synorogenic melting of mafic lower crust constraints from geochronology petrology and sr nd pb and o isotope geochemistry of quartz diorites damara orogen namibia quartz diorites represent the earliest ca 540 ma and most primitive plutonic rocks in the pan african damara belt and they pre date the main phase of high t regional metamorphism two suites of synorogenic quartz diorites are unusual among damaran intrusive rocks in their elemental and isotopic features comparison of the diorite compositions with melts from amphibolite dehydration melting experiments points to a garnet bearing meta tholeiite probably enriched in k2o as a likely source rock partial melting processes generated mafic ca 50 wt sio2 quartz diorites in the deep crust at temperatures of between 1 000 and 1 100 c based on comparison with experimental results and similar temperature estimates based on p2o5 solubility in mafic rocks subsequently the quartz diorites evolved by multistage polybaric differentiation processes including fractional crystallization of mainly hornblende and plagioclase and assimilation of felsic basement gneisses although their chemical characteristics high lile low hfse resemble those of other quartz diorites with calc alkaline affinities they differ in their enriched sr initial 87sr 86sr 0 70943 0 71285 nd initial e nd 9 1 to 15 2 and o 18o 6 8 8 1 isotope compositions neodymium model ages tdm that range from 1 7 to 2 2 ga and large variation in 207pb 204pb relative to 206pb 204pb indicates involvement of ancient crustal material lead 206pb 204pb 17 08 17 23 207pb 204pb 15 53 15 62 208pb 204pb 37 71 38 16 isotope compositions are strongly retarded indicating that the source underwent a pre pan african u pb fractionation and u depletion it is proposed that the quartz diorites originated by synorogenic high temperature melting of mafic lower crust this contrasts with previous suggestions favouring an origin of these rocks by melting of an enriched mantle during pan african times with characteristics modified by subduction of oceanic crust and sedimentary rocks

adakite like and normal arc magmas distinct fractionation paths in the east serbian segment of the balkan carpathian arc are used to assess petrogenetic and regional geodynamic processes associated with late cretaceous subvolcanic intrusions within the sparsely studied timok magmatic complex tmc and ridanj krepoljin zone rkz of eastern serbia the tmc and rkz form part of the apuseni banat timok srednogorie abts magmatic belt a cu au mineralized calc alkaline magmatic arc related to closure of thetethys ocean that extends through romania serbia and bulgaria in se europe zircon ages based on u pb laser ablation inductively coupled plasma mass spectrometry supplemented by existing isotope dilution thermal ionization mass spectrometry data respectively range from 89 to 79 ma and from 76 to 71 ma for the tmc and rkz this age pattern corresponds to cross arc younging away from the european continent adakite like trace element signatures y 18 ppm are linked with samples that extend across the arc these overlap in space and time with samples that conform to a normal arc differentiation trend we performed energy constrained assimilation fractional crystallization ec afc modeling of sr la nd yb concentrations and sr and nd isotopic data results suggest that the two distinct fractionation trends may be explained in terms of a common mantle derived parental magma but distinct fractionation and assimilation paths in the lower and upper crust petrogenesis of the adakite like magmas is consistent with extensive high pressure amphibole fractionation in the lower crust followed by ascent and plagioclase dominant fractionation and assimilation in the upper crust in contrast normal arc signatures appear to have evolved exclusively via an upper crustal differentiation process overall our interpretation supports mantle wedge melting related to weak extension during progressive rollback of a subducting slab

constraints on the application of long chain diol proxies in the iberian atlantic margin abstract long chain diols are lipids that have gained interest over the last years due to their high potential to serve as biomarkers and diol indices have been proposed to reconstruct upwelling conditions and sea surface temperature sst however little is known about the sources of the diols and the mechanisms impacting their distribution here we studied the factors controlling diol distributions in the iberian atlantic margin which is characterized by a dynamic continental shelf under the influence of upwelling of nutrient rich cold deep waters and fluvial input we analyzed suspended particulate matter spm of the tagus river marine spm and marine surface sediments along five transects off the iberian margin as well as riverbank sediments and soil from the catchment area of the tagus river relatively high fractional abundances of the c32 1 15 diol normalized with respect to the 1 13 and 1 15 diols were observed in surface sediments in front of major river mouths and this abundance correlated strongly with the bit index a tracer for continental input of organic carbon together with an even higher fractional abundance of the c32 1 15 diol in the tagus river spm and the absence of long chain diols in the watershed riverbank sediments and soils we suggest that this long chain diol is produced in situ in the river further support for this hypothesis comes from the small but distinct stable carbon isotopic difference of 1 3 with the marine c28 1 13 diol the 1 14 diols are relatively abundant in surface sediments directly along the northern part of the coast close to the upwelling zone suggesting that diol indices based on 1 14 diols would work well as upwelling tracers in this region strikingly we observed a significant difference in stable carbon isotopic composition between the mono unsaturated c30 1 1 14 and the saturated c28 1 14 diol 3 8 0 7 suggesting different sources in accordance with their different distributions in addition the long chain diol index ldi a proxy for sea surface temperature was applied to the surface sediments the results correlated well with satellite ssts offshore but revealed a significant discrepancy with satellite derived ssts in front of the tagus and sado rivers this suggests that river outflow might compromise the applicability of this proxy

petrogenesis of archaean trondhjemites tonalites and granodiorites from eastern finland major and trace element geochemistry

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

late quaternary productivity changes from offshore southeastern australia a biomarker approach reconstructions of primary productivity at low latitudes have been the focus of several studies to better understand how the export of nutrient rich intermediate southern ocean so waters influences productivity at these latitudes this was triggered by the general observation of minima in the planktonic foraminiferal delta c 13 values during deglaciations which was interpreted as an isotopic signal of intermediate so waters together with a concomitant increase in diatom productivity at some equatorial sites however the impact of these so waters on productivity at higher latitudes is not well constrained here we compare a high resolution planktonic foraminiferal delta c 13 record with total organic carbon and biomarker records for proboscia diatoms and haptophytes in marine sediments from offshore southeastern australia the planktonic foraminiferal delta c 13 record shows distinct minima during deglaciations and the marine isotope stage 4 3 transition tentatively suggesting that c 13 depleted so waters reached the coast of southeastern australia however it did not result in increased productivity during these periods instead the highest primary productivity period as indicated by total organic carbon and alkenone accumulation rates occurred during the last glacial maximum while proboscia diatoms mainly proliferated during interglacials and marine isotope stage 3 matching periods of increased diatom productivity in some sites of the eastern equatorial pacific our study suggests that increased primary productivity offshore southeastern australia was mainly due to stronger westerly winds during glacial periods while proboscia diatom productivity was probably controlled by the transport of silicic acid to this area

age of variscan magmatism from the balkan sector of the orogen central bulgaria abstract new high resolution secondary ion mass spectrometry u th pb data obtained from zircon and monazite from representative variscan intrusions in the balkan sector of the variscan orogen central bulgaria constrain the ages of magmatism to the interval 315 285 ma the samples investigated are granitoids from two contrasting intrusive suites calc alkaline granitoids of the first suite include the san nikola granite 311 9 4 1 ma and the petrohan granodiorite 304 6 4 0 ma from the balkan terrane and the smilovene 304 1 5 5 ma and hisara 303 5 3 3 ma granites from the sredna gora terrane zircons from these intrusions predominantly lack inherited cores the second suite consists of two mica leucocratic granites and includes the koprivshtitsa 312 0 5 4 ma and strelcha 289 5 7 8 ma plutons zircons from intrusions of the second suite are 80 90 xenocrystic apparent ages of inherited cores are the magmatic age and slightly older 300 400 ma to ordovician 450 ma ages and to neoproterozoic 600 900 ma ages gabbroic magmas related to the first suite are found only in the more northerly balkan terrane while the leucogranites occur only in the southerly sredna gora terrane although coeval the two suites of intrusions are not genetically related and furthermore were likely derived from different source regions via different melt generating mechanisms we propose a tectonic and petrogenetic model whereby following juxtaposition of the balkan and sredna gora terranes during variscan collision the two suites of magmas were generated by continued subduction under eastern europe due to the influx of mafic magmas into the base of the crust and by influx of water rich fluids into high grade metapsammitic rocks of the sredna gora metamorphic series the new ages are somewhat younger than ages for post collisional intrusions in the central european variscan massifs i e bohemian black forest and vosges where ages of intrusions are predominantly 340 320 ma although some younger intrusions may also occur within the intra alpine massifs both older 340 320 ma and younger 310 290 ma granitoids are present farther west intrusions in the iberian massif appear to be predominantly younger 325 290 ma similar to the intrusions of the balkans this may indicate that collision of adjacent crustal blocks culminated at earlier times in the central and more northerly portions of the orogen and moved both east west and south as the evolution of the orogen progressed

variscan vs alpine tectonothermal evolution of the southern carpathian orogen constraints from 40ar 39ar ages abstract 40 ar 39 ar hornblende and muscovite ages indicate that basement units exposed within all major alpine nappes of the southern carpathian orogen were penetratively deformed and metamorphosed during late variscan carboniferous tectonothermal events subsequent exhumation resulted in cooling from ca 500 c hornblende k ar retention temperature to ca 375 c muscovite k ar retention temperature between ca 320 and 295 ma late variscan exhumation of middle crustal levels is interpreted to have resulted from intracontinental contraction and regional uplift subsequent to variscan continental collision between gondwana derived tectonic elements e g africa and laurussia muscovite ages within mylonite zones suggest that late variscan shear zones were probably associated with a regional shear system that developed along the southern margins of laurussia alpine metamorphic effects within the southern carpathians are generally nonpenetrative and are only significant within narrow zones of retrogression that are interpreted to have formed during initial attenuation of variscan crust associated with formation of the jurassic severin rift

nd isotopic mapping of the sri lanka basement update and additional constraints from sr isotopes abstract the high grade crystalline basement of sri lanka can be subdivided into three provinces distinguished by distinct isotopic model ages this confirms the conclusions of milisenda et al 1988 made on the basis of much more limited data high grade ortho and paragneisses from the highland complex in central sri lanka yield palaeoproterozoic to archaean nd model ages from 2 0 to 3 4 ga and reflect an extended premetamorphic crustal history the wanni complex in the western and northwestern part of the island is characterized by meso to neoproterozoic nd model ages ranging from 1 0 to 2 0 ga the vijayan complex in the southeast is occupied by neoproterozoic i type granitoids with nd model ages from 1 0 to 1 8 ga this distinct crustal province appears to fit best a detached continental margin plutonic terrane the isotopic data preclude a common premetamorphic history of the wanni and vijayan complexes with the ancient highland complex the combined nd sr and pb isotope data together with recent geochronological studies strongly suggest that the distinct crustal age provinces are separated by tectonic discontinuities and that they represent terranes that were accreted just prior to the high grade metamorphic event in neoproterozoic time

origin of high potassium talc alkaline i type granitoids many i type granitoid magmas are generated through partial melting of older metaigneous rocks and the compositions of such melts are broadly calc alkaline and metaluminous these melts are granitic to tonalitic and result from thermal extremes in their lower crustal source regions data on the experimental partial melting of common crustal rocks suggest that high k i type granitoid magmas can be derived only from the partial melting of hydrous calc alkaline to high k calc alkaline mafic to intermediate metamorphic rocks in the crust because of their low k2o contents metabasaltic rocks of all kinds are unsuitable as sources and models that propose mixing of mantle derived basaltic magmas and crustal melts are also inadequate there is no requirement that i type calc alkaline magmatism be related in any way to subduction processes

pre alpine evolution of a segment of the north gondwanan margin geochronological and geochemical evidence from the central serbo macedonian massif abstract the serbo macedonian massif smm represents a composite crystalline belt within the eastern european alpine orogen outcropping from the pannonian basin in the north to the aegean sea in the south the central parts of the massif i e southeastern serbia southwestern bulgaria eastern macedonia consist of the medium to high grade lower complex and the low grade vlasina unit new results of u pb la icp ms analyses coupled with geochemical analyses of hf isotopes on magmatic and detrital zircons and main and trace element concentrations in whole rock samples suggest that the central smm and the basement of the adjacent units i e eastern veles series and struma unit originated in the central parts of the northern margin of gondwana these data provided a basis for a revised tectonic model of the evolution of the smm from the late ediacaran to the early triassic the earliest magmatism in the lower complex vlasina unit and the basement of struma unit is related to the activity along the late cadomian magmatic arc 562 522 ma subsequent stage of early palaeozoic igneous activity is associated with the reactivation of subduction below the lower complex and the eastern veles series during the early ordovician 490 478 ma emplacement of mafic dykes in the lower complex due to aborted rifting in the middle ordovician 472 456 ma and felsic within plate magmatism in the early silurian 439 2 ma the third magmatic stage is represented by carboniferous late to post collisional granites 328 304 ma these granites intrude the gneisses of the lower complex in which the youngest deformed igneous rocks are of early silurian age thus constraining the high strain deformation and peak metamorphism to the variscan orogeny the permian triassic 255 253 ma stage of late to post collisional and within plate felsic magmatism is related to the opening of the mesozoic tethys

localization of volcanic activity topographic effects on dike propagation eruption and conduit formation magma flow in a dike rising in a crack whose strike runs from a highland or a ridge to an adjacent lowland has been modeled to determine the effect of topography on the flow it is found that there is a distinct tendency for the flow to be diverted away from the highland end of the strike toward the lowland separation of the geometric effect of the topography from its effect on lateral confining stresses on the crack indicates that both contribute to the effect but that the effect of stress is less important although this analysis explains a tendency for volcanic eruptions to occur in low lands it does not preclude eruptions on highlands the particular configuration modeled mimics topography around the proposed nuclear waste repository at yucca mountain nevada so that the results may indicate some reduction in the volcanic hazard to the site

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

source constraints on the genesis of danubian granites in the south carpathians alpine belt romania abstract the pre alpine basement of the lower danubian nappes in the south carpathians is made up of two precambrian terranes dr gsan and lainici p ius that were intruded by pan african cadomian and variscan granitoid massifs we focus on the major and trace element geochemistry 1 in the dr gsan terrane of the variscan retezat and par ng intrusions 2 in the lainici p ius terrane of the variscan furc tura petreanu and frumosu intrusions and of the pan african v rful pietrii usi a and olte granites and granitic leucosomes of migmatites and 3 in the upper danubian nappes basement of the variscan muntele mic sf rdin cherbelezu and ogradena intrusions for each intrusion in which a range of composition is observed we decipher the differentiation mechanisms fractional crystallization hybridization melt laden with restite minerals etc in order to define the parental liquid compositions the latter are calc alkaline to alkali calcic except olte that is calcic and medium to high k in composition with la yb n 10 and sr y 15 most melts display the so called continental adakite affinities the parental melt compositions are compared with experimental data to determine the melting conditions and the nature of the source rock when the p t conditions can be estimated the temperatures range between 850 c and 875 c and the pressure between 5 and 15 kbar regardless of the ages of the granites and the terrane in which they have intruded the source rock composition is dominated by a variety of mafic igneous compositions or metasediments rich in volcanic components clay rich pelitic protoliths have not been identified we confirm a variscan age c 300 ma for the frumosu intrusion granite and inherited precambrian ages c 1 7 1 9 and 2 6 2 9 ga for the motru dyke swarm thus both dr gsan and lainici p ius together with the upper danubian basement terranes were affected by variscan post collisional granitic plutonism in the south carpathians both pan african and variscan granites were generated in a crust thickened by stacking of terranes the source of the pan african granites in lainici p ius is different from that of the variscan granites from lainici p ius and dr gsan terranes and from the upper danubian nappe basement but all these sources were notably depleted in metapelite component

timing of k alkaline magmatism in the balkan segment of southeast european variscan edifice id tims and la icp ms study the variscan orogen in southeast europe is exposed in isolated remnants affected by a subsequent alpine tectono magmatic overprint unlike the central european variscides in se europe the juxtaposition and correlation of the events and products are impeded by the scarcity of variscan domains with preserved magmatic metamorphic sedimentological and structural characteristics to reveal the particular evolution of the variscan orogen in balkan mts we present the results of id tims and la icp ms dating of three potassic alkaline intrusions svidnya buhovo seslavtsi and shipka the age determinations from the plutons do not permit to establish their unequivocal ages but they bracket the time interval of emplacements based on geochronological tectonic and stratigraphic evidence the emplacement interval for plutons could be 317 310 ma for svidnya 330 310 ma for buhovo seslavtsi and 320 303 ma for shipka these results show that the generation of potassic alkaline magmas was post visean and is contemporaneous with the adjacent numerous calc alkaline granitoid plutons thus the variscan orogen in the balkan mts is not characterized by a time dependent geochemical evolution of magma generation hence the observed differences in the rocks compositions can be interpreted solely by distinction between the magma sources the available data for both potassic alkaline and calc alkaline rocks indicate that the major episodes of crustal stacking and shearing in the balkan part of the variscan edifice are pre visean 330 ma the present study reveals that the potassic alkaline rocks from the balkan mts are younger than the central european potassic granitoids durbachites it suggests that melting of enriched mantle source took place at different times throughout the variscan orogen in spite of the alkaline character of the magmas the studied zircons show a complex nature with inherited cores and magmatic overgrowths the observed heterogeneities in the zircons imply the presence of much older materials in the petrogenesis of the rocks from the potassic alkaline plutons

flow localization in fissure eruptions during a basaltic fissure eruption heat transfer from the hot magma to the surrounding rock causes a dramatic increase in the magmatic viscosity and solidification at the margins both viscosity contrast and solidification can amplify initial variations in the flow rate and lead to localization of the flow along the strike of the fissure however for typical parameters amplification driven by solidification is slower and significantly weaker than amplification driven by viscosity variations in fact for the parameters examined the amplification due to solidification is so weak that its effect is almost insignificant whereas viscosity variation provides a strong active mechanism for flow localization laboratory experiments illustrate viscous localization and suggest that this mechanism is robust the dependence of viscosity on temperature can cause a small change in the pressure of the magma chamber to lead to a large jump in the flow rate of magma through the fissure

experimental constraints on magma ascent rate for the crater flat volcanic zone hawaiite phase equilibria and isothermal constant rate decompression experiments conducted on a hawaiite from the crater flat volcanic zone near yucca mountain nevada provide insight into the dynamics of magma transport for this magmatic province h 2 o contents up to 4 6 wt in melt inclusions the lack of plagioclase phenocrysts and the presence of amphibole all suggest that phenocrysts and melt in the crater flat volcanic zone were equilibrated at near water saturated conditions during ascent comparison of decompression induced crystallization of plagioclase microlites in experiments with natural tephra implies that magma ascent rates for the region are 0 04 m s if the magmas are water saturated estimates of minimum ascent rates increase if the magmas are water undersaturated a two stage process is needed to generate reaction rims found on natural amphibole suggesting that small batches of magma were briefly stored 3 5 days at depths as shallow as 800 m prior to eruption

the fast evolution of a crustal hot zone at the end of a transpressional regime the saint tropez peninsula granites and related dykes maures massif se france granite and dolerite occurring in the eastern unit of the maures massif southern france variscan belt were emplaced in the waning stage of the evolution of a dextral shear zone along the gondwana border with laurasia we present a geochronological and petro geochemical study major and trace elements sr nd isotopes of 1 the foliated moulin blanc cordierite granite and related foliated dykes 2 the equant camarat granite and dyke and 3 the andesite basalt dolerite dykes frequently mingled with leucogranite material at pinet and capon tips and cross cutting leucogranitic dykes zircon and monazite dating of the moulin blanc granite gives a crystallization age of 301 2 ma shrimp dating on zircons from the leucogranite component of a pinet composite dyke only reveals zircon core ages of mainly 310 10 ma age of migmatization of the host gneiss undulating contacts of dolerite dykes within the c 300 ma old camarat granite suggest penecontemporary relationships between the two intrusions the age interval between the moulin blanc granite and the dolerite dykes would thus be very short the moulin blanc pluton is formed by mingling and mixing of melts of granitic and dioritic composition the latter occurring mainly as microgranular mafic enclaves two other types of diorites are also identified in the pluton the foliated dykes are similar in composition to the moulin blanc granite which confirms their relationship to the main pluton the moulin blanc granite is a typical example of a pluton formed by repeated recharges coming from a deeper magma chamber formation of the camarat dykes is controlled by hydrothermal fluids that are responsible for the non charac behavior of trace elements the pinet and capon leucogranite components of the dolerite dykes have distinct geochemical signatures different from the camarat granite and dykes the cross cutting leucogranitic dykes have much geochemical similarities with the capon granite the age of similar dykes in the tanneron massif supports the contemporaneity of camarat granite and dolerites the dolerite geochemistry was deeply modified by alteration processes but an andesite basalt composition is still recognizable by using immobile element ratios in a end vs sri diagram all rocks plot close to a mixing hyperbola between a depleted mantle component and a crustal component characteristic of the variscan crust in the french massif central there is a broad correlation between the ndtdm 2 stage model ages and the degree of fractionation of the rocks modeling of dehydration melting in a range of p t conditions reveals that a variety of lithologies were the source of the saint tropez magmas high alumina and alkali basalt amphibolites metagraywackes metapelites and meta arkoses these sources were melted almost simultaneously at different levels in the crust the calculated critical dyke width required to transport the granitic melt by buoyancy is far too large compared to the observed granitic dyke thicknesses therefore tectonic processes and or melt overpressure must have played a role in the emplacement mechanism thermo mechanical constraints on mixing between mafic and felsic melts suggest that in the pinet composite dykes both melts should have mixed the observed lack of mixing is interpreted as due to quick cooling the region was affected by a hot zone at the end of a transpressional regime

the controlling effect of viscous dissipation on magma flow in silicic conduits nearly all volcanic conduit models assume that flow is newtonian and isothermal such models predict that during high flux silicic eruptions gradients in pressure with depth increase upward as magma accelerates and becomes more viscous leading to extremely low pressure and fragmentation at a depth of kilometers below the surface in this paper i show that shear heating also known as viscous dissipation dramatically reduces the pressure gradient required for flow and concentrates shear in narrow zones along the conduit margin the reduction in friction may eliminate the zone of low pressure predicted by isothermal models and move the fragmentation level up to the surface

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

comparison of oxygen isotope records from the gisp2 and grip greenland ice cores recent results1 2 from the greenland ice core project grip summit ice core suggest that the climate in greenland has been remarkably stable during the holocene but was extremely unstable for the time period represented by the rest of the core spanning the last two glaciations and the intervening eemian inter glacial here we present the complete oxygen isotope record for the greenland ice sheet project 2 gisp2 core drilled 28 km west of the grip core we observe large rapid climate fluctuations throughout the last glacial period which closely match those reported for the grip core however in the bottom 10 of the cores spanning the eemian interglacial and the previous glacia tion there are significant differences between the two records it is possible that ice flow may have altered the chronological sequences of the stratigraphy for the bottom part of one or both of the cores considerable further work will be necessary to evaluate the likelihood of this and the extent to which it will still be possible to extract meaningful climate information from the lowest sections of the cores

chronology of late paleozoic tectonothermal activity in the southeastern bohemian massif austria moldanubian and moravo silesian zones 40ar 39ar mineral age controls abstract new 40ar 39ar hornblende and muscovite ages from the moldanubian and moravian zones of the southeastern bohemian massif indicate rapid cooling associated with continental underplating during early carboniferous plate collision and closure of the moravo silesian foredeep 40ar 39ar ages have been determined for hornblende concentrates from 1 amphibolite from the moldanubian nappe complex including the dobra gneiss rehberg amphibolite and loosdorf complex all part of the variegated unit 2 micaschist structurally overlying the bittesch gneiss and 3 amphibolite within the bittesch gneiss moravian zone the five hornblende concentrates display variably discordant 40ar 39ar age spectra because of contamination with extraneous argon components however 36ar 40ar vs 39ar 40ar isotope correlations are well defined for the five hornblende concentrates mswd the hornblende and muscovite ages are interpreted to date post variscan metamorphic cooling through ca 500 c and ca 400 c respectively no record of pre variscan thermal events is preserved in either the hornblende or muscovite argon systems however the widespread occurrence of extraneous argon components suggest a pre variscan stage of tectonothermal development the near concordancy of the hornblende and muscovite cooling ages suggest relatively rapid cooling through the contrasting argon closure temperatures and indicate that relatively high crustal levels had likely been attained during the early carboniferous

a 300 kyr record of upwelling off oman during the late quaternary evidence of the asian southwest monsoon in the northwest arabian sea upwelling occurs each summer driven by the strong sw monsoon winds upwelling results in high biological productivity and a distinctive assemblage of plankton species in the surface waters off oman that are preserved in the sediments along the oman continental margin creating a geologic record of monsoon driven upwelling sediments recovered from the oman continental margin during ocean drilling program leg 117 provide an opportunity to examine how upwelling has varied during the late quaternary spanning a longer interval than piston cores recovered prior to the odp cruise variations in foraminifer shell accumulation and in the relative abundance of globigerina bulloides indicate dominant cycles of variation at 1 100 kyr the dominant frequency of glacial interglacial variations and at 1 23 kyr the frequency of precessionally driven cycles in seasonal insolation the strongest monsoon winds indicated by increased upwelling occurred during interglacial times when perihelion was aligned with the summer solstice an orbital change that increased the insolation received during summer in the northern hemisphere during glacial times upwelling was reduced and although the precessional cycles were still present their amplitude was smaller at both frequencies the upwelling cycles are in phase with minimum ice volume evidence that glacial interglacial climate changes also include changes to the climate system that influence the low latitude monsoon we attribute the decrease in the monsoon winds observed during glacial times to changes in bare land albedo over asia and or to changes in the areal extent and seasonal cycle in asian snow cover that decrease the summer land sea temperature contrast other mechanisms may also be involved these new upwelling time series differ substantially from previous results however the previous work relied on cores located farther offshore where upwelling is less intense and other physical mechanisms become important our results support the observations derived from atmospheric general circulation models of the atmosphere that indicate that both glacial boundary conditions and the strength of summer insolation are important variables contributing to cycles in the monsoon winds during the late quaternary

igneous charnockites and related rocks from the bjerkreim sokndal layered intrusion southwest norway a jotunite hypersthene monzodiorite derived a type granitoid suite the upper part of the bjerkreim sokndal layered intrusion bksk introduction comprises a suite of charnockitic granitoids mangerite quartz charnockitic granitoids are a major component of mangerite and charnockite with some jotunites the petrology and anorthosite mangerite charnockite rapakivi granite geochemistry major and trace elements of eight main rock types amcg complexes and therefore play a crucial role in 88 samples are considered the rocks form a suite of k2o rich the formation and evolution of the proterozoic crust alkali calcic granitoids of a type deriving from jotunitic magma their origin has been long debated though intimately two trends of inferred liquids are distinguished the main liquid associated with massif anorthosites they are generally line of descent which passes from jotunites through two pyroxene considered to be derived from distinct parental magmas quartz mangerites to amphibole charnockites the second one which generated in different sources emslie 1978 1991 morse encompasses olivine bearing quartz mangerites and charnockites and 1982 duchesne 1984 wiebe 1992 ashwal 1993 it is rooted into mangeritic liquids comparison with the tellnes rock has however been recognized that some charnockitic series reveals that contamination by leucogranitic material has taken rocks could also be derived from an intermediate monplace simultaneously with fractional crystallization in both bksk zodioritic to ferrodioritic jotunitic magma duchesne trends zr rb cs and th are particularly sensitive to assimilation et al 1989 wilmart et al 1989 owens et al 1993 and the higher water content in bksk zircon and apatite have whose origin is also controversial the jotunitic magma saturated at the liquidus of quartz mangerite around 900 c close could either be derived from a crustal source by the to the fayalite magnetite quartz fmq buffer the two pyroxene partial melting of basic rocks duchesne et al 1989 quartz mangerites cannot have been equilibrated with the mangerite duchesne 1990 or be residual magmas after the forcumulates on which they rest a major influx of magma took place mation of massif anorthosites which have been conwhen mangeritic cumulates were being deposited it mingled and partly mixed with the resident contaminated magma taminated to various degrees by crustal material emslie et al 1994 the latter hypothesis seems to explain a large number of amcg complexes in the grenville and nain provinces and elsewhere accepting that some charnockites are derived from jotunites there is a logical

climate conditions in the westernmost mediterranean over the last two millennia an integrated biomarker approach abstract climate conditions in the westernmost mediterranean alboran sea basin over the last two millennia have been reconstructed through integration of molecular proxies applied for the first time in this region at such high resolution two temperature proxies one based on isoprenoid membrane lipids of marine thaumarchaeota tex 86 h tetraether index of compounds consisting of 86 carbons and the other on alkenones produced by haptophytes u 37 k ratio were applied to reconstruct sea surface temperature sst both records reveal a progressive long term decline in sst over the last two millennia and an increased rate of warming during the second half of the 20th century this is in accord with previous temperature reconstructions for the northern hemisphere tex 86 h temperature values are higher than those inferred from u 37 k probably due to differences in the bloom season of haptophytes and thaumarchaeota and reflect summer sst the branched vs isoprenoid tetraether index bit index suggests a low contribution of soil organic matter om to the sedimentary om the stable carbon isotopic composition of long chain n alkanes indicates a predominant c3 plant contribution with no major change in vegetation over the last 2000 yr the distribution of long chain 1 14 diols most likely sourced by proboscia spp in this setting provides insight into variation in upwelling conditions during the last 2000 yr and depicts a correlation with the north atlantic oscillation nao index providing evidence of enhanced wind induced upwelling during periods of a persistent positive mode of the nao

variscan collisional magmatism and deformation in nw iberia constraints from u pb geochronology of granitoids u pb geochronology of variscan granitoid rocks from the west asturian leonese zone of the nw iberian belt documents the episodic nature of magmatism in this section of the western european variscides each magmatic episode is characterized by granitoids with distinct features and has a duration on the scale of several millions of years the ages of these granitoids place new constraints on the age and duration of magmatic and tectonic events that are consistent with previous structural studies and proposed models for the tectonic evolution and migration of deformation in the nw iberian variscan belt granitoid rocks in this zone belong to two main magmatic episodes syn and post tectonic relative to the variscan orogeny and are broadly representative of the granitoid types found in the nw iberian variscan belt the syntectonic association is formed by i tonalite granodiorite monzogranite intrusions emplaced synchronously with the main phase of crustal deformation d 2 at c 325 ma and ii younger leucogranite intrusions emplaced synchronously with syn convergence extensional structures at c 320 310 ma the post tectonic association is composed of i volumetrically dominant tonalite granodiorite monzogranite intrusions and associated minor mafic intermediate rocks emplaced at c 295 290 ma and ii scarce leucogranite intrusions emplaced at c 290 285 ma

currents and transports of the great whirl socotra gyre system during the summer monsoon august 1993 from august 11 to 22 1993 a conductivity temperature depth acoustic doppler current profiler survey was carried out in the somali socotra region to investigate currents and transports associated with the great whirl and socotra gyre circulation during the height of the summer monsoon the monsoon circulation was confined to the upper 300 m depth with intense surface currents up to 2 2 m s 1 in the great whirl and up to 1 4 m s 1 in the socotra gyre deeper reaching flow was found in the northwestern part of the somali basin and in the passage between the shelf of somalia and abd al kuri the great whirl transport was 58 sv of which nearly 25 were due to ageostrophic flow components the northern part of the great whirl thereby appeared as a closed circulation cell in which the offshore transport was balanced by a southward transport of the same magnitude upwelled water was advected from the cold wedge of the upwelling regime at the somali coast along the edge of the gyre the water in the center of the gyre had the characteristics of indian equatorial water iew the socotra gyre carried 23 sv of modified arabian sea water asw with the transports in the two anticyclonic gyres nearly balanced the exchange of water masses between the somali basin west of the carlsberg ridge and the arabian sea occurred in two areas about 16 sv of warm and saline surface water of southern offshore origin entered the northern somali basin within a 120 km wide swift current between the great whirl and the socotra gyre the other key region for the exchange of water masses was the passage between somalia and abd al kuri there the total northward transport was 13 sv with contributions of iew of upwelled water close to the surface and asw underneath

a 90 kyr upwelling record from the northwestern indian ocean using a novel long chain diol index abstract presently upwelling is of major importance for driving primary productivity in the arabian sea but its intensity in the past is not well constrained here we used long chain 1 14 alkane diols specific lipids of diatoms of the genus proboscia as new proxies to reconstruct upwelling conditions in the arabian sea variations in the seasonal lipid fluxes were determined using sediment traps in the somalia upwelling system deployed 80 km off the coast on the somali continental slope niop 905 10 45 444 n 51 56 655 e at 1265 m water depth 268 m above the sea floor and 270 km off the coast in the deep somali basin south of socotra niop 915 10 43 068 n 53 34 422 e at 3047 m depth 1000 m above the sea floor highest fluxes of c 28 and c 30 1 14 diols up to almost 600 g m 2 day 1 were only observed during nutricline shoaling at the onset of the southwest monsoon swm prior to massive upwelling by contrast fluxes of c 30 1 15 diols derived from as yet undefined biological sources only increased marginally during the swm and also during the northeast monsoon nem when instead of upwelling enhanced vertical mixing led to a second productivity pulse sediment core niop 905 taken at the continental slope site showed strong fluctuations in relative concentrations of long chain 1 14 and 1 15 diols with time which we quantified as the summed concentrations of c 28 and c 30 1 14 diols divided by the summed concentrations of c 28 and c 30 1 14 diols and c 30 1 15 diols this diol index follows the same trend as other upwelling intensity records from the arabian sea that are based on sea surface temperature reconstructions organic carbon content barium aluminium ratios and abundance and stable isotope composition of specific foraminiferal species the diol index was relatively high during the holocene ca 0 7 but much lower during the late glacial maximum ca 0 2 it was generally low during the last glacial but elevated values were found during the first half of marine isotope stage 3 between 60 and 45 ka and at the end of marine isotope stage 5 1 approximately 80 ka suggesting intensified glacial upwelling our data shows that long chain diols are suitable proxies to reconstruct past upwelling intensities in the arabian sea

magma flow and interaction with waste packages in a geologic repository at yucca mountain nevada abstract the likelihood that a nuclear waste repository at yucca mountain could be intersected by igneous activity is very low but its potential consequences are nevertheless important to performance assessments an ongoing critical area of concern is the nature and magnitude of the thermal interaction of magma with tunnel walls high level nuclear waste packages and waste forms previous assessments consider a variety of dynamic scenarios but large uncertainties remain in understanding the rheological nature of the magma likely to be involved and its behavior within a repository drift here we specifically address the issue of magma rheology during degassing cooling and solidification as basaltic magma approaches earth s surface and enters a drift magma containing significant amounts 2 wt of dissolved water wet magma as is anticipated for this region at or near its liquidus temperature and saturated with water at 200 mpa is at a temperature near or below the 1 atm solidus temperature isentropic ascent from this near liquidus temperature promotes extensive solidification and or glassification exsolving water with approach to the surface promotes rapid vesiculation leading to fragmentation and tephra production with continued ascent the still water saturated magma traverses the solidification phase field and undergoes a combination of rapid crystallization and quenching becoming a glassy highly viscous 108 pa s mass of greatly reduced mobility this immobility is reflected in the high effective viscosity regulating flows from nearby cinder cones associated with wet basalt this also matches well with the experimentally determined rheology of dry basalt glass this rheology greatly restricts the mobility of basalt within repository drifts amounting to

lipid biomarker fluxes in the arabian sea with a comparison to the equatorial pacific ocean abstract fluxes and distributions of organic carbon oc and lipid biomarkers were measured in the western arabian sea as a function of season depth and distance from the coast of oman during the us jgofs arabian sea process study in 1994 1995 a strong seasonal pattern in oc and lipid flux is related to the annual monsoon cycle in the western arabian sea with the highest fluxes measured during the southwest monsoon fluxes were greatly attenuated with depth in the water column and in surface sediments as remineralization effectively consumed particulate organic matter a comparison of water column fluxes with oc and lipid accumulation rates in sediments confirms that the water sediment interface is a hot spot for organic matter degradation biomarker compositions also varied seasonally and with distance offshore reflecting seasonal and spatial succession of their biological sources and their subsequent export through the water column degradation of oc and biomarkers was extremely efficient with only a tiny fraction

u pb zircon and monazite geochronology of post collisional hercynian granitoids from the central iberian zone northern portugal abstract in the central iberian zone ciz of the iberian massif large volumes of granitoids were emplaced during the post collisional stage of the hercynian orogeny syn to post d3 the last ductile deformation phase twelve granitic units and a quartz monzodiorite were selected for a u pb zircon and monazite geochronological study they represent successive stages of the d3 event the ucanha vilar lamego sameiro and refoios do lima plutons are coeval 313 2 ma 319 4 ma 316 2 ma and 314 2 ma respectively and belong to the earliest stage later on the braga massif was emplaced its different units yielding the same age 309 3 ma for the braga granite 309 1 ma for the gonca granite and 311 5 ma for a related quartz monzodiorite the braga massif is subcontemporaneous with the agrela and celeiros plutons 307 3 5 ma and 306 2 ma respectively in agreement with field data the briteiros granite is younger 300 1 ma followed by the emplacement of the peneda geres massif geres paufito illa and carris granites the geres granite emplaced at 296 2 ma seems to represent a first magmatic pulse immediately followed by the intrusion of the paufito granite at 290 2 5 ma for the carris granite a minimum emplacement age of 280 5 ma was obtained based on these results the following chronology is proposed 1 syn d3 biotite granitoids 313 319 ma 2 late d3 biotite dominant granitoids 306 311 ma 3 late to post d3 granitoids ca 300 ma 4 post d3 granitoids 290 296 ma these chronological data indicate that successive granitic intrusions were emplaced in the ciz during a short time span of about 30 ma that corresponds to the latest stages of the hercynian orogeny a rapid and drastic change occurred at about 300 ma between a compressive ductile tectonic regime d3 ca 300 320 ma associated to calc alkaline monzonitic and aluminopotassic plutonism and a fragile phase of deformation d4 which controlled the emplacement of the subalkaline ferro potassic plutonism at 290 296 ma

convective heat extraction from molten magma the convective heat of molten magma in the upper 10 km of the continental crust represents a significant geothermal energy resource shallow basaltic magmas 10 km near the liquidus 1250 c are predicted to offer heat extraction rates in the range of 15 50 kw m2 20 80 mw well more accessible andesitic and wet rhyolitic magmas are predicted to offer heat extraction rates in the range of 5 25 kw m2 8 40 mw well convective heat transfer correlations are used which include corrections for high prandtl number fluids and cylindrical boundary layers the calculations based on these correlations agree well with laboratory tests using molten basalt at superliquidus temperatures 1450 1650 c at liquidus and subliquidus temperatures an additional correction is developed for the thick solidified crust that forms on the heat exchanger non newtonian rheology is considered and shown to have a possible effect on the initiation of convection in the liquidus and subliquidus temperature range in addition to heat extraction estimates the analysis presented here is also relevant to convective heat loss to walls of magma bodies

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

organic geochemical changes in pliocene sediments of odp site 1083 benguela upwelling system the intensification of the northern hemisphere glaciation inhg was a major event in the development of the current climate state and as one of the most productive regions in the world s oceans the behaviour of the benguela upwelling system bus following the inhg is of wide interest to investigate post inhg changes in productivity and organic matter accumulation total organic carbon and biomarker accumulation rates were determined for sediments from cop site 1083 and compared to alkenone derived sea surface temperatures and nitrogen isotopic compositions these data indicate that the interval between 2 6 and 2 4 ma was characterized by dramatic changes in upwelling intensity and organic carbon export on the northern edge of the modern bus the upwelling is reflected by significant changes in alkenone derived sst estimates between glacial and interglacial intervals with a total variability of 16 degrees c the studied interval is also characterized by large changes in organic matter export as reflected by changes in toc and biomarker accumulation rates which show maxima during ois 98 and during the transition from ois 97 to 96 intervals of elevated toc are also characterized by elevated concentrations of sedimentary microbial biomarkers and lower caco 3 suggesting that enhanced delivery of labile organic matter to the seafloor resulted in enhanced remineralisation with released co 2 being consumed by caco 3 dissolution however in apparent contrast to recent pleistocene sediments at the same site organic matter export after the inhg was not solely driven by upwelling intensity of the three pliocene glacial interglacial cycles examined ois 101 to 96 each is unique with respect to the timing and magnitude of changes in organic matter accumulation each is also characterized by different algal assemblages as inferred from biomarker distributions with ois 97 and 96 particularly dominated by diatoms we suggest that these differences reflect the important but evolving role of southern ocean waters in the pliocene bus nutrient depletion of so waters occurred during parts of pliocene glacial intervals such that even intense upwelling did not persistently result in enhanced organic matter accumulation rates c 2009 elsevier b v all rights reserved

modeling the late quaternary indian ocean circulation an ocean general circulation model ogcm of the indian ocean is forced by paleoclimate simulations for five time slices over the last 126 000 years using an annual period sinusoidal fit to the perpetual january and july paleoclimatic model forcing the ogcm produces seasonal cycles in velocity fields both vertical and horizontal and temperature salinity fields at these five times the simulations indicate that the southern hemisphere upper ocean circulation of the indian ocean is essentially invariant to climatic fluctuation on this time scale they also suggest that the low insolation 18 000 years b p northern hemisphere upper ocean summer circulation was very much weaker compared to high insolation periods such as 9000 years b p and 126 000 years b p by perhaps an order of magnitude by contrast the simulated low insolation winter northern hemisphere upper ocean circulation was substantially stronger than during high insolation periods equatorial upwelling as simulated is shown to be a mainly boreal summer event reduced by an order of magnitude during low insolation conditions a similar reduction in upwelling is seen along the arabian coast but a less severe decrease along the somalian coast the model simulation of february and august sea surface temperature at 18 000 years b p the height of the last glaciation is generally within 1 2 c of paleoclimate reconstructions the effect of lower glacial sea level on the circulation is shown to be only local

climate variability and socio environmental changes in the northern aegean ne mediterranean during the last 1500 years abstract we provide new evidence on sea surface temperature sst variations and paleoceanographic paleoenvironmental changes over the past 1500 years for the north aegean sea ne mediterranean the reconstructions are based on multiproxy analyses obtained from the high resolution decadal to multi decadal marine record m2 retrieved from the athos basin reconstructed ssts show an increase from ca 850 to 950 ad and from ca 1100 to 1300 ad a cooling phase of almost 1 5 c is observed from ca 1600 ad to 1700 ad this seems to have been the starting point of a continuous sst warming trend until the end of the reconstructed period interrupted by two prominent cooling events at 1832 15 ad and 1995 1 ad application of an adaptive kernel smoothing suggests that the current warming in the reconstructed ssts of the north aegean might be unprecedented in the context of the past 1500 years internal variability in atmospheric oceanic circulations systems as well as external forcing as solar radiation and volcanic activity could have affected temperature variations in the north aegean sea over the past 1500 years the marked temperature drop of approximately 2 c at 1832 15 yr ad could be related to the 1809 d unknown and the 1815 ad tambora volcanic eruptions paleoenvironmental proxy indices of the m2 record show enhanced riverine continental inputs in the northern aegean after ca 1450 ad the paleoclimatic evidence derived from the m2 record is combined with a socio environmental study of the history of the north aegean region we show that the cultivation of temperature sensitive crops i e walnut vine and olive co occurred with stable and warmer temperatures while its end coincided with a significant episode of cooler temperatures periods of agricultural growth in macedonia coincide with periods of warmer and more stable ssts but further exploration is required in order to identify the causal links behind the observed phenomena the black death likely caused major changes in agricultural activity in the north aegean region as reflected in the pollen data from land sites of macedonia and the m2 proxy reconstructions finally we conclude that the early modern peaks in mountain vegetation in the rhodope and macedonia highlands visible also in the m2 record were very likely climate driven

the influence of the ne winter monsoon on productivity changes in the gulf of aden nw arabian sea during the last 530ka as recorded by foraminifera abstract benthic and selected planktic foraminifera and stable isotope records were determined in a piston core from the gulf of aden nw arabian sea that spans the last 530 ka the benthic foraminifera were grouped into four principal assemblages using q mode principal component analyses comparison of each of these assemblages with the fauna of the nearby regions enabled us to identify their specific environmental requirements as a function of variability in food supply and strength of the oxygen minimum zone and by that to use them as indicators of surface water productivity the benthic foraminiferal productivity indicators coupled with the record of globigerina bulloides a planktic foraminifer known to be sensitive to productivity changes in the region all indicate higher productivity during glacial intervals and productivity similar to present or even reduced during interglacial stages this trend is opposite to the productivity pattern related to the sw summer monsoon of the arabian sea and indicates the role of the ne winter monsoon on the productivity of the gulf of aden a period of exceptionally enhanced productivity is recognized in the gulf of aden region between 60 and 13 kyr indicating the intensification of the ne winter monsoon to its maximal activity contemporaneous indication of increased productivity in other parts of the arabian sea unexplained so far by the sw summer monsoon variability might be related to the intensification of the ne winter monsoon another prominent event of high productivity second in its extent to the last glacial productivity event is recognized between 430 and 460 kyr these two events seem to correspond to periods of similar orbital positioning of rather low precession and eccentricity amplitude for a relatively long period glacial boundary conditions seem to control to a large extent the ne winter monsoon variability as also indicated by the dominance of the 100 ka cycle in the investigated time series secondary in their importance are the 23 and 41 ka cycles which seem also to contribute to the ne monsoonal variability following the identification of productivity events related to the ne winter monsoon in the gulf of aden it is possible now to extend this observation to other parts of the arabian sea and consider the contribution of this monsoonal system to the productivity fluctuations preserved in the sedimentary records

variations in tropical convection as an amplifier of global climate change at the millennial scale the global expression of millennial scale climatic change during the glacial period and the persistence of this signal in holocene records point to atmospheric teleconnections as the mechanism propagating rapid climate variations we suggest rearrangements in the tropical convection system globally affected the concentration and location of atmospheric water vapour and modulated terrestrial and marine emissions of ch4 and n2o providing a tropical mechanism of amplifying and perpetuating millennial scale climate changes a multi proxy reconstruction reflecting various aspects of the intensity of the arabian sea summer monsoon shows strong millennial scale variability over the past 90 kyr in which low intensity is associated with a southern shift of the intertropical convergence zone itcz and an eastward shift in the equatorial convergence zone the monsoon reconstruction which is based on new data from a somali margin sediment core is supported by previously reported tropical paleoclimatic records and suggests that global scale millennial climatic variability is in part driven by modulations in the tropical hydrological cycle and tropical emissions of the greenhouse gases ch4 and n2o

thermal effects of magma degassing abstract the thermodynamics of diffusive bubble growth is dominated by latent heat of water exsolution vaporization and the work of gas expansion p dv work a numerical assessment of the effects of these on cooling of bubbly magma water in albite indicates that a magma can exsolve volatiles at equilibrium or with varying degrees of oversaturation depending on decompression history and degassing kinetics heat of water exsolution vaporization from magmatic melts has not previously been experimentally or analytically determined and we have evaluated it from others thermodynamic functions known for the albite water system heat of exsolution is small for pressures over 100 mpa but can reach 20 kj mole at 1 2 mpa 10 20 bar oversaturation degassing at 10 20 bar can cause cooling of albite by 8 k wt of exsolved water the thermal effect of equilibrium degassing depends on the starting pressure of decompression because it follows the solubility curve for a saturated melt at 100 mpa 4 wt water it can cool a magma at least by 35 k before it disrupts into spray as gas volume fraction exceeds 0 8 although we do not specifically consider the dynamics of bubble interactions in this study our results suggest that the dynamic cooling rate could be significant at the vent of an erupting magma column and under extreme eruption conditions can lead to glass formation around fast growing bubbles of magmatic foam this could cause fragmentation into fine ash by brittle failure conversely bubble wall cooling even before glass formation can serve to reduce diffusive volatile flux into bubbles decreasing the overall cooling of the system and lead to solidification of oversaturated magmas as occasionally observed in eruption products

the c 32 alkane 1 15 diol as a tracer for riverine input in coastal seas long chain alkyl diols are lipids that occur ubiquitously in marine sediments and are used as a proxy for sea surface temperature sst using the long chain diol index ldi and for upwelling intensity high nutrient conditions the distribution of 1 13 and 1 15 diols has been documented in open marine and lacustrine sediments and suspended particulate matter but rarely in coastal seas receiving a significant riverine and thus continental organic matter input here we studied the distribution of diols in four shelf seas with major river outflows the gulf of lion the kara sea the amazon shelf and the berau delta covering a wide range of climate conditions the relative abundance of the c32 1 15 diol is consistently higher close to the river mouth and particularly in the suspended particulate matter of the rivers suggesting a terrigenous source this is supported by statistical analysis which points out a significant positive correlation between the c32 1 15 diol and the branched and isoprenoid tetraether index a proxy reflecting soil and riverine input in marine environments however the c32 1 15 diol was not detected in soils and is unlikely to be derived from vegetation suggesting that the c32 1 15 diol is mainly produced in rivers this agrees with the observation that it is a dominant diol in most cultivated freshwater eustigmatophyte algae we therefore suggest that the relative abundance of the c32 1 15 diol can potentially be used as a proxy for riverine organic matter input in shelf seas our results also show that long chain alkyl diols delivered by rivers can substantially affect ldi reconstructed ssts in coastal regions close to river mouths

testing claims about volcanic disruption of a potential geologic repository at yucca mountain nevada 1 yucca mountain is a potential repository site for high level radioactive waste we examine claims that the frequency of future basaltic dike intersection could be 1 10 6 yr or higher i e on average one penetration every million yrs these claims fail simple tests at four time scales spatial temporal models that predict intrusion frequencies 2 10 7 yr are overly pessimistic because no dikes have been found in the 13 myr old potential repository footprint more realistic models are developed by considering this non detection of dikes and by applying probabilistic hazard assessments based on known patterns of pleistocene volcanism using a hazard assessment code we estimate the frequency of dike intersection at 5 4 10 8 yr with an upper 95 confidence bound of 9 8 10 8 yr

understanding the arabian sea reflections on the 1994 1996 arabian sea expedition abstract the arabian sea expedition now five years past its field observations is at a stage when some of its dominant themes can be summarized of the large range of possible topics five are considered here 1 is the arabian sea a source or sink for carbon dioxide 2 is the arabian sea mother nature s iron experiment 3 do grazing zooplankton control carbon flux to the seabed 4 does the paleoceanographic record help us predict the ocean s response to climate change and 5 what are the predominant physical processes of the arabian sea a short history of each issue and results from the field work of 1994 1996 are presented

mid chain diols and keto ols in se atlantic sediments a new tool for tracing past sea surface water masses abstract long mid chain diols and keto ols in se atlantic surface sediments have been studied in relation to the properties of the overlying surface waters the strongest change in compound composition occurs over the angola benguela front 14 16 s south of the front 1 13 and 1 14 diols notably the 1 14c 28 and 1 13c 30 homologs increase relative to 1 15 diols the 1 13c 30 keto ol is almost absent north of the front these changes probably reflect differences in sea surface temperature persistence of stratification and upwelling at opposite sides of the front elevated relative abundances of the 1 15c 32 diol and 1 15c 32 keto ol below the congo river plume 6 s may be outflow related which should be tested on other river plumes lower relative abundances of 1 15 diols close to walvis bay might relate to a higher upwelling intensity compared to the other sites investigated the applicability of the observed surface patterns is tested down core for the penultimate deglaciation the temporal changes in diol and keto ol composition not only have their spatial counterpart in the se atlantic surface sediments they are also readily interpretable on the basis of the modern diol and keto ol assemblages as well as the palaeoenvironmental reconstructions based on other proxies

a diatomaceous origin for long chain diols and mid chain hydroxy methyl alkanoates widely occurring in quaternary marine sediments indicators for high nutrient conditions for the first time a biological source for the long chain alkyl 1 14 diols and 12 hydroxy methyl alkanoates lipids widely occurring in the marine water column and sediments has been identified cultures of proboscia indica and proboscia alata rhizosolenoid diatoms belonging to the widespread diatom genus proboscia contain c28 c28 1 c30 and c30 1 alkyl 1 14 diols and c27 and c29 12 hydroxy methyl alkanoates as major neutral lipids these components form a substantial fraction of lipid fractions from sediment traps or sediments especially in areas with an elevated primary production such as upwelling regions examination of literature data reveals that as much as 20 to 35 of the total lipid flux in the arabian sea is derived from proboscia diatoms during the start of the upwelling season their rapid transfer to the water sediment interface may explain why corresponding 1 14 keto ols inferred oxidation products of diols are hardly formed these interpretations are supported by compound specific carbon isotopic analysis of long chain keto ols and diols in surface sediments of the arabian sea the data indicate that long chain alkyl 1 14 diols and 12 hydroxy methyl alkanoates can be applied as indicators for high nutrient conditions in the photic zone

impact of productivity events on the benthic foraminiferal fauna in the arabian sea over the last 150 000 years we have studied the sediment geochemistry and benthic foraminiferal fauna in a piston core from the northwest arabian sea covering the last 150 000 years and compared the results with the stable isotopic record from both benthic uvigerina peregrina and planktonic globigerinoides sacculifer foraminifera the 18o record of the planktonic foraminiferal species shows excursions towards heavier 18o values when compared to the benthic record and the specmap stack particularly in stage 3 between approximately 30 and 45 50 kyr we call this the stage 3 event species diversity and relative abundance data on benthic foraminifera reveal that some species e g cibicidoides wuellerstorfi oridorsalis umbonatus pullenia bulloides pyrgo spp and the uvigerinids increased in relative abundance during glacial stages 2 and 4 and during the stage 3 event whereas other e g astrononion novozealandicum cibicidoides bradyi eggerella bradyi gyroidina altiformis hoeglundina elegans pullenia subcarinata and sigmoilina edwardsii decreased using correspondence analysis we determined that approximately 50 of the total sample variation may be accounted for by three first factors which all are interpreted as primarily related to surface water productivity and the quality of the organic matter that reaches the seafloor the relative abundance of some species appears to vary on a precessional cycle perhaps responding to monsoon driven upwelling and associated increased food supply whilst the abundances of other species are related to the 100 kyr ice volume cycle and may be responding to changes in intermediate and deep water chemistry geochemical paleoproductivity tracers such as the ba content of the sediment have a very similar distribution to specific foraminiferal factors in both time and frequency domains certain planktonic foraminifera e g globigerina bulloides also display obvious maxima in the stage 3 event the stage 3 event occurs at a time of reduced rate of amplitude change in both solar radiation and monsoon pressure index we conclude that there was a period 15 to 20 kyr duration during stage 3 with cooler than normal surface waters enhanced productivity and rapid settling of biogenic matter

bound forms compositional features major sources and diagenesis of long chain alkyl mid chain diols in lake baikal sediments over the past 28 000 years abstract to elucidate the possibility of long chain alkyl mid chain diols hereafter mid chain diols in lake baikal sediments over the past 28 ka being paleoproxies we studied their i bound forms and compositional features ii major sources and iii diagenesis during sedimentation of the seven bound forms investigated i e free form free type three base hydrolysable types base 1 base 2 and base 3 and acid hydrolysable type acid 1 type in solvent extractable lipids and base hydrolysable nb and acid hydrolysable na types in non solvent extractable nonex lipids only three viz free nb and base 3 types were found the relative compositions of the three types were 70 100 0 30 and 0 8 respectively the most abundant component of the free type diols was the c 32 1 15 diol whereas that of the base 3 and nb types was the c 30 1 13 diol the average chain length ratio of total amount of even chain lengths to that of odd chain lengths the relative composition of positional isomers for each carbon number and the diol index obtained using the equation c 30 1 15 diol c 30 1 15 diol c 32 1 15 diol 100 hardly responded to reported major paleoenvironmental changes around the lake baikal region over the last 28 ka comparison of mid chain diol compositions and their bound forms with those in possible sources suggested that the major biological source of all mid chain diols in the sediments might be the eustigmatophyceae class of algae in the alga the occurrence of mid chain diols in the five bound forms free base 3 acid 1 nb and na types was suggested while the acid 1 and na types were not found in the sediments under the oxic depositional conditions of lake baikal most of the acid 1 and na type diols and part of the base 3 and nb type diols might be degraded and or released free type diols in the anoxic sediments of the lake the base 3 and nb diols seem to be resistant to diagenesis all investigated parameters for the free base 3 and nb diols in the sediments did not provide any information on paleoenvironments around the lake on the other hand among the fluxes of the three diol types the base 3 type diol flux seems to have responded to the climatic events around the lake especially over the last 15 ka hence this flux might be a potential paleoproxy for the productivity of the biological source s and associated environmental factors

paleoceanographic changes in the eastern equatorial pacific over the last 10 myr to examine the late neogene evolution of tropical pacific oceanography we determined multiple geochemical proxy records for temperature u 37 k and tex86h indices and primary productivity algal biomarkers and diol indices in sediments recovered at odp site 1241 in the east equatorial pacific eep spanning a record of the last 10 myr the tex86h temperatures are lower than those recorded by u 37 k indices exhibiting large fluctuations and suggesting strong warming during the mid pliocene warm period mpwp 4 5 3 2 ma and significantly colder temperature during the late miocene cooling period 7 5 ma and after the middle pliocene warm period mpwp such variations could reflect changes in the eep thermocline temperatures but we suggest that they instead reflect changes in the depth of export production of glycerol dialkyl glycerol tetraether lipids in response to changes in the upper ocean structure a combination of temperature records inferred to represent different and likely varying depths in the water column as well as algal biomarker records for export production and ecosystem structure suggest that both productivity and inference upwelling were reduced in the eep during warmer periods such as the mpwp and prior to 7 ma in contrast stronger upwelling conditions and associated increased productivity likely prevailed from 7 to 5 ma and for the past 3 myr both corresponding to globally cool intervals a further increase in eep productivity occurred at ca 1 8 ma coincident with the development of the e w pacific sst gradient these results confirm previous work that protracted el nino like conditions prevailed during warmer intervals of the pliocene before ultimately descending into the current climate state

partial melting of two amphibolites contrasting experimental results under fluid absent conditions a large portion of the lower continental crust may be amphibolitic in composition and without a free fluid phase as a consequence h2o undersaturated or fluid absent melting of amphibolites may be responsible for the formation of some granites and migmatites produced during major orogenic events in an attempt to determine the systematics of melting under fluid absent conditions a series of piston cylinder experiments was conducted on two natural amphibolites one a meta alkali basalt aba with a total water content of wt contained in hornblende and the other a meta island arc tholeiite iat which has 1 1 3 wt water contained in hornblende cummingtonite and biotite the experimentally determined melting ranges of the two amphibolites showed that the solidus temperatures and sta temperature interval over which amphibole was stable were controlled by the amphibolites different bulk compositions and their resulting metamorphic assemblages the volume of melt produced by melting of the two amphibolites were compared with estimated amounts based on burnham s 1979 water melt solubility model and the fluid absent melting model presented by clemens and vielzeuf 1987 the observed melt volumes were greater than estimated as the water content of melt largely detemines the volume of melt produced independent measurements of the water content of the glass formed during partial melting in the aba were made by thermogravimetric analyses the water content of the aba glass is 2 wt which is less than the assumed melt water content water content of the melt used in previous modeling of fluidabsent anatexis in mafic lithologies as a consequence more melt can be expected during fluid absent partial melting of mafic lower crust as is observed in the experiments a modification of the clemens and vielzeuf 1987 fluid absent melting model for mafic compositions has been made using the experimental data available on melting in basaltic systems and is presented here for pressures of 5 8 and 10 kbar tectonic scenarios in which the crust is thickened i e by collision then undergoes extension or where a previously thinned crust is later rethickened provide enough heat so that amphibolite melting under fluid absent conditions can become importan and hence responsible for some melts produced during post collisional magmatism the results may also have applications to melting in hydrated oceanic crust in subduction zones and in island arc terains

early time multiphase interactions between basaltic magma and underground openings at the proposed yucca mountain radioactive waste repository 1 we investigate the interaction between yucca mountain repository drifts horizontal emplacement tunnels and a hawaiitic magma in three scenarios 1 a single feeder dike that extends above an intersected drift 2 same as 1 but with an additional secondary dike extending upward from the drift 3 same as 1 with the drift initially filled with pyroclasts and gas under high pressure which is then decompressed as might happen if some blockage is rapidly removed in the volcanic system above the drift our results indicate that the drift is likely to experience dynamic pressure waves from expansion of rising magma and subsequent pyroclastic flows with a maximum possible dynamic pressure of 107 pa a secondary dike above the drift has negligible effects upon the flow dynamics in the third scenario particles settle fairly quickly along the floor of the drift suggesting that a swift decompression within the drift will not be able to remove all the magmatic materials

air pressure waves from mount st helens eruptions weather station barograph records as well as infrasonic recordings of the pressure wave from the mount st helens eruption of may 18 1980 have been used to estimate an equivalent explosion airblast yield for this event pressure amplitude versus distance patterns in various directions compared with patterns from other large explosions such as atmospheric nuclear tests the krakatoa eruption and the tunguska comet impact indicate that the wave came from an explosion equivalent of a few megatons of tnt the extent of tree blowdown is considerably greater than could be expected from such an explosion and the observed forest damage is attributed to outflow of volcanic material the pressure time signature obtained at toledo washington showed a long 13 min duration negative phase as well as a second hour long compression phase both probably caused by ejacta dynamics rather than standard explosion wave phenomenology the peculiar audibility pattern with the blast being heard only at ranges beyond about 100 km is explicable by finite amplitude propagation effects near the source compression was slow taking more than a second but probably less than 5 s so that it went unnoticed by human ears and susceptible buildings were not damaged there was no damage asmore toledo 54 km where the recorded amplitude would have broken windows with a fast compression an explanation is that wave emissions at high elevation angles traveled to the upper stratosphere where low ambient air pressures caused this energetic pressure oscillation to form a shock wave with rapid nearly instantaneous compression atmospheric refraction then returned part of this wave to ground level at long ranges where the fast compressions were clearly audible copyright american geophysical union 1987 less

lipid biomarker signatures in a hypersaline lake on isabel island eastern pacific as a proxy for past rainfall anomaly 1942 2006ad isabel lake is a hypersaline crater lake on isabel island mexico situated in the eastern tropical pacific an area highly sensitive to hydrological changes today annual rainfall mostly occurs during the wet season from june to october when the northern edge of the intertropical convergence zone itcz extends over the island in order to evaluate the potential of sedimentary lipid biomarker signatures as a proxy of past hydroclimatic variability we have performed a calibration analysis comparing changes in biomarker distribution in the upper 16 cm of the sediment core with a regional instrumental data set annual laminations present in the sediment sequence allow for precise chronological control 1942 2006 more than 80 different lipid compounds were identified in the sediment and could be assigned to three major groups of source organisms 1 algal populations 2 a mixed community of ciliates bacteria and cyanobacteria and 3 photosynthetic sulfur bacteria we found that the observed changes in the relative contribution of the different lipid biomarkers to the sediment record were determined by the regional rainfall variability over the last 65 years the planktonic community of isabel lake was highly sensitive to salinity fluctuations related to rainfall variability seasonal precipitation results in freshwater input into the lake driving an annual algal bloom and a relative decrease in the abundance of the more halotolerant populations of cyano bacteria and ciliates consequently the concentration ratio between the two most abundant biomarkers in the isabel lake sediments n alkyl diols and tetrahymanol which we define as the dite index representing algal and ciliate planktonic populations respectively was significantly correlated with the seasonal rainfall anomaly r 0 68 p 0 01 we propose that the dite index is a proxy of changes in the aquatic ecosystem of isabel lake and by extension regional hydrological changes in a sensitive climatic area of the eastern tropical pacific

post collisional melting of crustal sources constraints from geochronology petrology and sr nd isotope geochemistry of the variscan sichevita and poniasca granitoid plutons south carpathians romania the sichevita and poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the getic nappe in the south carpathians the present work provides shrimp age data for the zircon population from a poniasca biotite diorite and geochemical analyses major and trace elements sr nd isotopes of representative rock types from the two intrusions grading from biotite diorite to biotite k feldspar porphyritic monzogranite u pb zircon data yielded 311 2 ma for the intrusion of the biotite diorite granites are mostly high k leucogranites and biotite diorites are magnesian and calcic to calc alkaline sr and nd isotope and trace element data ree th ta cr ba and rb permit distinguishing five different groups of rocks corresponding to several magma batches the poniasca biotite diorite p1 shows a clear crustal character while the poniasca granite p2 is more juvenile conversely sichevita biotite diorite s1 and a granite s2 are more juvenile than the other sichevita granites s2 geochemical modelling of major elements and ree suggests that fractional crystallization can account for variations within p1 and s1 groups dehydration melting of a number of protoliths may be the source of these magma batches the variscan basement a subduction accretion wedge could correspond to such a heterogeneous source the intrusion of the sichevita poniasca plutons took place in the final stages of the variscan orogeny as is the case for a series of european granites around 310 ma ago especially in bulgaria and in iberia no alleghenian granitoids late carboniferous early permian times being known in the getic nappe the geodynamical environment of sichevita poniasca was typically post collisional of the variscan orogenic phase

flow and instability of a viscous current down a slope if viscous fluid is released on a horizontal surface it rapidly takes up a circular plan form as it spreads this form is observed1 2 to be stable to any small disturbances which are initiated on the front due for example to irregularities in the horizontal surface or to chance perturbations alternatively if some fluid is released onto a sloping surface for example some liquid detergent on a slanted plate a quite different plan form occurs one two or more extended regions of fluid develop downslope as shown in fig 1a b a situation intermediate between these two is now discussed consider a broad band of viscous fluid uniform in depth across a slope released so as to flow down a constant slope by following the motion which is initially independent of the cross slope coordinate the speed of advance and the depth of the flow before it breaks up into a series of waves of ever increasing amplitude can be determined i present an expression for the wavelength of the front which is determined by surface tension and is independent of the coefficient of viscosity

anomalous strain accumulation in the yucca mountain area nevada global positioning system gps surveys from 1991 to 1997 near yucca mountain nevada indicate west northwest crustal elongation at a rate of 1 7 0 3 millimeters per year 1 over 34 kilometers or 50 9 nanostrain per year global positioning system and trilateration surveys from 1983 to 1997 on a 14 kilometer baseline across the proposed repository site for high level radioactive waste indicate that the crust extended by 0 7 to 0 9 0 2 millimeter per year 50 to 64 14 nanostrain per year depending on the coseismic effect of the m s 5 4 1992 little skull mountain earthquake these strain rates are at least an order of magnitude higher than would be predicted from the quaternary volcanic and tectonic history of the area

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

alpine polyphase tectono metamorphic evolution of the south carpathians a new overview abstract the main terrains involved in the cretaceous tertiary tectonism in the south carpathians segment of the european alpine orogen are the getic supragetic and danubian continental crust fragments separated by the severin oceanic crust floored basin during the early middle cretaceous times the danubian microplate acted initially as a foreland unit strongly involved in the south carpathians nappe stacking multistage folding thrusting events uplift erosion and extensional stages and the development of associated sedimentary basins characterize the south carpathians during cretaceous to tertiary convergence and collision events the main cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the south carpathians are mid cretaceous austrian phase and latest cretaceous laramide or getic phase in age the architecture of the south carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom the getic supragetic basement cover nappes the severin and arjana cover nappes and danubian basement cover nappes all tectonically overriding the moesian platform the severin nappe complex including obarsia and severin nappes with late jurassic early cretaceous ophiolites and turbidites is squeezed between the danubian and getic supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred mid to late cretaceous subduction collision followed by tectonic inversion processes early cretaceous thick skinned tectonics was replaced by thin skinned tectonics in late cretaceous thus the former middle cretaceous austrian nappe stack and its albian lower senonian cover got incorporated in the intra senonian laramide getic stacking of the getic supragetic severin arjana nappes onto the danubian nappe duplex the two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the banatitic magmas 84 73 ma the overthrusting of the entire south carpathian cretaceous nappe stack onto the fold thrust foredeep units and to the moesian platform took place in the late miocene intra sarmatian times and was followed by extensional events and sedimentary basin formation

1 57 ga magmatism in the south carpathians implications for the pre alpine basement and evolution of the mantle under the european continent abstract chemical and isotopic analyses of amphibolites and gneisses from the oldest lithostratigraphic group in the south carpathians produce new insights regarding the chronology and evolution of the mobile proterozoic crust in central eastern europe these results date an episode of magmatism related to oceanic crust consumption reveal a period of continental stabilization and put constraints on the underlying mantle composition amphibolites from the cump na group have their origin in basalts chemically similar to island arc tholeiites a whole rock isochron age of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand

formation of clastogenic lava flows during fissure eruption and scoria cone collapse the 1986 eruption of izu oshima volcano eastern japan the 1986 eruption of b fissure at izu oshima volcano japan produced among other products one andesite and two basaltic andesite lava flows locally the three flows resemble vent effused holocrystalline blocky or aa lava however remnant clast outlines can be identified at most localities indicating that the flows were spatter fed or clastogenic the basaltic andesite flows are interpreted to have formed by two main processes a reconstitution of fountain generated spatter around vent areas by syn depositional agglutination and coalescence followed by extensional non particulate flow and b syn eruptive collapse of a rapidly built spatter and scoria cone by rotational slip and extensional sliding these processes produced two morphologically distinct lobes in both flows by a earlier non particulate flow of agglutinate and coalesced spatter which formed a thin lobe of rubbly aa lava ca 5 m thick with characteristic open extension cracks revealing a homogeneous holocrystalline interior and b later scoria cone collapse which created a larger lobe of irregular thickness 20 m made of large detached blocks of scoria cone interpreted to have been rafted along on a flow of coalesced spatter the source regions of these lava flows are characterized by horseshoe shaped scarps 30 m high with meso blocks ca 30 m in diameter of bedded scoria at the base one lava flow has a secondary lateral collapse zone with lower ca 7 m scarps backward tilted meso blocks are interpreted to be the product of rotational slip and forward tilted blocks the result of simple toppling squeeze ups of coalesced spatter along the leading edge of the meso blocks indicate that coalescence occurred in the basal part of the scoria cone this low viscosity coalesced spatter acted as a lubricating layer along which basal failure of the scoria cone occurred rotational sliding gave way to extensional translational sliding as the slide mass spread out onto the present caldera floor squeeze ups concentrated at the distal margin indicate that the extensional regime changed to one of compression probably as a result of cooling of the flow front sliding material piled up behind the slowing flow front and coalesced spatter was squeezed up from the interior of the flow through fractures and between rafted blocks the andesite flow although morphologically similar to the other two flows has a slightly different chemical composition which corresponds to the earliest stage of the eruption it is a much smaller lava flow emitted from the base of the scoria cone 2 days after the eruption had ceased this lava is interpreted to have been formed by post depositional coalescence of spatter under the influence of the in situ cooling rate and load pressure of the deposit extrusion occurred through the lower part of the scoria cone and subsequent non particulate flow of coalesced material produced a blocky and aa lava flow the mechanisms of formation of the lava flows described may be more common during explosive eruptions of mafic magma than previously envisaged

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

the impact of oxic degradation on long chain alkyl diol distributions in arabian sea surface sediments oxygen exposure has a large impact on lipid biomarker preservation in surface sediments and may affect the application of organic proxies used for reconstructing past environmental conditions to determine its effect on long chain alkyl diol and keto ol based proxies the distributions of these lipids was studied in nine surface sediments from the murray ridge in the arabian sea obtained from varying water depths 900 3000 m but in close lateral proximity and therefore likely receiving a similar particle flux due to substantial differences in bottom water oxygen concentration 3 77 mol l and sedimentation rate substantial differences exist in the time the biomarker lipids are exposed to oxygen in the sediment long chain alkyl diol and keto ol concentrations in the surface sediments 0 0 5 cm decreased progressively with increasing oxygen exposure time suggesting increased oxic degradation the 1 15 keto ol diol ratio doxi increased slightly with oxygen exposure time as diols had apparently slightly higher degradation rates than keto ols the ratio of 1 14 vs 1 13 or 1 15 diols used as upwelling proxies did not show substantial changes however the c30 1 15 diol exhibited a slightly higher degradation rate than c28 and c30 1 13 diols and thus the long chain diol index ldi used as sea surface temperature proxy showed a negative correlation with the maximum residence time in the oxic zone of the sediment resulting in ca 2 3 5 c change when translated to temperature the uk 37 index did not show significant changes with increasing oxygen exposure this suggests that oxic degradation may affect temperature reconstructions using the ldi in oxic settings and where oxygen concentrations have varied substantially over time

sedimentation in the western arabian sea the role of coastal and open ocean upwelling monsoon induced coastal and open ocean upwelling explain 84 of the variations of the organic carbon fluxes measured in the deep western arabian sea in this paper sea level measurements satellite derived wind speeds sea surface temperatures and nutrient profiles are used to discern the relative importance of these factors on fluxes measured during nine years of continuous sediment trap deployments this exercise shows i the increase in fluxes observed during the initial stages of the sw monsoons are caused by open ocean upwelling which develops faster than the coastal upwelling ii coastal upwelling triggers diatom blooms from nutrients from subsurface water and sediment resuspension and more importantly by injecting resting stages of diatoms back into the euphotic zone iii silica depletion resulting from diatom blooms in laterally advecting water masses leads to a replacement of diatoms by other nitrate limited organisms iv organic carbon fluxes to the deep arabian sea increase in response to an intensification of both coastal and open ocean upwelling weak coastal upwelling and strong open ocean upwelling also increase organic carbon fluxes the varying dominance of their influence is reflected in the timing and the composition of the peak fluxes v the link between organic carbon flux and monsoon strength is non linear probably due to changes in the surface currents and to vigorous turbulence in the surface water during strong sw monsoons these processes could reduce the organic carbon flux in the western arabian sea by about 65

on lava dome growth with application to the 1979 lava extrusion of the soufriere of st vincent abstract a theoretical analysis is presented for the spread of a viscous liquid flowing under its own hydrostatic pressure on a horizontal surface in order to model lava dome formation two situations are considered in detail the spreading of a constant volume of liquid and the case where the amount of liquid is continually increased experiments with silicone liquids show close agreement with theory the formation of a basaltic andesite lava extrusion in 1979 on the crater floor of the soufriere of st vincent west indies provided the motivation for and an application of the model the extrusion reached a diameter of 868 m and a height of 133 m over a period of 150 days over the first 90 days the growth relationships were consistent with those predicted by theory application of the theory to the soufriere dome suggests an effective viscosity of 2 x 10 12 poise for the basaltic andesite lava the large effective viscosity calculated for the lava may be attributed to the dominant influence of a high viscosity skin which forms at the margins of the flow as it cools after 70 days the rate of growth of the extrusion markedly decreased because a substantial collar of rubble accumulated at the flow front due to this collar the growth of the extrusion ceased after 150 days from approximately two weeks after the initiation of the extrusion the discharge rate of lava decreased approximately linearly with increasing dome height this observation suggests that the lava ascended under a decreasing hydrostatic driving pressure and that extrusion ceased when the lava column reached hydrostatic equilibrium

viscoelastic thermal stress in cooling basalt flows polygonal fractures commonly form in basaltic lava flows during cooling of the molten lava a transient thermomechanical model is constructed to apply the temperature history in a cooling basalt flow as a boundary condition in a mechanical model of viscoelastic stress in cooling basalt nearly all past modeling of stress in cooling basalt has treated the material as purely elastic below a well defined glass transition temperature an important distinction of this model is that the viscosity of the material is allowed to be temperature dependent and the effects of viscoelastic relaxation are included on the basis of this research faster cooling and higher strain rates lead to markedly higher effective glass transition temperatures consistent with previous observations by researchers the total thermal strain in the system is constant yet the percentage of strain that is not relaxed by viscous flow varies with position relative to the cooling surface this elastic strain partition is the portion of the total strain that creates stress in the material and it is directly dependent on cooling rate thus a genetic link between cooling rate and magnitude of stress is identified

palaeoclimate and palaeoceanographic conditions in the westernmost mediterranean over the last millennium an integrated organic and inorganic approach previous studies have revealed the excellence of the westernmost mediterranean records for reconstructing climate conditions over the last two millennia in particular inorganic and organic proxies have revealed a coherent signal of climate and oceanographic responses during this time here we compare and integrate both proxy records for reconstructing climate and oceanographic conditions with focus on the last millennium the higher temperatures indicated by lipid based proxies during the medieval climate anomaly mca are coincident with drier conditions indicated by inorganic proxies in contrast lower temperatures and humid conditions are indicated during the little ice age lia the industrial period was characterized by increasing humidity in comparison with the previous lia however a progressive aridification occurred since the second half of the twentieth century coexisting with a warming trend and higher contribution of c3 grasses proxy records are also interpreted to show atlantic water inflow at ad 1450 and 1950 and an intensification of the upwelling conditions coinciding with a prolonged positive north atlantic oscillation nao phase in the intervals ad 1000 1450 and 1960 1990 large scale oceanic atmospheric circulation patterns the nao and the atlantic meridional circulation and solar irradiance variations seem to have played the major key role during the last millennium together with anthropogenic contributions in the more recent record

geochemical constraints on crustal anatexis a case study from the pan african damara granitoids of namibia major and trace element models of recently published vapour absent mica dehydration melting experiments are used to identify granitoids generated by muscovite and biotite dehydration melting and to distinguish between plagioclase limited and biotite limited biotite dehydration melting in the case of granitoids from the pan african damara mobile belt namibia many of the leucogranites and salem type granitoids may be modelled by biotite dehydration melting the low rb sr granitoids e g donkerhuk onanis salem onanis donkerhuk nomatsaus salem goas probably reflect feldspar limited biotite dehydration melting a pelitic source whereas the high rb sr suites e g bloedkoppie leucogranite stinkbank leucogranite salem swakopmund leucocratic stink bank granite reflect biotite limited biotite dehydration melting a greywacke source alaskites from the damara belt have major element compositions which are consistent with muscovite dehydration melting and their positive eu anomalies are linked to high k2o reflecting k feldspar entrainment combined zr and lree light rare earth element solubility models indicate that insufficient time probably less than 104 years had elapsed between melt generation and melt extraction to ensure that the alaskite melts attained their equilibrium concentrations of zr and the lrees in contrast the leucogranites and salem type granites have attained their equilibrium inventories of these trace elements combined fe2o3 and mgo contents in some samples from two granitoids the salem goas and donkerhuk onanis intrusions are higher than those readily attainable by biotite dehydration melting indicating either 1 that they contain a contribution from melts generated by incipient garnet breakdown or 2 that they contain small amounts of an entrained ferromagnesian phase

coherent response of arabian sea upwelling and pollen transport to late quaternary monsoonal winds the indian summer monsoon causes large seasonal changes in the environments of both eastern africa and the arabian sea here we compare time series 140 kyr long of selected pollen types and foraminiferal upwelling faunas preserved in marine sediments to identify the frequencies of their variability and the coherence and phase of the terrestrial and marine responses to monsoonal circulation during interglacial intervals the pollen and upwelling records of the western arabian sea indicate stronger monsoons and are both coherent and in phase at periodicities near the precession of the earth s rotational axis 23 kyr we conclude that the strength of the monsoonal southwesterlies accounts for this high coherence of marine and terrestrial records during interglacial intervals low correlation during glacial phases indicates weaker monsoons and some decoupling of these two records these data indicate that two distinct modes of monsoon variability may exist an interglacial mode with strong monsoons and effective coupling of terrestrial and marine records and a glacial mode with both weaker monsoons and decreased linkage between arabian sea pollen and upwelling records

on bimodal differentiation by solidification front instability in basaltic magmas part 1 basic mechanics extensive coarse grained silicic lenses are common in the upper portions of large diabase sills lava lakes and gabbroic intrusions these lenses which often contain up to 10 wt more silica than their host rocks record a clear process of bimodal differentiation that may play a fundamental role in generating significant quantities of silicic magma in predominantly basaltic systems the spatial compositional textural and contact relations suggest that these silicic segregations form by infilling of tears formed during gravitational instability of the upper solidification front this process is investigated in some detail by exploring the thermal and mechanical conditions leading to internal failure of the front and segregation formation as the upper solidification front grows inward and thickens the local strength of the developing crystalline network must increase upward through the front sufficiently fast to offset the increasing weight of the front itself this necessary local variation in strength dictates how crystallinity must vary to prevent failure but the actual variation in crystallinity is determined by phase equilibria which in general varies in a fashion that is noncovariant with that required for mechanical stability it is this mismatch that apparently leads to failure and formation of silicic segregations the rate of filling of the tears by porous flow of interstitial melt from below regulates the rate of tear opening and the overall size of the tears is regulated by the local rate of advance of the solidification front segregations therefore thicken downward as the growth of the front slows and then die out altogether with approach of the lower solidification front this process irreversibly introduces siliceous noise into basaltic systems the silicic signal can be enhanced through subsequent reprocessing of the host rock to form volumetrically important masses of silicic magma this process may be fundamental to achieving the strong compositional diversity of the igneous rocks to yielding continental masses and to the differentiation of earth itself

solidification front fractionation in phenocryst free sheet like magma bodies basal cumulate zones are common in sills formed of magma carrying phenocrysts upon emplacement and the process leading to these cumulates and the corresponding roofward depleted zones are well understood many large sills which seem to have been emplaced with phenocryst free magma are nearly uniform in composition and show little tendency to differentiate by crystal settling we examine whether for an initially crystal free sill solidifying inwardly from top and bottom crystals nucleated and grown along the roof can escape incorporation survive resorption in settling through the hotter central region and reach the basal solidification front to form a cumulate we call this process solidification front fractionation and build a relatively simple model to examine the rheologic dynamic and crystal growth rate conditions leading to the downward escape of newly grown single crystals from the roof of a sheet like body of mafic magma cooling by conduction our results suggest that whereas a thin micro

a molecular and stable carbon isotopic study of lipids in late quaternary sediments from the arabian sea the distribution of apolar and polar lipids and their stable carbon isotopic compositions were determined for a number of sediment samples from different sites in the arabian sea lipids are mainly derived from planktonic archaea and a range of algae including haptophytes eustigmatophytes and diatoms the stable carbon isotopic compositions of compounds from diatoms highly branched isoprenoids fall into distinct groups suggesting other sources beside the diatom species rhizosolenia setigera for these compounds high amounts of sterol ethers which may be derived from diatoms were also detected a recently identified triterpenoid malabaricatriene was also present in high abundance in these samples the terrestrial input of lipids consists of n alkanes and their carbon isotopic compositions show that they are derived from aeolian dust input from the arabian peninsula the isotopic compositions of c37 alkenones from two cores during the last 15 ka is relatively constant and suggests that growth conditions for haptophyte algae averaged over 500 years did not change significantly over this period