solids and melts also underscores the need for integrated field petrologic and geochemical studies of igneous systems while it appears that a number of volcanic events or systems may be characterized by continuous influx or eruption of magma steady state systems reports describing compositional homogeneity for products that represent eruptions of more than one event are relatively rare in support of this ec rafc results indicate that very specific combinations of recharge conditions bulk distribution coefficients and element concentrations are required to achieve geochemical homogeneity during cooling of a magma body undergoing rafc in summary critical points are that ec rafc provides a method to quantitatively investigate complex magmatic systems in a thermodynamic context it predicts complex nonmonotonic geochemical trends for which there are natural analogues that have been difficult to model and finally ec rafc establishes the link between the chemical and physical attributes of a magmatic system application of ec rafc promises to improve our understanding of specific tectonomagmatic systems as well as enhance our grasp of the essential physiochemical principles that govern magma body evolution

observing silicic magma transport in dykes at depths of 8 19 km evidences from crustal xenoliths and numerical modelling abstract within the context of magma transport processes in a dyke this paper integrates petrography and thermodynamic modelling together with fluid dynamics to model the melting of the wall rock in three magma dykes at crustal depths from 8 to 19 km using this combination we explore the interaction between thermal and mechanical processes during silicic magma ascent and the implications for the relative abundance of different crustal xenoliths erupted at the surface we utilize a two dimensional thermal model of dacitic magma injection and flow in dykes of different thickness lengths and depths and associated partial melting of the wall rock and compare the results with field examples from the neogene volcanic province se spain the modelling results open the possibility to relate the range of observed xenoliths information microstructures size distribution at the surface p t evolution to their position in a transient thermal regime in the wall rock of a magma conduit and to the time spent immersed in magma in addition the effects of the modelled stress in the wall rock during magma ascent by the presence or absence of planar features in the xenoliths reveal that the stress patterns are independent of the dyke length and thickness

a mathematical model of trace element and isotopic behavior during simultaneous assimilation and imperfect fractional crystallization the process of coupled assimilation and fractional crystallization afc is one of the most popular petrogenetic concepts that explains magmatic differentiation conventional geochemical models for this process assume that crystals are removed instantaneously from the magma body as they are produced however recent advances in isotopic microanalysis have clarified that the crystals are suspended within the magma body for a certain period affecting the whole rock composition in response to the intra grain isotopic zoning this study develops a mass balance model for simultaneous assimilation and imperfect fractional crystallization aifc to describe the effects of suspended crystals on the path of magma evolution the mass balance differential equations for the liquid and suspended crystals are solved simultaneously the analytical solution of the aifc equations gives a quantitative account of the evolution paths of trace elements and isotopes within bulk crystals liquid and magma crystals plus liquid the chemical path of the magma differs markedly from that predicted by the conventional afc model

repeated recharge assimilation and hybridization in magmas erupted from el chichon as recorded by plagioclase and amphibole phenocrysts abstract compositional and isotopic zoning patterns in plagioclase and amphibole phenocrysts from el chichon record multiple cycles of country rock assimilation magma injection hybridization and mixing laser ablation icp ms and electron microprobe analyses of plagioclase crystals from 7 eruptions spanning 3100 years reveal four types of zoning these compositional and isotopic zones are often associated with textural changes observed in the crystals in thin section e g sieved or patchy regions amphiboles are frequently zoned in al and si and in two magmas may have clinopyroxene rims interestingly most plagioclase show multiple and repeated zoning patterns moreover all magmas contain all zoning patterns and textures and crystals with substantially different sequences of zones occur within mm of one another the most reasonable explanation for the origin of these textures is a frequently recharged chamber plagioclase zones with increasing anorthite contents an and decreasing 87sr 86sr ratios record injection by a hotter possibly wetter and more primitive magma lower 87sr 86sr ratio zones with decreasing an and increasing 87sr 86sr ratios record assimilation of country rock and or hybridization of the host and injected magmas injection of hot magma may provide the heat for country rock assimilation changes in an without corresponding changes in 87sr 86sr ratio likely record slight variations in pressure or temperature during crystallization or the far field thermal effects of magma injection variations in 87sr 86sr ratio unaccompanied by anzoning record assimilation of country rock amphibole zoning patterns also record periodic heating events amphibole with clinopyroxene rims record episodes where the magma was heated beyond the amphibole stability field bulk compositional homogeneity and the juxtaposition of many crystals with disparate zoning patterns in single pumice require the magmatic system to be well mixed strontium diffusion rates indicate that the plagioclase zoning patterns cannot have persisted at magmatic pressures and temperatures for more than 500 years thus cycles of injection and assimilation occur on timescales equal to or shorter than the eruption recurrence interval long term compositional and isotopic homogeneity indicate that there is a balance between recharge assimilation and crystallization

differentiation of tholeiitic basalt to a type granite in the sept iles layered intrusion canada the undeformed 564 ma sept iles layered intrusion quebec canada is a large igneous body of c 20 000km3 from the base to the top it consists of a layered series dominated by troctolite and gabbro an anorthositic upper border series and a dominantly granitic upper series the parent magma of the layered series is inferred to be an iron rich tholeiitic basalt 48 wt sio2 15wt feot whole rock compositions from the chilled margin dykes cross cutting the layered series and silicic rocks from the upper series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous a type granites 77 wt sio2 initial 143nd 144nd 0 51201 0 51207 and 87sr 86sr 0 70353 0 70548 indicate a juvenile mantle source and minimal contamination by old crust 1 2 during crystallization geochemical modeling using the melts thermodynamic calculator combined with equations predicting mineral melt equilibria from experiments on tholeiitic basalts indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the layered series fe ti oxides saturate early in the layered series after 14 fractionation of plagioclase olivine cumulates further fractionation of fe ti oxide bearing gabbros drives the residual liquids toward silica enrichment and iron depletion major and trace element modeling indicates that the a type granites from the upper series were produced by protracted fractional crystallization of an iron rich basaltic parent magma at a fraction of residual liquid of only 8 the observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations most of the intermediate compositions correspond to magmatic mafic enclave bearing granitoids and display geochemical evidence of hybridization intermediate compositions produced by fractional crystallization are scarce and a daly gap occurs from 57 to 67 wt sio2 this gap could result either from the fractional crystallization process or from silicate liquid immiscibility during that compositional interval

the most recent large earthquake on the rodgers creek fault san francisco bay area the rodgers creek fault rcf is a principal component of the san andreas fault system north of san francisco no evidence appears in the historical record of a large earthquake on the rcf implying that the most recent earthquake mre occurred before 1824 when a franciscan mission was built near the fault at sonoma and probably before 1776 when a mission and presidio were built in san francisco the first appearance of nonnative pollen in the stratigraphic record at the triangle g ranch study site on the south central reach of the rcf confirms that the mre occurred before local settlement and the beginning of livestock grazing chronological modeling of earthquake age using radiocarbon dated charcoal from near the top of a faulted alluvial sequence at the site indicates that the mre occurred no earlier than a d 1690 and most likely occurred after a d 1715 with these age constraints we know that the elapsed time since the mre on the rcf is more than 181 years and less than 315 years and is probably between 229 and 290 years this elapsed time is similar to published recurrence interval estimates of 131 to 370 years preferred value of 230 years and 136 to 345 years mean of 205 years calculated from geologic data and a regional earthquake model respectively importantly then the elapsed time may have reached or exceeded the average recurrence time for the fault the age of the mre on the rcf is similar to the age of prehistoric surface rupture on the northern and southern sections of the hayward fault to the south this suggests possible rupture scenarios that involve simultaneous rupture of the rodgers creek and hayward faults a buried channel is offset 2 2 1 2 0 8 m along one side of a pressure ridge at the triangle g ranch site this provides a minimum estimate of right lateral slip during the mre at this location total slip at the site may be similar to but is probably greater than the 2 0 3 0 2 m measured previously at the nearby beebe ranch site

strong localised country rock contamination and partial homogenisation of a mafic magma an example from west central sweden a dolerite sill cutting slightly older basalt in west central sweden shows a strong chemical variation 54 sio2 73 within a restricted area 100x100 m 2 the linear correlation among almost all elements is extremely high in addition epsilon ndt is strongly correlated with the sio2 content least square hyperbolic ratio and three element ratio modelling common denominator suggests that most of the chemical variation is explained by mixing and or micro mingling in all we test 407 hyperbolas of which 402 are fitted the five ratio pairs which could not be fitted to a hyperbola using a least square fitting procedure have the ratio th eu in common testing the goodness of fit is problematic for hyperbolic distributions for comparing purposes we 4 sum the distances to chords approximating the hyperbola mobile and immobile elements behave similarly suggesting that no a elements are lost or added from outside the system the data suggests that already the most mafic of the analysed rocks is a mixture of the normal dolerite and a siliceous crustal rock a mafic magma intruded into the base of the crust where it fractionated resulting in a decreased mg number the magma was then contaminated with country rocks in an intermediate magma chamber due to country rock melting during mixing mingling almost no fractionation took place the contaminated rock suggests the presence of a fluid phase this was probably a prerequisite for country rock melting enrichment in some incompatible elements suggests that besides major mixing mingling a thermochemical separation process has affected the most felsic rock enriching it in light rare earths and zr less

late holocene δ13c and pollen records of paleosalinity from tidal marshes in the san francisco bay estuary california abstract records of stable carbon isotopes 13c are presented from cores collected from four san francisco bay marshes and used as a proxy for changes in estuary salinity the 13c value of organic marsh sediments are a reflection of the relative proportion of c3 vs c4 plants occupying the surface and can thus be used as a proxy for vegetation change on the marsh surface the four marshes included in this study are located along a natural salinity gradient that exists in the san francisco bay and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity the 13c values complement pollen data from the same marsh sites producing a paleoclimate record for the late holocene period in the san francisco bay estuary the data indicate that there have been periods of higher than average salinity in the bay estuary reduced fresh water inflow including 1600 1300 cal yr b p 1000 800 cal yr b p 300 200 cal yr b p and ca a d 1950 to the present periods of lower than average salinity increased fresh water inflow occurred before 2000 cal yr b p from 1300 to 1200 cal yr b p and ca 150 cal yr b p to a d 1950 a comparison of the timing of these events with records from the california coast watershed and beyond the larger drainage of the bay reveals that the paleosalinity variations reflected regional precipitation

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

energy constrained recharge assimilation and fractional crystallization ec raχfc a visual basic computer code for calculating trace element and isotope variations of open system magmatic systems 1 volcanic and plutonic rocks provide abundant evidence for complex processes that occur in magma storage and transport systems the fingerprint of these processes which include fractional crystallization assimilation and magma recharge is captured in petrologic and geochemical characteristics of suites of cogenetic rocks quantitatively evaluating the relative contributions of each process requires integration of mass species and energy constraints applied in a self consistent way the energy constrained model energy constrained recharge assimilation and fractional crystallization ec ra fc tracks the trace element and isotopic evolution of a magmatic system melt solids undergoing simultaneous fractional crystallization recharge and assimilation mass thermal and compositional trace element and isotope output is provided for melt in the magma body cumulates enclaves and anatectic i e country rock melt theory of the ec computational method has been presented by spera and bohrson 2001 2002 2004 and applications to natural systems have been elucidated by bohrson and spera 2001 2003 and fowler et al 2004 the purpose of this contribution is to make the final version of the ec ra fc computer code available and to provide instructions for code implementation description of input and output parameters and estimates of typical values for some input parameters a brief discussion highlights measures by which the user may evaluate the quality of the output and also provides some guidelines for implementing nonlinear productivity functions the ec ra fc computer code is written in visual basic the programming language of excel the code therefore launches in excel and is compatible with both pc and mac platforms the code is available on the authors web sites http magma geol ucsb edu and http www geology cwu edu ecrafc as well as in the auxiliary material

open system magma chamber evolution an energy constrained geochemical model incorporating the effects of concurrent eruption recharge variable assimilation and fractional crystallization ec e raχfc significant petrogenetic processes governing the geochemical evolution of magma bodies include magma recharge including formation of quenched inclusions or enclaves heating and concomitant partial melting of country rock with possible contamination of the evolving magma body assimilation and formation and separation of cumulates by f ractional crystallization rafc although the importance of modeling such open system magma chambers subject to energy conservation has been demonstrated the effects of concurrent removal of magma by eruption and or variable assimilation involving imperfect extraction of anatectic melt from wall rock have not been considered in this study we extend the ec rafc model to include the effects of eruption and variable amounts of assimilation ax this model called ec e 0racfc tracks the compositions trace elements and isotopes temperatures and masses of magma body liquid melt eruptive magma cumulates and enclaves within a composite magmatic system undergoing simultaneous eruption recharge assimilation and fractional crystallization the model is formulated as a set of 4 t i s coupled nonlinear differential equations where the number of trace elements radiogenic and stable isotope ratios modeled are t i and s respectively solution of the ece 0racfc equations provides values for the average temperature of wall rock ta mass of melt within the magma body mm masses of cumulates mct enclaves men and wall rock m o a and the masses of anatectic melt generated m a and assimilated cm a in addition t trace element concentrations and i s isotopic ratios in melt and eruptive magma cm em dm cumulates cct em dm enclaves cen er d o r and anatectic melt ca ea d o a as a function of magma temperature tm are also computed input parameters include the user defined equilibration temperature teq a factor describing the efficiency of addition of anatectic melt c from country rock to host magma the initial temperature and composition of pristine host melt tom c o m em d o m recharge melt t o r c o r er dor and wall rock t o a c o a ea d o a distribution coefficients dm dr da and their temperature dependences dhm dhr dha latent heats of transition melting or crystallization for wall rock dha pristine magma dhm and recharge magma dhr as well as the isobaric specific heat capacity of assimilant cp a pristine cp m and recharge cp r melts the magma recharge mass and eruptive magma mass functions mr tm andme tm respectively are specified a priori mr tm and me tm are modeled as either continuous or episodic step like processes melt productivity functions which prescribe the relationship between melt mass fraction and temperature are defined for end member bulk compositions characterizing the local geologic site ec e 0racfc has potential for addressing fundamental questions in igneous petrology such as what are intrusive to extrusive ratios i e for particular magmatic systems and how does this factor relate to rates of crustal growth how does i e vary temporally at single long lived magmatic centers what system characteristics are most profoundly influenced by eruption what is the quantitative relationship between recharge and assimilation in cases where the extraction efficiency can be shown to be less than unity what geologic criteria are important and

magmatic evolution of the skye igneous centre western scotland modelling of assimilation recharge and fractional crystallization the skye igneous centre forming part of the british tertiary magmatic province developed over a 7 myr period 61 54 ma and is characterized by a complex suite of lavas hypabyssal and intrusive rocks of picritic to granitic composition the intrusion of magma from mantle to crust at 2 10 3 km 3 yr 6 mt yr advected magmatic heat of roughly 0 2 gw averaged over the period of magmatism supporting an excess heat flux of about 130 mw m 2 or about twice the present day average continental heat flow the volume of new crust generated at skye 15 000 km 3 spread over the present day area of skye corresponds to 9 km of new crust the geochemical evolution of the skye magmatic system is constrained using the energy constrained recharge assimilation and fractional crystallization ecrafc model to understand variations in the sr and pb isotopic and sr trace element composition of the exposed magmatic rocks with time the character composition and specific enthalpy of both assimilant and recharge magma appears to change systematically up section suggesting that the magma reservoirs migrated to progressively shallower levels as the system matured the model of the magma transport system that emerges is one in which magma batches are stored initially at lower crustal levels where they undergo rafc evolution residual magma from this stage then migrates to shallower levels where mid crustal wall rock is assimilated the recharge magma at this level is characterized by an increasingly crustal signature for some of the stratigraphically youngest rocks the data suggest that the magma reservoirs ascended into and interacted with upper crustal torridonian metasediments

magma chambers emplaced in carbonate substrate petrogenesis of skarn and cumulate rocks and implications for co2 degassing in volcanic areas crystal rich lithic clasts occurring in volcanic deposits are key tools to understand processes of storage cooling and fractionation of magmas in pre eruptive volcanic systems these clasts represent snapshots of the magma chamber host rock interface before eruption and provide information on crystallization differentiation and degrees of interaction between magma and wall rock in this study we have focused on the petrology of clasts of cumulate and skarn rocks from the colli albani volcanic district with the aim of shedding light on magma carbonate interaction and co2 emission in volcanic areas by means of phase relations bulk rock chemistry mineral compositions and isotope data we have identified different types of cumulates and skarns cumulates containing either clinopyrox

isotopic responses to basaltic injections into silicic magma chambers a whole rock and microsampling study of macrorhythmic units in the pleasant bay layered gabbro diorite complex maine usa the pleasant bay layered gabbro diorite complex 420 ma formed via repeated injections of mafic magma into a felsic magma chamber it is dominated by repeating sequences macrorhythmic units with chilled gabbroic bases which may grade upward into medium grained gabbro diorite and granite each unit represents an injection of mafic magma into the chamber followed by differentiation increases in sri and decreases in endi with stratigraphic height indicate open system isotopic behaviour and exchange between the mafic and felsic magmas isotopic variations of whole rock samples in individual macrorhythmic units do not conform to bulk mixing or afc models between potential parental magmas sr isotopic studies of single feldspar crystals from one macrorhythmic unit indicate that exchange of crystals between the resident felsic magma and mafic influxes was important that some of the rocks contain feldspar xenocrysts and that the rocks are isotopically heterogeneous on an intercrystal scale xenocryst abundance increases with stratigraphic height suggesting that crystal exchange occurred in situ the lack of disequilibrium textures in the xenocrystic feldspar indicates the evolved macrorhythmic magma and resident silicic magma were of a similar composition and likely in thermal equilibrium at the time of crystal transfer mafic chilled margins are enriched in alkalis and isotopically evolved compared with mafic dikes representing the parental melts and suggest rapid in situ diffusional exchange following emplacement of individual mafic replenishments

corry bog pennsylvania a case study of the radiocarbon dating of marl abstract new radiocarbon dates carbon and oxygen isotope analyses of mollusks and marl and palynologic analysis have clarified age relationships at the corry kettle bog in northwestern pennsylvania a 4000 yr difference in radiocarbon dates between basal peat and marl top previously interpreted as caused by the presence of an unconformity is reinterpreted as due to hard water effects from carbonate bedrock and glacial deposits a radiocarbon date of 14 000 yr from basal marl previously used as a minimum age for glacial deposition is also likely too old instead a similar age is estimated for the base of the underlying lake clay radiocarbon dates on marl should be used with caution and supported by isotopic and pollen analyses

rapid climatic change in coastal southern california inferred from pollen analysis of san joaquin marsh pollen analysis and five radiocarbon dates of a 687 cm core provide a detailed chronology of environmental change in a marsh at the head of newport bay orange county california sediment deposition kept pace with sea level rise during the early history of the marsh from ca 7000 to 4500 yr b p the site was a freshwater marsh trees were more abundant than today and grassland was the regional vegetation as sea level rose salt marsh gradually invaded the site brief periods of freshwater marsh 3800 2800 2300 and after 560 yr b p correlate with episodes of global cooling during the neoglacial the historic period is marked by the appearance of exotic species particularly erodium cf cicutarium and eucalyptus and the spores of fungi sporormiella and thecaphora peak influx of pollen spores and charcoal probably reflect greater frequency of flooding and erosion ca 5000 yr b p and during the last 1000 yr

origin and evolution of a migmatite the development of a stromatic migmatite exposed east and southeast of arvika western sweden is described in four stages beginning with the country rock and following evolution through three areas characterized by low medium and high amounts of leucosomes areas l m and h respectively

a geochemical approach to model periodically replenished magma chambers does oscillatory supply account for the magmatic evolution of epr 17 19 s abstract we propose a new approach to model the geochemical evolution of continuously replenished and tapped steady state magma chambers we use a sinusoidal function to model cyclic magma supply the temporal evolution of a reservoir is described using differential equations in which the amount of refilling magma does not depend on the size of the chamber these equations can be used to calculate incompatible trace element concentrations and magma quantities we examine the geochemical consequences of episodic injections noises and wall rock assimilation we also explore possible variations in crystallization rate to show its potential the theoretical treatment has been applied to the epr 17 19 s a site with a strong magma budget which has been the subject of several geological geophysical studies the practical application requires geological parameters to be constrained as well as the extreme values of the lava concentration range a first step specifies the incompatible trace element composition of the replenishing melt which corresponds in the epr case to a magnesian liquid mgo 9 5 wt it is then possible to determine other parameters such as cycle period 750 years magma residence time 300 years and reservoir size from 4 1 to 8 6 km3 per 20 km segment lastly variations in crystallization rate do not significantly alter the results

magma mixing recharge and eruption histories recorded in plagioclase phenocrysts from el chichon volcano mexico operative throughout the 200 ky history of the el chichon magma consistent core to rim decreases of sr sr ratios and coincident system increases in sr concentrations in plagioclase phenocrysts of varying size 1 cm to 2 mm are reported from samples of the 1982 and pre 1982 200 ka eruptions of el chichon volcano maximum sr sr ratios of 0 7054 significantly higher than the wholerock isotopic ratios 0 7040 0 7045 are found in the cores

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

biot number and thermos bottle effect implications for magma chamber convection thermal boundary conditions model the coupling between a convecting magmatic body and its host such conditions need to be considered in models of igneous systems that involve thermal histories crystallization and fractionation of melt formation of aureoles by contact metamorphism and any other processes in which transport of heat plays a role usually investigations of magmatic systems have tended to emphasize modeling the interior convective regime relative to treatment of the thermal coupling yet it is found that the thermal nature of an intrusion is likely to be influenced more by coupling to its host than by the details of internal convective flows evaluation of a parameter having the form of a biot number bi provides a basis for estimating which boundary conditions are most appropriate it is found that bi 0 1 constant heat flux limit for models of several caldera systems for such values of the biot number the host regime behaves somewhat like a thermos bottle by limiting the flow of heat through the magma host system so that convective stirring of magma has little effect on the cooling rate of the intrusion because of this insulating effect boundary temperatures assumed in convection models should approach magmatic values even if an active hydrothermal system is present however high boundary temperatures do not imply that melting and assimilation of host rock by magma must occur despite the thermos bottle effect magmatic convection can still be quite vigorous

felsic enclave swarms in the gouldsboro granite coastal maine a record of eruption through the roof of a silicic magma chamber prominent zones of large globular fine grained felsic enclaves occur at the highest exposed levels of the gouldsboro granite along the coast of maine the physical characteristics of these enclaves and their chemical relations to the host granite indicate that they represent globules of resident magma that were trapped probably during eruption in the crystal mush at the top of the magma chamber these zones can appropriately be termed eruption trails enclave compositions provide a record of magma compositions within the chamber at the time of eruption they fall into two groups high k and low k with similar wt sio2 suggesting that magma in the chamber consisted of discrete compositional batches the distribution of these two types of enclaves within the swarms is consistent with the low k source magma residing as a layer beneath the high k source magma chilled and vesiculated inclusions of basalt occur only in the low k enclaves their presence there suggests that basaltic magma was injected

holocene palaeoenvironmental changes in agia paraskevi prehistoric settlement lamia central greece abstract holocene palaeoenvironmental changes in the area of the prehistoric settlement of megali vrysi close to the village of agia paraskevi in central greece 5 km east of lamia city were investigated the area is situated in the low flat alluvial plain on the outskirts of sperchios valley that is bordered nnw to ene by a rocky hilly ridge of the othrys mountain foothills 5 5 km away from the present coastline the megali vrysi site is considered to be an important mediterranean prehistoric commercial centre reconstruction of the palaeoenvironmental changes of the broader area adds new information concerning the general palaeogeographical setting of the settlement multidisciplinary research involved a detailed geomorphological survey combined with stratigraphical palaeontological and geophysical studies the penetrated strata differentiated into 4 units from top to bottom the first represents the archaeological strata the second consists of the freshwater marshy sediments while the third is the transition layer between the second and the deeper fourth group of marine lagoonal sediments the holocene stratigraphy data was combined with the 14 c ams dating results and showed a marine palaeoenvironment 5500 bc gradually having shifted to a coastal lagoonal one 3500 bc and finally changed to a freshwater marshy environment 2500 bc the comparison between ages and depths of the relative sea level points allowed the estimation of the sea level rise rate for the agia paraskevi area which is considerably lower than the one proposed for the aegean sea in the same time period this considerable offset is attributed to the intensive tectonic uplift of the study area due to the tectonic deformation of the sperchios valley and this is probably why the prehistoric coastal settlement remained on the surface and unaffected from the sea transgression for more than 7000 yrs during holocene

sr isotope zoning in plagioclase from parinacota volcano northern chile quantifying magma mixing and crustal contamination we present analyses of sr isotope zoning by microdrilling and thermal ionization mass spectrometry in plagioclase crystals from parinacota volcano central volcanic zone northern chile which were analysed for major and minor element zoning in a previous study although the isotopic range of the bulk rock samples is small at this volcano 0 7067 0 7070 except for one flow of mafic andesite at 0 7061 significant variations are seen 0 70649 0 70700 within and between plagioclase crystals a general negative correlation is observed between sr isotope composition and sr concentration in the liquid in equilibrium with each plagioclase zone as calculated from chemical zoning data and partition coefficients additional scatter is superimposed on this general trend indicating a decoupling between isotopic and chemical variations for sr in one dacite sample a detailed isotopic profile shows increasing contamination during crystal growth except for an abrupt decrease correlated with a dissolution surface and interpreted as a recharge event we apply energy constrained recharge assimilation and fractional crystallization modelling to the melt evolution recorded in the chemical and isotopic zoning in this crystal results suggest 20 assimilation of the local wall rock gneiss at high initial temperatures the isotopic data confirm the involvement of two contrasting mafic magmas which are sampled at flank cinder cone vents one lower ajata has a low sr content with high 87sr 86sr the other upper ajata has a high sr content with lower 87sr 86sr in some samples from parinacota the isotopic composition of plagioclase crystal rims or groundmass crystals is significantly higher than that of the high 87sr 86sr mafic magma in others where chemical zoning profiles suggest that recharge was from the low 87sr 86sr magma the 87sr 86sr of the groundmass and crystal rims is higher than expected this indicates either additional parent magmas to the two previously identified or further crustal assimilation either at lower crustal depths before crystallization of plagioclase or just after the last recharge our results illustrate the complexity of magma crust interaction beneath parinacota which is likely to be representative of many other central andean volcanoes formed on thick crust such complex interactions can be revealed by combined study of chemical and isotopic zoning in plagioclase in a textural petrographic context despite a small whole rock isotopic range the distinct contamination patterns of various samples suggest an important role for the geometry location and evolution of the magma plumbing system and in general variations of the thermal and compositional structure of the crust underneath the volcano

magma recharge and reactive bulk assimilation in enclave bearing granitoids tonglu south china national nature science foundation of china 41530211 mlr special funds for public welfare projects 201211013 2 state administration of foreign expert affairs of china b07039 most special funds of the state key laboratory of geological processes and mineral resources msfgpmr01

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

an integrated zircon geochronological and geochemical investigation into the miocene plutonic evolution of the cyclades aegean sea greece part 1 geochronology we use 369 individual u pb zircon ages from 14 granitoid samples collected on five islands in the cyclades in the aegean sea greece for constraining the crystallisation history of i and s type plutons above the retreating hellenic subduction zone miocene magmatism in the cyclades extended over a time span from 17 to 11 ma the ages for s type granites are systematically 2 million years older than those for i type granites considering plutons individually the zircon data define age spectra ranging from simple and unimodal to complex and multimodal seven of the 14 investigated samples yield more than one distinct zircon crystallisation age with one i type granodiorite sample from mykonos island representing the most complex case with three resolvable age peaks two samples from s type granites on ikaria appear to have crystallised zircon over 2 3 million years whereas for the majority of individual samples with multiple zircon age populations the calculated ages deviate by 1 1 5 million years we interpret our age data to reflect a protracted history involving initial partial melting at deeper lithospheric levels followed by crystallisation and cooling at shallower crustal levels our study corroborates published research arguing that pluton construction is due to incremental emplacement of multiple magma pulses over a few million years assuming that multiple age peaks of our 14 samples can indeed serve to quantify time spans for magmatic emplacement our data suggest that aegean plutons were constructed over a few million years our tectonic interpretation of the u pb ages is that the s type granites resulted from partial melting and migmatisation of the lower crust possibly starting at 23 ma the i type granites and associated mafic melts are interpreted to reflect the magmatic arc stage in the cyclades starting at 15 ma

a trace element geochemical model for imperfect fractional crystallization associated with the development of crystal zoning abstract although many petrological studies of volcanic rocks have suggested that crystallization proceeds within magma bodies highly compatible trace elements do not display the marked variations and extreme depletions predicted to result from perfect fractional crystallization imperfect crystal liquid separation is a key process in explaining this paradox the presence of suspended crystals greatly affects variations in highly compatible elements and has been quantitatively modeled by assuming perfect equilibrium between the suspended crystals and the liquid equilibrium crystallization and imperfect separation ecis however volcanic rocks generally contain zoned phenocrysts that reflect the absence of solid state equilibration the present study develops a mass balance model for zoned crystallization and imperfect separation zcis the zcis process is more efficient than the conventional ecis process in generating depleted compatible elements these two end member models are able to explain the compositional range of igneous rocks that experienced imperfect fractional crystallization under natural conditions the predicted compositional regions in bivariate trace element diagrams successfully account for the sizes and shapes of the regions defined by whole rock and melt inclusion data from the bishop tuff ca usa

prehistoric fires and the shaping of colonial transported landscapes in southern california a paleoenvironmental study at dune pond santa barbara county using a novel combination of paleoecologic proxies including pollen non pollen palynomorphs npps macroscopic charcoal and spheroidal carbonaceous particles scps 5000 years of landscape change fire history and land use have been reconstructed from dune pond santa barbara county california the pond was sensitive to holocene regional climatic variability showing different phases of lower 4600 3700 cal yr bp 2100 700 cal yr bp historical period and higher 3700 2100 cal yr bp 700 150 cal yr bp local moisture availability during this period the landscape was dominated by a coastal mosaic vegetation including dune mats coastal scrub and salt marshes on the dunes and backdunes with chaparral and oak woodland growing in the valley plains and foothills fire was intimately linked with such dominating mosaic vegetation and the combination of wet conditions and the presence of nearby human settlement were a trigger favoring coastal fires for at least two periods from 3100 to 1500 cal yr bp and from 650 cal yr bp until the 18th century in both cases fire was an important tool to keep an open coastal landscape attractive to hunting wildlife finally matching this varied range of high resolution paleoecological proxies with historical records we could characterize the development of colonial transported landscapes following the euro american settlement of santa barbara the introduction of livestock grazing by spanish colonists favored erosive processes and the introduction of fecal borne parasites in freshwater bodies negatively impacted salt and brackish coastal marshes and promoted the invasion of alien grasses and ruderals this agro pastoral landscape was consolidated during the american period with a greater role for cultivation the development of industrial activities and increased population despite negative environmental consequences such as the loss of native habitats exotic land uses and plants introduced during the historical period significantly contributed to the configuration of a cultural landscape which forms part of the cultural heritage of california

trace element mobility during magma mixing preliminary experimental results abstract magma mixing tests have been performed experimentally in a taylor couette like experimental setting the variation of trace element concentrations along transects crossing the resultant melt column has been measured results indicate a strongly variable mobility of the different trace elements in the same mixing system such a different behaviour of trace elements tends to be enhanced as the mixing time increases leading to the production of highly heterogeneous volumes of melts in which depletion and enrichment of trace elements occurred depending on their potential of spreading across the magma mixing system the results presented here offer new insights into the complexity of processes expected to be operating during mixing of magmas it is demonstrated that on short mixing times also the trace elements may become highly non correlated this is due to the development of chaotic advection diffusion processes in the system these results indicate that the onset of diffusive fractionation processes may strongly influence the patterns of data on inter elemental diagrams depending on the relative mobility of the different elements

spores of the dung fungus sporormiella increased abundance in historic sediments and before pleistocene megafaunal extinction abstract spores of the dung fungus sporormiella become abundant following the historic introduction of grazing herbivores at seven sites in the western united states during the holocene they are generally rare but at six sites sporormiella spores are abundant before the extinction of pleistocene megaherbivores ca 11 000 yr b p sporormiella spores are directly linked to extinct megaherbivores by their presence in mammoth dung preserved in bechan cave southern utah their abundance in late glacial sediments may reflect the abundance of megaherbivores during quaternary thereby indicating the age of pleistocene extinctions where other indicators are absent

time scales of magmatic processes new insights from dynamic models for magmatic assimilation we present a computational model that predicts the consequences of time dependent isenthalpic assimilation fractional crystallization afc our model combines an existing paradigm for fractional crystallization based on equilibrium thermodynamics with a kinetic model for predicting rates of mineral dissolution the isenthalpic constraint directly links the sensible heat of the magma and the latent heat of crystallization to the energy necessary for assimilation thus we predict liquid lines of descent rates of crystallization rates of cooling and ratios of assimilation to crystallization r as a function of time model simulations predict the time scale of afc processes weeks to years and show the extent to which temperature and composition of the assimilant control these time scales

phase equilibria constraints on the chemical and physical evolution of the campanian ignimbrite the campanian ignimbrite is a 4200 km trachyte phonolite pyroclastic deposit that erupted at 39 3 0 1ka within the campi flegrei west of naples italy here we test the hypothesis that campanian ignimbrite magma was derived by isobaric crystal fractionation of a parental basaltic trachyandesitic melt that reacted and came into local equilibrium with small amounts 5 10 wt of crustal rock skarns and foid syenites during crystallization comparison of observed crystal and magma compositions with results of phase equilibria assimilation fractionation simulations melts is generally very good oxygen fugacity was approximately buffered along qfm 1 where qfm is the quartz fayalite magnetite buffer during isobaric fractionation at 0 15 gpa 6 km depth the parental melt reconstructed from melt inclusion and host clinopyroxene compositions is found to be basaltic trachyandesite liquid 51 1 wt sio2 9 3 wt mgo 3 wt h2o a significant feature of phase equilibria simulations is the existence of a pseudo invariant temperature 883 8c at which the fraction of melt remaining in the system decreases abruptly from 0 5 to50 1 crystallization at the pseudo invariant point leads to abrupt changes in the composition properties density dissolved water content and physical state viscosity volume fraction fluid of melt and magma a dramatic decrease in melt viscosity from 1700 pa s to 200 pa s coupled with a change in the volume fraction of water in magma from 0 1 to 0 8 and a dramatic decrease in melt and magma density acted as a destabilizing eruption trigger thermal models suggest a timescale of 200 kyr from the beginning of fractionation until eruption leading to an apparent rate of evolved magma generation of about 10 3 km year in situ crystallization and crystal settling in density stratified regions as well as in convectively mixed less evolved subjacent magma operate rapidly enough to match this apparent volumetric rate of evolved magma production

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

late holocene vegetation changes in greenwater valley mojave desert california abstract small scale late holocene vegetation changes were determined from a series of 13 modern and fossil packrat middens collected from a site in the greenwater valley northern mojave desert california although the site is above the modern lower limit of coleogyne ramosissima black brush macrofossils of this shrub are only present in samples younger than 270 yr b p in order to measure changes more subtle than presence vs absence macrofossil concentrations were quantified and principal components and factor analyses were used to distinguish midden plant assemblages both the presence absence data and the statistical analyses suggest a downward shift of 50 to 100 m for coleogyne blackbrush communities between 1435 and 1795 a d

deciphering magma mixing the application of cluster analysis to the mineral chemistry of crystal populations abstract cluster analysis a classification technique used to group data in many fields is developed here as a tool to study magma mixing and mixed crystal populations in volcanic rocks the method is based on the quantification of the chemical degree of similarity among populations of mineral chemistry data which allows identification of discrete clusters in order to apply the technique for the particular problem of mixed crystal populations the mineral chemistry of a given crystalline phase is represented by a vector with n coordinates in which each coordinate is a real number that represents the amount of a given component in cations per formula unit present in the phase these vectors are in a set which is a subset of rn the real vector space of n dimensions because mineral chemistry data are a particular case of compositional data i e the components sum to a constant value usually 100 or the numbers of cations per formula unit the conventional euclidean distance cannot be used to quantify how similar the data are in order to apply cluster analysis to avoid this predicament aitchison s metric is proposed to measure similarities instead here average linkage a hierarchical clustering technique combined with the aitchison metric and stoichiometrical constraints is applied to mineral chemistry data this approach is evaluated using well characterized lava samples from the vancori period of activity 26 13 8 ky of stromboli volcano italy in which magma mixing has been identified between a basaltic andesite latite hosted in the magma chamber and a less evolved basaltic recharge magma the results are in agreement with previous interpretations of magma mixing which validates the use of the cluster analysis technique in the context of magma mixing relationships and opens the possibility to expand this methodology to other aspects of igneous petrology

petrogenesis and metallogenesis of the xinjie layered mafic ultramafic intrusion china modeling of recharge assimilation and fractional crystallization abstract the xinjie layered mafic ultramafic intrusion in the central emeishan large igneous province elip sw china hosts fe ti v oxide ore in the upper part and ni cu platinum group element pge sulfide deposits in the lower part in this study we use published sr nd isotopic data to simulate and evaluate the energy constrained recharge assimilation and fractional crystallization ec rafc model with a view to track the petrogenesis and mineralization in contrast to the energy constrained assimilation fractional crystallization ec afc model the ec rafc modeling shows that the xinjie intrusion may represent a shallow crustal magma chamber system where it experienced the rafc processes in the early stage of the magmatic process tm 1460 c a pulse of magma was injected into an actively evolving magma chamber minor melting ma 0 257 and assimilation of the wallrock underlying emeishan basalts occurred when the temperature of magma tm 1245 c decreased close to the equilibration temperature teq 1165 c the mass temperature plots indicate that fractional crystallization was significantly affected by the recharge and assimilation processes whereas the contaminated magma recharge favored the early crystallization of fe ti oxides as well as the formation of the pge bearing immiscible melt in the lower part of the intrusion in contrast the formation of the fe ti oxides ores in the upper part occurred probably through fractional crystallization and or immiscibility of the evolved fe ti rich magma resulting in the paragenesis of fe ti v oxides and ni cu pge sulfides in the xinjie layered intrusion

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

holocene paleoecology of an estuary on santa rosa island california abstract the middle to late holocene history and early anglo european settlement impacts on santa rosa island california were studied through the analysis of sediments in a small estuarine marsh a 5 4 m long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr three major zones are distinguishable in the core the lowermost zone 5200 to 3250 yr b p represents a time of arid climate with predominantly marine sediment input and high chenopodiaceae and ambrosia pollen values the intermediate zone 3250 yr b p to 1800 a d is characterized by greater fresh water input and high values for asteraceae and cyperaceae pollen and charcoal particles the uppermost zone 1800 a d to present documents the unprecedented erosion sedimentation and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during anglo european settlement the identification of pollen grains of torrey pine pinus torreyana documents the persistence of this endemic species on the island throughout the middle to late holocene

early silurian granitic rocks and associated enclaves as evidence of rapid cooling in a cognate magma system the case of the xuehuading panshanchong pluton south china block

isotope and chemical microsampling constraints on the history of an s type rhyolite san vincenzo tuscany italy fine scale heterogeneities in strontium isotope ratios 40ar 39ar ages and chemical com sition have been determined for individual mineral grains and enclaves in the rhyolites of san vincenzo italy the rhyolites are peraluminous with phenocrysts of alkali feldspar piagioclase biotite and cordierite and have previously been divided into two groups on the basis of whole rock major element chemistry group b lavas are distinguished from group a in having higher mgo and cao contents as well as containing two pyroxenes and chilled latite enclaves the group b lavas show textural evidence for d sequilib um such as resorption and sieve zones in feldspars laser fusion 40ar 39ar dating of individual alkali feldspar crystals suggests that the eruption of these rhyolites took place 4 38 0 04 ma though small amounts of excess argon are present in subhedral and cloudy crystals the groundmass in the group a sample has a higher initial r7sr 86sr 0 725 than that of the group b 0 7 13 the sr isotope compositions of chemically and texturally characterized individual grains reveal marked disequilibrium between minerals and the host glass as well as within grain zonation the feldspars and coarse grained biotites have initial 87sr 8 sr that are intermediate between those of the group a and b glasses with alkali feldspar generally having higher initial 87sr 86sr ratios than plagioclase chilled latite enclaves which are present in only the group b lavas have relatively low initial 8 sr 86sr ratios in the range 0 7082 0 7088 the mineral chemistry and isotope data indicate that restite does not form a significant portion of the crystalline assemblage and therefore cannot be the source of the strontium isotope dis equilibrium xenocrysts mixed into the rhyolite from a mafic magma were identified as clinopyroxene megacrysts clinopyroxene orthopyroxene clots orthopyroxene plagioclase clots and plagioclase with extensive sieve textures these grains all have relatively low initial 87sr 86sr ratios other grains that may be xenocrysts are cordierites with cores containing inclusions of biotite spinel and sillimanite and alkali feldspars with excess 4 ar the strontium isotope di quilib um in phenocrysts of plagioclase alkali feldspar and biotite is attributed to a changing melt chemistry that was too rapid for strontium diffusive equilibration a mode1 for the san vincenzo magma chamber is proposed in which the sr isotope evolution of the group b rhyolites is due to magma mixing of a crustal melt with latite magma containing unra diogenic strontium the variable initial strontium isotope compositions of group a phenocrysts may be due to assimilation or crystallization along the interface between mingled group a and b magmas

open system processes in the differentiation of mafic magma in the teide pico viejo succession tenerife oceanic island basalts are commonly thought to differentiate by fractional crystallization yet closed system fractionation models have so far failed to reproduce major and trace element variations observed in mafic lavas from the teide pico viejo stratovolcano complex on tenerife here new high precision plagioclase trace element data are fed into such a fractionation model the results confirm that fractionation of phenocrysts found in the lavas does not reproduce trace element variations in particular enrichment of sr and zr observed in the teide pico viejo mafic suite this enrichment of sr and zr is tested by an energy constrained recharge assimilation and fractional crystallization ec rafc model at high t and low t intervals consistent with previously determined magma storage beneath tenerife at sub moho depths published mineral melt equilibrium relations using the plagioclase anorthite content 0 4 x an supplementary material detailed average mineral compositions of low and high sr zr lavas composition of the bulk extracts and full graphs of the recalculated closed system model are available at www geolsoc org uk sup18604

zircon trace element and isotopic sr nd hf pb effects of assimilation fractional crystallization of pegmatite magma a case study of the guangshigou biotite pegmatites from the north qinling orogen central china abstract evidence for open system magmatic processes related to wallrock assimilation accompanied by fractional crystallization afc is present in the guangshigou biotite pegmatites north qinling orogen the biotite pegmatite gneiss contacts generally coincide with the greatest enrichment of u and th zircon u pb dating constrains the crystallization ages of the biotite pegmatite rim zone 415 2 6 ma internal zone 413 5 2 5 ma in line with a pyrite pb pb isochron age 413 22 ma metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive pb internal zone samples representing uncontaminated magma have negative to positive zircon 413 ma ehf t 1 53 3 24 low end t values 2 4 and old hf and nd model ages tdm2 1 5 1 19 ga t2dm 1 35 ga respectively indicating a dominantly recycled mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region the magmatic oxygen fugacity fo2 and crystallization temperatures ranges from 24 81 to 13 34 of log fo2 and 570 c to 793 c respectively compared to the internal zone pegmatite rim samples display a variable and lower end t values 3 9 to 2 8 and t2dm 1 47 1 37 ga but similar hf isotopic compositions favouring a three component isotopic mixing model recycled mesoproterozoic lower crust materials juvenile materials and host gneiss pronounced variations of ti y u th hf and ree concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim hosted zircons crystallized variable and high radiogenic pb ratios of pyrites forming in the hybridized magma were inherited from the matrix zircons from both zones exhibit similar hf isotope patterns indicating the rim hosted zircons crystallized during the early stage of hybridization of magma however the heterogeneous nd isotopic composition in individual pegmatites imply an incorporation of wallrock derived melt with less radiogenic nd

re evaluating the origins of late pleistocene fire areas on santa rosa island california usa abstract at the close of the pleistocene fire regimes in north america changed significantly in response to climate change megafaunal extinctions anthropogenic burning and possibly even an extraterrestrial impact on california s channel islands researchers have long debated the nature of late pleistocene fire areas discrete red zones in sedimentary deposits interpreted by some as prehistoric mammoth roasting pits created by humans further research found no evidence that these red zones were cultural in origin and two hypotheses were advanced to explain their origin natural fires and groundwater processes radiocarbon dating x ray diffraction analysis and identification of charcoal from six red zones on santa rosa island suggest that the studied features date between 27 500 and 11 400 cal yr bp and resulted from burning or heating not from groundwater processes our results show that fire was a component of late pleistocene channel island ecology prior to and after human colonization of the islands with no clear evidence for increased fire frequency coincident with paleoindian settlement extinction of pygmy mammoths or a proposed younger dryas impact event

thermal and rheological controls on the formation of mafic enclaves or banded pumice magma mixing can occur in a fluid manner to produce banded pumice or in a brittle manner to form enclaves we propose that the critical control on mixing style is a competition between developing networks of crystals in the intruding magma that impart a strength to the magma and melting and disrupting those networks in the host x ray computed tomography analysis demonstrates that banded pumice from the 1915 mt lassen eruption lacks crystal networks in contrast rhyodacite hosts with mafic enclaves from chaos crags contain well developed networks of large crystals we present a one dimensional conductive cooling model that predicts mixing style either ductile or brittle as a function of magma compositions temperatures and the size of the intruding dike our model relies on three assumptions 1 mixing is initiated by the injection of a hot dike into a cooler magma body with a yield strength 2 when magma crystallinity exceeds a critical value 13 vol plagioclase the magma develops a yield strength and 3 when total crystallinity exceeds 40 vol the magma has a penetrative crystal network and is effectively solid importantly because the two magmas are of different compositions their crystallinities and viscosities do not have the same variations with temperature as the intruding magma cools it crystallizes from the outside in while simultaneously host magma temperature near the intruder rises mixing of the two magmas begins when the host magma is heated sufficiently to 1 disrupt the crystal network and 2 initiate convection if the shear stress exerted by the convecting host magma on the dike is greater than the yield strength of the dike margin and dike crystallinity does not exceed 40 then fluid mixing occurs otherwise enclaves form by brittle deformation of the dike application of the model to magma compositions representative of lassen and chaos crags shows that emplacement of dikes 1 m thick should produce enclaves whereas thicker dikes should generate fluid mixing and form banded pumice within days to weeks of emplacement similar relationships apply to other modeled magmatic systems including pinatubo unzen and ksudach shtuybel volcanoes for all studied systems the absolute size of the intruding dike not just its proportion relative to the host influences mixing style

energy constrained open system magmatic processes 3 energy constrained recharge assimilation and fractional crystallization ec rafc 1 geochemical data for igneous rock suites provide conclusive evidence for the occurrence of open system processes within thermally and compositionally evolving magma bodies the most significant processes include magma recharge with possible enclave formation and magma mixing assimilation of anatectic melt derived from wallrock partial melting and formation of cumulates by fractional crystallization rafc in this study we extend the energetically constrained assimilation and fractional crystallization ec afc model spera and bohrson 2001 bohrson and spera 2001 to include the addition of compositionally and thermally distinct recharge melt during simultaneous assimilation and fractional crystallization energy constrained recharge assimilation and fractional crystallization ec rafc tracks the trace element and isotopic composition of melt cumulates and enclaves during simultaneous recharge assimilation and fractional crystallization ec rafc is formulated as a set of 3 t i s coupled nonlinear differential equations where the number of trace elements and radiogenic and stable isotope ratios modeled are t i and s respectively solution of the ec rafc equations provides values for the average wallrock temperature ta mass of melt within the magma body mm mass of cumulates mct and enclaves men mass of wallrock involved in the thermal interaction mao mass of anatectic melt assimilated m a concentration of t trace elements and i s isotopic ratios in melt cm cumulates cct enclaves cen and anatectic melt ca as a function of magma temperature tm input parameters include the equilibration temperature teq the initial temperature and composition of pristine melt tmo cmo emo recharge melt tro cro ero and wallrock tao cao eao temperature dependent trace element distribution coefficients dm dr da heats of transition for wallrock ha pristine melt hm and recharge melt hr and the isobaric specific heat capacity of assimilant cp a pristine melt cp m and recharge melt cp r the magma recharge mass function mr tm is specified a priori and defines how recharge magma is added to standing magma the present ec rafc simulator incorporates a weak coupling to major element mass balance and phase relations based on laboratory experiments or gibbs energy minimization e g ghiorso 1997 ec rafc can be applied to a variety of magmatic systems including volcanic suites that show evidence of magma mixing layered mafic intrusions and granitoid plutons predictions for masses as well as compositions of magmatic products are part of the ec rafc solution the systems approach provides an opportunity to quantitatively assess the roles of assimilation fractional crystallization and magma recharge in magma evolution using trace element and isotopic constraints together with energy conservation

the role of supercritical fluids in the potassium enrichment of magmas at mount etna volcano italy abstract the enrichment in potassium shown by the basic lavas erupted at mount etna volcano after 1971 k2o max 2 2 wt has been considered by previous researchers to be too high to be related to simple crystal fractionation and instead linked this high k2o content to either crustal assimilation or changes in the magma source unfortunately all existing models for the post 1971 k2o enrichment fail to explain the phenomenon satisfactorily leaving the question still open we present a critical re examination of published data for major elements 633 whole rock analyses trace elements 376 whole rock analyses and isotopic ratios 136 87sr 86sr analyses for historical and pre historical lavas potassium enrichment is not limited to the products of the last 35 years a comparable increase in potassium is noticed in lavas erupted during the pre historic phase of the recent mongibello k2o max 2 5 wt and in lavas related to the early phase of the ancient mongibello k2o max 3 wt moreover data from melt inclusions in olivines from the 2001 and 2002 eruptions reveal that potassium contents remain constant for melts with entrapment pressure between 490 to 100 mpa and increase significantly in melts entrapped at pressures below 100 mpa we propose that supercritical fluids coming from deeper magmas and carrying alkali cl complexes migrate through basic to intermediate magmas residing in the shallow feeding system as chlorine exsolves and leaves the system alkalis are released contributing to the observed potassium enrichment of the shallow magma fluctuations of the volatiles influx throughout time are likely related to the magma supply rate considering that the amount of magma entering a plumbing system is determined by the rate of regional extension the flux of alkali cl complexes entering the melt might be related to an extensional regime acting in the etnean area

self organisation and fracture connectivity in rapidly heated continental crust abstract volume expansion 1 5 volume strain with v melting positive and fluid absent partial melting in which v melting is positive of continental crust by intruding basaltic magma is a strongly irreversible process involving the dissipation of both thermal energy and matter partial melt using a simple random graph model we show by analogy how isolated fractures that form during rapid thermal perturbation in the source region can combine to form a single interconnected structure with high permeability once connected the fracture network may be thought of as a single structure or pattern that will remain stable so long as a strong temperature gradient is maintained in the source region estimates of fracture permeability that take into account changes in connectivity and fracture spacing range from approximately 10 10 to 10 5 m 2 many orders of magnitude greater than values considered typical during large scale crustal deformation and prograde regional metamorphism the ability of the isotropic fracture network to develop a top bottom directionality is crucial for buoyancy driven melt transport a physical model based on non linear evolution rules during thermal expansion is given that predicts the emergence of directionality vertical fracture alignment on a time scale of the order of 10 5 y the necessary ingredients are a deviatoric strain path a heterogeneous medium and a stiffness that evolves as a function of the local strain