high precision u pb zircon id tims dating of two regionally extensive bentonites cenomanian stage western canada foreland basinthis article is one of a series of papers published in this special issue on the theme of geochronology in honour of tom krogh the stratigraphy of cretaceous rocks in the western canada foreland basin is well constrained by dense borehole data that allow three dimensional mapping of transgressive regressive events paleogeography and subsidence patterns however it is difficult to estimate rates of change or to place events in a precise temporal framework because very few of the many bentonite beds have been dated using modern techniques in this study two bentonites of at least regional extent were dated using isotope dilution thermal ionization mass spectrometry id tims u pb methods on chemically abraded zircon crystals the older bentonite correlates with the x bentonite of the late middle cenomanian and yields an age of 95 87 0 10 ma the bighorn river bentonite which lies just below the cenomanian turonian boundary yields an age of 94 29 0 13 ma and is interpreted to equate with the b bentonite and bed 80 at pueblo colorado both bentonites dated here are older than the previously reported 40ar 39ar ages

isotopic and chemical compositions of bentonites as paleoenvironmental indicators of the cretaceous western interior seaway oxygen and hydrogen isotopic compositions of volcanic ashes extensively deposited in the cenomanian turonian greenhorn and campanian claggett seas of the cretaceous western interior basin are commonly at variance with the isotopic compositions of the seas themselves as inferred from well preserved fossils the 18o values of montmorillonite from bentonite beds in manitoba montana south dakota wyoming colorado kansas oklahoma and new mexico range from 13 to 28 and translate into values for the greenhorn and claggett seas of 14 to 4 at 10 25 c these values are significantly more variable than the 18o values of fossils which translate into values of 8 to 2 for the same seas the discrepancies are attributed to post formational alteration of the bentonites the d values of turonian and campanian bentonites are unusually low at 120 to 110 relative to those to be expected from the respective late greenhorn and claggett seas whereas some samples of the cenomanian x bentonite seem to be in oxygen and hydrogen isotopic equilibrium with the earlier greenhorn sea mg and ca contents of montmorillonite from the bentonites vary regularly with 18o values but not with d values and sem analyses show the presence of neoformed fibrous smectite in bentonites with the highest 18o and mg and ca contents the chemical and isotopic data indicate that the variations in mineralogy and alteration of the bentonites result from widely disparate depositional environments and alteration of smectites by interaction with basinal brines

chemical signature of quartz from s and a type rare metal granites a summary abstract about 800 new and 1200 already published laser ablation inductively coupled plasma mass spectrometry analyses of quartz from rare metal granites and related greisens quartz tourmaline rocks and quartz veins were evaluated in order to define typical trace element signatures of quartz of different origin the studied dataset comprises typical examples of sub aluminous to slightly peraluminous plutons a type granites of the kimi stock finland eastern erzgebirge czech republic orlovka russia and ongon chairchan mongolia and strongly peraluminous plutons s type granites of beauvoir france cornwall england panasqueira and argemela portugal western erzgebirge czech republic additional 700 mostly already published analyses of quartz from barren granites of all geochemical types i s a type rhyolites and barren and rare element pegmatites were evaluated for comparison compiled data reveal high diversity in the contents of trace elements in quartz even among rocks of similar geochemical composition the most common trace elements in magmatic quartz are al li and ti with medians of 447 39 6 and 17 4 ppm in s type rare metal granites and 160 15 and 6 6 ppm in a type rare metal granites the contents of all these elements in greisens and quartz veins are significantly lower than in their parental granites al contents above 450 ppm should serve as a reliable indicator of s affinity of the analyzed granite while contents

carbon sequestration activated by a volcanic co 2 pulse during ocean anoxic event 2 ninety four million years ago during ocean anoxic event 2 there was a marked increase in the burial of organic carbon in marine sediments measurements of stomata in fossil leaves show that the two main pulses of carbon burial were associated with a decline in atmospheric co2 levels of up to 26 the cretaceous ocean anoxic event 2 about 94 million years ago is thought to be linked to extensive volcanism which triggered a biogeochemical chain of events that eventually led to widespread marine anoxia and a remarkable increase in carbon burial in marine sediments1 2 3 it has been suggested that the event was accompanied by a substantial decrease in atmospheric co2 concentrations4 but the quantification of the drawdown remains controversial5 6 here we reconstruct atmospheric co2 concentrations throughout the ocean anoxic event from counts of the stomata in fossil leaves and use terrestrial carbon isotopes to link the reconstruction to marine records of the event7 8 we find that before the onset of ocean anoxia atmospheric co2 concentrations increased by 20 over background levels of 370 100 70 ppm this was part of a long term rise in atmospheric co2 levels presumably caused by volcanism which reached a peak of 500 400 180 ppm however two pulses of extensive carbon burial during the ocean anoxic event as indicated by positive carbon isotope excursions are associated with decreased atmospheric co2 concentrations we conclude that the sequestration of marine organic carbon led to a decrease in atmospheric co2 concentration of up to 26 during ocean anoxic event 2

albian to santonian carbon isotope excursions and faunal extinctions in the canadian western interior sea recognition of eustatic sea level controls on a forebulge setting abstract the forebulge region of the cretaceous canadian western interior sea cwis was susceptible to subaerial exposure and marine erosion during sea level lowstands the middle albian to santonian record as cored at cold lake east central alberta canada documents numerous disconformities that are expressed in bioclastic concentration horizons and faunal extinctions and turnovers detailed comparison between a newly established 13 c org record measured on bulk sediment at cold lake and a combined 13 c carb reference curve based on the cretaceous english chalk and se france hemipelagic marlstones highlights missing positive and negative 13 c excursions at the cwis forebulge and thus missing sections that precisely corroborate with sequence boundaries disconformable boundaries correlate closely with global sea level lowstands as established for the cretaceous north atlantic suggesting a pronounced eustatic influence on the cwis forebulge setting sequence boundaries occur in the uppermost middle albian lowermost upper albian albian cenomanian boundary cenomanian turonian boundary middle turonian to lower coniacian and uppermost middle santonian each followed by a positive 13 c excursion oceanic anoxic events 1d 2 and 3 are recognized and linked to major faunal and floral assemblage changes of these the albian cenomanian biotic turnover is the most severe in the cwis marked by the total loss of albian benthic foraminifera species causes of this benthic extinction might be linked to a period of anoxia oae 1d during the latest albian followed by sea level controlled basin restriction

marine 187os 188os isotope stratigraphy reveals the interaction of volcanism and ocean circulation during oceanic anoxic event 2 high resolution osmium os isotope stratigraphy across the cenomanian turonian boundary interval from 6 sections for four transcontinental settings has produced a record of seawater chemistry that demonstrates regional variability as a function of terrestrial and hydrothermal inputs revealing the impact of palaeoenvironmental processes in every section the 187os 188os profiles show a comparable trend radiogenic values in the lead up to oceanic anoxic event 2 oae 2 an abrupt unradiogenic trend at the onset of oae 2 an unradiogenic interval during the first part of oae 2 and a return to radiogenic values towards the end of the event above the cenomanian turonian boundary the unradiogenic trend in 187os 188os is synchronous in all sections previous work suggests that activity of the caribbean lip large igneous province was the source of unradiogenic os across the oae 2 and possibly an instigator of anoxia in the oceans here we assess this hypothesis and consider the influence of activity from other lips such as the high arctic lip a brief shift to high radiogenic 187os 188os values occurred in the western interior seaway before the onset of oae 2 we evaluate this trend and suggest that a combination of factors collectively played critical roles in the initiation of oae 2 differential input of nutrients from continental and volcanogenic sources coupled with efficient palaeocirculation of the global ocean and epeiric seas enhanced productivity due to higher nutrient availability which permitted penecontemporaneous transport of continental and lip derived nutrients to trans equatorial basins

biogeography of planktonic foraminifera and regional carbon isotope variations productivity and water masses in late cretaceous europe the first appearances of species of marginotruncana planktonic foraminifera are found stratigraphically earlier in boreal northwestern germany than in the tethys helvetoglobotruncana helvetica bolli is rare in northwestern germany and common in the tethys its stratigraphic range is probably comparable between both areas the biogeographic patterns are discussed with respect to influences of water depths based on isotope evidence for the depth distribution of species of hedbergella praeglobotruncana and rotalipora and water temperatures the regional variation of 13c values of cenomanian turonian pelagic carbonates was mapped for the european epicontinental basins and the southern european shelf helvetic zone of the alps the highest 13c values up to 5 were found in northwestern germany and the eastern north sea and are coincident with an upwelling zone numerically predicted by three independent climate models intermediate values in france and england 2 4 correspond to predicted weak upwelling lowest values occur in the alpine helvetic zone and the south german regensburg area 1 2 and coincide with predicted absence of upwelling the 13c values are interpreted as indicators of increased biogenic productivity in the upwelling zone semiquantitative nannofossil data suggest abundance patterns influenced by latitude neritic oceanic gradients and productivity observations agree with east to west wind driven surface current systems regional differences in nutrient supply and subsequently different primary productivity could have been a major factor controlling the evolution and the biogeographic distribution of planktonic foraminifera in cenomanian turonian europe

evolution from magmatic to hydrothermal activity beneath the cerro escorial volcano nw argentina as sampled by erupted quartz and brines abstract large quartz pebbles erupted with the escorial ignimbrite provide insight into the late magmatic evolution of the shallow cooling magmatic hydrothermal system below the cerro escorial volcano of the southern central volcanic zone in the argentine andes the ignimbrite is of relatively small volume crystal rich dacitic in composition and not particularly water rich as amphibole is absent eruption temperature was estimated to be close to 850 c the quartz pebbles provide insight into the magmatic hydrothermal transition beneath the volcano based on textures trace element composition analyzed by laser ablation inductively coupled plasma mass spectrometry and inclusion content the pebbles can be separated into pegmatite like megacrysts and lower temperature epithermal microcrystalline quartz both types are distinct from magmatic phenocrysts present in porphyritic clasts ejected by the ignimbrite the megacrysts show a wide range of trace element concentrations with elevated al concentrations and al ti and ge ti ratios compared to quartz phenocrysts although some contamination by submicroscopic inclusions and cooling to near solidus temperatures may perturb the signal in some cases the range of trace element concentrations in quartz crystals from this system may reflect a change in crystallization conditions from initial precipitation from typical evolved silicate melt to fast growth from residual melt and or fluid in pegmatitic pockets or coarse grained hydrothermal veins at locally variable precipitation conditions abundant primary and secondary silicate melt inclusions and a variety of secondary fluid inclusions are present within the megacrysts in particular brine inclusions are densely packed with salt crystals sometimes anhydrite and or a silicate crystal but no visible liquid at room temperature and co existing vapor inclusions are of very low density heating experiments of brine inclusions reveal last salt and vapor bubble dissolution temperatures around 600 700 c but an immiscible silicate melt surrounding the homogenized salt globule remains even at unreasonably high temperature the co existence of silicate melt and fluid inclusions reinforces the magmatic nature of the fluids while boiling trails of brine with cu concentrations of several percent and vapor point to relatively low pressures

volcanic ash layers in the upper cretaceous of the central apennines and a numerical age for the early campanian at montagna della maiella and at gola del furlo central apennines two discrete layers of bentonic clay are intercalated within the pelagic furlo and turbiditic pelagic limestones maiella of the upper cretaceous basinal succession of the umbrian basin scaglia facies the bentonite layers are dated by planktonic foraminifera to the globotruncanita elevata zone early campanian and by calcareous nannofossils to the aspidolithus parcus zone cc 18 they fall into the reversed interval of chron 33 detailed correlation shows the layers to be of exactly the same age the upper layer is dated by u pb on magmatic zircons to 81 67 0 21 ma an age compatible with the cretaceous time scale of obradovich the mineralogy of the bentonitic clays is almost pure montmorillonite and contrasts sharply with the clay mineral assemblage of the enclosing pelagic and turbiditic limestones which is dominated by soil derived smectite and illite in different proportions the bentonite seams are interpreted as the submarine alteration products of wind borne volcanic ashes they can be followed with only minor changes in thickness over 200 km and must be derived from distant volcanic sources and related to extreme volcanic events a possible source area is present in the dinarides where upper cretaceous subduction related magmatic rocks are widespread

tourmaline as a petrogenetic monitor of the origin and evolution of the berry havey pegmatite maine u s a the berry havey pegmatite oxford pegmatite field androscoggin county maine u s a enriched in li f b be and p is intruded in hornblende rich amphibolite with minor biotite or diopside the pegmatite has a complex internal structure with four texturally and compositionally different zones that show an increasing degree of evolution inward wall zone intermediate zone core margin and core zone the main minerals are quartz feldspars al micas tourmaline with minor fe micas garnet beryl amblygonite montebrasite fe mn phosphates and apatite tourmaline is present in all zones of the pegmatite showing different textures black anhedral crystals in the wall and intermediate zones black prisms of up to 40 cm in length in the intermediate zone black tapered prisms surrounded by a pseudo graphic intergrowth of quartz or albite with black green bluish tourmaline and constituting a continuous layer under the core zone multicolored and watermelon zoned crystals in the core zone and gemmy deep green and color zoned watermelon tourmaline prisms up to 15 cm length inside the pockets a complete chemical evolution from mg rich schorl in the wall zone to elbaite with an important deprotonation in the pockets inside the core zone is observed the most plausible exchange vectors for this chemical evolution are femg 1 y al w o y r 2 w oh 1 and al x x r 2 na 1 where r 2 fe 2 mg 2 mn 2 zn 2 for the tourmalines from the wall and intermediate zones in the core margin tourmaline composition evolves from schorl toward li rich species through the substitution y al y li y r 2 2 later during the crystallization of the core zone this exchange vector combined with the substitution x y al 0 5 x na 1 y li 0 5 finally the gemmy tourmalines from the pockets show a deprotonation related to the exchange vector y al w o 2 y li 1 w oh 2 and may be classified as darrellhenryite these substitutions may reflect an increase in oxygen fugacity and a decrease in li and f related to the crystallization of lepidolite and amblygonite montebrasite in the core zone adjacent to or within the pockets the crystallization of these minerals would reduce the availability of li and f for the very latest tourmaline crystals growing inside the pockets where the deprotonation becomes important chemical and textural variation in tourmaline is consistent with a fractional crystallization process for the internal evolution of the berry havey pegmatite crystallization of the tourmaline layer under the core zone may be related to the exsolution of the fluid phase implied in the formation of pockets

discriminant function analysis of late quaternary tephras from five volcanoes in new zealand using glass shard major element chemistry abstract the microprobe determined glass shard major element chemistry of tephras derived from five north island new zealand volcanoes mayor island okataina taupo tongariro and mount egmont and younger than ca 20 000 yr b p was subjected to discriminant function analysis four separate approaches were adopted to test the match of the tephras with their known sources 1 an analysis of raw microprobe data 2 an analysis of normalized data 3 an analysis of the data transformed by calculating the log 10 of oxide scores divided arbitrarily by the chlorine content and 4 a repeat of 3 with multivariate outlier scores as determined by principal components analysis deleted all yielded excellent classification functions efficiencies of 91 100 with the eruptives associated with each of the five volcanoes being chemically distinct from one another in each approach the first two canonical discriminant functions accounted for 90 of the variation between groups the removal of multivariate outliers from the data set had only minor effects on the performance of the discriminant function procedures separate discriminant function analysis of the relatively alike taupo and okataina eruptives gave a greater degree of multivariate separation the numerical classifications generated should enable unidentified tephras erupted since ca 20 000 yr b p from the five volcanoes to be provisionally matched with their sources

petrogenetic relationships between pegmatite and granite based on geochemistry of muscovite in pegmatite wall zones black hills south dakota usa abstract the compositions of large samples of granitic pegmatite wall zones have been determined for a suite of ten pegmatites of diverse geochemical character and degree of compositional evolution in the keystone area of the black hills whole rock compositions are strongly peraluminous and they deviate substantially from the granite minimum composition in quartz albite orthoclase normalized components showing considerably more scatter than harney peak granite whole rocks wall zone minerals are commonly coarsely segregated leading to large modal variability among whole rocks these features make whole rock samples of wall zones unsuitable for the determination of initial pegmatite bulk compositions trace and minor element compositions of muscovite separates from the wall zones were thus determined to eliminate the effects of modal variability on trace element concentrations so that geochemical differences between pegmatites could be modeled estimates of initial pegmatite melt trace element concentrations range from 800 4000 ppm rb 100 1000 ppm cs 200 2000 ppm li and 1 50 ppm ba trace element concentrations of muscovite from a given pegmatite generally cluster together although several show considerable intra pegmatite scatter and there are large overlaps among different pegmatites the geochemical characteristics of samples from the etta pegmatite indicate mixing with and assimilation of country rocks exceptionally low rb cs ratios of muscovite from the etta pegmatite are similar to those of muscovite from k feldspar rich assemblages of other pegmatites where the rb concentration of melt may have been buffered by crystallizing assemblages that had bulk rb distribution coefficients close to 1 the large degree of scatter of geochemical parameters among these pegmatites precludes derivation of the entire suite by either single stage crystallization or partial melting processes nor can the pegmatites be satisfactorily related by any fractionation trajectory from a single starting composition fractional crystallization is difficult to model due to an apparent geochemical decoupling that exists among several of these elements in different pegmatites e g rb from cs or li from rb cs and nonsystematic variation of ba concentrations however the magnitude of observed rare element enrichments could be achieved by 75 90 fractional crystallization of melts that crystallized harney peak granite in nearby exposures the inter pegmatite scatter and apparent geochemical decoupling that characterize the suite indicate an origin by partial melting of a heterogeneous source rock or rock sequence followed by an intermediate episode of fractional crystallization prior to final emplacement of the pegmatite melts additional compositional variations among samples from the wall zones of individual pegmatites were caused by processes during or after emplacement including local interaction with host metamorphic rocks and fractionation during internal evolution of the pegmatites as they crystallized

the metamorphic aureole of the nisa alburquerque batholith sw iberia implications for deep structure and emplacement mode the nisa alburquerque granitic batholith southern variscan belt iberian peninsula has been studied by petrological structural and geophysical approaches obtaining contrasting models for its deep structure and emplacement sequence in order to test these models and gain knowledge on the thermal increase induced by the intrusion we have studied its contact aureole which was developed in similar country rock lithologies mica schists alternating with metasandstones and feldespatic schists all along the northern external contact of the batholith our results indicate no change in metamorphic grade and some variations in aureole width which narrows toward the western sectors of the batholith cordierite is the only contact metamorphic mineral developed together with a high temperature biotite probably related to the granite thermal input by considering these new data together with zircon saturation temperatures within the granite and previous petrological and geophysical studies we propose a model in which the feeder zones of the granitic magmas were an eastern main one and a western secondary one we have also made comparisons of the metamorphic grade in the country rocks and the xenoliths within the granite most of the xenoliths have the same metamorphic facies as the country rocks crd zone though some of them contain slightly different assemblages and crd which could be explained in different ways 1 differences in the primary schist compositions 2 increased time span of xenoliths in contact with the melt and 3 xenolith incorporation at slightly higher depths during final granite ascent

the chemistry of quartz in granitic pegmatites of southern norway petrogenetic and economic implications trace element concentrations in quartz from 188 granitic pegmatites in the froland and evje iveland pegmatite fields southern norway have been determined to establish exploration targets for high purity quartz and to gain a better understanding of the genesis of pegmatites hosting these deposits both pegmatite fields were formed during the sveconorwegian grenvillian orogeny 1145 900 ma at the western margin of the fennoscandian shield in situ raster analyses within single quartz crystals were undertaken by laser ablation inductively coupled plasma mass spectrometry la icp ms spot size 75 m to assess levels of lattice bound impurities rather than mineral and fluid inclusions that are relatively easily removed during high purity quartz processing quartz in the froland pegmatites has relatively pure and homogeneous compositions containing 46 24 gg 1 al 8 3 gg 1 ti 1 4 0 8 gg 1 ge and 11 7 gg 1 li the ti in quartz geothermobarometer gives an average pegmatite crystallization temperature of 537 39 c temperature estimates are highest along the northwestern margin of the pegmatite field 550 c whereas the most differentiated pegmatites occur toward the northeast the area of greatest economic potential for high purity quartz lies just north of the central part of the field where individual pegmatites contain 1 million metric tons mt quartz with low average trace element contents of 67 11 gg 1 from mineral chemical criteria and a range of other geologic factors we propose that pegmatite melts in the froland field were generated by fluid present crustal melting at about 1060 ma in zones of localized high strain deformation during progressive thrusting along the porsgrunn kristiansand fault zone quartz in the evje iveland pegmatites has more variable compositions with 69 57 gg 1 al 19 11 gg 1 ti 2 3 1 8 gg 1 ge and 7 5 gg 1 li from its ti content it crystallized at temperatures of 613 70 c the regional spatial distribution of ti in quartz temperatures appears irregular mainly due to the scattered distributions of chemical evolved pegmatites with amazonite cleavelandite replacement zones which show crystallization temperatures down to 442 c quartz from the evje iveland pegmatites is unlikely to be of current economic interest due to its moderate to high trace element contents heterogeneous chemistry and low volume the evje iveland pegmatites show no apparent genetic link to a granite intrusion instead they probably formed as a result of partial melting at the depth of their amphibolite country rocks at around 910 ma this is related to a regional low pressure high temperature metamorphic event at about 930 to 920 ma

extreme fractionation in a granite pegmatite system documented by quartz chemistry the case study of tres arroyos central iberian zone spain abstract the tres arroyos granite pegmatite system is located in the sw margin of the nisa alburquerque variscan batholith two granitic facies monzogranite and marginal leucogranite and three types of aplite pegmatite dykes barren intermediate and highly evolved li rich have been distinguished in the area with a zoned distribution from the granite southwards trace elements in quartz from the five facies have been analysed by la icp ms in order to obtain information about the petrogenetic links among the different lithologies of this system as well as to better understand the regional and individual fractionation processes that led to the distinct rocks aluminium ti li and ge show continuous trends from the monzogranite through the marginal granitic facies the barren and intermediate aplite pegmatites up to the most evolved li rich dykes titanium and ge contents respectively decrease and increase gradually with fractionation in contrast al and li show a more complex trend with an initial descending trend to the marginal granitic facies and then showing the highest al and li contents in the quartz from the most fractionated li rich aplite pegmatites this suggests the influence of different competing factors controlling the incorporation of these trace elements in quartz such as the chemical composition of the melt the p and t conditions and the rate of crystallization based on the good correlation between al and li the substitution si4 al3 li seems to be the dominant mechanism of li incorporation into quartz the negligible amount of other trace elements suggests that the remaining al was mainly compensated with h ions via the si4 al3 h substitution a continuous fractionation trend from the monzogranite up to the most fractionated aplite pegmatites is inferred from geochemical modelling by applying the rayleigh equation for fractional crystallization fractionation rates over 50 are needed to obtain the marginal granite and the barren aplite pegmatites compositions and over 99 for the most evolved dykes no pattern in the chemical variation of the trace elements in quartz from different layers in the layered aplite pegmatites has been found suggesting the lack of internal fractionation processes most probably due to the rapid crystallization of the pegmatitic melt intruded into a colder country rock

trace element composition of quartz from porphyry systems a tracer of the mineralizing fluid evolution trace element composition of hydrothermal quartz reflects the p t x conditions of the mineralizing fluids and can be a potential tracer of the fluid evolution to explore this potential quartz trace element data from 21 porphyry cu au mo and epithermal polymetallic deposits were compiled in addition quartz trace element data from six granite related systems granite pegmatite greisen sn w mo veins and from a subset of calc alkaline arc related volcanic rocks were also compiled for comparison for porphyry cu au mo deposits quartz compositions are from publications in which the sequence of quartz bearing veins and their potential reopening were documented as well as their precipitation temperatures and pressures the compiled dataset shows that trace element composition of quartz continuously evolved between the different porphyry veins and quartz generations a b c d and e the observed evolution reflects the cooling and or compositional variations of the hydrothermal fluids the quartz al ti sb ti ge ti and sb ge ti ratios allow for the discrimination of quartz from different vein generations of porphyry cu au mo deposits this study shows that quartz composition preferentially combined with cathodoluminescence images is an efficient proxy for tracing the evolution of the hydrothermal fluids in porphyry systems and can be used as a vectoring tool to target the centers of porphyry systems

the cretaceous polar and western interior seas paleoenvironmental history and paleoceanographic linkages abstract this study reviews the cretaceous histories of the polar and western interior seas as recorded in the canadian high arctic sverdrup basin beaufort mackenzie basin of northwest canada and western canadian foreland basin newly emerging stratigraphic paleoclimatic and paleoenvironmental interpretations from the polar realm allow for a fresh look at the response of this oceanic system to global climatic trends and sea level histories over 35 ma sverdrup basin localities on axel heiberg and ellef ringnes islands represent shelf to slope environments that contrasted with the shallow water and low gradient settings of the canadian western interior sea both marine systems connected throughout aptian to maastrichtian time responded to global transgressive regressive cycles resulting in dynamic paleogeographic changes the upper aptian to campanian succession of the polar sea shows at least two unconformable boundaries one at the albian cenomanian transition and another within the upper cenomanian the shallow basin setting and in particular the forebulge and backbulge settings of the western canadian foreland basin are characterized by multiple erosional surfaces throughout the cretaceous succession the upper albian disconformity is widely discernible close to the entrance of the western interior sea to the polar sea this suggests a short lived closure of the latest albian mowry sea that might have been responsible for the large loss of benthic foraminiferal species at this time several oceanic anoxic events are documented in these basins representing their response to global climate dynamics during the late cretaceous temperature maximum benthic foraminiferal communities were severely restricted by bottom water hypoxia in both basins a stratified water column might have been the result of increased freshwater runoff under warm humid conditions these conditions supported vegetation up into the polar latitudes that added abundant organic matter to marine shelf systems conversely the canadian western interior sea biotic communities were controlled by watermasses of two or maybe three different sources and physical properties including the polar tethyan and a possibly third source from the emerging labrador sea through the hudson seaway where the southern and northern watermasses mixed plankton might have been influenced by oceanic fronts forming mass kills through sinking of dense waters migration of calcareous phyto and zooplankton was controlled by a temperature and salinity gradient and did not invade northern regions siliceous plankton occurred and is more commonly found in the sverdrup basin but taphonomic loss through deep burial needs to be taken into account

late aptian palaeoclimatic turnovers and volcanism insights from a shallow marine and continental succession of the apennine carbonate platform southern italy abstract this study reports an integrated facies analysis carried out on a new section from the upper aptian of the se matese mts civitella licinio northern campania s italy which includes several decimeter to meter scale lacustrine intervals straddling a meter scale plant rich plattenkalk these intervals are assigned to the late gargasian early clansayesian by their stratigraphic relationship with the upper salpingoporella dinarica acme as well as lithologic and biostratigraphic supra regional key markers found in the apennine carbonate platform apcp including the orbitolina level we infer that the monogeneric parautochthonous plant remains frenelopsis sp were deposited in a supratidal to paralic coastal mudflat close to a restricted shallow marine lagoon at the verge of an arid semiarid climatic phase the plattenkalk was rapidly replaced by persistent lacustrine lithofacies at the onset of a major climatic turnover glacial trigger the overlying shallow marine deposits are capped by a deeply incised palaeokarstic surface and in turn by unconformable middle clansayesian transgressive shallow marine deposits interlayering of reliable lithologic indicators of palaeoclimate and high resolution event stratigraphic hires correlation of the civitella licinio succession with the astrochronologically tuned mt faito reference section of the apcp bring evidence of rapidly fluctuating hydroclimatic conditions wet and arid phases in the short 100 ky and long 400 ky eccentricity time band hires and astrochronological age assignment to crucial key markers and humid arid phases at civitella licinio permit to further refine the detailed stratigraphy of the mt faito reference section and to assign the upper s dinarica acme of the apcp to a numerical age of 118 55 118 50 my sem and eds analyses document common to abundant windblown volcanic particles glass shards and sanidine crystals throughout the frenelopsis rich plattenkalk 118 3 to 118 2 my and the encasing units especially in the overlying brackish lacustrine deposits palaeogeographic and palaeoclimatic reconstructions suggest that the pyroclastic material was probably transported by northeasterly trade winds from orogenic volcanic centers located within the dinaridic carpatho balkan arc trench system and have been supplied to the apcp for a time span of 3 my during the late aptian a preliminary tephrostratigraphic correlation of the upper aptian volcaniclastic levels of the apcp with the bentonite levels of the vocontian basin is proposed

an experimental study of element partitioning among biotite muscovite and coexisting peraluminous silicic melt at 200 mpa h2o

a new proxy for cretaceous paleoceanographic and paleoclimatic reconstructions coiling direction changes in the planktonic foraminifera muricohedbergella delrioensis among some modern and recent fossil species of planktonic foraminifera the proportion of left to right coiled shells in a population appears to be temperature dependent the relative abundance of each morphotype reflecting ecological preferences a similar relationship is identified among muricohedbergella delrioensis carsey 1926 at the cenomanian turonian stage boundary in mid latitude sites of the western interior seaway including the pueblo type section the increase of sinistral m delrioensis in the assemblage is related to higher 18 o carb values and decrease in inner porosity which suggests that changes in the coiling direction in this morphospecies could represent a new proxy for constraining sea surface temperature sst variations as surface dwellers muricohedbergellids were not accepted manuscript 2 affected by oceanic anoxic event oae2 and provide a continuous paleoclimatic signal throughout the cenomanian turonian boundary interval furthermore genetic evidence obtained from extant foraminifera indicates that shifts of coiling ratios in planktonic foraminifera species can express the signature of distinct genetic types which are revealed through their opposite coiling directions coiling direction could be a genetic trait implying that cryptic species may occur in the mesozoic

re evaluation of the ages of 40ar 39ar sanidine standards and supereruptions in the western u s using a noblesse multi collector mass spectrometer abstract the rewards from resolving the tempo of magmatic paleobiologic paleoclimatic and tectonic processes at better than the per mil level of precision have spurred a quest within the geochronology community to improve the precision accuracy and calibration of several chronometers including the 40 ar 39 ar variant of the k ar clock a new generation of multi collector mass spectrometers for 40 ar 39 ar geochronology provides the means to address these issues as well as to evaluate the ages of 40 ar 39 ar standards and key marker horizons deposited by large volume caldera forming supereruptions in the western u s at unprecedented temporal resolution we highlight the utility of a 5 collector noblesse mass spectrometer that has a sufficiently high mass resolving power to distinguish 36 ar h 35 cl from a 36 ar h 35 cl 12 c 3 sum peak at m e 36 maintains a remarkably low and stable background and thus yields 40 ar 39 ar dates of exceptionally high precision we have calibrated a reference gas and developed a simple analytical routine involving one peak hop both of which are used to evaluate detector bias correction factors because the 40 ar 39 ar chronometer is a relative dating technique that relies on calibration against mineral standards of known age precise and accurate determination of the ages of these standards and verification of isotopic composition and homogeneity is essential we present results from both total fusion and incremental heating experiments on single crystals of the widely used alder creek acs and fish canyon fcs sanidine standards several recent independent measurements of acs using multi collector mass spectrometers including those presented herein favor an age of 1 1864 0 0003 0 0012 ma 95 confidence analytical full external uncertainty that is 1 younger than the widely used value obtained by nomade et al 2005 using a single collector mass spectrometer incremental heating experiments on single crystals of fcs most commonly do not yield plateau ages instead many crystals appear to be affected by ar loss or excess ar our findings obtained using ion counters independently confirm those recently obtained using a multiple faraday detectors or a combination of faraday and ion counting detectors thus careful consideration must be given to using fcs in future high precision 40 ar 39 ar calibrations of the geologic timescale notwithstanding 40 ar 39 ar dating of sanidine using the 5 collector noblesse can now provide leverage critical to interpreting the large range of u pb zircon dates commonly found in rhyolitic lavas and tuffs

distribution and petrogenetic behaviour of trace elements in granitic pegmatite quartz from south norway the present study documents that the trace element distribution in granitic quartz is highly sensitive to cafc processes in granitic melts igneous quartz efficiently records both the origin and the evolution of the granitic pegmatites aluminium p li ti ge and na in that order of abundance comprises 95 of the trace elements most samples feature 1 ppm of any of these elements the remnant 5 includes k fe be b ba and sr whereas the other elements are present at concentrations lower than the detection limit potassium fe be and ti are relatively compatible hence obtain the highest concentrations in early formed quartz phosphorous ge li and al are relatively incompatible and generally obtain the highest concentrations in quartz that formed at lower temperatures from more evolved granitic melts the ge ti the ge be the p ge and the p be ratios of quartz are strongly sensitive to the origin and evolution of the granitic melts and similarly the rb sr and the rb k ratios of k feldspars may be utilised in petrogenetic interpretations however the quartz trace element ratios are better at distinguishing similarities and differences in the origin and evolution of granitic melts after evaluating the different trace element ratios the ge ti ratio appears to be most robust during subsolidus processes in the igneous systems hence probably should be the preferred ratio for analysing and understanding petrogenetic processes in granitic igneous rocks

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

phase relations of peraluminous granitic rocks and their petrogenetic implications peraluminous granitic rocks are magmatic rocks that contain quartz po tassic feldspar and or sodic plagioclase and one or more aluminum rich minerals thus these rocks contain more aluminum than could be accom modated by feldspar in a cipw normative calculation and show normative corundum peraluminous granites are defined by their chemical nature but their recognition is often based on petrography this discrepancy thus may lead to inconsistency although peraluminous granitic rocks are com monly true granite streckeisen 1973 they range from tonalite to granite of special interest are strongly peraluminous as defi ned below granite granodiorite or in rare instances trondhjemite these rocks contain alumi nous minerals almandinic garnet cordierite tourmaline muscovite that are thought to be stable in silicate magmas only if these magmas are themselves peraluminous the origin of peraluminous granite and related intrusive rocks is of much current interest many of these form shallow level intrusions and they can reach enormous sizes examples are the batholiths in the lachlan fold belt in southeastern australia white chappell 1983 the cornub ian batholith in england exley stone 1966 the south mountain batholith in nova scotia mckenzie clarke 1975 the manaslu batho lith in the himalayas lefort 1981 much of the idaho batholith

the ti saturation surface for low to medium pressure metapelitic biotites implications for geothermometry and ti substitution mechanisms the ti content of biotite can serve as a geothermometer for graphitic peraluminous metapelites that contain ilmenite or rutile and have equilibrated at roughly 4 6 kbar the relationship between ti content temperature and mg mg fe value was calibrated empirically using an extensive natural biotite data set 529 samples from western maine and south central massachusetts in combination with the petrogenetic grid of spear et al 1999 the calculated ti saturation surface is curved such that for a given mg mg fe value ti concentration increases as a function of temperature in a nonlinear fashion and for a given temperature ti concentrations decrease with an increase in mg mg fe the fit to the ti saturation surface can be reformulated as the geothermometric expression t ln ti a c x mg 3 b 0 333 in which t is temperature in degrees celsius ti is the number of atoms per formula unit apfu normalized on the basis of 22 o atoms x mg is mg mg fe a 2 3594 b 4 6482 10 9 and c 1 7283 the calibration range for this expression is x mg 0 275 1 000 ti 0 04 0 60 apfu and t 480 800 c precision of the ti in biotite geothermometer is estimated to be 24 c at the lower temperature range and improves to 12 c at higher temperatures application of the ti in biotite geothermometer to ilmenite or rutile bearing graphitic peraluminous metapelites equilibrated at 3 6 kbar is generally consistent with independent temperature determinations but with some deviations that represent local reequilibration consequently the ti systematics in biotite can also serve as the basis of a very sensitive indicator of chemical equilibrium or lack thereof application of the geothermometer to metapelites not containing the requisite mineral assemblages can lead to minor to significant errors in estimated temperatures biotite ti substitution mechanisms are controlled by several factors based on the biotite calibration data set magnesian biotites x mg 0 65 incorporate ti in accordance with the exchange vector tial2r 1si 2 where r is the sum of the divalent cations mg fe mn this substitution mechanism is primarily a response to misfit of the octahedral and tetrahedral layers in magnesian biotites intermediate biotites x mg 0 65 particularly at higher temperatures exhibit enhanced ti concentrations most consistent with the ti deprotonation tio2r 1 oh 2 exchange vector dominance of ti deprotonation substitution is largely a function of reduction of h2o activity at higher metamorphic grades supplementary biotite data from metaluminous amphibolites and mafic granulites metamorphosed isothermally with variable h2o activities reveal that low al biotite incorporates significantly higher concentrations of ti relative to peraluminous biotite as a result of a combination of the exchange vectors tio2r 1 oh 2 and rsial 2 substituting in roughly an 8 1 ratio

cooling rates and crystallization dynamics of shallow level pegmatite aplite dikes san diego county california pegmatites of the pala and mesa grande pegmatite districts san diego county california are typically thin sheet like composite pegmatite aplite dikes aplitic portions of many dikes display pronounced mineralogical layering referred to as line rock characterized by fine grained garnet rich bands alternating with albite and quartz rich bands thermal modeling was performed for four dikes in san diego county including the 1 m thick himalaya dike the 2 m thick mission dike the 8 m thick george ashley dike and the 25 m thick stewart dike calculations were based on conductive cooling equations accounting for latent heat of crystallization a melt emplacement temperature of 650 c into 150 c fractured gabbroic country rock at a depth of 5 km and an estimated 3 wt initial h 2o content in the melt cooling to 550 c at the center of each dike occurred in 9 years for the stewart dike 340 days for the george ashley dike 22 days for the mission dike and 5 days for the himalaya dike based on these calculations growth rates for large pegmatitic minerals such as the 10 cm long himalaya hanging wall tourmaline crystals may have been on the order of 10 5 cm s crystal size distribution csd studies of garnet from layered aplites suggest growth rates of about 10 6 cm s these results indicate that the dikes cooled and crystallized rapidly with variable nucleation rates but high overall crystal growth rates initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter size aplite grains lower nucleation rates coupled with high growth rates can explain the decimeter size minerals in the hanging walls cores and miarolitic cavities of the pegmatites the presence of tourmaline and or lepidolite throughout these dikes suggests that although the melts were initially h 2o undersaturated high melt concentrations of incompatible or fluxing components such as b f and li h 2o aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models

geometry of upper cretaceous bentonite beds implications about volcanic source areas and paleowind patterns western interior united states four bentonite beds near the cenomanian turonian stage boundary ca 90 ma can be traced through much of the western interior of the united states isopach maps constructed for these bentonite beds indicate that volcanic source areas were positioned both northwest and southwest of the central u s western interior basin and also indicate both easterly and southeasterly paleowind directions volcanism of this age has not been reported previously in the southern source area

trace element evolution of quartz in the charnockitic kleivan granite sw norway the ge ti ratio of quartz as an index of igneous differentiation article i nfo trace element analyses of quartz from the layered charnockitic kleivan granite in the rogaland igneous province rogaland municipality sw norway reveal that the trace element composition of quartz can track igneous evolution during differentiation of the magma combined sem cl imaging and la icp ms analyses allow identification and analysis of primary igneous quartz al ti li and ge are the most abundant trace elements in the kleivan quartz and each element shows a characteristic evolution during differentiation of the granitic magma the ge ti ratio of quartz is a reliable index of the magmatic evolution of granitic igneous systems since ti and ge show pronounced compatible and incompatible characteristics respectively the temperature of the quartz crystallisation varies from 850 c during charnockite formation to 645 c in the most evolved aplitic granite and granitic pegmatite therefore the regular evolution of ti and ge in quartz during cooling of the melt may be used as an igneous geothermometer the li evolution pattern of quartz is mostly controlled by the li content of the melt hence by the absence or presence of li bearing phases forming during solidification of the melt al in quartz is controlled by the aluminium saturation index of the melt accordingly al in quartz is constant during crystallisation of a metaluminous magma and increases during peraluminous conditions the study of rock mineralogy and whole rock geochemistry are not the only methods that can be used to assess the petrogenesis of silica oversaturated rocks the purpose of this study is to demonstrate that the trace element chemistryof quartz and inparticular the ge ti ratio can be used as a petrogenetic tool to characterise an evolving igneous system and can provide information that otherwise may be difficult to obtain quartz is a good mineral for recording and storing the differentiation processes in granitic systems compared to other

wolframite solubility and precipitation in hydrothermal fluids insight from thermodynamic modeling abstract wolframite a solid solution series between hubnerite mnwo4 and ferberite fewo4 is the main tungsten bearing ore mineral in vein type tungsten deposits much progress has been made on characterizing the mineralizing fluids precipitating wolframite but it remains poorly understood what are the mechanisms depositing wolframite effectively and the variables controlling mn fe ratios in wolframite this study examines chemical controls on wolframite solubility in hydrothermal fluids and mn fe ratios in wolframite using thermodynamic models for fluids in the systems of w mn cl na o h and w fe cl na o h the fluid buffered models are established based on the characteristics of vein type tungsten deposits the modeling results indicate that solubilities of hubnerite and ferberite in hydrothermal fluids at typical w mineralizing conditions 300 400 c 500 1500 bars 5 15 wt nacl equivalent ph 4 6 reach up to hundreds of ppm the predominant tungsten manganese and iron species in fluids are h w o 4 m n c l 2 0 and f e c l 4 2 respectively an increase in ph and a decrease in fluid temperature and salinity are efficient mechanisms precipitating hubnerite and ferberite from acidic hydrothermal fluids hubnerite and ferberite are also significantly dissolved in alkaline hydrothermal fluids but their solubilities in alkaline fluids are insensitive to fluid temperature and salinity this may affect w mineralization at stages with different ph levels e g the greisen stage and the alkaline stage the mn fe ratio of mineralizing fluids is the principal variable controlling mn fe ratios in wolframite more supply of fe than mn from the fertile magma tends to produce fe rich mineralizing fluids this may be one of reasons why ferberite is more common than hubnerite in tungsten deposits and why hubnerite is more likely to precipitate at an early stage

k bentonites a review pyroclastic material in the form of altered volcanic ash or tephra has been reported and described from one or more stratigraphic units from the proterozoic to the tertiary this altered tephra variously called bentonite or k bentonite or tonstein depending on the degree of alteration and chemical composition is often linked to large explosive volcanic eruptions that have occurred repeatedly in the past k bentonite and bentonite layers are the key components of a larger group of altered tephras that are useful for stratigraphic correlation and for interpreting the geodynamic evolution of our planet bentonites generally form by diagenetic or hydrothermal alteration under the influence of fluids with high mg content and that leach alkali elements smectite composition is partly controlled by parent rock chemistry studies have shown that k bentonites often display variations in layer charge and mixed layer clay ratios and that these correlate with physical properties and diagenetic history the following is a review of known k bentonite and related occurrences of altered tephra throughout the timescale from precambrian to cenozoic

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

geochemical relationships in cretaceous bentonites as inferred from linear discriminant analysis abstract bentonites serve as an important stratigraphic tool for facies correlation due to their instantaneous deposition and preservation across multiple depositional environments correlating one bed to another can be a complex issue limited by the 3 dimensional availability of outcrops and core this process is reliant on the assumption that the geochemical signatures of ash beds do not vary enough to statistically alter the correlation coefficients that tie one ash fall to another this assumption may be faulty however and the problem compounds as bentonite bed thickness increases because the chemical composition varies through an eruption due to stratification of the magma chamber and through physical transport linear discriminant analysis lda can significantly aid with this issue allowing for the utilization of a multivariate dataset to statistically separate chemically similar groups here we present a statistical approach to assessing the primary discriminatory variables on a suite of 87 cretaceous bentonites deposited in the bighorn basin wyoming usa that span five geologic stages and seven formations from the cloverly formation 110 ma to the meeteetse formation 70 ma and includes nine named ash beds using lda bentonites were sorted into groups based on geologic stage formation and unique beds using key elemental concentrations and radiogenic isotopes e g 87sr 86sr tio2 sc na and th additionally distinct similarities in the discrimination pattern between formations reveal two periods of magmatism the development of the idaho batholith and the migration and development of the boulder batholith and surrounding related plutons with well preserved temporally constrained ash lda can correlate ancient tephra deposits while also shedding light on the cyclical nature of geochemical trends in a migrating subduction zone

application of cathodoluminescence to magmatic quartz in a tin granite case study from the schellerhau granite complex eastern erzgebirge germany a model of the cooling history of tin bearing granitic magma forming the schellerhau granites eastern erzgebirge germany is shown on the basis of quartz textures similar grain size similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the schellerhau granite varieties were intruded four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth the parental melt of the schellerhau granites is interpreted to have contained 2 5 wt h2o originally the water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt and characterizes highly evolved residual melts that enable the formation of tin deposits this study contributes to a better understanding of the development and behaviour of fractionated tin bearing granitic melts and links quartz cathodoluminescence cl with microanalytical studies

analysis of the wallowa baker terrane boundary implications for tectonic accretion in the blue mountains province northeastern oregon the baker terrane exposed in the blue mountains province of northeastern oregon is a long lived ancient late paleozoic early mesozoic accretionary complex with an associated forearc this composite terrane lies between the partially coeval wallowa and olds ferry island arc terranes the northern margin of the baker terrane is a broad zone 25 km wide of fault bounded imbricated slabs and slices of meta igneous and metasedimentary rocks faulted into chert argillite melange of the elkhorn ridge argillite metaplutonic rocks within tectonic units in this zone crystallized between 231 and 226 ma and have low initial 87 sr 86 sr ratios 0 7033 0 7034 and positive initial e nd values 7 7 to 8 5 in contrast siliceous argillites from the chert argillite melange have initial 87 sr 86 sr values ranging from 0 7073 to 0 7094 and initial e nd values between 4 7 and 7 8 we interpret this broad imbricate fault zone as a fundamental tectonic boundary that separates the distal wallowa island arc terrane from the baker accretionary complex terrane we propose that this terrane boundary is an example of a broad zone of imbrication made up of slabs and slices of arc crust tectonically mixed within an accretionary complex providing an on land ancient analogue to the actualistic arc arc collisional zone developed along the margins of the molucca sea of the central equatorial indo pacific region

the geochemical differentiation of s type pegmatites constraints from major trace element and li b isotopic composition of muscovite and tourmaline pegmatites often exhibit regional as well as internal zonation in this study we use major and trace element and li b isotopic composition of muscovite and tourmaline from internally zoned and un zoned s type pegmatites and their host granites to characterize the geochemical and isotopic fractionation associated with their formation the internally zoned pegmatites comprise three distinct textural zones namely wall intermediate and core muscovite and tourmaline occur in all the zones of these pegmatites the trace element concentrations ratios of muscovite from the three zones form well defined differentiation trends marked by enrichment of incompatible elements such as rb cs sr b zn nb ta p and the depletion of ni co v sc ti ba from the wall zone through the intermediate zone to the core zone this is suggestive of a strong role of fractional crystallization in producing the compositional diversity in the internally zoned pegmatites alkali element ratios such k rb and k cs in muscovite exhibit near exponential decline from the wall to the core zone which is suggestive of rayleigh type fractional crystallization fractional crystallization modelling reveals that the formation of the wall zone requires 69 crystallization the intermediate zone 85 95 and the core zone ca 99 crystallization leading to extreme enrichment of rb and cs and other incompatible elements muscovites and tourmaline from the un zoned pegmatites display similar compositional trends as the internally zoned ones but with a significant compositional gap between the host granite and the pegmatite lithium isotopic composition of muscovites and b isotopic composition of tourmalines become progressively lighter from wall to core zone of the internally zoned pegmatite and from the granite to the pegmatite for the un zoned pegmatites this is suggestive of an important role of vapour exsolution in the formation of the pegmatites taken together the geochemical and isotopic trends in the pegmatites can be explained by rayleigh fractional crystallization operating in tandem with vapour exsolution

paleogene postcompressional intermontane basin evolution along the frontal cordilleran fold and thrust belt of southwestern montana the paleogene renova formation is the earliest record of postcompressional sedimentation within and adjacent to the helena salient of the cordilleran fold and thrust belt in southwestern montana paleocurrent and compositional data from basin margin facies document radiating paleodispersal away from high relief 2 km highlands coincident with modern mountainous areas source rocks within the paleohighlands included the same archean metamorphic proterozoic paleozoic and mesozoic sedimentary and mesozoic plutonic and vo l canic rocks as exposed in modern uplifts paleocurrent and compositional data from trunk fluvial conglomerates and sandstones document the existence of an interbasinal drainage system that connected the three forks western gallatin and townsend basins with headwaters farther to the west and southwest near the present day montana idaho border overall the distribution of paleogene mountainous areas and basins closely resembled modern geography and the paleogene drainage network was strikingly similar to the modern missouri river headwater system the renova formation records the early stages of decay of the cordilleran orogenic belt including the evolution of a complex intermontane basin network in southwestern montana high energy late cretaceous to early eocene fluvial systems carved deep large scale paleovalleys into the orogenic wedge along zones of structural and stratigraphic weakness at least a 5 km thickness of overburden was removed during this time incision was temporally correlative with early cenozoic regional uplift and subtropical climatic conditions subsequent deposition of the renova formation was temporally correlative with the cessation of uplift the initiation of crustal extension and climatic cooling however extension is not interpreted to have played a major role in earliest basin development

pollen analysis of some mid pleistocene interglacial lagoonal sediments from southern delaware abstract results of pollen analysis on lagoonal sediments from southern delaware dated at 500 000 1 000 000 yr b p by amino acid racemization are presented three pollen zones are identified in sediments that were deposited during the final stage of an interglacial cycle a closed forest of mixed conifer deciduous trees dominated by tsuga pinus fagus liquidambar and quercus is recorded in the basal zone zone i the inferred climate at this time was temperate and moist a probable lowering of sea level during the deposition of zone ii exposed large areas in the surrounding estuaries and tidal flats which were colonized by marsh and bog plant taxa zone iii is characterized by pinus quercus and picea pollen a scrub oak pine association may have been favored on the coarse sandy soils of the delmarva peninsula at this time because of a drop in the local water table the inferred climate during this interval was colder and probably drier than in zone i

petrogenesis of garnet two mica granites in the ruby mountains nevada garnet two mica granites of jurassic 160 3 m y and cretaceous 83 1 3 m y ages intrude amphibolite facies metasedimentary rocks of precambrian age and lower paleozoic sedimentary rocks in the northern part of the ruby mountains nevada high initial 87sr 86sr and high values of 18o for minerals suggest a dominantly sedimentary source for the magmas total rare earth contents are low and less fractionated cen ybn 10 than granitic rocks of similar composition in the sierra nevada and show a negative eu anomaly eu eu 0 57 these data are consistent with melting in the stability field of plagioclase with little contribution to the melt from refractory minerals such as zircon sphene and apatite minor euhedral garnets are manganese rich and magnesium poor al60sp34py3 6gr2 8 compared to garnet al79sp6py13gr2 in the intruded metamorphic rocks and show an increase in manganese and a decrease in calcium in the outer few microns fractionation of magnesium iron between garnet and biotite and of sodium potassium between k feldspar and plagioclase in the granites suggest submagmatic equilibration temperatures in the range of 365 to 505 c whereas oxygen isotope equilibration temperatures for two granites are higher at 480 and 570 c the compositions of the granites plot near minimum melting compositions in the water saturated quartz albite orthoclase system comparison of muscovite plus quartz stability the water saturated granite solidus and experimental garnet melt equilibria suggests pressures of crystallization no lower than about 3 5 kbar this pressure is compatible with that estimated from garnet plagioclase sillimanite quartz equilibria for the intruded metasedimentary rocks

time stratigraphic aspects of a formation interpretation of surficial pleistocene deposits by analogy with holocene paralic deposits southeastern delaware pleistocene shoreline deposits in close spatial and temporal proximity to holocene deposits permit detailed interpretation of the development of pleistocene coastal deposits when a modern ancient analog approach is used peak sea levels during the past 1 m y or more have allowed the preservation of transgressive shoreline systems here referred to as paralic units along the inner continental margin these pleistocene paralic units are similar to holocene coastal deposits now forming on delmarva peninsula the omar formation early to late pleistocene age incorporates at least four juxtaposed transgressive paralic units of different ages each containing deposits of lagoonal sands and muds tidal marsh barrier sands and gravels tidal delta sands and silty sands and tidal channel sands and gravels the successive paralic units become younger in the seaward direction thus although the omar formation in the study area is almost entirely made up of transgressive deposits produced during rising sea levels in a longer time frame it forms a progradational sequence only about 2 to 5 of the elapsed time during the deposition of the studied part of the omar formation is represented by sedimentary units the internal time stratigraphy of the omar formation is extremely complex this makes the time stratigraphic interpretation of any one outcrop or drill hole difficult any lithologic change may represent a wide variety of time gaps from minutes to tens of thousands of years the analog approach in which sedimentary lithosome mapping is used allows one to infer a time stratigraphic framework of the deposits these concepts can aid in the interpretation of depositional history of older paralic deposits and the nature of the development of certain types of clastic formations

fallout and distribution of volcanic ash over argentina following the may 2008 explosive eruption of chaiten chile 1 the major explosive eruption of chaiten volcano chile in may 2008 provided a rare opportunity to track the long range dispersal and deposition of fine volcanic ash the eruption followed 10 000 years of quiescence was the largest explosive eruption globally since hudson chile in 1991 and was the first explosive rhyolitic eruption since novarupta alaska in 1912 field examination of distal ashfall indicates that 1 6 1011 kg of ash dense rock equivalent volume of 0 07 km3 was deposited over 2 105 km2 of argentina during the first week of eruption the minimum eruption magnitude estimated from the mass of the tephra deposit is 4 2 several discrete ashfall units are identifiable from their distribution and grain size characteristics with more energetic phases showing a bimodal size distribution and evidence of cloud aggregation processes ash chemistry was uniform throughout the early stages of eruption and is consistent with magma storage prior to eruption at depths of 3 6 km deposition of ash over a continental region allowed the tracking of eruption development and demonstrates the potential complexity of tephra dispersal from a single eruption which in this case comprised several phases over a week long period of intense activity

tio2 activity in metamorphosed pelitic and basic rocks principles and applications to metamorphism in southeastern canadian cordillera the activity of tio2 can be precisely defined as a function of pressure temperature and activities of other components for common mineral assemblages in metapelites ilmenite quartz garnet plagioclase al2sio5 and in metabasites plagioclase sphene ilmenite quartzgarnet these mineral assemblages can be modelled by the equilibria 1 3ilmenite al2sio5 2quartz almandine 3tio2 2 anorthite 2sphene grossular 2tio2 quartz 3 3anorthite 3quartz 6ilmenite grossular 6tio2 2almandine these mineral assemblages can be used at a text tio text 2 1 rutile saturation and a given t to get maximum pressure limits of some metapelites and metabasites when electron microprobe analyses of mineral grains adjacent to ti bearing phases are made these data give maximum pressure estimates in reasonable agreement with other geobarometers the activity of tio2 in many metapelites is very near rutile saturation but for metabasites the activity of tio2 in some sillimanite zone rocks is as low as 0 6 the solubility of tio2 in biotite hornblende and garnet is a complex function of t p the activities of components in coexisting minerals and crystal chemical constraints in these minerals at a given p and t the solubility of tio2 in biotite and hornblende does not appear to be strongly dependent upon a text tio text 2 1 for sphene and ilmenite versus rutile bearing assemblages

controls on chemical evolution and rare element enrichment in crystallising albite spodumene pegmatite and wallrocks constraints from mineral chemistry abstract internal differentiation and consequent geochemical evolution in pegmatites are significant processes in the development of economically viable deposits of metal bearing minerals albite spodumene pegmatites which represent important resources of li and ta worldwide challenge the general rules of pegmatite petrogenesis as these are nearly homogeneous bodies with little or no intrusion scale pegmatite zonation bulk intrusion concentrations of li are in the uppermost range obtained by magmatic enrichment experiments around 2 wt li2o and extensive volumes of saccharoidal or platy albite are present in leinster southeast ireland weakly zoned to homogeneous albitised spodumene pegmatites and their wallrocks were studied to compare mineral chemistry variations and understand the internal evolution of pegmatites characteristics linked to the poor development of zonation and links between internal evolution and pegmatite wallrock interactions leinster pegmatites present mineralogical textural and geochemical characteristics coherent with li saturation and possibly supersaturation prior to crystallisation weak border to centre zonation in the thickest bodies can be attributed to geochemically evolved initial melt likely leading to nearly contemporaneous crystallisation throughout the intrusion and resulting in limited internal geochemical fractionation increased abundance of minerals bearing highly incompatible elements e g columbite group minerals and cassiterite and network modifiers e g phosphates in albitite indicates it is a fractionation product from pegmatite crystallisation enrichment in incompatible elements b li rb cs and f in spodumene pegmatite exocontacts in different country rock types suggests unmixing of a hydrous fluid from the residual melt after the crystallisation of main pegmatitic assemblages and that the h2o rich component was mobilised into country rocks

trace elements in hydrothermal quartz relationships to cathodoluminescent textures and insights into vein formation high resolution electron microprobe maps show the distribution of ti al ca k and fe among quartz growth zones revealed by scanning electron microscope cathodoluminescence sem cl from 12 hydrothermal ore deposits formed between 100 and 750 c the maps clearly show the relationships between trace elements and cl intensity in quartz among all samples no single trace element consistently correlates with variations in cl intensity however in vein quartz from five porphyry cu mo au deposits cl intensity always correlates positively with ti concentrations suggesting that ti is a cl activator in quartz formed at 400 c ti concentrations in most rutile bearing vein quartz from porphyry copper deposits indicate reasonable formation temperatures of 750 c using the titaniq geothermometer titanium concentrations of 10 ppm in all veins that formed at temperatures 350 c suggest a broad correlation between ti concentrations and temperature of quartz precipitation in quartz from most deposits formed at 2000 ppm but in high temperature quartz al concentrations are consistently in the range of several hundred ppm aluminum concentrations in quartz reflect the al solubility in hydrothermal fluids which is strongly dependent on ph aluminum concentrations in quartz therefore reflect fluctuations in ph that may drive metal sulfide precipitation in hydrothermal systems

bentonite chemical features as proxy of late cretaceous provenance changes a case study from the western interior basin of canada abstract bentonite beds are fairly common in both marine and terrestrial upper cretaceous campanian maastrichtian deposits of the western interior basin of western canada and northwestern united states a detailed stratigraphic sedimentologic geochemical x ray fluorescence and mineralogical x ray diffraction study of twenty one bentonites from the puskwaskau and wapiti formations in the grande prairie area west central alberta canada is here presented major and trace element concentrations from altered volcanic ashes document the presence in the study area of predominantly trachyandesitic and rhyolitic volcanogenic products resulted from intense volcanic arc to within plate pyroclastic activity concentration values of high field strength elements hfse and selected large ion lithophile elements lile e g nb zr th and y obtained by x ray fluorescence spectroscopy strongly support the presence of multiple volcanic sources integrated paleoenvironmental and geochemical criteria for provenance determination indicate a bimodal occurrence of basic and acid volcanic products interpreted as reflection of source areas characterized by different tectonic setting and magmatic composition a comparative analysis of geochemical compositions between grande prairie bentonites and 30 known volcanic beds from central and southern alberta manitoba and montana 1 documents a trend toward more acidic and alkali depleted volcanic products during the late campanian early maastrichtian interval and 2 suggests a well constrained stratigraphic and geographic subdivision of the non marine successions of the foreland basin on the basis of geochemical characteristic of volcanic ash beds furthermore geochemical fingerprints of several decimeter to meter thick bentonite beds have been coupled with volcanic ash subsurface signature in order to investigate their role as marker beds this multiple approach provides a reliable tool for basin scale identification and correlation of non marine sedimentary successions

millennial and orbital scale climate variability in southeastern united states and in the subtropical atlantic during marine isotope stage 5 evidence from pollen and isotopes in odp site 1059 abstract we present directly correlative high resolution pollen and isotopic data from marine isotope stage mis 5 from a marine core taken on the continental margin off the southeastern united states 31 40 n 75 24 w 2985 m these data provide the first chronostratigraphically controlled pollen data for the last interglacial from this region comparison of the pollen and benthic isotope stratigraphies demonstrate that vegetation and climate development in southeastern united states did not always coincide with global ice volume changes deglacial terrestrial climate amelioration which was nearly synchronous with ice decay peaked slightly before the ice volume minimum in mis 5e cooling in the latter part of the last interglacial began at c27 prior to ice growth vegetation and climate were not stable during mis 5e suborbital climate oscillations persisted throughout mis 5 both onshore and in the subtropical atlantic offshore the largest correlative suborbital oscillations in the pinus pine and quercus oak forests of coastal georgia and south carolina and sea surface variability correspond to stadial interstadials documented in greenland ice cores however coupled oscillations also occur more frequently

the geochemistry and petrogenetic relationships of two granites and their inclusions in the keimoes suite of the namaqua mobile belt south africa abstract the colston and straussburg plutons consist of two dissimilar granites belonging to the proterozoic 1100 1200 ma keimoes suite along the eastern margin of the namaqua mobile belt the intrusives and their enclaves were investigated to establish their genetic relationships the peraluminous colston granite exhibits s type characteristics while the strausaburg intrusive shows marked similarity with i type granites one set of quartz rich melanocratic inclusions are present in the colston granite the corresponding melanocratic enclaves in the straussburg pluton are comprised of a porphyritic type and a non porphyritic type while leucocratic inclusions are also abundant field relationships mineralogical and chemical compositions as well as ree patterns point to a strong genetic relationship between the granites and their enclaves genetic models involving fractional crystallization wall rock assimilation two magma mixing and minimum melt restite mobilisation were considered to explain the nature and origin of the inclusions and the host granites and the observed ree characteristics make most of the models unlikely it is concluded that the quartz rich melanocratic inclusions in both plutons formed as products of partial batch melting from a common source possibly a basic or intermediate gneiss or granulite under relatively high xco 2 conditions after the intrusion and consolidation of the first melts water undersaturated granitic magmas intruded as a secondstage incorporating the first melt products as melanocratic inclusions the different crystallization conditions of the melanocratic inclusions and the host granites are highlighted by the difference in chemical composition of the biotites as for instance illustrated in ti al diagrams the biotite is accompanied by hornblende in all the rock types with the exception of the colston granite and the leucocratic inclusions of the straussburg granite the leucocratic enclaves in the straussburg granite are interpreted as depleted restite material which formed at a pressure near 5 kbar and which was transported to the surface by the granite magma when the compositions of the granitic rocks are compared with the experimental results for the haplogranitic ab or an q system they prove to be quite near the expected minimum melt compositions for a total pressure of 5 kbar

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

formation and evolution of snowball quartz phenocrysts in the dongping porphyritic granite hebei province china insights from fluid inclusions cathodoluminescence trace elements and crystal size distribution study abstract quartz phenocrysts are common in many granites volcanic rocks metamorphic rocks and hydrothermal deposits the dongping porphyritic granite contains large amounts of rounded to sub rounded quartz phenocrysts minerals in this porphyritic granite show weak but distinct orientation dense clusters of fluid inclusions and albite crystals exist in the quartz showing snowball texture two types of snowball quartz are recognized 1 large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle and 2 small snowball quartz crystals containing small albite grains the granite is characterized by high sio2 7 15 73 44 wt k2o 4 70 5 10 wt and na2o 4 93 5 21 wt contents low cao 0 41 0 71 wt mgo 0 03 0 05 wt fe2o3 0 87 0 94 wt tio2 0 02 0 03 wt and ree 7 10 9 80 ppm contents the granite has similar mineral and chemical composition with the aplite in the area and they were derived from the residual melt of the shuiquangou magma that suffered assimilation fractional crystallization process fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260 380 c and salinities of 1 4 12 4 wt nacl equiv for liquid vapor type inclusions and 34 1 44 3 wt nacl equiv for brine ones the quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning the trace element contents in the quartz phenocrysts are extremely low ti 3 4 5 1 ppm al 13 118 ppm li

new u pb id tims and la icpms and 40ar 39ar geochronological constraints of the cretaceous geologic time scale calibration from hokkaido japan abstract we present new radiometric ages in order to constrain the calibration of the cretaceous time scale they have been obtained from volcanic tuffs sampled at hokkaido japan within the northwest pacific marine succession of the yezo group and are compared with ages from the western interior and boreal basins the good coherency between the u pb 40ar 39ar and k ar chronometers when applied simultaneously and their comparison with previous determinations argue for the previously proposed global synchronicity of biotic events the u pb ages allow us to identify that a thermal event has affected some of the k ar ages through argon diffusion furthermore the very low uncertainties associated with the u pb ages argue for the use of this technique for calibrating the geologic time scale we obtain an age of 84 9 0 2 ma from the base of the campanian which provides an upper bound for the santonian campanian limit the cenomanian turonian limit is dated here at 94 3 0 3 ma using u pb applied to zircons from the north pacific basin and at 94 2 1 0 ma using 40ar 39ar applied to a western interior basin tuff the albian cenomanian is constrained here between 99 7 0 3 and 99 7 1 3 ma using the id tims and la icpms u pb techniques respectively the age of 112 6 1 1 ma proposed here for the aptian albian limit is supported by both 40ar 39ar and k ar data finally the approach followed here combining the u pb and k ar and 40ar 39ar isotopic dating allowed us to limit the systematic biases inherent to each approach the very low absolute uncertainties associated with the u pb ages further reinforces the use of this technique for calibrating the cretaceous time scale

high initial sr isotopic ratios and evidence for magma mixing in the pioneer batholith of southwest montana the northeast part of the composite pioneer batholith of southwest montana consists of late cretaceous calc alkaline plutons that vary in composition as a function of age changing from minor hornblende biotite quartz diorite at about 76 m y to a small pluton of hornblende biotite tonalite at about 74 m y to abundant biotite hornblende granodiorite and biotite granite at about 72 m y to some biotite granodiorite and 2 mica granite at 67 to 65 m y initial 87 sr 86 sr ratios sirs for the plutons range from 0 7112 to 0 7160 magmas having a sir near 0 7112 appear in most episodes of emplacement whereas those having higher values are restricted to individual episodes two granodiorite plutons of 72 m y age show a mutual gradational contact across which the sir varies over a distance of 7 km from 0 711 to 0 714 the variation is ascribed to mixing between contemporaneous but isotopically distinct granodiorite magmas the high sirs of the batholith are interpreted as reflecting partial melting

from granite to highly evolved pegmatite a case study of the pinilla de fermoselle granite pegmatite system zamora spain abstract the pinilla de fermoselle pegmatite is a cap like body with an asymmetrical vertical zoning from a granitic facies at the bottom to the upper contact with the metamorphic country rocks the granite grades imperceptibly into the pegmatite which includes three main zones with different degrees of enrichment in li f b p rb cs be sn the essential minerals are quartz feldspar al micas from the muscovite lepidolite series fe micas biotite and zinnwaldite tourmaline schorl elbaite rossmanite and fe mn phosphates apatite beryl cassiterite and cookeite are the most significant accessory minerals the trace elements li be and sr show similar trends in feldspar micas and tourmaline with an increase in the li and be contents and a decrease in sr from the granite to the most evolved pegmatitic zone similar trends are shown by rb cs and ba for micas and k feldspar rb and cs increasing gradually from the granite to most evolved pegmatitic zones simultaneously to the decrease of ba in tourmaline nb and ta contents increase upwards whereas zn contents decrease in the same way the mn contents increase until intermediate degrees of evolution and decrease again in the pinkish elbaite combined field petrographic and geochemical data are consistent with a fractional crystallization model from a granitic melt with a clear petrogenetic relationship between the underlying peraluminous granite and the pegmatite body k feldspar and particularly micas and tourmaline appear as good geochemical monitors using trace elements such as li rb be sr and ba which offer intriguing insights into the petrogenesis of pegmatites

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

origin of the cretaceous bridge creek cycles in the western interior united states abstract alternating beds of burrowed limestone and laminated organic carbon rich marlstone in the bridge creek member of the greenhorn formation were deposited during maximum transgression of the cenomanian turonian sea in the western interior of the united states one view of the origin of the bridge creek limestone marlstone rhythms holds that they represent dilution cycles produced by alternating climates within the western interior the marlstones recording wet episodes when high runoff produced a sediment laden brackish lid on the seaway and the limestones recording dry episodes when runoff was low and the water column well mixed a second view holds that the rhythms represent productivity cycles the limestones representing times of high productivity of calcareous planktonic skeletons and the marlstones representing times of low productivity in this view the rhythms were produced by alternations in vertical circulation that characterized much of the world ocean at the time the productivity origin of the rhythms is supported by the presence of abundant calcispheres in the limestone beds the concentration of clay size quartz in many of the limestone beds the comparatively high 18 o and low 13 c in limestone beds the similarity in proportion of clay minerals in marlstone and limestone beds the pelagic depositional rate of the bridge creek member and by the discovery that bridge creek deposition began with a marlstone and not a limestone bed the dilution model is not consistent with these features and it has not been supported by modeling of paleoclimates and lithofacies that were predicted from it nor by macrofaunal distributions within the seaway the dilution model is not consistent with the occurrence of diverse and abundant planktonic foraminifera in both marlstone and limestone beds which indicate that near normal marine salinities prevailed during deposition of both bed by bed analysis of the bridge creek member may provide an analog for events in the tethys that are poorly recorded in deposits from the deep sea itself

quartz trace element composition by la icp ms as proxy for granite differentiation hydrothermal episodes and related mineralization the beauvoir granite echassieres district france despite quartz being a ubiquitous mineral in the earth s crust only little is known about its trace chemical composition and whether and how this is influenced by the medium from which it precipitated using in situla icp ms analysis we investigated the trace element composition of several types of quartz from a magmatic hydrothermal system in the echassieres district of the french massif central this system consists of the colettes granite the beauvoir rare element granite a w bearing stockwork and dispersed mineralized veins all of the elements tested li be b na al ti ge rb sr nb sn sb ta w were detected in quartz from at least one sample a rigorous multivariate statistical approach permitted to assign a specific chemical signature to each of the quartz groups that were recognized by petrographic observations differences among these groups were interpreted to reflect different sources or genetic evolutionary trends within magmatic and hydrothermally derived quartz groups for example the evolution of al rb ge li and ti could be related to genetic processes such as the degree of magma differentiation and crystallization temperatures quartz from the w stockwork anterior to the beauvoir leucogranite clearly stands out from that related to the beauvoir mineralization system i e the greisen facies and proximal ta nb sn w mineralized veins it was also possible to demonstrate a similarity in composition notably the sb contents between quartz from the greisen and from distal stibnite bearing veins in addition elevated values of sb sn as well as li and rb in quartz correspond to similarly high values of these elements in the rock indicating that quartz trace chemistry can provide useful information for the mineralization potential of its host at least for these elements on the other hand nb ta and w are less reliable as they occur mostly at very low levels in quartz the highest values corresponding to samples that were not particularly enriched in these metals a comparison of our quartz data with those from a similar granitic complex at cinovec czech republic breiter et al 2017a shows a similar trend for the ge ti ratio reflecting magmatic differentiation conversely the al ti ratio values differ in the two complexes the al content of quartz from the various cinovec granites being systematically lower than in quartz from echassieres nevertheless caution must be taken when analyzing quartz for its trace element chemistry as processes occurring during i e trapping of fluid inclusions and formation of zoning and after crystal growth i e diffusion and alteration can introduce heterogeneities thus affecting the original chemistry

elemental abundance anomalies in the late cenomanian extinction interval a search for the source s elemental abundances have been measured by neutron activation methods across the cenomanian turonian late cretaceous extinction interval in samples collected from sixteen sites in the western interior basin of north america and from twelve widely separated locations around the globe including six odp dsdp sites in most western interior basin sites in colombia and in western europe weaker two closely spaced elemental abundance peaks occur in the upper cenomanian 92 m y spanning the ammonite zones ofsciponoceras gracile throughneocardioceras juddii elements with anomalously high concentrations include sc ti v cr mn co ni ir pt and au the lower peak coincides with the disappearance extinction of the foraminiferrotalipora cushmani in north american sectionsr greenhornensis also disappears at or just below this horizon but in europe it disappears considerably earlier thanr cushmani a series of molluscan extinction and speciation or migration events also begins near the stratigraphic level of the lower elemental abundance peak the well documented positive 13c excursion begins just before the extinctions and the elemental anomalies and continues into the lower turonian well above the upper anomaly this carbon isotope excursion has been observed in east european sections where we find little or no evidence of the elemental anomalies suggesting that the two phenomena may not be tightly coupled elemental abundance ratios in the anomalies closely resemble those of mid atlantic ridge basalt or hawaiian lava tholeiitic but not those of c1 chondrite black shale average crustal rocks or lamproite and kimberlite of roughly similar age in southeastern kansas the excess ir and other siderophiles hint at possible large body impact s for the source however we have not located microspherules other than biogenic calcispheres or shocked mineral grains in any of our samples furthermore sc ti v and mn are not enriched in differentiated solar system bodies although the weak geochemical signal from comet impact s could be masked by the strong terrestrial like overprint these anomalies more likely resulted either from intense seafloor spreading activity or merely from increased circulation of deep metal rich water associated with the large late cenomanian through early turonian eustatic rise and deep water opening of the south atlantic the flooding of continental seaways and margins also could have contributed to the anomalies by preventing much continental detritus from diluting the normal background marine geochemical component

correlation of physical surfaces bentonites and biozones in the cretaceous colorado group from the alberta foothills to southwest saskatchewan and a revision of the belle fourche second white specks formational boundary new allostratigraphic correlations in west central alberta show that flooding surfaces in the sunkay and basal vimy members of the blackstone formation can be traced eastward from burnt timber creek for 500 km to western saskatchewan and for 350 km northward into the dunvegan and kaskapau formations at burnt timber creek a miliammina manitobensis microfauna in the lowest 1 m of the sunkay member indicates equivalence to the westgate formation and an overlying 70 cm conglomerate is correlative with the fish scales formation overlying mudstones contain foraminifera of the verneuilinoides perplexus zone indicative of the middle cenomanian belle fourche formation the base of the second white specks formation as currently defined in core in eastern alberta equates in outcrop with the lower part of the sunkay rather than the base of the vimy member as previously thought the base of the second white specks formation should be placed about 35 m higher in the stratotype core a bentonite located 9 3 m

the record of middle jurassic volcanism in the carmel and temple cap formations of southwestern utah altered volcanic ash beds in the middle jurassic temple cap and carmel formations in southwestern utah record a pulse of active arc related volcanism between 166 and 171 ma a second pulse between 148 and 155 ma has previously been documented in the upper jurassic morrison formation volcanic and volcaniclastic rocks of these same ages have also been identified closer to or within the arc in california in the inyo mountains the cowhole mountains the palen mountains and the central mojave desert the upper part of the volcaniclastic mount wrightson formation and the strata of cobre ridge in southern arizona are ca 170 ma in age and appear to be time correlative with the middle jurassic formations in southwestern utah the altered ash beds found in the temple cap and carmel formations typically contain phenocrysts of sanidine quartz biotite apatite zircon and titanite plagioclase was likely present originally in all of the ashes but was removed by alteration and is now found only in the temple cap red beds quartz and sanidine are absent in two crystal poor ash beds that contain two pyroxenes hornblende and biotite although major and trace element concentrations in the ash beds have been substantially modified compositions of relict phenocrysts reveal that the magmas were calc alkaline rhyolites to andesites two pyroxene two feldspar biotite and biotite apatite thermometers suggest that crystallization occurred at temperatures ranging from 740 to 910 8c hornblende geobarometry yields pressures of 1 2 kilobars for the two ash beds that contain the appropriate buffer assemblage the mafic silicates all have moderately high mg fe ratios this fact combined with the presence of hornblende biotite and titanite suggests that the phenocrysts crystallized at high oxygen fugacities similar to those of the granites of the batholiths of california the ash probably erupted from a low lying arc cut by strikeslip faults in what is now southern california and western nevada major jurassic unconformities occur near or within the ash bearing formations in southwestern utah laser fusion singlecrystal 40 ar 39 ar measurements have defined the ages of the unconformities and the associated volcanism the age of the j 1 unconformity found at the base of the temple cap formation in southwestern utah is older than ca 170 5 ma the j 2 unconformity which lies between the temple cap and carmel formations formed between ca 169 and 168 ma the origin of these unconformities is still unclear but may be related to the middle jurassic pulse of magmatism and the oblique plate convergence along the western margin of north america the age range of ash beds in the carmel formation between 166 3 and 168 0 6 0 5 ma is consistent with a bajocian bathonian boundary of ca 166 ma

paleoenvironmental and paleoceanographic changes across the cenomanian turonian boundary event oceanic anoxic event 2 as indicated by foraminiferal assemblages from the eastern margin of the cretaceous western interior sea abstract two sites near the eastern margin of the cretaceous western interior sea wis were investigated the section at cuba kansas ck is 630 km east of the gssp for the cenomanian turonian boundary at rock canyon colorado rc and the section near sioux city iowa sci is 315 km northeast of the cuba site surprisingly planktic foraminifera dominate all the studied samples despite the relative proximity of the sites to the paleo shoreline and presumed neritic water depths such dominance suggests inhospitable benthic environments and benthic foraminiferal assemblages indicate that seafloor oxygen in the wis decreased eastward therefore the hypothesis of an influx of freshwater into the wis from the western margin forming a fresh water cap that diminished eastward is not supported benthic foraminifera are scarce in most studied samples and species diversity is low in the ck section diversity and abundance increase abruptly in the uppermost cenomanian benthonic zone at the initiation of the 13corg positive excursion marking the onset of oceanic anoxic event oae 2 in the sci section however the benthonic zone is recognized only by presence of nodosaria bighornensis that has a stratigraphic range restricted to this interval other benthic taxa are very rare or absent the favorable conditions of the benthonic zone were short lived while relatively diverse planktic foraminiferal assemblages including keeled species characterize the initial 13c excursion at the ck site dwarfed specimens of heterohelix and hedbergella dominate the assemblages at the more proximal sioux city site furthermore most of the biostratigraphic events recognized in the basin center rc section can be traced into the ck section but not into the sci section including the rotalipora spp and globigerinelloides bentonensis extinctions the heterohelix shift event and the brief benthic recovery event correlation between eastern wis sites shows that the sci section is thicker suggesting a major sediment source to the east this may explain the inhospitable benthic conditions and development of a dead zone seasonal hypoxia analogous to the modern shelf of the northern gulf of mexico proximal to active discharge of the mississippi river development of estuarine circulation in the wis provided the eastern part of the basin with input of calcareous plankton from the south including planktic foraminifera foraminiferal assemblages total organic carbon toc and 13c data of the studied sections suggest a two fold history of greenhorn transgression and oae 2 development the initial phase is a global signal characterized by a positive 13c excursion low toc values and high foraminiferal species diversity the second phase is characterized by overprinting by local conditions in the wis including high fluvial input relatively high toc values and low foraminiferal species diversity these findings suggest that the eastern margin records unique depositional and biotic environments further revealing the dynamic and complex nature of the wis and its sedimentary cycles

magmatic hydrothermal transition of mo w mineralized granite pegmatite greisen system recorded by trace elements in quartz krupka district eastern krusne hory erzgebirge abstract magmatic hydrothermal transition of highly evolved granitic melts enriched in volatile and incompatible elements can involve disequilibrium intermediate products between aluminosilicate melt and hydrothermal fluid hydrosilicate liquids with high ore forming potential we investigate evolution from li f rich granites through pegmatites greisens and quartz veins in a composite stock at knottel in the krupka district eastern krusne hory erzgebirge mountain range by monitoring trace element variations in quartz interelemental correlations reveal si4 li al3 and likely si4 h al3 to be the most important substitution mechanisms variations in ti vs li be and al define distinct evolutionary trends i magmatic high li ti or al ti trend granites aplites k feldspar pegmatite ii transitional medium li ti trend quartz megacrysts and pegmatite lenses in granite quartz protolithionite pegmatite iii hydrothermal low li ti or al ti trend stockwork of coarse grained hydrothermal quartzites and quartz veins quartz replacement in greisens the medium li ti trend represents hydrosilicate liquid an h2o and sio2 rich medium with low density and effective viscosity that was probably formed during disequilibrium crystallization in front of rapidly propagating solidification front thermal evolution of the magmatic hydrothermal system was monitored by ti in quartz thermometry calculated rutile activity of the granites is very low 0 3 0 05 but it increases up to 1 that is saturation towards pegmatites and hydrothermal veins magmatic crystallization granites and aplites is constrained to 700 580 c pegmatite and bulk greisenization stage occurred at 600 500 c followed by a late hydrothermal stage associated with the formation of distal quartz veins at 500 390 c the granite pegmatite systems at knottel and in erzgebirge in general reach extremely high al li rb and ge and low ti concentrations in quartz in comparison with igneous rocks worldwide the knottel stock belongs to p poor a type granites in the erzgebirge and is linked with them by similar evolutionary trends in quartz trace elements furthermore the knottel system exhibits be enrichment in quartz probably related to high contents of f and this appears to be typical feature of mo w mineralized systems in general the hydrothermal phase with mo w mineralization at knottel is closely related to the magmatic phase of parental granite body which seems to be an important condition for mo w mineralization formation

the origin of tonsteins an overview and links with seatearths fireclays and fragmental clay rocks abstract tonsteins are volcanic ash falls in coal bearing sequences that have altered to kaolinite only in the last twenty years or so has the volcanic origin become firmly established the evidence for the volcanic origin encompasses bed form including lateral extent structures textures volcanogenic mineralogy and geochemistry the lines of evidence are reviewed from a historical perspective tonsteins came to prominence over a hundred years ago because of their stratigraphic value tonsteins continue to be of value in coalfield exploration but their stratigraphic value has been enhanced in recent years with the ability to determine radiometric ages with a high level of accuracy the geochemistry not only provides good evidence for the volcanic origin but also enables tectomagmatic deductions to be made for areas external to the coal basin in addition some tonsteins are the indicators for the discovering of rare metal ore deposits nb rees and ga there is also the potential to use the geochemistry to identify specific tonsteins essentially a chemostratigraphic approach tonsteins are seen as one class of bentonites others include k bentonites metatonsteins and possibly illitic bentonites tonsteins have been linked to seatearths fireclays and fragmental clay rocks although all such rocks contain kaolinite the origins differ the seatearths contain rootlets and were subjected to pedogenic activity alteration of the silicate minerals is limited under conditions of a high water table and in the presence of organic matter reducing conditions prevailed leading to gleization on the other hand the fireclays show extensive alteration to kaolinite there is a link with the major marine bands and this has implications in terms of sequence stratigraphy the fragmental clayrocks have also been linked to soil forming processes but in this case possibly the reworked soil was the product of an open system containing free alumina minerals that reacted with silica in solution during diagenesis

trace element composition of quartz from the variscan altenberg teplice caldera krusne hory erzgebirge mts czech republic germany insights into the volcano plutonic complex evolution abstract in this study the internal structures and appropriate trace element distributions within quartz grains were investigated using a laser ablation icp ms technique combined with a hot cathode and scanning cathodoluminescence analysis the studied variscan magmatic suite is located in the altenberg teplice caldera eastern krusne hory erzebirge along the czech republic germany border and composed of co magmatic volcanics peraluminous basal rhyolite and associated dacite overlying three units of subaluminous teplice rhyolite and granite porphyry and plutonic granites two intrusions of a type biotite and zinnwaldite granites the trace element distribution in the granite porphyry and rhyolite quartz demonstrates a distinct zoning in the cathodoluminescence images and chemical compositions the core is poor in ti the outer rim zones are enriched in ti and the trends recorded for al are opposite to those of ti the quartz from granites is either very weakly zoned or homogeneous based on the chemical composition of quartz and its zoning we assume that the quartz crystals began to crystallize gradually in the primary deep seated magma chamber with a p t condition of 10 kbar and 750 c and in an environment with an increasing concentration of al and decreasing concentration of ti the early stage was followed by the subsequent adiabatic ascent into a shallow magma chamber estimated by the ti in quartz thermobarometry at approximately 700 c 2 kbar during which crystal rims rich in ti formed and then extruded after the caldera collapse part of the magma intruded as granite and in the environment of the residual melt rich in water and flux agents late quartz grew in the form of snowball quartz with an increased al content and decreased ti content

behavior of trace elements in quartz from plutons of different geochemical signature a case study from the bohemian massif czech republic article i nfo in this study the trace element content in igneous quartz from granitoids of different geochemical types was investigated using the laser ablation icp ms technique the variscan granitoids in the bohemian massif pro vide an excellent opportunity to study the chemical composition of magmatic quartz from the following granite types 1 geochemically primitive i type tonalites and granodiorites 2 peraluminous s type two mica granites 3 moderately fractionated a type volcano plutonic complexes of the teplice caldera and 4 highly fractionated s and a type rare metal granites this diversity of granitoids permitted the study of the chemical composition of magmatic quartz as the result of i different magma protoliths and ii variable degrees of differentiation there were only small differences in the quartz trace element con tents ranging from weakly to moderately differentiated plutons of all geochemical types al mostly in the range between 20 and 250 ppm ti mostly 20 110 ppm b b13 ppm be b0 7 ppm ge b1 ppm li b30 ppm and rb b2 ppm only the s type granites from western erzgebirge contain al enriched quartz mostly 200 400 ppm al since the beginning of its evolution however quartz from the highly fractionated granites group 4 differs significantly this quartz is generally poor in ti b20 ppm ti and enriched in al up to 600 ppm in a type and up to 1000 ppm in s type granites be up to 3 2 ppm ge up to 5 7 ppm li up to 132 ppm particularly in the s type granites and rb up to 15 ppm the contents of the analyzed lithophile elements in the quartz from the highly fractionated granites are similar to the contents reported to be present in evolved complex pegmatites although the input of ti into quartz is controlled mainly by the temperature and pressure of quartz crystallization the entry of al into quartz increases as a function of the water and fluorine content of the residual melt the contents of ge and li increase significantly with the fractionation of parental melt the concentrations of these elements in quartz from highly fractionated granites are controlled by the order of crystallization of the major minerals comb quartz crystallizing before li mica is strongly li enriched whereas groundmass and snowball quartz crystallizing after mica is relatively enriched in ge