precious metals in magmas of east greenland factors important to the mineralization in the skaergaard intrusion a survey of precious metals ni and cu levels and their mutual relationships in several magma suites of the east greenland volcanic passive margin shows that the magma type which was parental to the skaergaard intrusion was markedly enriched in pt pd and especially au and relatively depleted in cu compared to the preceding voluminous plateau basalt volcanism it is likely that elevated levels of platinum group minerals pgm and au were critical to the generation of ore grade precious metals in the intrusion the discovery of a major pcm and au deposit within the intrusion combined with these results suggests a set of criteria which might be critical to the formation of skaergaard type pcm deposits elsewhere in the province and worldwide the skaergaard mineralization appears to be a hitherto undescribed class of pgm and au mineralizations

oxygen and hydrogen isotope ratios in tree rings how well do models predict observed values we have measured annual oxygen and hydrogen isotope ratios in the cellulose of the latewood of oak quercus robur l growing on well drained ground in norfolk uk we compare the observed values of isotope ratios with those calculated using equations that allow for isotopic fractionation during the transfer of oxygen and hydrogen from source water taken by the tree to cellulose laid down in the cambium the equations constitute a model in which isotopic fractionation occurs during evaporative enrichment within the leaf and during isotopic change between carbohydrates and water in the trunk during cellulose synthesis from the relationship between isotope ratios in precipitation and cellulose we deduce that the source water used by the tree comprises a constant mixture of groundwater and precipitation chiefly from the months of may june and july of the growth year by selection of isotopic fractionation factors and the degree of isotope exchange within the trunk we are able to model the observed annual values of oxygen isotope ratios of cellulose to a significant level r 0 77 p 0 01 when we apply the same model to hydrogen isotope ratios however we find that although we can predict the average value over the time series we can no longer predict the year to year variation we suggest that this loss of environmental signal in the hydrogen isotopes is caused by differences in the kinetic isotope effects of the biochemical reactions involved in the fixation of hydrogen in different positions of the glucose molecule owing to these effects the hydrogen isotope ratios of cellulose can vary in a way not anticipated in current models and hence may induce non climatic noise in the hydrogen isotope time series

metasomatic replacement in the skaergaard intrusion east greenland preliminary observations abstract several unusual types of replacement structures in the layered series and marginal border series of the skaergaard intrusion indicate that metasomatic changes have altered the modal proportions and in places the mineral composition of the gabbro the geometrical forms and compositional patterns of these features indicate that they result from reactive fluids moving through the rocks at high temperatures shortly after the magma had reached an advanced stage of crystallization the principal effect of metasomatism has been to produce strongly contrasting mafic and felsic rocks

the nature and genesis of marginal cu pge au sulphide mineralisation in paleogene macrodykes of the kangerlussuaq region east greenland the kangerlussuaq region of east greenland hosts a variety of early tertiary extrusive and intrusive igneous rocks related to continental break up and the passage of the ancestral iceland plume these intrusive bodies include a number of gabbroic macrodykes two of which the miki fjord macrodyke and the newly discovered togeda macrodyke contain cu pge au sulphide mineralisation along their margins sulphides occur as disseminated interstitial blebs and rounded globules of chalcopyrite and pyrrhotite with some fe ti oxides and platinum group minerals comprising largely pd bismuthides and tellurides the globules are interpreted to have formed from fractionation of trapped droplets of an immiscible cu and pd rich sulphide melt and show geopetal indicators sulphur isotopes imply a local crustal source of s in these from pyritic sediments of the kangerlussuaq basin thus generation of these sulphide occurrences was controlled by local country rock type low ni cu and pt pd ratios also present in the platinova reefs in the skaergaard intrusion indicate that early fractionation of olivine may have depleted the magma of ni and suggest the likely presence of a large magma chamber at depth xenoliths of ni rich olivine cumulates in the miki fjord macrodyke may have been sourced from such a body the location of thus far unidentified conduit or feeder zones to the macrodykes beneath the present day surface may represent potential targets for more massive sulphide orebodies

precipitation variations in the central zagros mountains iran since a d 1840 based on oak tree rings abstract we established three tree ring width chronologies from oak species in the central zagros mountains iran where instrumental climate data only cover a short period 1951 2010 due to high similarity of the individual ring width series we included all studied sites in a regional chronology covering 306 years correlation functions with regional climate data revealed significant positive correlations p

model evaluation for reconstructing the oxygen isotopic composition in precipitation from tree ring cellulose over the last century the oxygen isotope composition of tree rings is controlled by many factors including temperature amount of precipitation and changes in relative humidity in this study we present a modified leaf water model from dongmann et al radiation and environmental biophysics 11 1974 41 that can be used to calculate the isotopic composition of the source water and thus of precipitation that a tree used during the growing season the calibration of the model was accomplished by comparing a previously measured oxygen isotope tree ring chronology from central switzerland with the swiss network for isotopes in the hydrologic cycle station at bern from 1971 to 1995 and integrating temperature relative humidity data and ring width in particular our efforts focused on understanding the significance of the dampening factor f which we relate to changes in humidity and its variability over both the calibration period 1971 to 1995 and the study period 1913 to 1995 our results indicate that f ranging between 0 27 to 0 49 is variable based on correlation with relative humidity average daily temperature and ring width index using this model we have constructed a record of the oxygen isotope composition of precipitation during the growing season may through september for the last century in central western europe this approach can be potentially used in other locations where isotopic and meteorological data are available to extend records of the isotopic composition of precipitation back in time beyond observational records

the complete synthesis of seismic crustal phases at regional distances using a new method to evaluate green s functions for elastic layered media we compute complete synthetic seismograms at regional distances for an earthquake in the earth crust we choose as source parameters the ones inferred for an earthquake in central france and compare the computed seismograms to the ones recorded at several short period stations of the french seismic network the major features of the records including complexity and duration are well reproduced by the synthetics lg waves which are the prominant phase are shown to be guided waves made up of sh and sv waves incident on the moho at angles of incidence more grazing than the critical angle and multiply reflected within the crust the length of the computed lg wave coda extends between group velocities of 3 5 and 2 8 km s and is in good agreement with the data

petrochemistry of the okiep copper district basic intrusive bodies northwestern cape province south africa copper mineralization is associated with noritic and pyroxenitic rocks in the granulite facies metamorphic terrane in the okiep district of namaqualand in the northwestern cape province of south africa these bodies have been interpreted to be postmetamorphic and the mineralization has been inferred to be magmatic however the sulfide mineralogy of many of the orebodies is dominated by bornitc whereas immiscible magmatic sulfide ores contain pyrrhotite and chalcopyrite hence the okiep ores cannot be primary magmatic sulfides geochemical evidence is presented to demonstrate that the ores have undergone an extensive oxidative event in which pyrrhotite and chalcopyrite were converted to magnetite and bornite up to 90 percent of the sulfur has been lost in the case of some samples from the carolusberg mine the high fe 2 o 3 tio 2 and cu s ratios the low s se ratio of whole rock samples and their variation in different orebodies provide quantitative evidence for this process it is possible to recalculate the original sulfide from these data and a cu content of approximately 10 percent is indicated however these ores only contain on the order of hundreds of parts per million of ni and so the cu ni ratio is extremely high compared to that of most sulfide ores derived from a differentiated basic magma the textural and mineralogieal evidence for this oxidation is best seen in samples from the carolusberg mine in many of the other mines a later low temperature hydrothermal alteration has obliterated the evidence for these reactions

the kap gustav holm tertiary plutonic centre east greenland the plutonic centre is exposed on the narrow headland of kap gustav holm in east greenland it was emplaced into the hinge zone of a major crustal flexure that developed during initial rifting between greenland and northwest europe the earliest intrusion is a funnel shaped tholeiitic gabbro that was emplaced into the developing flexure probably about 55 ma ago the intrusion comprises a basal contact zone of gabbro 100m thick showing syn plutonic deformation and recrystallization a lower zone of massive olivine gabbro 250 1500 m thick and an upper zone of layered gabbro with a minimum thickness of 500 700 m all are cut by sheets of gabbro pegmatite abrupt reversals in cryptic and phase layering suggest that the gabbro intrusion is the result of several injections of magma the gabbro intrusion was tilted steeply seawards before emplacement of plutons and sheets of monzonite syenite and granite about 50 ma ago the main monzonite body forms a vertical cylinder 2 5 km in diameter with saucer shaped mineral graded layering and abundant volcanic inclusions regular stratigraphic variation in the composition of plagioclase and augite with structural height is interrupted by an abrupt reversal suggesting emplacement of a new pulse of magma syenite forms ring dykes and partial ring dykes of two distinct compositions an older subalkaline syenite related to the monzonite and gabbro and a younger mildly peralkaline syenite granite forms a small composite pluton abundant syn plutonic bodies of microdioite are associated with monzonite syenite and granite intrusions

textural maturity of cumulates a record of chamber filling liquidus assemblage cooling rate and large scale convection in mafic layered intrusions textural maturity describes the extent to which a rock has evolved from the initial reaction controlled texture towards textural equilibrium controlled by the minimization of interfacial energy solidification in a magma chamber results in the formation of an impingement texture by the random juxtaposition of planar sided grains orthocumulates in which the initial melt filled pores are pseudomorphed by later crystallizing phases have an ophitic or intersertal texture immediately after complete solidification which then evolves towards solid state equilibrium by rounding of initially planar grain boundaries and an increase in the median dihedral angle subtended at the junctions of two primocrystic grains with the interstitial phase the bulk of the increase in angle occurs just below the solidus temperature in kilometre scale mafic plutons quantification of textural maturity via measurement of dihedral angle populations in troctolitic and gabbroic cumulates from the rum eastern layered intrusion and the skaergaard intrusion demonstrates that the rocks preserve a record of thermal events related to magma chamber replenishment and the onset of chamber wide convection textural maturity is also a function of the liquidus phase assemblage for systems in which only olivine and plagioclase are liquidus i e cumulus phases in the main magma body above the crystal mush the texture is significantly less mature than that in systems in which clinopyroxene is an additional liquidus phase the difference in textural maturity reflects differences in the cooling and solidification rate and demonstrates directly that the liquidus phase assemblage plays a role in determining the thermal history of plutons

a view of the lower crustal component of hydrothermal systems at the mid atlantic ridge an extensive suite of hydrothermally altered gabbros was recovered by alvin and dredging from the mid atlantic ridge in the vicinity of the eastern ridge transform intersection rti of the kane fracture zone mark where tectonic extension has provided a window into the lower crustal component of hydrothermal cells four alteration types are distinguished on the basis of metamorphic assemblage mineral composition and deformation textures a conceptual model is presented that places temperature fluid rock ratio relationships in conjunction with styles of deformation into a spatial and temporal framework exsolution of late stage magmatic fluids in the vicinity of the magma hydrothermal interface at temperatures 700 c marks the onset of fluid rock interaction in the mark gabbros kelley et al this issue with subsequent alteration involving seawater derived fluids being strongly influenced by deformation mechanisms in zones of ductile shear hydration was initiated at temperatures between 550 and 700 c and moderate fluid rock ratios elsewhere in the lower crust the onset of seawater penetration occurred at temperatures of 400 550 c and was facilitated by brittle fracturing early vein networks indicate very low initial fluid rock ratios and are interpreted as being related to the solidification of plutons later fractures indicate higher water rock ratios and may be related to the downward propagation of shallow fault systems throughout the crust fluid rock interaction ceased at temperatures 180 300 c subsequent cataclastic deformation associated with the unroofing and emplacement of crustal blocks in the rti massif produced moderate fluid rock ratios within localized zones hydrothermal alteration in the crustal section exposed at mark was initiated at lower temperatures and water rock interaction proceeded to lower temperatures than many other plutonic suites these differences must reflect the temporal and spatial evolution of magmatic and tectonic extension that is particular to each section of sampled crust

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

fluorian garnets from the host rocks of the skaergaard intrusion implications for metamorphic fluid composition zoned silica deficient calcic garnets containing up to 5 mol f substitution for 0 formed during contact metamorphism of basalts by the skaergaard intrusion in east greenland fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30 70 m from the intrusion paragenetically equivalent phases include fluorite wollastonite calcic clinopyroxene prehnite quartz and calcite electron microprobe analysis shows that the garnets are 93mol grossular andradite grandite solid solutions and that the f content does not fully compensate for the silica deficiency suggesting the presence of a hydrous component in the garnets the garnets display discontinuous zoning with respect to al and fe and increases in f calculated oh and the si deficiency with increasing al concentration are observed the garnets formed at temperatures between 200 and 420 c based on the coexisting mineral assemblage and stratigraphic reconstructions indicate pressures of 1 kbar assessment of isobaric isothermal phase relations in the system cao a1203 si02 h20hf allows estimation of fluid characteristics in equilibrium with fluorian grandite bearing assemblages the presence of fluorite wollastonite quartz and calcite with these garnets combined with fluid inclusion data require that the activity a of h20 was 1 and that ah af was 10 105 to 10 10 0in the coexisting hydrothermal solutions at 200 420 c and 1 kbar if ph was neutral at these pressure and temperature conditions 5 3 0 1 the value of af associated with fluorian garnet formation was 10 4 7to 10 52 the f content of garnet is extremely sensitive to minor changes in fluid composition the calculations show that a decrease in ph or an increase in log af of 0 3 at constant pressure and temperature will decrease the f concentration in garnet from 5 to 0 mol the results of this study show that fluorian hydrous grandites provide a mineralogical record of the activities off species in coexisting metamorphic and hydrothermal fluids

comparison of stable carbon isotope ratios in the whole wood cellulose and lignin of oak tree rings abstract the stable carbon isotope ratios 13c of whole wood cellulose and acid insoluble lignin from annual latewood increments of quercus robur l from modern and sub fossil wood were measured and their potential use as palaeoenvironmental indicators examined the resulting time series demonstrate a very high degree of coherence with 13c of cellulose isotopically enriched by approximately 3 compared to 13c of lignin the 13c values of all three components are influenced by the climate of july and august modern whole wood retains the strongest climate signal perhaps because its composition is closest to that of leaf sugars in sub fossil wood there is no evidence that differential decay leads to fractionation of carbon within either cellulose or lignin but differential decay can alter the cellulose to lignin ratio

a gold and platinum mineralized layer in gabbros of the kap edvard holm complex field petrologic and geochemical relations the lower layered series a cumulates of the kap edvard holm complex contain a stratiform layer 1 to 20 m thick and 6 km long that is mineralized with gold and platinum group elements pges the lower layered series a cumulates 650 m thick are dominated by modally layered gabbro with lesser volumes of granular anorthosite and troctolite that together form 2 to 30 m thick layers that are most abundant above the mineralized layer minor volumes of poikilitic wehrlite form a few 1 to 2 m thick layers throughout the section field and petrographic relations as well as cryptic variations in cumulus mineral compositions indicate that the lower layered series a formed in an open system magma chamber from repeated magma injections within the mineralized layer average concentrations over 3 m thickness are 250 ppb pt 40 ppb pd and 50 ppb au with individual samples containing up to 5 ppm pt and 6 ppm au the concentrations of ir os ru and rh are uniformly low 20 ppb stratigraphic zoning of pt pd and au is consistent along strike with peak au concentrations overlying pt and pd peaks platinum minerals are primary pt fe alloy sperrylite and moncheite with secondary pt sulfide overgrowths gold occurs as alloys with ag and cu these minerals are found in contact with primary and secondary silicates and oxides and with intercumulus base metal sulfides that consist of the assemblage bornite chalcopyrite digenite deposition of the mineralized layer is associated in space and time with injections of plagioclase saturated primitive magma that mixed with more evolved resident magma these events caused efficient partitioning of au and pge into sulfides derived from a large volume of magma deposition of these sulfides to form the mineralized layer and subsequent deposition of the overlying anorthosite layers the wehrlite layers however were formed by postcumulus reactions between gabbro cumulates and hydrous intercumulus melts probably derived from the compacting cumulus pile subsolidus reactions between primary minerals and meteoric hydrothermal solutions caused extensive alteration of the mineralized gabbro oxidation and desulfurization of cu fe sulfides and local recrystallization of pge minerals

oxygen isotope exchange and mineral alteration in gabbros of the lower layered series kap edvard holm complex east greenland multiple intrusions of gabbros mafic dikes and syenites in the kap edvard holm complex gave rise to prolonged circulation of meteoric hydrothermal solutions and extreme isotope exchange and mineral alteration in the 3600 m thick lower layered series gabbros in the lower layered series 18o of plagioclase varies from 0 3 to 5 8 and it decreases with an increase in the volume of secondary talc chlorite and actinolite in the same gabbros pyroxenes have a more restricted range in 18o from 5 0 to 3 8 and values of 18opyroxeneare independent of the abundance of secondary minerals which ranges from 14 to 30 these relations indicate that large amounts of water continued to flow through the rocks at temperatures of 500 600 c altering the gabbros to assemblages of talc chlorite actinolite epidote albite and causing significant oxygen isotope exchange in plagioclase but not in pyroxene the extensive low temperature secondary mineralization and 18o depletion of plagioclase in the lower layered series are associated with the later emplacement of dikes and gabbros and syenites which created new fracture systems and provided heat sources for hydrothermal fluid circulation this produced subsolidus mineral alteration and isotope exchange in the lower layered series that are distinct from those in the skaergaard and cuillin gabbros of the north atlantic tertiary province but are similar to those observed in some oceanic gabbros

low stable isotope ratios of tropical cyclone rains tropical cyclone rains have distinctly lower stable isotope ratios than rains in other tropical and summer precipitation systems with a mean value slightly above that of water vapor near the sea surface the isotope ratios also decrease radially inward to the eye wall but appear to be anomalously low even near the periphery of the rain shield these findings indicate that tropical cyclones are highly efficient precipitation systems and suggest the use of stable isotope ratios as dynamic tracers of a tropical cyclone s water and energy budgets

weathering of pge sulfides and pt fe alloys in the freetown layered complex sierra leone fresh and weathered rocks and saprolite from horizon b of the freetown layered complex contain platinum group minerals pgm the pgm in the fresh rocks are 1 7 m across including cooperite pts isoferroplatinum pt3fe minor tetraferroplatinum ptfe tulameenite pt2fecu os bearing laurite rus2 and other base metal sulfide bms bearing pgm the weathered rocks contain fewer of those pgm but a high proportion of disordered cu pd bearing pt fe alloys the saprolite hosts scarce smaller 1 3 m ordered ptfe and disordered ptfe3 the pt fe alloys became increasingly fe rich as weathering proceeded pt fe oxides appeared during weathering copper sulfides associated with the primary pgm and cooperite with 3 pd were destroyed to provide the minor cu and pd found in some of the disordered pt fe alloys platinum and pd bearing saprolites have retained the original rock fabric and to a depth of about 2 m surround residual rocks that show progressive weathering corestones ground water passing through the saprolite has transported pt and pd and probably au in solution down slope into saprolite over unmineralized rocks transport is marked by changes in the pt pd ratio indicating that the metals have moved independently palladium is present in marginally higher concentrations in the deeper saprolite than in the corestones suggesting some retention of pd in the deeper saprolite platinum and pd are less concentrated in the upper saprolite than the deeper saprolite indicating surface leaching alteration occurred over a long period in an organic and microbial rich environment that may have contributed to the leaching and transport of pge

oceanic faulting and fault controlled subseafloor hydrothermal alteration in the sheeted dike complex of the josephine ophiolite based upon detailed mapping 1 10 and 1 100 of a large water polished outcrop of the sheeted dike gabbro transition zone in the josephine ophiolite of nw california and sw oregon the following history of alternating episodes of magmatic structural and hydrothermal events has been documented using crosscutting relationships petrography geochemistry and strontium and oxygen isotopic data 1 crystallization of gabbro and later subvertical mafic dike injection 2 amphibolite facies metamorphism 3 extensional faulting and tilting of dikes 4 continued faulting tilting and dike injection associated with retrograde metamorphism at greenschist facies conditions 5 continued extensional faulting and tilting synchronous with the development of a variety of hydrothermal veins at decreasing temperature and increasing fluid rock ratios and 6 subvertical injection of a highly fractionated dike which truncates all previous features features 1 5 trace element geochemistry indicates the highly fractionated dike feature 6 is genetically related to the other dikes and thus was intruded at or near the paleospreading axis hence all previous events features 1 5 can be constrained to have occurred at the rift axis including large scale tilting 50 of the sheeted dikes and extensional faulting the 87sr 86sr initial ratios from recrystallized whole rocks and from hornblende epidote and prehnite separates from veins display a systematic increase with relative age from 0 7033 for altered gabbro screens and mafic dikes to 0 7049 for prehnite in the youngest oceanic fault rock calculated oxygen isotope fluid compositions for the same suite of samples range from 18ofluid 5 to 1 with time indicating a change to a seawater dominated hydrothermal system with time consistent with observed increased permeability due to seafloor extensional faulting the crosscutting relationships alteration mineral assemblages and isotopic data suggest 1 an early stage of high temperature 450 c hydrothermal alteration with low permeability i e grain scale flow followed by 2 a decrease in temperature 350to 200 c and an increase in permeability due to faulting and accompanied by tectonic tilting at the rift axis the consistency of these crosscutting relationships at similar pseudo stratigraphic levels at different localities in the josephine ophiolite suggests that alternating magmatic and structural extension with synchronous retrograde alteration is common in crust formed at similar rates of spreading slow to intermediate spreading centers such as the modern mid atlantic ridge

geothermal type alteration in a burial metamorphosed volcanic pile central chile the upper cretaceous and tertiary volcanic sequences in the chilean andes are affected by burial metamorphism for example in central chile between 32 30 and 35 s the abanico formation a folded upper cretaceous to palaeogene unit composed of basic lavas tuffs and ash flows of intermediate composition and volcaniclastic sandstones is characterized by heulandite to laumontite bearing zeolite facies assemblages in its upper part passing with depth to prehnite pumpellyite facies assemblages however at c 33 30 s in the abanico hill area located just east of a graben at santiago the longitudinal central valley the alteration pattern is unrelated to stratigraphic depth it is characterized by a lateral increase in grade defined by assemblages with yugawaralite reported for the first time in the andes laumontite then wairakite epidote and finally with abundant epidote successively closer to the graben boundary this pattern was formed in a palaeogeothermal system with a high t and a very low p gradient geothermal alteration has also been inferred from the border zone of a neogene caldera in the abanico hill area and from the western fault boundary of the graben these expressions of geothermal alteration together with the occurrence of caldera structures the huge volume of ignimbrites and numerous epithermal precious metal deposits of late cretaceous and tertiary age in central and northern chile suggest that fossil geothermal systems of this age are probably common features in the chilean andes

regional hydroclimate and precipitation δ18o revealed in tree ring cellulose δ18o from different tree species in semi arid northern china abstract oxygen isotopic ratios 18o of tree ring cellulose grown from 1954 to 2003 in semi arid northern china demonstrate a common inter annual variability despite coming from three different species in two distinct growth environments an alpine meadow and a rocky ridge the variability was significantly negative correlated with precipitation and relative humidity during the growing season this suggests that the past summer hydroclimate can be inferred from tree ring cellulose 18o from various kinds of trees growing in semi arid northern china in addition we evaluated past changes in 18o of precipitation from the tree ring cellulose 18o and relative humidity using the mechanistic model for tree ring cellulose 18o in roden et al 2000 by fixing the species dependent exchange rate of oxygen between carbohydrate and xylem water for larix principis rupprechtii and picea koraiensis we could also reconstruct the variations in precipitation 18o from the different tree species which are similar to the observed 18o of precipitation during 1985 2002 although the reconstructed 18o of precipitation does not have any significant relation to local temperature or precipitation during 1954 2003 its long term variation pattern is similar to that of the asian summer monsoon indices and 18o of stalagmite in the heshang cave 30 27 n 110 25 e fig 1 suggesting that 18o of precipitation is not controlled by local meteorology but is influenced by large scale atmospheric circulation

fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration rocks from the lower oceanic crust show both petrologic and isotopic evidence for extensive alteration by circulating hydrothermal fluids derived from seawater deeply circulating fluids may have a substantial but as yet largely undetermined impact on the thermal regime of spreading centers magmatic processes at mid ocean ridges and elemental fluxes at ridge hydrothermal systems in the present study the consequences of water rock interactions during the penetration of seawater into hot lower oceanic crust were investigated using thermodynamic reaction path models alteration assemblages predicted for reaction of an evolving seawater with olivine gabbro gabbronorite and troctolite during heating from 300 to 900 c closely resemble alteration assemblages observed in rock samples from the lower oceanic crust these assemblages include sodic plagioclase actinolite diopsidic clinopyroxene epidote chlorite prehnite analcime quartz at lower temperatures 300 500 c and plagioclase hornblende diopside chlorite trace magnetite at intermediate temperatures 500 700 c the relative abundances of these alteration products show much greater variation with temperature than with water rock w r ratio indicating that variations in the amounts of hydrated minerals such as amphiboles may not be an accurate indication of the w r ratio experienced by rocks in the lower crust since the same amount of fluid may produce widely differing amounts of amphibole at slightly different temperatures depending on the temperature of interaction some rocks in the lower oceanic crust may have experienced much higher w r ratios than has previously been proposed based on the amount of amphibole present at higher temperatures 750 900 c the models predict that very little alteration occurs before the fluid equilibrates with the rock producing only trace amounts of amphibole as an alteration phase with the remainder of the rock retaining its igneous mineral composition essentially unchanged this result suggests that extensive penetration of rocks by aqueous fluids may occur in the lower ocean crust at temperatures 700 c and leave very little conspicuous petrologic evidence for their presence such cryptic alteration is consistent with isotopic evidence for hydrothermal alteration of oxygen and sr isotopes by seawater in lower ocean crust rock samples which otherwise retain their igneous compositions and textures taken together the model results allow for much more extensive circulation of fluids in the lower oceanic crust and at much higher temperatures than has been proposed by previous studies based on petrologic interpretations

magma mixing and constitution zone refining in the lac des iles complex ontario genesis of platinum group element mineralization the lac des iles complex is a 2 74 ga old composite intrusion emplaced into a granite and or granite gneiss terrane of the wabigoon subprovince northwestern ontario the complex consists of a gabbroic and ultramafic part the latter has been subdivided into northern and southern intrusive phases both the gabbroic and ultramafic parts contain platinum group element bearing ni cu sulfide mineralization although only the roby zone in the gabbro is of economic importance the southern ultramafic complex consists of a wehrlite to olivine clinopyroxenite core which is surrounded by websterite and gabbronorite cumulates petrographic and geochemical studies suggest that the northern ultramafic complex consists of at least eight cyclic units which ideally are composed of dunite and wehrlite to olivine clinopyroxenite cumulates at the base followed by clinopyroxenite and websterite locally grading into gabbronorite this indicates similar crystallization sequences in both ultramafic centers olivine olivine clinopyroxene clinopyroxene clinopyroxene orthopyroxene or plagioclase in the ultramafic complex platinum group element bearing sulfide mineralization occurs at the top of cyclic units in websterite and orthopyroxenite cumulates sulfide bearing samples up to 1 wt sulfide are enriched in au pd pt and cu relative to ni ir os and ru with pd ir ratios on the order of 250 sulfide immiscibility probably was caused by mixing of fractionated residual melt with more primitive liquid which periodically intruded the magma chamber evidence of mixing is seen in gradational chemical variations across the interface of cyclic units and in the occurrence of inclusions of olivine crystals and crystal aggregates in websterite and gabbronorite cumulates these inclusions are not in equilibrium with their present host rock and presumably formed before mixing in the more primitive magma a mineralized orthopyroxenite cumulate at the top of cyclic unit 2 could not have been produced by the normal crystallization sequence consideration of the phase relationships in the ternary system olivine clinopyroxene plagioclase quartz suggests that these cumulates are the crystallization product of a hybrid magma formed during magma mixing at the interface of cyclic units the gabbroic complex consists mainly of largely altered gabbro and gabbronorite cumulates and is intruded by mafic ultramafic dikes the center of the gabbroic complex contains the economically important roby zone with its platinum group element bearing cu ni sulfide mineralization this is a lithologically and texturally very complex zone in which high grade platinum group element mineralization is associated with pegmatite and mafic ultramaflc dikes the roby zone is characterized by strong enrichments of au pd and pt relative to ir and os and by variable but extremely high pd ir ratios of greater than 10 000 high au pt and pd pt ratios indicate a fractionation of pt from au and pd it is suggested that the high volatile content of the residual magma of the gabbroic complex triggered partial remelting of surrounding gabbro cumulates a process called constitutional zone refining by mcbirney 1987 during the partial melting event compatible elements such as ir and os are buffered by the residual silicate and oxide mineralogy whereas incompatible elements such as au pd and pt as well as volatile components such as h 2 o and h 2 s become highly concentrated in the partial melt phase eventually this newly formed magma may become sulfide saturated either by cooling and fractional crystallization or due to the continuous dissolution of sulfides when the zone of melting proceeds through the gabbro cumulates ratios such as pd ir and pd pt would strongly depend on the degree of remelting and fractional crystallization until the time of sulfide saturation the matrix of the varitextured zone is interpreted as the residuum of this melting process whereas pegmatoids and pegmatites segregationlike gabbro phases and quartz bearing plagioclase and incompatible element rich dikes are regarded as the final crystallization products of the partial melting

horizontal and vertical variations in noble metal distribution in the great dyke of zimbabwe a model for the origin of the pge mineralization by fractional segregation of sulfide abstract a study based largely on diamond drilling undertaken specifically for research purposes has shown that in the darwendale subchamber of the great dyke of zimbabwe there are three principal sulfide zones that are located in subunits 1a and 1b of cyclic unit 1 sulfide zone 1 the main sulfide zone msz is subdivided into three subzones the base of the msz occurs at the top of the main bronzitite layer of cyclic unit 1 extending into the overlying websterite the noble metals are concentrated at the bases of each sulfide zone and subzone and decrease in concentration rapidly upwards whereas variations in the concentrations of base metals such as cu correlate well with variations in the amounts of sulfide across each zone when calculated in terms of their concentration in 100 sulfides it is found that pd decreases upwards most rapidly followed by pt and then au with the cu concentration remaining essentially constant the decrease of the noble metals is interpreted in terms of simple rayleigh fractionation as the consequence of the removal of sulfide the observed correlation between the tops and bottoms of sulfide zones with small variations in the mg number of bronzite is taken to indicate that in zones 2 and 3 sulfide segregation started as a result of crystallization increasing the s content of the resident magma in the chamber until it reached that of sulfide saturation coupled with fresh inputs of sulfide unsaturated more primitive magma causing the resident magma to become unsaturated again this recharge by primitive magma also raised the pge content of the sulfides segregating from the trapped intercumulus liquid indicating that the resident magma was becoming recharged in pge in this way subunits i and ii of sulfide zone 1 are thought to contain too much sulfide to be explicable in this way and it is suggested that mixing with a plagioclase saturated magma possibly generated around the flanks of the intrusion was responsible for these subunits the sulfides of each of the sulfide zones are more concentrated at the margin than at the axis of the great dyke but have a lower tenor of noble metals it is proposed that the axially located sulfides were the consequence of magma sulfide equilibration at a higher r factor magma sulfide ratio than those at the margin the magma sulfide partition coefficients required to explain the percentage difference in the tenors of the different noble metals between axis and margin in this way are the same as those required to explain the vertical variations in noble metal tenor in terms of the fractional segregation model

the skaergaard layered series part vii sr and nd isotopes the initial isotopic ratios of strontium and neodymium in the skaergaard layered series vary both vertically and laterally on every scale from the intrusion as a whole down to coexisting minerals in a single rock the magma that filled the skaergaard chamber was contaminated to various degrees with the metamorphic rocks through which it rose and was never completely homogenized after being intruded the contamination was most pronounced in contact zones and aureoles around rare xenoliths the greater concentrations of lithophile trace elements in the upper border series was previously attributed to assimilation of buoyant fragments of gneiss that collected under the roof but most of the rocks of the upper border series are isotopically indistinguishablefromthoseofthelayeredseries itisdoubtful therefore that this part of the intrusion assimilated much more of the metamorphic basement than did the rest of the magma similarly the marked increase in the concentrations of excluded elements in the upper part of the layered series is not matched by a change in the isotopic character of the rocks and cannot be attributed to a later influx of new magma analyses of minerals separated from rocks with exceptionally mafic or felsic modal compositions revealed marked inhomogeneities in the isotopic compositions of their constituent minerals for example coexisting plagioclase and pyroxene from closely associated anorthosites and pyroxenites have very different initial isotopic ratios of both strontium and neodymium the same is true of mafic and felsic layers in modally graded gabbros these differences are unrelated to the low temperature alteration shown by oxygenisotopes they must have been introduced when the original gabbro was largely crystallized and underwent local metasomatic replacement by nearly mono mineralic mafic and felsic assemblages

an ocean ridge type magma chamber at a passive volcanic continental margin the kap edvard holm layered gabbro complex east greenland the gabbros of the tertiary kap edvard holm layered serieshave a stratigraphic thickness of more than 5000 m earlier work has shown that the range in cumulus mineral compositions is restricted plagioclase an 81 an 51 olivine fo 85 fo 66 pyroxenes ca 43 mg 46 fe 11 to ca 43 mg 37 fe 20 field evidence of magma injections is common which together with the restricted range in mineral chemistry suggests that the magma chamber was frequently replenished by a less fractionated magma a detailed study of a 600 m section 900 1500 m in the lower layered series reveals a period of crystallization when the magma chamber behaved as a closed system 900 1300 m the rocks formed during this periodare well laminated olivine gabbros 900 110 m which evolved to well laminated oxide gabbros 1100 1300 m compositional trends in the cumulusminerals are towards more evolved compositions plagioclase an 64 an 58 pyroxene mg from 80 to 76 with stratigraphic height from 1300 m to 1500 m granular olivine gabbros dominate with moreprimitive mineral compositions plagioclase an 67 an 76 pyroxene mg from 78 to 82 the transition olivine gabbro to oxide gabbro at 1100m is a consequence of fractional crystallization and it is shown how changes in activities of feo and fe 2 0 3 in the magma are reflected in the total iron content of plagioclases the transition from oxide gabbro to olivine gabbro at 1300 m results from replenishment by less evolved basaltic magma on the basis of calcic pyroxene chemistry and the mineral crystallization sequence it is concluded that the kap edvard holm layered series crystallized from a tholeiitic magma similar to morb melanogabbroic units occur throughout the intrusion as discordant to subconcordant sill like bodies 0 2 2 0 m thick the melanogabbroic units consist of cr rich augite olivine plagioclase heteradcumulates and contain deformed mica crystals of pre emplacement origin these units crystallized from a wet mgo rich magma which was injected into the layered host gabbros after the formation of the cumulus pile but before the magma was completely solidified the kap edvard holm layered series has several parallels with the plutonic part of ophiolite sequences these include cumulus mineral assemblage compositions of the minerals and the restricted range in compositions with stratigraphic height field evidence of repeated replenishment of basaltic magma dyke swarms overlying the roof zone of the magma chamber and the existence of a late intrusive suite of wet mgo rich magma these parallels suggest that the processes involved in the formation of the kap edvard holm layered series were similar to those involved in the formation of the crustalpart of many ophiolites and beneath present day spreading ridges the kap edvard holm layered series is therefore believed to represent a shallow level magma chamber which acted as a reservoir for basaltic flows at the continental margin during the opening of the north atlantic ocean

orogenic gold mineralisation hosted by archaean basement rocks at sortekap kangerlussuaq area east greenland a gold bearing quartz vein system has been identified in archaean basement rocks at sortekap in the kangerlussuaq region of east greenland 35 km north northeast of the skaergaard intrusion this constitutes the first recorded occurrence of au mineralisation in the metamorphic basement rocks of east greenland the mineralisation can be classified as orogenic style quartz vein hosted au mineralisation two vein types have been identified based on their alteration styles and the presence of au mineralisation mineralised type 1 veins occur within sheared supracrustal units and are hosted by garnet bearing amphibolites with associated felsic and ultramafic intrusions gold is present as native au and au rich electrum together with arsenopyrite and minor pyrite and chalcopyrite in thin alteration selvages in the immediate wall rocks the alteration assemblage of actinolite clinozoisite muscovite titanite scheelite arsenopyrite pyrite is considered to be a greenschist facies assemblage the timing of mineralisation is therefore interpreted as being later and separate event to the peak amphibolite facies metamorphism of the host rocks type 2 quartz veins are barren of mineralisation lack significant alteration of the wall rocks and are considered to be later stage fluid inclusion microthermometry of the quartz reveals three separate fluids including a high temperature th 300 350 c h2o co2 ch4 fluid present only in type 1 veins that in interpreted to be responsible for the main stage of au deposition and sulphidic wall rock alteration it is likely that the carbonic fluids were actually trapped at temperatures closer to 400 c two other fluids were identified within both vein types which comprise low temperature 100 200 c brines with salinities of 13 25 wt eq nacl and at least one generation of low salinity aqueous fluids the sources and timings of the secondary fluids are currently equivocal but they may be related to the emplacement of paleogene mafic intrusions the identification of this occurrence of orogenic style au mineralisation has implications for exploration in the underexplored area of east greenland between 62 and 69 n where other similar supracrustal units are known to be present

spring precipitation variations over the western himalaya india since a d 1731 as deduced from tree rings 1 spring precipitation representative of regional scale features was reconstructed since a d 1731 using 15 site ring width chronologies of himalayan cedar cedrus deodara roxb ex lambert g don prepared from distantly located moisture stressed sites in the western himalayan region this is so far the strongest tree ring based precipitation reconstruction in terms of variance explained in the calibration model a d 1897 1986 from the western himalayan region the twentieth century experienced the driest and wettest years in the whole reconstructed series the 10 and 20 year means also indicate extreme precipitation periods in the twentieth century the increasing precipitation trend noticed in the reconstructed data of the late twentieth century closely matches with instrumental data

comment on geochemistry of tectonically expelled fluids from the northern coast ranges rumsey hills california usa by m l davisson t s presser and r e criss

the upper critical zone of the bushveld complex and the origin of merensky type ores the mg number mg mg fe atomic ratio of bronzite in each unit at the top of the critical zone of the bushveld complex decreases upward in a manner consistent with fractional crystallization the base of each unit is marked by an increase in the mg number suggesting that crystallization of fresh magma is responsible for the initiation of the unit bulk trace and major element concentrations in pegmatoids of the merensky reef which itself forms the basal part of one of a series of these cyclic units are similar to those in medium grained feldspathic bronzitite the base of each unit is also marked by pockets or a layer of sulfide with a higher ni cu and much higher pt cu ratio than the sulfides of the remainder of the unit thus the pt tenor alternates from high to low three times upward through the three units these data indicate strongly that the pt tenor was established with the stratigraphy of the rocks and are inconsistent with models calling upon upward migration of hydrothermal or magmatic fluids to enrich the sulfides in platinum group elements there are no features in the rocks to indicate that fluids could have been channeled to flow laterally for the tens to hundreds of kilometers occupied by continuous merensky reef a model based on that of campbell et al 1983 in which small amounts of sulfides form during injection of fresh magma as a turbulent plume and then settle after becoming thoroughly mixed with a large mass of magma accounts well for all of our observations and many other features of the upper part of the critical zone

oxygen isotope ratios of oak in east england implications for reconstructing the isotopic composition of precipitation annual latewood 18o values from oak quercus robur l are presented for the period 1895 1994 for four trees growing in eastern england we demonstrate using the 18o values of precipitation from wallingford 1982 1994 and the longer time series from groningen 1965 1994 that the 18o values of winter precipitation had the strongest influence on the 18o values of tree ring cellulose the influence of winter precipitation on the spring summer formed latewood may be explained by several factors most soil water is replenished during the winter water may take several months to penetrate the unsaturated zone and oaks may sample water from lower in the profile during times of water stress the 18o values of oak latewood cellulose were also significantly p 0 01 correlated with summer relative humidity therefore although precipitation 18o values may be altered by partial isotopic exchange with xylem water and the influence of stomatal conductance upon evapotranspiration some of the original 18o signature remains

sampling strategy and climatic implications of tree ring stable isotopes on the southeast tibetan plateau we explore the potential of tree ring cellulose d18o and d13c records for reconstructing climate variability in the southeast tibetan plateau our sampling strategy was designed to investigate intra and inter tree variability and the effects of the age of tree on d18o variation we show that intra tree d13c and d18o variability is negligible and inter tree coherence is sufficient to build robust tree ring d18o or d13c chronologies based on only four trees there is no evidence of an age effect regarding d18o in contrast with tree ring width in our warm and moist sampling site young tree d13c is not clearly correlated with monthly mean meteorological data tree ring d18o appears significantly anti correlated with summer precipitation amount regional cloud cover and relative humidity simulations conducted with the orchidee land surface model confirm the observed contribution of relative humidity to tree cellulose d18o and explain the weak correlation of d13c with climate by the non linear integration linked with photosynthesis altogether the tree ring cellulose d18o is shown to be a promising proxy to reconstruct regional summer moisture variability prior to the instrumental period 2010 elsevier b v

effects of h2o on phase relations during crystallization of gabbros in the kap edvard holm complex east greenland in the kap edvard holm complex of east greenland layered monly results in the formation of discordant igneous bodies within crystallizing cumulus sequences in some olivine gabbros host numerous small discordant bodies of ultramafic cases partially molten cumulates appear to have reacted rock and magnetite gabbro that formed by late magmatic metasomatic with liquids or fluids that originated within the cumulus replacement of partially solidified gabbroic cumulates similar repile resulting in resorption of cumulus minerals crysplacive rocks are also present as large semi conformable sheet like tallization of intrusive or replacive bodies and rebodies within the layered gabbro sequence replacive bodies of all distribution of mass within the intrusion e g robins sizes are spatially associated with xenoliths of metabasaltic lava 1982 butcher 1985 butcher et al 1985 helz 1987 the small bodies cluster around xenoliths and the large bodies host irvine 1987 boudreau 1988 mcbirney sonnenthal swarms of xenoliths the replacive bodies are inferred to have formed 1990 larsen brooks 1994 scoon mitchell 1994 by reaction of gabbroic cumulates with pore liquids that were mathez 1995 meurer et al 1997 boudreau 1999 in enriched in h2o by degassing or dehydration melting of the other cases partially molten cumulates are inferred to metabasalts as these liquids migrated through the cumulus pile have reacted with externally derived magmas that inthey resorbed plagioclase and produced ultramafic bodies where the truded the cumulus pile resulting in the development liquids came to rest they reacted with gabbroic cumulates to produce of discordant replacive bodies via the reaction of the bodies of magnetite rich gabbro the most evolved pore liquids cumulates with intruding magmas e g morse et al 1987 segregated to form hornblende rich pegmatitic dikes of roughly dacitic bedard et al 1988 tegner wilson 1993 tegner composition suggesting that hydration and possibly oxidation of the robins 1996 because cumulus rocks preserve records magma shifted the liquid line of descent from a tholeiitic trend toward of magmatic fractionation and replenishment in large a calc alkaline trend these inferences imply that contamination of mafic intrusions recognizing and understanding postmagmas by dehydration of hydrothermally altered crustal rocks may cumulus processes such as these can provide insights significantly influence the evolution of mafic magma systems into the evolution of mafic magma chambers and the differentiation of basaltic magmas within the crust near the western margin of the kap edvard holm

dehydration partial melting and assimilation of metabasaltic xenoliths in gabbros of the kap edvard holm complex east greenland

2 5d sh wave propagation in heterogeneous crustal wave guides using the phase screen method abstract one way approximations for regional phases slice the half space crustal wave guide into a number of slabs perpendicular to the propagation direction the moho discontinuity can be easily treated as a perturbation from the crustal background the advantage of one way propagation methods is their great saving of computing time and memory compared to full waveform numerical methods especially for 3d simulations in this article we present general 2 5d sh formulas for the thin slab method and a generalized screen propagator gsp for simulating sh wave propagation in the heterogeneous half space crustal wave guide comparisons of numerical results with a finite difference fd algorithm for a standard flat crustal model show excellent agreement demonstrating the validity and accuracy of the 2 5dgsp for the half space problem we then compare the curves of energy attenuation calculated by the 2d and 2 5d formulas the comparison shows that the energy attenuation of the 2 5d case is about 1 5 3 times greater than that of the 2d case when the trapped mode is formed the sh screen propagator is also used to simulate two laterally unvarying in the y direction crustal models showing the path effects on regional wave propagation

recrystallization and the origin of layering in the bushveld complex abstract three rock types are distinguished in this study a the layered rocks b the reef pegmatites which are parallel to the layering and form prominent marker horizons and c the iron rich ultramafic irum pegmatites which are transgressive to the layered rocks reaction textures are observed in the layered rocks adjacent to reef pegmatites and are compared with similar reaction textures from alteration zones adjacent to and caused by the iron rich ultramafic irum pegmatites these include a clinopyroxene coronas around orthopyroxene b hornblende lamellae along 100 of orthopyroxene c orthopyroxene altered to olivine serpentine talc and or chlorite in the alteration zones adjacent to irum pegmatites the textures were generated by interaction between the pegmatite forming fluid and the wallrocks a similar origin is proposed for reaction textures in the layered rocks in the latter case they were formed by the fluid responsible for the formation of reef pegmatites in the layered rocks the reaction textures were modified to variable degrees during and after the emplacement of reef pegmatites these modifications include in leuconorites a clinopyroxene coronas overgrown by feldspar b orthopyroxene overgrown by feldspar and hornblende lamellae transforming to biotite and in olivine pyroxenites c olivine serpentine textures overgrown by a second generation of orthopyroxene the modifications suggest the subsolidus dissolution of orthopyroxene and precipitation of feldspar in leuconorites and the reverse process in pyroxenites the textures suggest considerable transfer of matter in the solid rock due to a fluid gradient orthopyroxene recrystallized in areas with a high ah2o plagioclase in regions of low ah2o this process is believed to be responsible for the stratification of the rock into pyroxene and plagioclase rich layers spherical mineral inclusions are relict textures in the three main minerals chromite orthopyroxene and plagioclase a number of similarities between the different inclusions suggest a similar origin the high content of hydrous minerals in all three suggests their formation during the emplacement of reef pegmatites these hydrous minerals were then trapped in the recrystallizing plagioclase orthopyroxene and chromite also spherical mineral inclusions witness the late crystallization of pyroxene in melanorite pyroxenite and the crystallization of plagioclase in leuconorite anorthosites after the emplacement of reef pegmatites

the structure and geochemistry of the gabbro zone of the annieopsquotch ophiolite newfoundland implications for lower crustal accretion at spreading ridges the annieopsquotch ophiolite exposes a c 5 5 km thick section of tholeiitic gabbros sheeted dykes and pillow basalts based on the along strike consistency in thickness of the major crustal units and lack of significant throw on spreading related normal faults the annieopsquotch ophiolite is interpreted to have formed at an intermediate to fast spreading ridge the upper c 400 m of the gabbro zone is composed of massive texturally heterogeneous gabbros with compositions that approach those of the sheeted dykes and basalts below this is c 1 6 km of 10 30 m thick planar intrusive sheets or sills the lowermost part of the gabbro zone is composed of gabbroic rocks with relict troctolite and troctolitic gabbro enclaves which are veined and partly replaced by gabbro and pyroxenite sill contacts within the central sill dominated part of the gabbro zone are sub parallel to boundaries between the major ophiolite lithostratigraphic units the upper and lower contacts of individual gabbro sills may have finer grain sizes indicating that the intrusions cooled from the top and bottom locally well preserved comb structures crescumulates indicate downward growth supporting a sill interpretation the sills are composed of weakly or un deformed plagioclase clinopyroxene olivine cumulates trace element modeling suggests that the parental magmas of these cumulates had compositions very similar to the overlying sheeted dykes and basaltic lavas as do dykes emplaced within the gabbro zone model liquids calculated from the gabbroic sills generally become more evolved up section indicating that magma evolution in the annieopsquotch ophiolite was dominated by fractionation in lower crustal conduits below the level of a putative axial melt lens aml the model liquids sheeted dykes and basalts preserve a similar wide range of compositions which may indicate that aggregation homogenization and fractionation in an aml was inefficient similar intra conduit fractionation of mantle derived melts might also contribute to morb evolution at mid ocean ridges

tertiary plutons monitor climate change in east greenland the d values of amphibole and biotite in tertiary plutons in central eastern greenland decreased by 30 between 55 and 50 ma and then increased by 35 between 50 and 43 ma the d values of amphibole and biotite in in the plutons range from 160 to 123 these low values reflect isotopic exchange between the igneous rocks and hydrothermal fluids that were dominated by meteoric water the changes in mineral d values between 55 and 43 ma are explained most plausibly by shifts in the isotopic composition of meteoric waters that fed hydrothermal recharge areas at 50 ma uplift related to the iceland mantle plume elevated hydrothermal recharge areas by 1 2 km high altitude low d meteoric waters collected by the uplifted recharge areas caused the 30 decrease in mineral d values between 55 and 50 ma the subsequent increase in mineral d values from 50 to 43 ma corresponds to widening of the north atlantic ocean and a change from continental to maritime climate thus tertiary plutons in central eastern greenland represent a network of paleoclimate stations that monitored the d of meteoric water during opening of the north atlantic ocean basin

finite difference seismograms for sh waves the accuracy of the finite difference method for generating synthetic seismograms of sh wave propagation in cylindrically symmetric media is discussed the finite difference method has the advantage that arbitrary density and velocity fields in the medium may be specified a point source is generated by a simple transformation of a line source the accuracy of the finite difference seismograms in flat and dipping layered media is confirmed by comparison with the generalized ray method a source radiation pattern is inserted by introducing a near field which has permanent displacement near the source strong motion synthetics are constructed with this new method for the 1968 borrego mountain earthquake as recorded at el centro good fits to the data are achieved using the laterally varying model determined by a detailed refraction survey and the source parameters determined by teleseismic waveform modeling shallow faulting is no longer necessary to explain the long period surface wave development

formation of wehrlites through dehydration of metabasalt xenoliths in layered gabbros of the noe nygaard intrusion southeast greenland the noe nygaard intrusion is a 4 2 5 km stock composed of layered gabbros and wehrlites within the precambrian basement of the coastal mountains west of the kialineq plutonic complex transgressive relationships to tertiary mafic dykes and the occurrence of abundant metabasaltic xenoliths signify a tertiary age for the intrusion the intrusion is characterized by alternating zones of gabbro and wehrlite gabbro is both intruded and replaced by wehrlite and the wehrlite zones are characterized by abundant metabasaltic xenoliths based on 87 sr 86 sr ratios mica olivine and oxide gabbros are all cumulates crystallized at different differentiation stages from a common parental magma field relations together with similarities in strontium isotope ratios and in the major and rare earth element ree mineral chemistry between gabbros and wehrlites indicate that the wehrlite bodies were formed by the dissolution of plagioclase from a gabbro cumulate mush by h 2 o derived from dehydration and the partial assimilation of metabasaltic xenoliths in terms of their ree characteristics melts from which the noe nygaard intrusion crystallized are within the compositional range of melts for other early tertiary mafic ultramafic complexes of east greenland however they were generated at a greater mean melting pressure and have less radiogenic strontium isotope ratios than the nearby imilik mafic ultramafic complex supporting existing models for mantle heterogeneity at the time of continental break up the abundance of metabasaltic xenoliths in the noe nygaard intrusion provides further evidence for the lateral extent of the north atlantic flood basalt province which onshore has been mostly removed by glacial erosion south of 68 n in greenland

assimilation and fractionation in adjacent parts of the same magme chamber vandfaldsdalen macrodike east greenland the vandfaldsdalen macrodike which lies in the skaergaard region of east greenland is a remarkably zoned fossil magma chamber with a granophyric cap overlying cumulate gabboros the intrusion is distinctly bimodal with a large compositional discontinuity at the contact between the gabbro and granophyre although the exposed part of the macrodike is in contact with tertiary basalts and sediments the granophyre originated by assimilation of xenoliths derived from the underlying archean basement sr and nd isotopic ratios throughout the cumulate sequence are remarkably similar indicating insignificant contamination of the gabbro by the granophyre modelling of the compositional effects of cooling and crystallization indicate that the cumulate pile resulted from fractional crystallization with the complicating effects of trapped liquid and post cumulus fractionation the uppermost rocks in the mafic part of the chamber sio2 62 feo 12 4 resulted from about 85 fractional crystallization a transgressive sill of strongly fractionated magma sio2 67 feo 8 8 formed from extracted intercumulus liquid that was the result of 90 fractional crystallization of the original magma mass balance indicates that typical granophyre is made up of about 75 dissolved xenoliths by weight and 25 mantle derived basaltic magma the magmas were not measurably affected by material exchange across the interface between the gabbro and granophyre this magma chamber evolved by both assimilation and fractional crystallization but the residual liquids formed by fractional crystallization were unaffected by assimilation heat exchange between were unaffected by assimilation heat exchange between the two parts of the chamber was obviously important but there was insignificant material exchange the inability of fractional crystallization and assimilation to affect the same liquid is related to the dynamic behavior of this particular magma chamber particularly the buoyancy of granophyre relative to evolving tholeiitic magma

propagation and attenuation characteristics of the crustal phase lg thelg wave consists of the superposition ofs waves supercritically reflected and thus trapped in the crust this mode of propagation explains the strong amplitude of this phase and the large distance range in which it is observed the numerical simulation leads to successful comparison between observed seismograms in stable continental areas and synthetics computed for simple standard crustal models in regions with strong lateral variations the influence of large scale heterogeneities on thelg amplitude is not yet clearly established in terms of the geometrical characteristics of the crustal structure

δ18o values of tree rings as a proxy of monsoon precipitation in arid northwest china abstract it is important to understand the history and dynamics of east asian monsoon system which is the key control of environmental conditions in china this work investigates the relationship between precipitation amount and oxygen isotopic compositions recorded in tree ring cellulose as a potential tool for reconstruction of summer monsoon strength in arid northwest china we found a significant positive correlation between the total annual precipitation and the 18o value of tree rings this correlation results from the fact that summer monsoon precipitation in the study area is relatively more enriched in 18o than winter precipitation and the total amount of annual precipitation predominantly varies with the amount of summer precipitation brought by summer monsoons the amount effect the negative relationship between the precipitation amount and the precipitation 18o is often used to explain the seasonal isotopic distribution in meteoric water of china this study presents a case where the 18o value of tree rings and precipitation is positive associated we point out that the amount effect which was originally used for tropical convective storms should not be simplistically considered as a mechanism for determining isotopic variations in china particularly at high latitude 30 n and or inland locations

40ar39ar geochronology of tertiary mafic intrusions along the east greenland rifted margin relation to flood basalts and the iceland hotspot track abstract the east greeland tertiary igneous province includes the largest exposed continental flood basalt sequence within the north atlantic borderlands more than ten layered gabbro complexes including the 55 ma skaergaard intrusion and a large dolerite sill complex are the plutonic equivalents of flood basalts both lavas and intrusions have been regarded as synchronous with continental breakup at 57 54 ma we report ten new ages of the mafic intrusions determined by40ar 39ar incremental heating experiments demonstrating that the mafic intrusions formed in two distinct time windows only intrusion ii of the imilik gabbro complex the skaergaard intrusion and the sorgenfri glestcher sill complex formed at 57 55 ma coeval with the eruption of regional flood basalts and continental breakup other layered gabbro intrusions at imilik intrusion iii kruuse fjord igtutarajik nordre aputite q kap edvard holm and lilloise are distinctly younger and formed between 50 and 47 ma plate kinematic models indicate the axis of the ancestral iceland mantle plume was located under central greenland at 60 ma and subsequently crossed the east greenland rifted continental margin we propose that tholeiitic magmatism along the east greenland rifted margin largely occurred in three distinct pulses at 62 59 ma lavas and dykes 57 54 ma lavas dykes sills and some gabbros and 50 47 ma gabbros dykes and rare lavas related to discrete mantle melting episodes triggered by plume impact continental breakup and passage of the plume axis respectively this model implies northwestward continental drift of greenland relative to the plume axis by 3 9 5 0 cm yr between 60 and 49 ma consistent with estimates from seismic studies of submerged flood basalts

the behaviour of platinum group elements in basalts from the east greenland rifted margin the continental flood basalts of the east greenland volcanic rifted margin were extruded during continental breakup above the ancestral iceland mantle plume at 55 ma three distinct magma types the low ti high ti and very high ti series lts hts and vhts respectively are found intercalated in the 6 km thick plateau lava sequence incompatible trace elements indicate that the lts are derived from a more depleted mantle source compared to hts and vhts the lts is characterised by increasing cu 105 to 248 ppm and pd 7 to 24 ppb constant cu pd ratio 10 000 and decreasing ir 1 1 to 0 05 ppb and ru 1 8 to 0 3 ppb concentrations during magmatic differentiation 16 to 7 wt mgo the constant cu pd ratio reflects silicate and chromite dominated fractionation without concurrent segregation of sulphide s undersaturated differentiation is also indicated in the hts which also displays increasing pd 6 16 ppb and decreasing ir concentrations 1 to 0 05 ppb during differentiation and the cu pd ratios for the entire series average 21 000 however some hts samples have elevated cu pd ratios up to 33 000 cu pd ratios in the hts do not correlate with mgo and this is interpreted to reflect varying cu pd ratios of hts parental magmas rather than s saturated differentiation during s undersaturated differentiation of the lts and hts pt pd ratios decrease from 1 3 to 0 11 and 1 1 to 0 2 respectively which indicates that pd is much more incompatible than pt during s undersaturated differentiation the vhts consists exclusively of highly evolved samples with low mgo 6 6 6 1 wt and pd ir ratios 98 228 here cu pd ratios increase from 17 500 to 35 000 with decreasing cr concentrations which indicate that these magmas experienced silicate fractionation with concurrent segregation of sulphide the lts represent melting of a depleted source and show high pge concentrations and constant cu pd ratios during s undersaturated differentiation melting of a normal depleted upper mantle source generates s saturated melts morb and the depleted lts source is therefore considered an extraordinary s poor component within the ancestral iceland plume of the three series the vhts contain the largest contribution from enriched mantle portions the vhts have similar pge but much higher nb concentrations for instance compared to the most evolved lts and hts samples indicating that the enriched source contributes nb but not pge

the triple group and the platinova gold and palladium reefs in the skaergaard intrusion stratigraphic and petrographic relations this paper describes the setting structure and textural relations of the platinova reefs in the skaergaard intrusion the reefs comprise a strata bound occurrence of au pge estimated at 91 million tons of rock with 1 8 ppm au and similar amounts of pd the precious metals occur in two major zones a lower major pd reef which is concordant with the modal layering and followed by at least ten minor pd reefs also concordant and an au concentration which fringes the pd reefs outward and upward through the triple group units the major pd concentration and the au concentration are separated in a systematic way across the intrusion near the center of the intrusion the au concentration occurs some 60 m higher in the stratigraphy than the main pd reef but the separation decreases gradually outward being only a few meters near the margins the dominant precious metal minerals are small grains of cu fe au pd pt alloys which typically are included in interstitial sulfides bornite digenite and smaller amounts of chalcopyrite the textural relations suggest a close genetic association between the sulfides and au pge minerals an association which is confirmed by whole rock compositional data our observations demonstrate that the platinova reefs formed after significant concentration of the au pge and s in the residual magma during fractional crystallization before it became saturated with respect to a sulfide fe cu s o liquid this sulfide liquid acted as a collector of au pge and settled into the layered series cumulates we propose that the structure of the deposit evolved through fractional crystallization of the au pge bearing sulfide liquid as it was filter pressed along with the interstitial silicate melt upward into the overlying unconsolidated cumulates the fractional crystallization resulted in an evolution of the au pge bearing phases with progressive fractionation from pd rich alloys at the base of the deposit to au rich alloys at the top we argue that the sulfides evolved to their present extreme cu rich fe poor composition during oxidation desulfurization reactions in the same event which oxidized the iron titanium oxides of the intrusion this oxidation desulfurization probably had no overall effect on the distribution of au and pge

40ar39ar dating of the skaergaard intrusion we report the first 40ar 39ar data for the skaergaard intrusion based on analyses of hornblende and biotite from a transgressive granophyre from upper zone a uza of the layered series hornblende separates heated in a resistance furnace and laser heated single crystals of biotite from the granophyre give plateau ages that are consistent with isochron ages of 55 48 0 30 and 55 40 0 14 ma respectively 2 internal uncertainty with initial 40ar39ar ratios of 292 4 19 0 and 291 1 7 2 if uncertainties in the ages of 40ar 39ar standard fluence monitors are considered external uncertainties 2 errors are 0 76 and 0 72 ma respectively resistance heating analysis of biotite separated from a gabbro from lower zone a lza of the skaergaard layered series indicates that the sample has been extensively contaminated by ar inherited from old crust and does not constrain the intrusion age apart from indicating that it is less than approximately 57 ma old the ar cooling ages are consistent within uncertainty with both pluton cooling models presented by norton and taylor 1 but the data agree best with their model s2 which assumes a smaller permeability 10 13 cm2 combination of the new ages and the norton and taylor cooling models constrains the emplacement and final crystallization of the skaergaard magma chamber to be at 55 75 0 30 ma and 55 65 0 30 ma respectively evidence for late crystallizing quartz and tridymite near the sandwich horizon sh combined with phase equilibria constraints on the near solidus crystallization temperature of the sh 975 25 c require the pressure of sh solidification to be 60 15 mpa this means that the tertiary basalts and sediments overlying the kangerdlugssuaq region were 3 2 0 8 km thick at 55 65 0 30 ma assuming that the 6 7 km thick tertiary section exposed further east along the east greenland coast is representative of that which accumulated above the skaergaard we infer that the skaergaard emplacement occurred during the main stage of the east greenland flood basalt event after approximately half of the tertiary section had erupted the onset of coastal flexure in the kangerdlugssuaq region was after 55 48 0 76 ma

speciation and solubility of palladium in aqueous magmatic hydrothermal solutions combining thermodynamic data at 25c and 1 bar with correlation algorithms enables prediction of equilibrium dissociation constants for aqueous platinum group element pge complexes at high pressures and temperatures we used these data 1 to calculate the speciation of pd ii in nacl solutions at temperatures to 750c pressures to 2 kbar and values from 3 to 8 and 2 to predict the solubility of palladium at 2 kbar as a function of temperature oxygen fugacity f sub o2 ph and total chloride concentration m sub t cl sup minus calculations indicate that as ph increases there is a sharp transition from chloride to hydroxide complex dominance at all chloride concentrations this shift occurs at or below neutral ph in dilute solution but at m sub t cl sup minus ge 1 0 pd ii chloride complexes account for the majority of dissolved pd ii well into alkaline conditions solubility of palladium increases with increasing temperature m sub t cl sup minus and f sub o2 at 700c 2 kbar and the f sub o2 set by the fmq buffer palladium solubility in a 3 0 m nacl solution is approximately 0 3 ppm at a ph of 4 and one unit ph variation can change palladium solubility by two orders of magnitude these results suggest that pge can be transported as chloridemore complexes in cl rich magmatic hydrothermal solutions like those inferred from petrologic studies of the stillwater and bushveld complexes less

an investigation of the common signal in tree ring stable isotope chronologies at temperate sites we observed a strong common high frequency interannual signal for thed 13 c chronologies whereas the low frequency decadal scale signal was more similar among thed 18 o chronologies for both carbon and oxygen isotopes we found significant positive relationships with annual and growing season temperatures and negative relationships with precipitation again of similar magnitude for all species except forfraxinus which contained only minor climatic information averaging of all chronologies resulted in an increase in the climatic signal of the mean chronology the combinedd 18 o record reflected decadal scale temperature variations remarkably well r 0 72 however the relationship between climate and carbon isotopes declined over the last 3 decades of the 20th century probably related to the steep increase in atmospheric co 2 concentrations resulting in strongly divergingd 13 c trends of the different chronologies our study indicates that combining chronologies from different species enhances the potential of isotope studies for extending climate reconstructions into areas of temperate climate

nitrogen rather than streamflow regulates the growth of riparian trees abstract in arid and semiarid regions riparian forests are crucial for maintaining ecological biodiversity and sustainability and supporting social and economic development for the typical arid and semiarid ecosystem streamflow variability is thought to be the dominant factor influencing the vulnerability and evolution of the riparian forests which often leads to the neglect of other potentially important factors such as nutrient availability and transport here we measured annual stable nitrogen isotopes 15n and nitrogen concentrations n in the tree rings of populus euphratica oliv euphrates poplar over a 90 year period 1920 2012 collected from the lower researches of the inland heihe river northwestern china coupling with our previous dual isotope 13c and 18o chronologies and estimated intrinsic water use efficiency iwue we examined the linkages between tree ring 15n and 18o iwue streamflow and then explored the contributions of each to tree growth during the study period our results show that after 1975 a statistically significant correlation between tree ring 15n and river streamflow appears indicating the river as a potential carrier of nitrogen from the upper and middle reaches to the lower research trees in addition the linkage between tree ring 15n and iwue suggests substantial influence of carbon and nitrogen together on photosynthesis and transpiration of trees although this connection become decoupled since ad 1986 the commonality analysis revealed that the nitrogen impacts indicated by tree ring 15n on tree growth cannot be ignored when evaluating riparian forest development the fertilization effects caused by rising co2 concentration complicate the nitrogen constraints on tree growth during the later part of the past century our results have potentially broad implications for identifying the limited factors for dryland forest ecosystems that are susceptible to natural water resource variations and human activities

variation in the composition of apatite through the merensky cyclic unit in the western bushveld complex microprobe analysis of interstitial apatite from a 100 m section through the merensky reef of the bushveld complex reveals that this stratigraphic section marks a transition from cl rich to more f rich compositions in the critical and main zones respectively apatite compositions across the section vary by more than 80 mole percent in the chlorapatite component the trend of decreasing cl concentration with stratigraphic height is not regular and cl contents in apatites from some samples may vary as much as 50 mole percent la 2 o 3 and ce 2 o 3 tend to be enriched in the more melanocratic orthocumulate parts of the section sro concentrations of apatite show an increase with stratigraphic position a trend which is opposite that observed in coexisting cumulus plagioclase the data are consistent with mineralogic and textural evidence for an influx of cl rich vapor into the cumulus section which has affected the cl f variations through the lower portion of the bastard unit this influx occurred above the crystallization temperature of apatite 1 000 degrees 1 050 degrees c it is suggested that much of the modal variation seen in the section may be the result of shifts in liquidus field boundaries caused by gain or loss of volatile components from the melt

partitioning of the platinum group elements and gold between silicate and sulphide magmas in the munni munni complex western australia geochimica et cosmochimica acta erratum to s j barnes 1993 57 1277 1290

variation in the composition of apatite in the munni munni complex and associated intrusions of the west pilbara block western australia abstract apatite is a ubiquitous intercumulus mineral in the archean munni munni radio hill and mount sholl layered igneous complexes of the west pilbara block in western australia apatite compositions from the three intrusions are relatively rich in the fluorapatite endmember and become more so in cumulates derived from compositionally evolved magmas the most extensive stratigraphic coverage is from the munni munni complex where the mole fraction of fluorapatite increases from approximately 60 70 in cumulates of the ultramafic zone to over 90 near the top of the gabbroic zone the chlorapatite component decreases from a high of 20 30 mol in the ultramafic zone to less than 10 in the uppermost part of the gabbroic zone the ree content of apatite parallels stratigraphic changes in whole rock incompatible element zr rb concentrations and is consistent with equilibration with the bulk assemblage the stratigraphic decrease in the cl f and oh f ratio of apatite can be modeled by assuming that fluid saturation of intercumulus liquids is a function of pressure and occurs prior to apatite saturation imposed on the stratigraphic trend are the effects of the combined processes of continuing fluid loss and fractional crystallization of apatite and locally biotite during solidification of the intercumulus liquid these processes produced relative compositional variations in endmember components on the order of 50 mol or more in individual thin sections because apatite crystallizes late in the solidification of intercumulus liquids it is estimated that the cl f ratio of the original trapped parent liquid prior to degassing could have been more than 2 orders of magnitude higher than is now recorded by intercumulus apatite compositions a comparison of literature apatite compositions from other intrusions shows that with the exception of the unusually cl rich assemblages of the stillwater and bushveld complexes processes affecting halogen geochemistry of layered intrusions do not appear to have changed significantly over the past 3 ga

ridge axis deformation and coeval melt migration within layer 3 gabbros evidence from the lizard complex u k ridge parallel extensional shear zones within the layer 3 gabbros of the lizard ophiolite have recorded varied and numerous chemical and mineralogical changes under a variety of p t conditions these changes accompany tectonic exhumation of lower crustal levels by a listric fault mechanism during amagmatic extension at a slow spreading centre deformation within the mid crustal level of layer three resulted in the migration and impregnation of an evolved iron titanium rich silica poor melt along the shear zones this syntectonic infiltration occurred along the lowermost portions of listric faults which rooted in a partially molten zone beneath the ridge axis residual melt was tapped from this underlying zone and tectonically redistributed about deforming gabbros situated immediately above the partially molten zone the occurrence of sub solidus synkinematic assemblages within the shear zones which were generated at various temperatures and water rock ratios is explained in terms of their simultaneous development on listric fault planes in the presence of a hydrothermal fluid phase the sequential overprinting of pre existing assemblages arises from repeated block rotation during amagmatic episodes of extension within an oceanic slow spreading environment

climate in southwestern ontario canada between ad 1610 and 1885 inferred from oxygen and hydrogen isotopic measurements of wood cellulose from trees in different hydrologic settings abstract oxygen and hydrogen isotopes were measured in wood cellulose and cellulose nitrate from trees that grew in different hydrologic settings in southwestern ontario canada an isotope model that accounts for isotopic fractionations associated with photosynthesis in plants was applied to the stable isotope data to infer past meteoric water isotopic composition and seasonal air moisture variations the model inferred climate data was rationalized in terms of the trees hydrologic environment and weather characteristics of the great lakes region the result is an account of summer and winter conditions in southwestern ontario for 275 years 1610 to 1885 prior to instrumental climate records conditions between 1610 and 1750 are inferred to have been cooler and drier than present this was followed by a warm moist climate interval between 1750 and 1885 during which there was an increase in winter precipitation cool dry conditions were recorded instrumentally in this region at the end of the nineteenth century

halogen geochemistry of the great dyke zimbabwe apatite from the great dyke of zimbabwe is relatively rich in the hydroxy fluorapatite end members the mole fraction of fluorapatite increases from approximately 40 in cumulates of the ultramafic sequence to over 60 in a sample near the top of the exposed mafic sequence the chlorapatite component decreases from a typical high of 10 20 mole in the ultramafic sequence to about 1 in the uppermost part of the mafic sequence however within sample variation may be as great as the entire stratigraphic variation halogen contents of marginal samples generally are similar to axial samples but tend not to have as high cl concentration and tend to oh enrichment biotite compositions approach hydroxyl end member compositions and apatite biotite oh f exchange geothermometers give an average closure temperature of 564 c apatite from the umvimeela dyke an unlayered dike that parallels the great dyke over much of its length contains less cl than is seen in the ultramafic sequence cumulates of the great dyke while the overall stratigraphic trend is characterized by a decrease in the cl f ratio with stratigraphic height within the p1 unit at the top of the ultramafic sequence there is a positive correlation between cl and other incompatible elements such as na and ce the apparent contradiction between the general stratigraphic trend of decreasing cl f ratio with fractionation and the apparent increase in cl and other incompatible elements seen in the p1 unit can be explained by assuming that the great dyke magma chamber was degassing near its top where confining pressure was lowest and cl was preferentially lost to a separating volatile rich fluid as cumulates formed on the floor they entrapped liquid that was increasingly depleted in cl at the higher stratigraphic levels however at any given stratigraphic interval either local fluid enrichment or the eventual crystallization of halogen bearing minerals that incorporate the smaller f ion in preference to the larger cl ion led to a local increase in the cl f ratio

petrology and geochemistry of the kruuse fjord gabbro complex east greenland the kruuse fjord gabbro complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies it was emplaced into archaean continental crust of east greenland during early tertiary rifting of greenland from eurasia the work to date has identified an outer gabbro series and an inner troctolite series and these are separated by a narrow zone of trondhjemitic intrusions in the southeast the partially crystallized cumulates of the gabbro series were intruded by a lenticular ultramafic pluton 800 m in thickness volumetrically minor syenite trachyandesite net veined dykes and later diabase dykes cross cut the plutonic rocks structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure the gabbro series is composed of a marginal gabbro unit about 20 m wide bordering more than a 2 km thickness of layered olivine and magnetite gabbro cumulates the marginal gabbro is interpreted to be chilled magma the layered cumulates are the product of repeated injections of magma that fractionated in an open system magma chamber anorthositic and troctolitic layers in the lower part of the sequence may represent inputs of magma and suggest that the order of cumulus mineral crystallization was 1 plagioclase an 39 85 2 olivine fo 46 82 3 augite wo 28 47 en 39 58 fs 8 18 and 4 magnetite the disappearance of cumulus magnetite and a reversal in mineral compositions at 1 5 km from the base of the succession suggests a major input of magma occurred at this height in the troctolite series the composition of cumulus minerals mineral crystallization sequence and style of emplacement are similar to those in the gabbro series the ultramafic pluton is composed of coarse grained wehrlite olivine melagabbro and troctolite that were formed by at least three injections of magma the typical mineral crystallization sequence was 1 cumulus chromite and olivine fo 84 88 2 poikilitic chrome diopside wo 29 51 en 43 63 fs 3 13 and 3 intercumulus plagioclase an 75 90 phlogopite apatite and localized disseminated sulphides containing au and platinum group elements comparison of crystallization sequences and the major and trace element compositions of clinopyroxene suggests that the gabbroic and troctolitic rocks formed from a magma represented by the chilled marginal gabbro a tholeiitic basalt magma similar to e morb whereas the ultramafic rocks formed from a magma that was relatively enriched in incompatible trace elements and volatiles the association of these two magma types is an example of bimodal mafic ultramafic magmatism in a rifting environment

sulfide and platinum mineralization in the merensky reef evidence from hydrous silicates and fluid inclusions the base metal sulfides of the merensky reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates biotite and phlogopite crystallized in the vicinity of sulfides from a volatile enriched highly fractionated intercumulus melt amphibole chlorite and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase biotite is often accompanied by zircon rutile and quartz accessory quartz hosts a complex suite of h2o nacl cacl2 co2 ch4 fluid inclusions which have thus far not been described from the merensky reef the earliest fluid inclusion compositions are nacl h2o with less than 10 vol water co2 coexisting with a halite daughter crystal and brine and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations the maximum trapping temperature is around 730 c at 4 to 5 kb pressure later inclusion generations are h2o nacl co2 h2o and pure co2 and ch4 the presence of cl rich fluids during the intercumulus stage of the crystallizing merensky reef is directly related to the mode of sulfide precipitation prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as h2s sulfur saturation causes reaction of h2s with oxides of the silicate melt to form a sulfide melt plus water during reaction the magma is enriched in water until a separate fluid unmixes it carries all compounds with high fluid melt partition coefficients as well as metals capable of forming oh and cl complexes precious metals are assumed to have fractionated into the cl rich fluid as cl complexes rather than being dissolved in the sulfide melt during the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets the model proposed explains the distribution pattern of platinum group minerals in the merensky reef better than any orthomagmatic mineralization concept offered so far

stable isotopic constraints on fluid rock interaction and cu pge s redistribution in the sonju lake intrusion minnesota the sonju lake intrusion part of the 1 1 ga midcontinent rift related beaver bay complex is a 1 200 m thick strongly differentiated layered sequence of mafic cumulates located in northeastern minnesota basal melatroctolite and dunite layers are overlain by troctolite gabbro fe ti oxide rich gabbro apatite diorite and monzodiorite stratigraphic intervals rich in pt pd cu and s occur over 500 m in the fe ti oxide rich gabbro and apatite diorite units peak concentrations show offsets that are similar to those found in other tholeiitic layered intrusions concentrations of pd in excess of 100 ppb are confined to the lowermost 25 m of the interval copper shows a sharp increase to 630 ppm above the pd rich interval sulfur contents are low 375 ppm in the cu rich interval but they increase to values as high as 3 150 ppm above in the apatite diorite disseminated sulfides in the intrusion have 34s values that range from 2 2 to 3 per mil vienna canyon diablo troilite v cdt and suggest that contamination by country rock sulfur was not an important process in the formation of the metal rich interval 18o values of plagioclase from the intrusion range from 5 6 to 12 0 per mil v smow and indicate that a relatively low 18o fluid 18o 3 5 interacted with the rocks of the intrusion at temperatures less than 275 c clinopyroxene and fe ti oxides ilmenite with minor amounts of titanomagnetite show much more restricted ranges in 18o values 4 6 5 7 and 5 5 6 7 per mil respectively and attest to the kinetic control of the oxygen isotope exchange process the externally derived fluid that interacted with rocks now enriched in platinum group elements pge cu and fe sulfide minerals locally liberated sulfur and replaced chalcopyrite and pyrite with goethite in the cu rich zone goethite that replaces chalcopyrite may contain up to 8 5 weight percent cu it is evident that hydrothermal alteration resulted in a decoupling of copper and sulfur with sulfur being transferred out of the cu rich interval interaction between rocks in the pge cu s interval of the sonju lake intrusion and an externally derived fluid at low temperatures modified what appears to have been a primary stratigraphic metal sulfur zonation the effects of hydrothermal alteration on pge and base metal sulfide mobility and redistribution must be understood before models of primary zonation processes can be meaningfully applied

δ18o of tree ring cellulose in two species spruce and oak as proxies of precipitation amount and relative humidity in northern japan abstract relationships between climatic factors and 18o values of tree rings in two species with different root systems were investigated in the northern area in hokkaido island northern japan this region has a heavy snow cover in winter and has a humid climate throughout the year in the case of spruce picea jezoensis which has shallow roots the 18o values are negatively correlated with precipitation in july and august probably due to higher relative humidity in summer and lower 18o of summer precipitation in a year of higher summer precipitation which is governed by the precipitation amount effect thus the 18o value of tree ring cellulose in spruce must be valuable as a proxy of summer precipitation in this area on the other hand the 18o value in oak quercus crispula which has deeper roots than spruce is not very sensitive to summer precipitation but is negatively correlated mainly with relative humidity in july and august this can be attributed to the smaller 18o enrichment in leaf water in the summer of higher relative humidity our results indicate that 18o values of tree rings in two species with different root systems from the same forest have the potential to reconstruct the two different climate factors

long term temperature trends and tree growth in the taymir region of northern siberia abstract the northernmost conifers in the world are located well above the arctic circle in the taymir region of northern siberia and have been recording the thermal environment for centuries to millennia the trees respond to temperatures beyond the narrow season of actual cambial cell division by means of root growth photosynthesis lignification of cell walls and other biochemical processes data from annual tree ring widths are used to reconstruct may september mean temperatures for the past four centuries these warm season temperatures correlate with annual temperatures and indicate unusual warming in the 20th century however there is a loss of thermal response in ring widths since about 1970 previously the warmer temperatures induced wider rings most major warming and cooling trends are in agreement with other high latitude temperature reconstructions based on tree ring analyses with some regional differences in timing of cooling in the late 18th century and of warming in the late 19th century

tectonics alteration and the fractal distribution of hydrothermal veins in the lower ocean crust abstract gabbros from hole 735b preserve the igneous structural and metamorphic history beneath the southwest indian ridge down to middle amphibolite facies conditions the gabbro was isolated from the zone of lithospheric necking by detachment faulting unroofing and block uplift at the inside corner high of the atlantis ii transform lower crustal accretion as preserved in the core is a complex integration of igneous hydrothermal and tectonic processes alteration began at anhydrous granulite conditions as surface faulting penetrated the brittle ductile transition to form brittle ductile shear zones in the amphibolite facies hydrous alteration around these zones was extensive while undeformed sections remained virtually unaltered amphibole veins formed during the brittle ductile deformation have a high fractal dimension reflecting an unclustered distribution consistent with high strain and cracking rates in the zone of lithospheric necking beneath the ridge however the fractal dimensions of the two major gneissic amphibolite zones in hole 735b are different and suggest that they represent discrete fault zones formed at different times below middle amphibolite facies a dramatic drop in the extent of alteration reflects cooling cracking and alteration under static conditions similar to layered intrusions initially fracture and vein formation exploited undeformed sections where elastic strain accumulated during cooling from high temperatures was unrelieved by recrystallization plagioclase diopside veins formed at this time have the same orientation as higher temperature veins but a mineralogy reflecting much lower rock permeabilities and a low fractal dimension reflecting a tight clustering of veins as would be anticipated for crack formation at low strain rates late zeolite and carbonate veins and irregular smectite lined near vertical cracks also have a very low fractal dimension reflecting clustering appropriate to low strain near static conditions these however show no preference for undeformed sections of the core and are oriented with subvertical and subhorizontal maxima this indicates crack formation under the present day stress field thus elastic strain due to cooling from high temperatures and extension during lithospheric necking dissipated after plagioclase diopside vein formation

a platform for kirchhoff data mapping in scalar models of data acquisition kirchhoff data mapping kdm is a procedure for transforming data from a given input source receiver configuration and background earth model to data corresponding to a different output source receiver configuration and background model the generalization of nmo dmo datuming and offset continuation are three examples of kdm applications this paper describes a platform for kdm for scalar wavefields the word platform indicates that no calculations are carried out in this paper that would adapt the derived formula to any one of a list of kdms that are presented in the text platform formulae are presented in 3d and in 2 5d for the latter the validity of the platform equation is verified within the constraints of high frequency asymptotics by applying it to a kirchhoff approximate representation of the upward scattered data from a single reflector and for an arbitrary source receiver configuration the kdm formalism is shown to map this kirchhoff model data in the input source receiver configuration to kirchhoff data in the output source receiver configuration with one exception the method does not map the reflection coefficient thus we verify that asymptotically the ray theoretical geometrical spreading effects due to propagation and reflection including reflector curvature are mapped by this formalism consistent with the input and output modelling parameters while the input reflection coefficient is preserved in this sense this is a true amplitude formalism as with earlier kirchhoff inversion a slight modification of the kernel of kdm provides alternative integral operators for estimating the specular reflection angle both in the input configuration and in the output configuration thereby providing a basis for amplitude versus angle analysis of the data