integrity assessment of rock mass behind the shotcreted slope using thermography this paper presents the results of a field study of using thermography to identify the existence of eroded caves behind shotcrete protected slopes the temperature variation calculated from the highest and lowest temperatures measured at each point on the shotcrete surface is utilized to evaluate the integrity of the rock mass behind the concrete in addition ground penetration radar gpr is performed at three selected locations near the toe of the slope of concern while the necked eye observation and knocking tests are conducted at two of the selected areas the soils taken out from the rock mass and the abnormal echo as well as strong gpr reflection patterns confirm the existence of eroded caves behind the shotcrete surface the agreement of the locations that show both strong gpr reflection and large temperature variation verifies the applicability of thermography in evaluating the integrity of rock mass behind the shotcrete surface

residence of ree y th and u in granites and crustal protoliths implications for the chemistry of crustal melts a systematic study with laser ablation icp ms scanning electron microscopy and electron microprobe revealed that 70 95 wt of ree except eu y th and u in granite rocks and crustal protoliths reside within reeythu rich accessories whose nature composition and associations change with the rock aluminosity the accessory assemblage of peraluminous granites migmatites and high grade rocks is composed of monazite xenotime in low ca varieties apatite zircon thorthosilicate uraninite and betafite pyrochlore metaluminous granites have allanite sphene apatite zircon monazite and thorthosilicaie peralkaline granites have aeschinite fergusonite samarskite bastnaesite fluocerite allanite sphene zircon monazite xenotime and th orthosilicate granulite grade garnets are enriched in nd and sm by no less than one order of magnitude with respect to amphibolite grade garnets granulitegrade feldspars are also enriched in lree with respect to amphibolite grade feldspars accessories cause non henrian behaviour of ree y th and u during melt solid partitioning because elevated fractions of monazite xenotime and zircon in common migmatites are included within major minerals their behaviour during anatexis is controlled by that of their host settling curves calculated for a convecting magma show that accessories are too small to settle appreciably being separated from the melt as inclusions within larger minerals biotite has the greatest tendency to include accessories thereby indirectly controlling the geochemistry of ree y th and u we conclude that ree y th and u are unsuitable for petrogenetical modelling of granitoids through equilibrium based trace element fractionation equations

a corollary to the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh attempts to explain part of the large and regular atmospheric co2 changes over the last glacial interglacial cycles it calls for a reduction in the carbonate pump through a growth in diatoms at the expense of coccolithophorids in low latitude surface waters driven by a leakage of high si n waters from the southern ocean recent studies that present low opal accumulation rates from the glacial eastern equatorial pacific have challenged salh in a corollary to salh we argue that the key to salh is the dominance of diatoms over coccolithophorids and this does not depend on the magnitude of diatom production per se in support of our claim we show in a numerical model that atmospheric co2 can be lowered with even a reduced absolute flux of silicic acid leakage provided that si n in the leakage is elevated and that the excess si can be used by diatoms to shift the floral composition in their favor

experimental resetting of the u th pb systems in monazite abraded fragments 200 400 m of a large chemically homogeneous and non metamict brazilian monazite crystal characterised by a concordant u pb ages of 474 1 ma 208pb 206pb 19 5 were hydrothermally treated at varying temperatures with solutions of different compositions product monazites were analysed with scanning electron microscope sem electron microprobe emp secondary ion mass spectrometer sims and isotope dilution thermal ionisation mass spectrometer id tims experiments with pure water over a temperature range of 800 1200 c at 700 mpa and durations ranging from 5 to 60 days showed that even at 1200 c any dissolution and recrystallization of new monazite is confined to the outermost surface of the grain neither pb diffusion at the emp scale nor significant discordancy were observed we performed experiments at 800 and 1000 c for different durations using different fluid compositions at quartz saturation a 10 wt cacl2 fluid a 10 wt srcl2 fluid a 10 wt nacl fluid and a fluid containing nbs 982 pb standard 208pb 206pb 1 for all runs emp traverses revealed no pb diffusion profiles significant overgrowths of newly formed monazite are documented by sem analyses they occurred only in the 1000 c experiments when either cacl2 or pb bearing fluids were present in the cacl2 experiment two zones could be distinguished within the crystal a core possessing the initial monazite composition and a rim consisting of newly formed monazite produced by dissolution precipitation which was enriched in ca and pb free id tims dating of single grains treated with srcl2 and cacl2 solutions at 1000 c are significantly discordant experiments employing the nbs pb standard produced sub concordant monazite for which the 207pb 206pb apparent age has become older than prior to the experiment 544 ma at 800 c and 495 ma at 1000 c the newly grown monazite rim had obviously incorporated pb from the fluid none of our reaction products contained a detectable diffusion profile the only resetting mechanism we detected involved dissolution precipitation the extent of the dissolution precipitation process depends on fluid composition and is a more efficient mechanism than diffusion for controlling the resetting of monazite in natural rocks

low pressure metamorphism of palaeozoic pelites in the aspromonte southern calabria constraints for the thermal evolution in the calabrian crustal cross section during the hercynian orogeny during hercynian low pressure high temperature metamorphism of palaeozoic metasediments of the southern aspromonte calabria a sequence of metamorphic zones at chlorite biotite garnet staurolite andalusite and sillimanite muscovite grade was developed these metasediments represent the upper part of an exposed tilted cross section through the hercynian continental crust p t information on their metamorphism supplements that already known for the granulite facies lower crust of the section and allows reconstruction of the thermal conditions in the calabrian crust during the late hercynian orogenic event three foliations formed during deformation of the metasediments the peak metamorphic assemblages grew mainly syntectonically s2 during regional metamorphism but mineral growth outlasted the deformation this is in accordance with the textural relationships found in the lower part of the same crustal section exposed in the northern serre pressure conditions recorded for the base of the upper crustal metasediments are c 2 5 kbar and estimated temperatures range from 350 c in the chlorite zone increasing to 500 c in the lower garnet zone and reaching 620 c in the sillimanite muscovite zone geothermal gradients for the peak of metamorphism indicate a much higher value for the upper crust c 60 c km 1 than for the granulite facies lower crust 30 35 c km 1 the small temperature difference between the base of the upper crust 620 c at c 2 5 kbar and the top of the lower crust 690 c at 5 5 kbar can be explained by intrusions of granitoids into the middle crust which in this crustal section took place synchronously with the regional metamorphism at c 310 295 ma it is concluded that the thermal structure of the calabrian crust during the hercynian orogeny as it is reflected by peak metamorphic assemblages was mainly controlled by advective heat input through magmatic intrusions into all levels of the crust

integrated geostructural seismic and infrared thermography surveys for the study of an unstable rock slope in the peloritani chain ne sicily abstract this paper presents a multidisciplinary study about the instability of a rock slope on peloritani chain northeastern sicily several rockfalls affected the studied slope in the last decades also causing the disruption of the main road connecting the shore villages to the city of messina the complex geology and tectonics are the main causes of the poor mechanical properties of the rocks exacerbated by high fracturing and weathering geostructural surveys allowed identifying the main discontinuity sets most of which matches with the regional fault systems kinematic and stability analyses were carried out to define the main failure typologies and to realize two models describing the past rockfalls as well as possible future events for the deep investigation of the slope horizontal borehole drilling and seismic active prospecting were performed so to estimate the thickness of the rock with poor mechanical properties the contours of the most unstable areas along the slope have been better outlined through infrared thermography images giving information about the thermal radiance behavior of the rock constituting the surface slope the integrated approach of different methodologies besides defining the instability features of the study area demonstrates the reliability of such techniques particularly in a geologically complex region where rockfalls represent one of the main causes of landslide fatalities

a record of pleistocene diatom preservation from the amundsen sea west antarctica with possible implications on silica leakage article i nfo accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time no quantitative proxy exists for estimating the amount of silica lost to dissolution in southern ocean sediment cores to address this gap cultured valves of fragilariopsis kerguelensis the dominant planktonic diatom in the pleistocene to recent southern ocean were dissolved progressively under controlled laboratory conditions expansion and eventual conjoining of the areolae of f kerguelensis advances through several phases which are presented herein as a measure of diatom dissolution in order to evaluate the validity of laboratory methods this proxy is applied to sediments from piston core ps58 254 from the amundsen sea dissolution induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments thus suggesting the laboratory conditions accurately reflect the natural process of dissolution these resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution tosouthernocean sediments revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves intensity of diatom dissolution in core ps58 254 does not correspond to the relative abundance of any diatom species clay mineralogy or linear sedimentation rates however a correlation does exist between glacial cyclicity and diatom dissolution indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall transit through the water column and eventual deposition higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials this result is consistent with the predictions of the silicic acid leakage hypothesis salh whereby reduced rates of si usage in the southern ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials thiswouldfuela decrease in atmospheric pco2duringglacials silica acidleakage isdrivenbya decreaseinthe si nratioofdiatoms caused by increased iron input to glacial aged southern ocean waters this resulted in more lightly silicified diatom valves in the southern ocean which dissolved more quickly in the upper water column thereby maintaining the high silica content of glacial aged so waters and allowing for export of si to upwelling zones in the lower latitudes

plio pleistocene diatom biostratigraphy from odp leg 177 atlantic sector of the southern ocean abstract seven sites were drilled during ocean drilling program leg 177 in the atlantic sector of the southern ocean so on a transect over the antarctic circumpolar current from the subantarctic to the antarctic zone at four sites sediments were recovered with a pliocene pleistocene sediment package of up to 580 m allowing the refinement of previous diatom zonation concepts samples were analyzed on stratigraphic distribution and abundance of diatom species a refined diatom biozonation tied to the geomagnetic polarity record is proposed for the middle and late pleistocene two zonations applicable to the northern and southern area of the so were constructed considering different latitudinal distributions of biostratigraphic diatom marker species the southern zonation for the pleistocene relies on the occurrence of species of the genus rouxia r leventerae and r constricta n sp as well as on a revised last occurrence datum lod of actinocyclus ingens 0 38 ma late marine isotope stage mis 11 the use of these new stratigraphic marker species refines the temporal resolution for biostratigraphic age assignment to up to 0 1 myr in particular the lod of r leventerae as an indicator for the mis 6 5 boundary termination ii will improve future dating of carbonate free antarctic sediments these new data were obtained from sediments of sites 1093 and 1094 antarctic zone the northern zonation for the middle and late pleistocene time interval is based on the pleistocene abundance pattern of hemidiscus karstenii which was already proposed by previous investigations e g gersonde and barcena 1998 one new species r constricta and two new combinations fragilariopsis clementia fragilariopsis reinholdii are proposed in this study

stability analysis of rock wedge slide subjected to groundwater dynamic evolution abstract heavy rainfall may increase the infiltration rate raising the groundwater table after a short period time variation in the hydrostatic pressure on potential sliding surfaces and trailing edges of fissures in a rock slope may contribute to slope failure the failure mechanisms of rainfall triggered rock wedge slides have been widely studied in the literature however studies on the dynamic evolution of groundwater in rock failure are still limited in this study a typical rock wedge slide that occurred in chengkou county chongqing china is selected as a case study to analyze the stability of rock wedge with double planes and tension crack subjected to groundwater dynamic evolution model tests were designed and performed to reproduce the dynamic evolution of groundwater in the rock slope and analyze its role in wedge failure development and distribution characteristics of water pressure are investigated through monitoring the water pressure distributed along the surfaces of wedge failures from the experimental study it is found that the initial formation process of water pressure along the sliding surface consists of four types of distribution patterns i e triangular distribution type i trapezoidal distribution type ii trapezoidal distribution and type iii trapezoidal distribution based on the model tests and theoretical analysis the order of the calculated safety factors of the chengkou rock wedge slide are triangle type i trapezoid type ii trapezoid type iii trapezoid the existence of inflection points in the trapezoidal distribution mode significantly increases water pressure on both sides of rock wedge which contributes instability the new approach for investigation of the effect of dynamic evolution groundwater on stability of rock wedge slide is developed based on fundamental mechanism and experimental study it can be adopted for stability assessment of similar rock wedge slides in other areas

dissolution of biogenic silica from land to ocean role of salinity and ph the dissolution rates of diatom frustules phytoliths two diatomaceous lake sediments a siliceous ooze from the southern ocean a diatomite deposit and a synthetic amorphous silica were measured in flow through reactors supplied with either seawater or freshwater although the rates varied by more than one order of magnitude among the different siliceous materials for any given solid the rate was systematically higher in seawater than freshwater on average by a factor of five flow through reactor experiments with the diatom frustules and synthetic silica using mixtures of freshwater and seawater indicated that most of the rate increase occurred for seawater fractions between 0 and 50 the observed rate enhancement is attributed to the higher ph of seawater and the catalytic effect of seawater cations on the hydrolysis of siloxane bonds at the silica surface because of their abundance in seawater na and mg2 are mainly responsible for the salinity induced rate increase the large difference in dissolution kinetics between freshwater and seawater helps explain the very efficient recycling of biogenic silica in marine environments compared with freshwater lakes enhanced dissolution at the land ocean transition of biogenic silica produced by terrestrial plants and freshwater diatoms may represent a significant but largely overlooked source of nutrient silicon for estuarine and nearshore marine ecosystems

u pb single zircon pb evaporation and sm nd isotopic study of a granulite domain in se madagascar madagascar is a poorly known precambrian domain at the eastern border of the mozambique belt strongly affected by the pan african orogeny this large island represents a key part of gondwanaland and the accurate dating of the major metamorphic event is critical for the reconstruction of that supercontinent in the southeastern zone of the island metamorphism has reached high temperature and low pressure conditions 850 c and 5 kbar with moderate retrogression a u pb conventional multigrain single zircon stepwise pb evaporation and sm nd geochronological study on meta felsic rocks has shown that basement of at least lower proterozoic age was strongly metamorphosed around 570 580 ma this tectometamorphic event nearly obliterated any pre pan african zircon isotopic memory the granulite facies metamorphism is associated with the syn metamorphic emplacement of the anosyan charnock ites and granites a strong channelized fluid contribution at 545 ma has produced the re crystallization of biotite apatite

composite rock slope kinematics at the current randa instability switzerland based on remote sensing and numerical modeling abstract kinematic analysis of slope instabilities in brittle rock is crucial for understanding the reaction of the rock mass to external forcing factors in steep terrain inaccessibility often limits collection of relevant data and remote sensing techniques must be applied this is the case at the current randa rock slope instability in southern switzerland where a total volume of about 5 6 million m3 moves at a rate of up to 30 mm yr a large portion of the unstable rock mass is exposed in an 800 m high inaccessible cliff the main scarp of the may 1991 rock slope failure between 2005 and 2007 a comprehensive suite of remote sensing techniques including photogrammetry lidar and gb dinsar was combined with 3d geodetic measurements to characterize the rock mass structure and displacement patterns photogrammetry and lidar data were measured simultaneously from a helicopter using a system allowing for oblique view angles which provided optimal observations of the steep rock cliff we used these datasets to map large scale structures and extract their orientation and minimum persistence as well as to characterize the 1991 failure scarp the northern part of the may 1991 failure surface shows a transition from stepped planar sliding at the base to failed rock bridges in the center to tensile failure close to the vertical head scarp kinematic analysis of the discontinuity sets in the currently moving rock mass shows that both toppling and translational sliding are feasible failure mechanisms toppling is more likely for steep faces above 2200 m whereas translational failure is more likely in the lower portion of the instability interpretation of gb dinsar displacement maps revealed similar kinematic behavior and also allowed identification of a basal rupture zone and lateral release plane bounding the instability displacement vectors derived from geodetic surveying provided new insights into the 3d kinematic behavior of the instability all information extracted from different data sets were integrated in a conceptual model which was then investigated with 2d numerical simulation using the discontinuum code udec the numerical models were able to reproduce the hypothesized kinematic behavior well

infrared thermography proposed for the estimation of the cooling rate index in the remote survey of rock masses abstract infrared thermography has been tested herein for the study of the fracturing condition of intensely jointed rock masses in order to find out what kind of information can be assessed although this technique is widely used in several scientific fields its direct application for rock mechanics purposes is still under development in this paper thermal imaging campaigns carried out in different climatic conditions are described a cooling rate index related to how fractured rock masses behave during the heat transfer towards the external environment is proposed such an index has been related to the degree of fracturing of the rock masses in order to find a relationship among thermal behavior and the main quantitative fracturing indexes results return interesting matches between some geostructural features and thermal outputs demonstrating the reliability of the application of such methodology to bare rock masses moreover new experimental considerations are proposed laying the foundations for future studies aimed to further validate the infrared thermography as an effective remote survey technique

comparing glacial and holocene opal fluxes in the pacific sector of the southern ocean 1 the silicic acid leakage hypothesis salh predicts that during glacial periods excess silicic acid was transported from the southern ocean to lower latitudes which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric co2 downcore records of 230th normalized opal biogenic silica fluxes from 31 cores in the pacific sector of the southern ocean were used to compare diatom productivity during the last glacial period to that of the holocene and to examine the evidence for increased glacial si export to the tropics average glacial opal fluxes south of the modern antarctic polar front apf were less than during the holocene while average glacial opal fluxes north of the apf were greater than during the holocene however the magnitude of the increase north of the apf was not enough to offset decreased fluxes to the south resulting in a decrease in opal burial in the pacific sector of the southern ocean during the last glacial period equivalent to approximately 15 gt opal ka 1 this is consistent with the work of chase et al 2003a and satisfies the primary requirement of the salh assuming that the upwelled supply of si was approximately equivalent during the holocene and the glacial period however previous results from the equatorial oceans are inconsistent with the other predictions of the salh namely that either the corg caco3 ratio or the rate of opal burial should have increased during glacial periods we compare the magnitudes of changes in the southern ocean and the tropics and suggest that si escaping the glacial southern ocean must have had an alternate destination possibly the continental margins there is currently insufficient data to test this hypothesis but the existence of this sink and its potential impact on glacial pco2 remain interesting topics for future study

contrasted monazite hydrothermal alteration mechanisms and their geochemical implications in spite of the major importance of monazite as a repository for the rare earths and th in the continental crust for u th pb geochronology and as a possible form for high level nuclear waste very little work has been carried out so far on the behaviour of this mineral during fluid rock events this contribution describes two contrasting examples of the hydrothermal alteration of monazite the first case comes from a sample of the carnmenellis granite cornwall southwest england chloritized at 284 16 c whereas the other occurs in the skiddaw granite lake district northwest england which underwent greisenization at 200 30 c an integrated study involving backscattered scanning electron microscopy electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry la icp ms reveals that the chloritization event was characterized by the coupled substitution 2ree3 th4 ca2 in the altered parts of the monazite thus leaving the p o framework of the crystal untouched in contrast greisenization led to the coupled substitution ree3 p5 th4 si4 and therefore involved a partial destruction of the phosphate framework the resulting rare earth element patterns are quite different for these two examples with a maximum depletion for dy and er in the altered parts of the carnmenellis monazite whereas the skiddaw monazite shows a light rare earth depletion but an yb and er enrichment during alteration this latter enrichment accompanied by an increase in u but roughly unchanged pb concentrations probably resulted from a decrease in the size of the 9 coordinated site in monazite thereby favouring the smaller rare earths these contrasted styles of monazite alteration show that the conditions of fluid rock interaction will not only affect the aqueous geochemistry of the lanthanides actinides and lead and the relative stability of the different minerals holding these elements variations in these conditions will also lead to various possible chemical exchanges between the crystalline phases and the hydrothermal fluids the occurrence of common lead along penetrative cracks in the carnmenellis monazite shows that only a leaching prior to the u pb analyses of the whole grain will permit an accurate determination of the magmatic crystallization age in contrast for the skiddaw case it may be possible to date the fluid rock event by in situ 207pb 206pb geochronology the observation that the altered parts of both monazite examples display nd leaching and no significant sm nd fractionation indicates that they should not affect the host whole rock nd isotopic signatures finally it appears that monazite like ceramics designed for the containment of high level nuclear wastes will retain th and the geochemically equivalent transuranic elements during fluid rock events similar to those documented in this study but may release nd u and the corresponding radionuclides to the environment

modelling the thermal perturbation of the continental crust after intraplating of thick granitoid sheets a comparison with the crustal sections in calabria italy thick granitoid sheets represent a considerable percentage of palaeozoic crustal sections exposed in calabria high thermal gradients are recorded in upper and lower crustal regional metamorphic rocks lying at the roof and base of the granitoids ages of peak metamorphism and emplacement of granitoids are mostly overlapping suggesting a connection between magma intrusion and low pressure metamorphism to analyse this relationship thermal perturbation following granitoid emplacement has been modelled the simulation indicates that in the upper crust the thermal perturbation is short lived in contrast in the lower crust temperatures greater than 700 c are maintained for 12 ma explaining granulite formation anatexis and the following nearly isobaric cooling an even longer perturbation can be achieved introducing the effect of mantle lithosphere thinning into the model

high resolution opal records from the eastern tropical pacific provide evidence for silicic acid leakage from hnlc regions during glacial periods abstract a shift from carbonate to silica dominated primary production could significantly affect the oceanic carbon cycle via changes in the particulate carbon rain rate ratio c organic c inorganic fluxes an increase in c rain rate ratio has been invoked to explain lower glacial p co 2 however firm evidence of an ecological shift towards silica dominated productivity during the last glacial period is lacking here we present new high resolution reconstructions of biogenic silica and total production over the past 40 000 yr bp in 3 cores from the eastern tropical north pacific etnp off mexico and nicaragua these records reveal a clear regional pattern of higher siliceous productivity with higher opal accumulation during the last glacial period compared to interglacial times higher si c and si n ratios of glacial sediments in these records suggest a net increase in siliceous production over total production we attribute this to the additional supply of silicic acid to the etnp margins favouring diatoms over other non siliceous algae this suggestion for increased supply of si during glacial periods is consistent with the proposed large scale redistribution of excess silicic acid from high nitrate low chlorophyll hnlc regions like the eastern equatorial pacific eep and the southern ocean by the silicic acid leakage hypothesis salh in these hnlc regions the si isotope composition of diatom frustules 30 si has provided evidence for the generation of surplus of silicic acid during diatom growth under conditions of higher fe availability during glacial periods we suggest that silicic acid leakage from the hnlc regions to the adjoining oceans may have increased the carbon rain rate ratio and ultimately contributed to the decrease in glacial atmospheric p co 2

dissolution and preservation of antarctic diatoms and the effect on sediment thanatocoenoses abstract comparison of southern ocean diatom populations from i surface ocean production ii underlying antarctic sediments and iii laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in southern ocean sediments increasing dissolution causes relative depletions in n kerguelensis k enrichments in t lentiginosa l and slight enrichments in e antarctica a this reflects the relative susceptibility to dissolution of the three species that dominate antarctic sediments we have devised a preservation index for the southern ocean based on the ratio k k l to estimate relative extents of dissolution and applied it to natural assemblages holocene southern ocean sediments display increasing opal preservation toward higher latitudes but south of the antarctic polar front preservation decreases in the order well preserved se indian s atlantic sw indian se pacific poorly preserved dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum lgm sediments of the indian and pacific sectors but in the atlantic increased e antarctica abundances at lgm must have resulted from an increase in surface ocean production of this species holocene and lgm diatoms in atlantic and pacific sector sediments are equally well preserved but in the indian sectors holocene sediments are better preserved than those of lgm age paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution

petrology and u th pb geochronology of the sapphirine quartz bearing metapelites from rajapalayam madurai block southern india evidence for polyphase neoproterozoic high grade metamorphism abstract strongly migmatitic sapphirine bearing granulites occur as dm to m sized enclaves in garnetiferous leucogranites in the southeastern part of the madurai block mb the largest section of neoproterozoic crust in the southern granulite terrain of india sgt early mineral assemblages biotite sillimanite quartz garnet biotite quartz break down via successive dehydration melting reactions to high t and high p phase assemblages e g garnet melt orthopyroxene sillimanite melt orthopyroxene cordierite melt melt consuming reactions along the retrograde path led to partial resorption of garnet to orthopyroxene sillimanite orthopyroxene sapphirine and or orthopyroxene cordierite as well as orthopyroxene sillimanite assemblages to cordierite biotite quartz symplectites the occurrence of uht metamorphism is indicated by the presence of small inclusions of sapphirine quartz intergrowths in garnet this reaction sequence is interpreted in a kfmash partial petrogenetic grid taking both melt producing and melt consuming reactions into account which yields a clockwise heating cooling decompression p t path culminating at 8 11 kbar and 1000 1100 c in situ u th pb monazite dating has been performed to more precisely constrain the ages given by chemical electron microprobe on monazite in various textural positions monazite inclusions in garnet often yield a bimodal distribution of early 950 850 ma and late neoproterozoic 600 500 ma ages which is in good agreement with the results of u pb and epma zircon dating in other places of the southeastern madurai block by contrast monazite inclusions in other mafic minerals orthopyroxene cordierite biotite or as interstitial phase exclusively yield ages between 550 and 480 ma the early neoproterozoic population is interpreted to reflect the timing of migmatisation and peak uht metamorphism whereas the late neoproterozoic ages are inferred to date cooling and exhumation with granitic magmas to a higher crustal level of the madurai block

morphometric variability in the diatom fragilariopsis kerguelensis implications for southern ocean paleoceanography abstract diatoms play a central role in the ecosystem of the southern ocean where they represent the main producers and carriers of organic carbon and dissolved silicon towards the deep ocean variability in space and time of the size of the most abundant species fragilariopsis kerguelensis may directly impact the way this ecosystem functions and also affect the nutrient balance of the global ocean as important water masses e g the antarctic intermediate water get their nutrient signature in this area we used a biometric approach and analyzed the size variability of f kerguelensis valves in sixty four surface sediment samples from the southern ocean in sediment trap samples from a mooring site pf3 at the antarctic polar front apf and along a nearby piston core ps1654 2 the average length and valve area of f kerguelensis displayed a distinct increase in the proximity of the apf and lower values to the north and south of it and also changed markedly over seasonal cycles as diatom blooms and nutrient availability waxe and wane the last glacial to interglacial transition also witnesses important changes in the general shape and valve size of f kerguelensis with specimens from glacial intervals being ca 30 larger than their interglacial counterparts 195 versus 150 m 2 valve area a sharp peak in average area and a very specific valve morphology correspond to the first signs of deglaciation and concurring sst sea surface temperature increase and sea ice retreat the latter together with melting icebergs may have contributed dissolved iron to surface waters the highest average sizes during glacial intervals are higher than what found anywhere in the southern ocean today the newly proposed proxy valve area and shape of f kerguelensis may thus prove useful for the reconstruction of the past position and nutrient characteristics of the apf and opal belt a region characterized by high production and export of biogenic silica in a particularly sensitive and dynamic area such as the southern ocean

displaced antarctic diatoms in the amirante passage abstract displaced antarctic source diatoms are found in surface sediments below 4100 in the amirante passage area but not above this depth their distribution tends to support the conclusion that a sharp velocity gradient exists within the antarctic bottom water aabw in this region below about 4100 m flow velocities are sufficient to resuspend and transport sediment while above this level the aabw is incapable of transporting sediment in suspension

u pb zircon rb sr and sm nd geochronology of high to very high pressure meta acidic rocks from the western alps three meta acidic rocks from the western italian alps a magnesiochloritoid bearing metapelite from the monte rosa massif a coesite pyrope quartzite from the dora maira massif and the monte mucrone granite in the sesia zone have been studied by u pb zircon rb sr on whole rock apatite and phengite and sm nd wholerock methods the mineral parageneses of the investigated rocks indicate high to very high pressure and medium to high temperature metamorphism this combined isotopic study has enabled us to constrain the ages of magmatic and metamorphic events and also to compare the behaviour of u pb zircon systems in three intensely metamorphosed areas of the pennine domain the u pb zircon data have yielded a magmatic age for the monte mucrone granite at 286 2 ma this result confirms the occurence of late hercynian magmatism in the sesia zone as in other austro alpine units and in other areas of the european crystalline basement in the monte rosa massif a geologically meaningless lower intercept age of 192 2 ma has been interpreted as an artefact due to a complex evolution of the u pb zircon system the magmatic shape of the zircons implies a magmatic or volcano sedimentary protolith for this rock originally considered as a metasediment the very high pressure metamorphism in the dora maira quartzite has produced an opening of the u pb zircon system at 121 12 29 ma the rb sr data support the occurence of high grade metamorphism during cretaceous times phengites model ages are slightly younger than the u pb zircon lower intercept ages due to cooling phenomena or possible response of the phengites to a later deformation the nd model ages from the whole rock samples as well as the u pb upper intercept ages from zircons of all three investigated rocks indicate the presence of proterozoic crustal components inherited from the precursors of these meta acidic rocks the studied zircon populations and their u pb systems apparently showed open system behaviour only when affected by extreme metamorphic conditions 700 750 c 28 kbar whereas eclogite facies conditions of 500 550 c and 14 16 kbar were not enough to disturb significantly the u pb zircon evolution it is also probable that the sedimentary or magmatic origin of the protoliths of these meta acidic rocks which involved different characteristics such as grain size and fluid phase concentration and composition could be another important factor controlling the u pb zircon system behaviour during metamorphic events

geochronology of the medium to high grade metamorphic units of the peloritani mts sicily the peloritani mountains are a fragment of an orogen variably attributed to the alpine or hercynian orogeny on the basis of 39ar 40ar u pb and rb sr dating the main metamorphism of the two medium high grade metamorphic units the mela and aspromonte units and most of the thrusting responsible for stacking the orogenic edifice are seen to be hercynian the main thrusting of the aspromonte unit over the lower grade units took place at 301 2 ma brittle deformation during tertiary reactivation of hercynian thrust planes did not generate any rejuvenation of white micas in the studied sector our dataset shows a great complexity and we propose to unravel it by considering different levels of information to first order the mela and aspromonte units differ in their metamorphic paths and their geochronological evolution the mela unit shows generally younger ages carboniferous than the aspromonte unit and unlike the latter was extensively retrogressed in greenschist facies the aspromonte unit is itself geochronologically heterogeneous proterozoic ages are preserved both in titanite and in amphibole relics of one tectonic subunit devonian to carboniferous amphibole ages are found in different other subunits tertiary overprint is minor and spatially limited we propose to consider the chronologically heterogeneous subunits as accreted pre hercynian terranes amalgamated late during the hercynian orogeny micas in both units give scattered mesozoic 39ar 40ar and rb sr ages with evidence for heterochemical mica generations we interpret them as a result of widespread hydrothermal circulation event s tertiary overprint is generally absent with the exception of a small area near messina where biotite and muscovite underwent a complex recrystallisation history in the interval between 48 and 61 ma

petrogenesis of contrasting hercynian granitoids from the calabrian arc southern italy abstract the granitoids of the southern calabrian arc have been investigated for whole rock and phase chemistry zircon typology ree sr and nd isotopes two distinct granitoid associations which are related in time and partly in space are present a calc alkaline one and a peraluminous one the prevailing calc alkaline association is compositionally expanded sio2 48 70 and biotite dominated with tonalites and granodiorites as predominant rock types the peraluminous association is compositionally restricted sio2 67 76 and contains two mica al silicates distinct peraluminous typologies occur also as core facies within the calc alkaline types all granitoids are ilmenite bearing the cittanova cn villa s giovanni vsg and capo rasocolmo cr peraluminous granites display zircon typology ree patterns srt 51 to 113 and ndt values 8 5 to 4 6 at 290 ma suggesting a dominantly quartzofeldspathic metasedimentary source in more detail the cn types and the cr vsg types require heterogeneous and different sources the calc alkaline granitoids display very variable ree patterns cen 25 227 and ybn 3 5 18 5 in the tonalites granodiorites and variable age corrected ndt values 8 5 to 0 25 whereas sr values vary little 82 to 93 thus in terms of ndt srt covariation the data points define a vertical array which is inconsistent with a model involving crustal contamination by mantle derivatives a more viable mechanism seems to be the melting of hydrous and heterogeneous mafic lower crust and or basic underplate producing distinct magma batches evolving independently crustal contamination mingling and fractionation processes may all have contributed to the observed geochemical variations within the granitoids the peraluminous granodiorites occurring within the serre and capo vaticano multipulse calc alkaline plutons exhibit isotopic ratios ndt 6 11 to 0 33 and srt 93 to 97 which are similar to those of the calc alkaline host rocks suggesting a possible genetic link geologic and geochemical data indicate a continental collision setting for this plutonic activity the magmas were produced during late thickening to exhumation phases following collision and moderate crustal overthickening and were emplaced subsequently during a short time span a mantle contribution should have favoured melting which affected various sectors of the continental crust

deglacial pulses of deep ocean silicate into the subtropical north atlantic ocean records of biogenic opal export in the north atlantic ocean show pronounced maxima during each glacial termination over the past 550 000 years consistent with a strong deglacial reduction in the formation of silicate poor glacial north atlantic intermediate water and a consequent increase in upward silicate transport the southern ocean is thought to have an important role in driving glacial interglacial changes in atmospheric carbon dioxide concentrations but the mechanism responsible for carbon dioxide release upon deglaciation remains unclear based on a record of biogenic opal export that exhibits opal maxima during each glacial termination of the past 550 000 years nele meckler et al propose that deglacial reduction in glacial north atlantic intermediate water led to downward mixing of warm low density surface water ultimately triggering antarctic overturning and carbon dioxide release to the atmosphere growing evidence suggests that the low atmospheric co2 concentration of the ice ages resulted from enhanced storage of co2 in the ocean interior largely as a result of changes in the southern ocean1 early in the most recent deglaciation a reduction in north atlantic overturning circulation seems to have driven co2 release from the southern ocean2 3 4 5 but the mechanism connecting the north atlantic and the southern ocean remains unclear biogenic opal export in the low latitude ocean relies on silicate from the underlying thermocline the concentration of which is affected by the circulation of the ocean interior here we report a record of biogenic opal export from a coastal upwelling system off the coast of northwest africa that shows pronounced opal maxima during each glacial termination over the past 550 000 years these opal peaks are consistent with a strong deglacial reduction in the formation of silicate poor glacial north atlantic intermediate water2 gnaiw the loss of gnaiw allowed mixing with underlying silicate rich deep water to increase the silicate supply to the surface ocean an increase in westerly wind driven upwelling in the southern ocean in response to the north atlantic change has been proposed to drive the deglacial rise in atmospheric co2 refs 3 4 however such a circulation change would have accelerated the formation of antarctic intermediate water and sub antarctic mode water which today have as little silicate as north atlantic deep water and would have thus maintained low silicate concentrations in the atlantic thermocline the deglacial opal maxima reported here suggest an alternative mechanism for the deglacial co2 release5 6 just as the reduction in gnaiw led to upward silicate transport it should also have allowed the downward mixing of warm low density surface water to reach into the deep ocean the resulting decrease in the density of the deep atlantic relative to the southern ocean surface promoted antarctic overturning which released co2 to the atmosphere

different age response of zircon and monazite during the tectono metamorphic evolution of a high grade paragneiss from the ruhla crystalline complex central germany results of tims sims and sem analyses show that zircon and monazite in a high grade paragneiss of the ruhla crystalline complex central germany were formed and or altered during different stages of a tectono metamorphic history between early devonian and permian times detrital zircon cores of 460 ma place an older limit on the age of anatexis and show that the paragneiss sequence contains rocks at least as young as early cambrian metamorphic zircon growth commenced at 365 ma peaking at 360 355 ma at the same time that granite dykes were emplaced in contrast monazite in the paragneiss preserves little record of the metamorphic peak most monazite grains grew or were recrystallised in the lower carboniferous at 339 ma contemporaneous with the emplacement of voluminous diorite and granite bodies these intrusions and related tectonics caused some of the high u zircon overgrowths to undergo moderate to severe pb loss a second pb loss event between 300 and 280 ma can be related to late carboniferous early permian large scale block faulting

petrological evidence for crustal thickening and extension in the serre granulite terrane calabria southern italy the paper presents the metamorphic trajectory recorded by metapelitic migmatites of the upper part of the hercynian lower continental crust of the serre southern calabria italy the relict minerals reaction textures and phase equilibria define a clockwise p t path the prograde metamorphism from temperature of about 500 c and pressure of 4 5 kbar to t 700 ca nd p 8 kbar stabilized the assemblage grt ky bt ms si 11ox 3 26 3 29 in the uppermost metapelites of the profile progressive heating led to h2o fluxed and dehydration melting first of ms then of bt at t 700 c in the stability field of sillimanite this process was followed by nearly isothermal decompression producing additional melt with a transition from grt to a grt crd stability field further decompression caused the formation of crd corona around garnet nearly isobaric cooling led to rehydration and retrogression across the stability field of andalusite up to the stability field of kyanite the lowermost metapelites of the studied profile have lost most of the memory of the prograde p t path they record decompression and cooling high temperature mylonites occur in which boudinage elongation and pull aparts characterize the porphyroclasts the pull aparts in the high t mylonites are filled with low p minerals crd spl the hercynian metamorphic trajectory and the microtextures are consistent with crustal thickening and subsequent extensional regime during extension an important tectonic denudation probably caused the isothermal decompression extension also occurred in post hercynian times as documented by pull aparts in sillimanite porphyroclasts filled with chloritoid within a low grade mylonite

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

a quantitative assessment of diatom dissolution and late quaternary primary productivity in the eastern equatorial pacific the eastern equatorial pacific eep is an important area for ocean atmosphere carbon exchange and yields different opal accumulation records for sites influenced by equatorial divergence and peru upwelling the divergence zone is characterized by a lower opal accumulation rate during the last glacial compared with the holocene but the reverse is true for the peru upwelling zone as a gauge of opal production versus preservation in the eep differential diatom preservation was investigated via a quantitative four stage preservation index using the vellum of the ubiquitous tropical centric diatom azpeitia nodulifer we find similar dissolution records at both sites from the last glacial maximum lgm through the holocene despite differing accumulation rates implying that production not preservation controlled the accumulation rates thus the increased silica accumulation in the peru upwelling region is related to increased production suggesting higher availability of silica in the photic zone in accord with the silica leakage hypothesis described by matsumoto et al 2002 silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric co global biogeochemical cycles 5 doi 10 1029 2001gb001442 and discussed by richaud et al 2007 furthermore we suggest an ecological control on opal preservation due to silica recycling by diatoms in the water column most likely in the photic zone increased production causes rapid silica recycling and thinner walled frustules resulting in enhanced water column dissolution in this setting diatom dissolution is independent of the rate of accumulation of silica or sediment high opal productivity does not necessarily lead to high preservation as proposed for southern ocean sediments sayles f martin w chase z anderson r 2001 benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west deep sea research ii 48 4323 4383 our observations are compatible with a production increase in the late deglacial and early holocene as reported by loubere 2001 nutrient and oceanographic changes in the eastern equatorial pacific from the last full glacial to the present global and planetary change 29 77 98 and inferred by spero h and lea d 2002 the cause of carbon isotope maximum events on glacial terminations science 296 522 525 and rickaby r and osborne a 2006 oceanic redistribution of phosphate during the last deglaciation in preparation

landslide susceptibility map refinement using psinsar data abstract landslide susceptibility maps lsm are commonly used by local authorities for land use management and planning activities representing a valuable tool used to support decision makers in urban and infrastructural planning the accuracy of a landslide susceptibility map is affected by false negative and false positive errors which can decrease the reliability of this useful product in particular false negative errors are generally worse in terms of social and economic losses with respect to the losses associated with false positives in this paper we present a new technique to improve the accuracy of landslide susceptibility maps using permanent scatterer interferometric synthetic aperture radar psinsar data the proposed approach uses two different data sets acquired in ascending and descending geometry the ps velocity measured along the line of sight is re projected into a new velocity along the steepest slope direction v slope integration between the lsm and the ground deformation velocity map along the slope was performed using an empirical contingency matrix which takes into account the average v slope and the susceptibility degree obtained using the random forests algorithm the results show that the susceptibility degree increased in 56 41 km 2 of the study area the combination of psinsar data and the landslide susceptibility map lsm improved the prediction reliability of slow moving landslides which particularly affect urbanized areas the use of this procedure can be easily applied in different areas where psi data sets are available this approach will help planning and decision making authorities produce reliable landslide susceptibility maps correcting some of the lsm errors

vertical budgets for organic carbon and biogenic silica in the pacific sector of the southern ocean 1996 1998 abstract during the 1996 1998 antarctic environment and southern ocean process study aesops a component of us jgofs we obtained seasonal or longer term data sets on the rates of production vertical transport remineralization and burial of particulate organic carbon poc and biogenic silica bsio2 in the southern ocean at 170 w between 55 s and 68 s the aesops data records enable us to construct vertical c and si budgets for the water column and upper sediments with all estimates derived from direct measurement of the relevant fluxes we constructed annual c and si budgets for each of four ecologically distinct zonal bands within the system for both poc and bsio2 the greatest annual delivery to the sea floor 200 and 1400 mmol m 2 yr 1 respectively and burial 6 and 160 mmol m 2 yr 1 respectively were observed in the southern antarctic circumpolar current acc between 61 5 s and 65 5 s that pattern is consistent with our observation that a diatom bloom propagated southward through the southern acc during the spring and summer of 1997 1998 following the receding ice edge and that this bloom was the main source of both poc and bsio2 in the system on an annual basis in the other zones the annual fluxes of poc and bsio2 to the sea floor ranged from 19 to 67 of those in the zone traversed by the summer diatom bloom the higher benthic fluxes of both poc and bsio2 in the southern acc imply that blooms similar to the one we observed in 1997 1998 occur commonly in the southern acc and that their high productivity signature is transmitted to the sea floor the data show preferential preservation of bsio2 over poc throughout the water column and upper seabed in the four zonal bands we consider bsio2 and poc are produced in mole ratios of 0 1 0 4 exported from the upper 100 m in ratios of 0 2 0 6 arrive at 1000 m in ratios of 1 5 4 5 reach the sea floor in ratios of 2 2 7 6 and are buried in ratios of 11 6 28 despite the preferential preservation of bsio2 accumulation of opal rich sediments beneath the acc does not result from unusually efficient preservation of siliceous material the estimated bsio2 preservation efficiency burial production ranges from 1 2 to 5 5 indistinguishable from the global average of 3 instead opal rich sediment accumulation in this region reflects very high annual rates of bsio2 production in surface waters along with very low accumulation rates of other sedimentary components e g caco3 and detrital material the observed high ratios of bsio2 production to poc production in surface waters are consistent with the known tendency for the si c ratio of diatoms to increase when fe is low if greater fe availability during the last glacial maximum permitted diatoms in the southern ocean to grow with lower more normal si c ratios export of diatom produced poc could have occurred at 2 3 times its present rate a corresponding increase in opal export or opal sediment accumulation is unlikely because silicic acid is almost totally depleted north of 65 s under present conditions thus even large increases in poc production and export during glacial periods would not be reflected in the opal accumulation record

climate mediated size variability of diatom fragilariopsis kerguelensis in the southern ocean abstract fragilariopsis kerguelensis o meara hustedt is the most abundant open ocean diatom species in southern ocean sediments and its average valve area has recently been used to infer glacial interglacial paleoceanographic conditions studies from the atlantic sector of the southern ocean demonstrated how larger average valve area of f kerguelensis during the last glacial compared to the interglacial possibly relate to greater availability of iron through wider sea ice coverage and higher eolian dust input we present here data on average valve area of f kerguelensis from three sediment cores covering the last 42 cal ka bp from different zones of the southern ocean our records confirm previous results from the atlantic sector but highlight a different pattern from the indian sector where the largest valves of f kerguelensis are encountered during the holocene fragilariopsis kerguelensis average valve area variations in the antarctic polar front apf of the atlantic sector and subantarctic front of the indian sector are in phase with records of opal burial while this correlation does not hold for the apf of the indian sector variations in circum polar upwelling were suggested as the main controlling factor of opal production during the last 20 000 years we here hypothesize that high nutrient input from the antarctic peninsula during the last deglaciation may have exerted a stronger control on f kerguelensis average valve area and opal export in the atlantic sector of the southern ocean than inferred changes in circum polar upwelling

experimental diatom dissolution and the quantification of microfossil preservation in sediments abstract four laboratory experiments on fresh modern diatoms collected from lakes in the northern great plains of north america were carried out to assess the effects of dissolution on diatom abundance and composition marked differences in mean dissolution susceptibility exist between species despite sometimes significant intra specific variation between heterovalves twenty four taxa were ranked according to susceptibility to dissolution using an exponential decay model of valve abundance this dissolution ranking was used to derive two weighted indices of sample preservation a third index f was based on a simple binary classification of valve morphology into dissolved and pristine categories as distinguished by light microscopy lm when compared against rank indices and a measure of species diversity this diatom dissolution index was found to be the best predictor of the progress of dissolution as estimated by total valve abundance or biogenic silica bisi loss strong empirical relationships between f index values and diatom abundance r2 0 84 n 32 and bisi r2 0 89 n 32 were developed and applied to a diatom sequence from a short core from devils lake north dakota and compared to diatom inferred and observed salinity at this site the f index is a simple effective diagnostic tool to assess important aspects of diatom preservation the index can provide insight into si cycling and record changes in conditions pertinent to diatom dissolution and has a role in validation of transfer functions or other inferences derived from compositional data

reactive surface area control of the dissolution kinetics of biogenic silica in deep sea sediments abstract flow through dissolution experiments demonstrate that the specific reactive surface area of biogenic silica decreases significantly with depth in surficial sediments of the southern ocean specific surface areas obtained from nitrogen gas bet adsorption isotherms however do not exhibit the systematic changes of the specific reactive surface area inferred from the kinetic experiments furthermore the decrease in surface reactivity of the siliceous skeleton fragments continues at depths in the sediments where there is no longer a net release of silicic acid to the pore waters thus the specific reactive surface changes most likely reflect a progressive reduction of the surface density of reactive sites aging during burial rather than the preferential dissolution of a more reactive fraction of siliceous debris deposited from the water column the observed aging of the silica surfaces has important consequences for the benthic regeneration of nutrient silicic acid from deep sea sediments

propagating long waves on oceanic density fronts an analytic model abstract an analytic model of long propagating free wave perturbations to an established upper ocean density front is developed the primary purpose of the model is to illuminate basic frontal wave mechanisms for possible subsequent use in more sophisticated numerical models the models is of the barotropic class but has ageostrophic dynamics because of the basic state adopted essentially stommel s model of the gulf stream with uniform potential vorticity and order one rossby number the model assumes inviscid dynamics apart from a narrow dissipative zone adjacent to the surface front the latter exerts a bulk effect on the large inviscid zone especially in generating small bur finite cross stream flow in the basic state for zero cross flow the resulting waves are stable have downstream phase speeds that are slow compared to the current speed and that increase with frequency and have anomalous dispersion the phase speeds compare well with the analysis of observations of propagating gulf stream me

middle precambrian provenance of jurassic sandstone in the mino terrane central japan th u total pb evidence from an electron microprobe monazite study precise electron microprobe analyses have been made on detrital monazites in jurassic sandstones of the mino terrane central japan and their th u pb relations are examined in terms of pbo and tho2 tho2 tho2 plus the equivalent of uo2 the pbo tho2 ratios of most detrital monazites 403 of 581 grains cluster in the range from 0 0763 to 0 0618 other grains show the ratio of about 0 0541 46 grains 0 0364 29 grains 0 0170 24 grains and 0 0116 79 grains the pbo tho2 ratio of 0 0763 0 0618 is nearly identical with that of monazites in a middle precambrian 1740 ma gneiss clast from the kamiaso conglomerate of the mino terrane this strongly suggests that the detrital monazites were derived from gneisses and or granitoids of middle precambrian age the ratio of 0 0116 is nearly the same as that of monazites in a permian 274 ma paragneiss of the hida terrane north to the mino terrane the pbo tho2 monazite data coupled with palaeocurrent analyses and petrological characteristics of sandstones show that middle precambrian high grade metamorphic rocks and granitoids were widespread both in the northern and southern source regions of the e w trending jurassic basin of the mino terrane the pbo tho2 ratio of detrial monazites is a useful new measure for the provenance analysis of clastic rocks

volcano surveillance using infrared cameras abstract volcanic eruptions are commonly preceded accompanied and followed by variations of a number of detectable geophysical and geochemical manifestations many remote sensing techniques have been applied to tracking anomalies and eruptive precursors and monitoring ongoing volcanic eruptions offering obvious advantages over in situ techniques especially during hazardous activity whilst spaceborne instruments provide a distinct advantage for collecting data remotely in this regard they still cannot match the spatial detail or time resolution achievable using portable imagers on the ground or aircraft hand held infrared camera technology has advanced significantly over the last decade resulting in a proliferation of commercially available instruments such that volcano observatories are increasingly implementing them in monitoring efforts improved thermal surveillance of active volcanoes has not only enhanced hazard assessment but it has contributed substantially to understanding a variety of volcanic processes drawing on over a decade of operational volcano surveillance in italy we provide here a critical review of the application of infrared thermal cameras to volcano monitoring following a summary of key physical principles instrument capabilities and the practicalities and methods of data collection we discuss the types of information that can be retrieved from thermal imagery and what they have contributed to hazard assessment and risk management and to physical volcanology with continued developments in thermal imager technology and lower instrument costs there will be increasing opportunity to gather valuable observations of volcanoes it is thus timely to review the state of the art and we hope thereby to stimulate further research and innovation in this area

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

a marine diatom record from the amundsen sea insights into oceanographic and climatic response to the mid pleistocene transition in the west antarctic sector of the southern ocean abstract the goal of this study is to assess the changes that have occurred during the mid pleistocene transition an important transitional period in cryosphere evolution by examining the siliceous microfossil record of sediments collected proximal to a major ice drainage outlet for the west antarctic ice sheet core ps58 254 was collected from a sediment drift on the upper continental rise in the amundsen sea directly offshore from pine island bay one of the three main discharge areas for the west antarctic ice sheet wais published data on physical properties geochemical composition grain size and clay mineral assemblages are complemented here by a high resolution record sample spacing 10 cm of the siliceous microfossil assemblages diatoms and silicoflagellates between 1200 ka and 621 ka the assemblage is relatively diverse with actinocyclus ingens thalassiothrix antarctica and fragilariopsis kerguelensis dominating the assemblages but diatom abundance is variable from low to barren additionally the occurrence of a ingens thalassiosira elliptipora and thalassiosira fasciculata is used to confirm and further refine the existing age model and extend it back to 1200 ka species composition during the last ca 621 ka is dominated by f kerguelensis which consistently comprises 80 90 of the assemblage a clear relationship between diatom abundance and glacial interglacial variability is apparent after 621 ka which resembles the glacial interglacial variability previously observed in other proxy data a significant change in both sediment composition and diatom assemblages is observed at 621 ka this change concurs with the last abundant occurrence of a ingens and the end of the mid pleistocene transition mpt i e the onset of modern eccentricity precession paced glacial cycles around 650 ka we suggest that during interglacial periods after 621 ka the amundsen sea low pressure system shifted seasonally southwestwards towards the shelf and thereby increased the advection of relatively warm circumpolar deep water cdw onto the amundsen sea shelf which is a major factor for present ice sheet melting in this part of west antarctica

sedimentation of biogenic siliceous particles in antarctic waters from the atlantic sector abstract sediment traps were deployed in the drake passage bransfield strait and west of south orkney islands powell basin during december 1980 january 1981 december 1983 and between march and december 1983 respectively most of the trapped material is biogenic opal except in the lower half of the water column in bransfield strait where large amounts of resuspended aluminosilicates and quartz grains were present frustules and skeletons of siliceous microorganisms diatoms silicoflagellates radiolarians chrysophycean cysts fragments and moults of crustaceans and tests of foraminifera were found quantitatively diatoms are the dominant constituent of the trapped biogenic material alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton it mainly affects large frustules e g corethron criophilum castracane in the uppermost part of the water column dissolution of frustules occurs mostly at the sediment water interface and leads to the enrichment of strongly silicified valves e g nitzschia kerguelensis o meara hasle thalassiosira antarctica comber resting spores at the bransfield strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods the bulk of pellet content consists of fragmented diatom frustules 1 10 m in size most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport e g settling as solitary particles or incorporated into or attached to marine snow or large amorphous aggregates

morphometry of the diatom fragilariopsis kerguelensis from southern ocean sediment high throughput measurements show second morphotype occurring during glacials abstract fragilariopsis kerguelensis is one of the most abundant diatoms in the sediments of the southern ocean its morphometric features have been proposed as proxies based on links with for example iron availability sea surface temperature and glacial interglacial conditions we investigated morphometric changes in f kerguelensis valves in a well studied sediment core record focusing on transition periods between glacials and interglacials by applying a high throughput diatom imaging and morphometry workflow we found two clearly distinct morphotypes which were differentiated by their rectangularity one of them occurred preferentially in glacial samples whilst the other persisted throughout this indicates that their relative abundances depend on environmental conditions and thereby points to the possibility that paleo proxies based on f kerguelensis valve morphometric features might in the future benefit from differentiating these two morphotypes as an initial exploration of this idea we show that the abundance ratio of both morphotypes correlates well with paleo temperatures which had been reconstructed using independent data from the same core distinguishing between the two morphotypes only became possible by image analysis for precisely measuring diatom valve outlines and area highlighting the potential of such methods for diatom analyses

geochronological constraints on the timing of granitoid magmatism metamorphism and post metamorphic cooling in the hercynian crustal cross section of calabria exposed cross sections of the continental crust are a unique geological situation for crustal evolution studies providing the possibility of deciphering the time relationships between magmatic and metamor phic events at all levels of the crust in the cross section of southern and northern calabria u pb rb sr and k ar mineral ages of granulite facies metapelitic migmatites peraluminous granites and amphibolite facies upper crustal gneisses provide constraints on the late hercynian peak metamorphism and granitoid magmatism as well as on the post metamorphic cooling monazite from upper crustal amphibolite facies paragneisses from southern calabria yields similar u pb ages 295 293 4 ma to those of granulite facies metamorphism in the lower crust and of intrusions of calcalkaline and metaluminous granitoids in the middle crust 300 10 ma monazite and xenotime from peraluminous granites in the middle to upper crust of the same crustal section provide slightly older intrusion ages of 303 302 0 6 ma zircon from a mafic to intermediate sill in the lower crust yields a lower concordia intercept age of 290 2m a which may be interpreted as the minimum age for metamorphism or intrusion u pb monazite ages from granulite facies migmatites and peraluminous granites of the lower and middle crust from northern calabria sila also point to a near synchronism of peak metamorphism and intrusion at 304 300 0 4 ma at the end of the granulite facies metamorphism the lower crustal rocks were uplifted into mid crustal levels 10 15 km followed by nearly isobaric slow cooling c 3 cm a 1 as indicated by muscovite and biotite k ar and rb sr data between 210 4 and 123 1 ma the thermal history is therefore similar to that of the lower crust of southern calabria in combination with previous petrological studies addressing metamorphic textures and p t conditions of rocks from all crustal levels the new geochronological results are used to suggest that the thermal evolution and heat distribution in the calabrian crust were mainly controlled by advective heat input through magmatic intrusions into all crustal levels during the late hercynian orogeny

internal structure and deformation of an unstable crystalline rock mass above randa switzerland part i internal structure from integrated geological and geophysical investigations 6m 3 of material occurred in fractured gneissic rock whose principal foliation faults and fracture zones dip into the slope above the scarp of the second rockslide the mountain continues to move at rates of up to 2 cm year in an attempt to understand failure mechanisms in fractured crystalline rock masses we have carried out a comprehensive multidisciplinary study that included detailed geological mapping borehole logging and imaging and surface and borehole geophysical surveys an integrated interpretation of the resultant data has revealed the presence of three prominent fault and fracture zone sets that define the internal structure of the rock mass some faults and fracture zones could be traced up to 85 m into the subsurface using borehole radar reflection methods the dips of the faults and fracture zones estimated from surface mapping matched those from radar reflection and borehole televiewer surveys no evidence was found for significant faults or persistent weakness planes that paralleled the 1991 rockslide failure surfaces instead the new observations were consistent with dominant failure mechanisms that involve the progressive development of major shear and brittle fracturezones and the eventual destruction of intact rock bridges immediately prior to catastrophic collapse this integrated study provides the first reliable model of the 3 d fault structure associated with and contributing to a large rock slope instability in a brittle crystalline rock mass

seismic tomography imaging of an unstable embankment abstract seismic tomography imaging was employed to make a diagnosis and choose a remedy for an embankment supported by a retaining wall showing clear evidence of structural instability the geometry and structural characteristics of the wall the inside geometry of cracks and the physical parameters of the underground materials were the primary objectives of the geophysical survey seismic data were acquired along two vertical sections each one delimited by the lines of the sources within an inclined borehole and of the receivers lying on the ground for each section a total of 744 travel times were inverted to obtain compressional wave velocities on a regular rectangular grid of squared cells 1 m 1 m using an inversion algorithm which is based on the simultaneous iterative reconstruction technique sirt ultrasonic tests carried out in laboratory on intact specimens together with other supplemental site information improved tomography resolution allowing global and node constraints that forced the solution of the inverse problem to match known boundary values tomography imaged two high velocity zones separated by a curved shape low velocity zone the first ones were found to be compatible with the concrete retaining wall and with the schist materials ranging from highly weathered to intact schist while the low velocity zone was interpreted as filling materials and or completely decomposed rock schist the combination of seismic tomography and laboratory measurements allowed extrapolation of important parameters over a large volume of rock mass otherwise only representative of small rock samples near boreholes it also enabled engineering characterization of subsurface rock mass providing useful and accurate information to design a remedy for the embankment

iron and silicic acid concentrations regulate si uptake north and south of the polar frontal zone in the pacific sector of the southern ocean abstract we investigated the relative roles of fe and silicic acid availabilities in regulating si uptake rates across the polar frontal zone in the pacific sector of the southern ocean 59 68 s 170 w during the us jgofs antarctic environment southern ocean process study aesops meridional gradients in silicic acid concentration si oh 4 of about 0 25 0 56 m km 1 were observed in this area during austral spring and summer 1997 1998 with si oh 4 ranging from 32 si oh 4 and 15 no 3 uptake rates biogenic silica concentrations and si oh 4 no3 uptake ratios fe addition had little or no effect on si uptake rates in enrichments conducted in the low si waters north of the si gradient however fe addition increased si uptake rates 3 5 times over controls in enrichments conducted in the high si waters south of the gradient in both spring and summer fe addition decreased si oh 4 no3 uptake ratios by 2 5 times largely due to stimulation of no3 uptake rates zn addition had no effect on si oh 4 and no3 uptake rates short term 24 h si additions had varying effects on si uptake rates depending on season and location in spring additions of 40 m si to water from bottle enrichments conducted north of the si gradient in situ si oh 4 15 m did not increase si uptake rates initially but did increase uptake rates after 8 days in the summer enrichment north of the si gradient in situ si oh 4 5 m 50 m si additions doubled in situ si uptake rates in the initial water collected for the enrichment and increased si uptake rates as much as 16 fold during the experiment south of the si gradient where in situ si oh 4 was 40 m in both spring and summer si addition had no effect on in situ si uptake rates in the initial enrichment water nor on any si uptake rates measured during the experiment our results indicate that both fe and si availabilities regulate si uptake rates and silica production in the southern ocean along 170 w fe limitation appears to restrict si uptake rates south of the si gradient and plays a role in preventing si depletion south of the acc where ambient si oh 4 never fell below 40 m during 1997 1998 our experiments in the seasonal ice zone at 62 suggest that si uptake in this area switched from being fe limited in the spring when in situ si oh 4 was 40 m to si limited in the summer when si oh 4 was

lower crustal rejuvenation and growth during post thickening collapse insights from a crustal cross section through a variscan metamorphic core complex the variscan lower crust of europe acquired its main features seismic layering intrusion of mantle derived magmas granulite grade metamorphism when the upper crust underwent post thickening extension through gravitational collapse we suggest that post thickening collapse is a geodynamic process that contributes to the growth and differentiation of continental lithosphere in collapsed mountain belts

age constraints on late paleozoic evolution of continental crust from electron microprobe dating of monazite in the peloritani mountains southern italy another example of resetting of monazite ages in high grade rocks in situ monazite microprobe dating has been performed for the first time on trondhjemite and amphibolite facies metasediments from the peloritani mountains in order to obtain information about the age of metamorphism and intrusive magmatism within this still poorly known sector of the hercynian belt all samples show single stage monazite growth of hercynian age one migmatite and one biotitic paragneiss yielded monazite ages of 311 4 and 298 6 ma respectively these ages fit with previous age determinations in similar rocks from southern calabria indicating a thermal metamorphic peak at about 300 ma at the same time as widespread granitoid magmatism the older of the two ages might represent a slightly earlier event possibly associated with the emplacement of an adjacent trondhjemite pluton previously dated by shrimp at 314 ma no evidence for pre hercynian events and only a little indication for some monazite crystallization starting from ca 360 ma were obtained from monazite dating of the metasediments suggesting either a single stage metamorphic evolution or a significant resetting of the monazite isotope system during the main hercynian event ca 300 ma rare monazite from a trondhjemite sample yields evidence for a late hercynian age of about 275 ma this age is interpreted as representing a post magmatic stage of metasomatic monazite crystallization which significantly postdates the emplacement of the original magmatic body

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

intense summer si recycling in the surface southern ocean 1 si cycle in surface waters was investigated in summer 2003 during a transect conducted from south australia to antarctica diatoms dominated the microphytoplankton silicic acid was depleted up to 60 s a subsurface maximum of biogenic silica biosilica was observed in the permanent open ocean zone in the 100 0 01 light zone the ratio of depth integrated biosilica dissolution rate d to depth integrated biosilica production rate p ranged between 0 to 3 1 being 1 for 5 of our 6 stations the biosilica dissolution was related to the percentage of dead diatoms but not to the temperature and might be at least partially under bacteria mediation this study shows that during summer the southern ocean silicate pump can be much less efficient than usually expected existence of scenarios with intense surface si recycling in the southern ocean has major consequences both for modelers and paleoceanographers index terms 4805 oceanography biological and chemical biogeochemical cycles 1615 1615 global change biogeochemical processes 4805 4855 oceanography biological and chemical plankton 4207 oceanography general arctic and antarctic oceanography 4870 oceanography biological and chemical stable isotopes

distribution and causes of landslides in the eastern peloritani of ne sicily and western aspromonte of sw calabria italy abstract the peloritani and aspromonte areas are tectonically active mountainous regions of ne sicily and sw calabria respectively where landslides are the most common hillslope mass wasting process this study aims to elucidate the primary controls on the distribution and size of landslides in these two different landscapes these regions either side of the messina strait have similar lithologies but show different morphological characteristics in response to varied neo tectonic activity and climate landslides were identified utilising aerial photographs and landsat images frequency area statistics were calculated to determine the length scale of the most frequent interpretable landslides and compare our results with previous studies the frequency area power law exponents 1 99 in peloritani and 1 94 in aspromonte fall within the range of values that have been observed 2 0 0 5 in similar landscapes the peloritani ridge sicily has range parallel normal fault segments with the majority of landslides occurring in their footwalls there seems to be a strong coupling between tectonic activity and landslides where slope instability is exacerbated by faulting fracturing or jointing in otherwise low permeability gneiss and granite bedrock conversely in aspromonte calabria landslides are restricted to steep valley walls and are absent from interfluves this is because landslides are controlled by fluvial incision processes these observations confirm a relationship between the spatial distribution of landslides and the processes controlling slope failures

streaks in the vicinity of an oscillating front the fate of particles continuously injected at a fixed location in the vicinity of an oscillating front is studied by numerical integration of the hydrodynamic equations the analysis is straightforward when the injection is at a location that is always on one side of the front in this case the curve traced by these particles i e a streak line may be complicated and generally does not resemble the path of the initial particle released but at least is continuous however when the front oscillates across the source location the streak line is broken into a series of discontinuous segments moreover some segments later may recirculate past the source this can produce a complicated streak line pattern in which old segments intertwine with recent segments

glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls 1 the valve area of fragilariopsis kerguelensis the most abundant diatom species in the southern ocean strongly changes in size in response to varying conditions in the surface ocean we examined the link both in two iron fertilization experiments and in sediment samples covering several glacial terminations between size variability in this species and environmental conditions across the antarctic polar front including sea ice extent sea surface temperature and the input of eolian dust the iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters which suggests the possibility of a causal relation between valve size of fragilariopsis kerguelensis and ambient surface water iron concentration larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage moreover our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the southern ocean however this correlation obvious for the fertilization experiments and for glacial terminations i ii iii and v does not seem to be valid for termination vi where size appears to be inversely correlated to dust input citation cortese g r gersonde k maschner and p medley 2012 glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls paleoceanography 27 pa1208 doi 10 1029 2011pa002187

thermal history vs fabric anisotropy in granitoids emplaced at different crustal levels an example from calabria southern italy the sila and serre granitoids of calabria were emplaced in the late carboniferous at depths ranging from 6 to 23 km in a postcollisional extensional regime their fabric which developed during and after final crystallization up to the solid state strongly increases in intensity with emplacement depth this relationship is attributed to the thermal history of the calabrian basement cooling histories of granitoids constrained by geological data and rb sr cooling ages on micas demonstrate that residence times of rocks at temperatures greater than those of the brittle ductile transition vary greatly as a function of initial emplacement depth this explains why shallow level granitoids that remained for about 10 myr at temperatures above those of the brittle domain retain their original magmatic fabric by contrast the strong fabrics of the deep seated granitoids are explained by solid state strain overprint that lasted more than 100 myr at temperatures above those of the brittle domain

the relationship between tectono metamorphic evolution and argon isotope records in white mica constraints from in situ 40ar 39ar laser analysis of the variscan basement of sardinia the basement of sardinia represents a nearly complete section of a segment of the variscan belt that experienced a polyphase tectonometamorphic evolution and barrovian metamorphism this basement is well suited to investigate the relationship between tectono metamorphic evolution and argon isotope records in white mica micaschists from the garnet zone maximum t of up to 520 560 c contain two texturally and chemically resolvable generations of white mica 1 deformed celadonite rich flakes defining a relict s1 foliation preserved within the main s2 foliation or enclosed in rotated albite porphyroblasts 2 celadonite poor white micas aligned along the main s2 foliation the s1 foliation developed earlier and at a deeper crustal level with respect to that at which the thermal peak was reached from the staurolite zone t of up to 590 625 c to the sillimanite k feldspar zone white mica is nearly uniform in composition muscovite and is predominantly aligned along the s2 foliation or is of later crystallization in situ ar ar laser analyses of white mica yielded ages of 340 315ma in the garnet zone and 320 300ma in the staurolite and sillimanite k feldspar zones results highlight a close link between argon isotope records in white mica and both textures and structure forming major elements the oldest ages were detected in samples where the earlier syn d1 white mica generation did not texturally and chemically re equilibrate at upper crustal levels this study suggests that the white micas that escaped recrystallization retain argon isotope records of an earlier metamorphic stage that survived a later event characterized by temperatures higher than 500 c

stability investigation and stabilization of a heavily fractured and loosened rock slope during construction of a strategic hydropower station in china abstract this paper presents a case history of the 205 m high intake slope at the huangjinping hjp hydropower station on the dadu river deformation and cracks developed on the cut slope during excavation and the deformation extended onto the natural slope above the cut giving rise to serious safety concerns research was conducted to study the engineering geological conditions and the deformation characteristics of the slope during excavation in situ monitoring data and possible causes of cracking were analyzed the results show that the zone of loosened rock mass extended much deeper into the rock mass than it did at other sites in the region because of the tectonic history of the site and cutting the empirically designed cable anchors with lengths of 40 m or 45 m were insufficient to stabilize the slope while the remedial cable anchors as long as 100 m successfully stabilized the slope the analytic method and procedure used in this paper could be useful to similar projects

equilibration and disequilibration between monazite and garnet indication from phase composition and quantitative texture analysis the integration of information which can be gained from accessory i e age t and rock forming minerals i e temperature t and pressure p requires a more profound understanding of the equilibration kinetics during metamorphic processes this paper presents an approach comparing conventional p t estimate from equilibrated assemblages of rock forming minerals with temperature data derived from yttrium garnet monazite ygm and yttrium garnet xenotime ygx geothermometry such a comparison provides an initial indication on differences between equilibration of major and trace elements regarding this purpose two migmatites two polycyclic and one monocyclic gneiss from the central alps switzerland northern italy were investigated while the polycyclic samples exhibit trace element equilibration between monazite and garnet grains assigned to the same metamorphic event there are relics of monazite and garnet obviously surviving independent of their textural position these observations suggest that surface processes dominate transport processes during equilibration of those samples the monocyclic gneiss on the contrary displays rare isolated monazite with equilibration of all elements despite comparably large transport distances with a nearly linear crystal size distribution of the garnet grain population growth kinetics related to the major elements were likely surface controlled in this sample in contrast to these completely equilibrated examples the migmatites indicate disequilibrium between garnet and monazite with a change in ree patterns on garnet transects the cause for this disequilibrium may be related to a potential disequilibrium initiated by a changing bulk chemistry during melt segregation while migmatite environments are expected to support high transport rates i e high temperatures and melt presence the evolution of equilibration in migmatites is additionaly related to change in chemistry as a key finding surface controlled equilibration kinetics seem to dominate transport controlled processes in the investigated samples this may be decisive information towards the understanding of age data derived from monazite

the dilemma of disappearing diatoms incorporating diatom dissolution data into palaeoenvironmental modelling and reconstruction abstract taphonomic issues pose fundamental challenges for quaternary scientists to recover environmental signals from biological proxies and make accurate inferences of past environments the problem of microfossil preservation specifically diatom dissolution remains an important but often overlooked source of error in both qualitative and quantitative reconstructions of key variables from fossil samples especially those using relative abundance data a first step to tackling this complex issue is establishing an objective method of assessing preservation here diatom dissolution that can be applied by different analysts and incorporated into routine counting strategies here we establish a methodology for assessment of diatom dissolution under standard light microscopy lm illustrated with morphological criteria for a range of major diatom valve shapes dissolution data can be applied to numerical models transfer functions from contemporary samples and to fossil material to aid interpretation of stratigraphic profiles and taphonomic pathways of individual taxa using a surface sediment diatom salinity training set from the northern great plains ngp as an example we explore a variety of approaches to include dissolution data in salinity inference models indirectly and directly results show that dissolution data can improve models with apparent dissolution adjusted error rmse up to 15 lower than their unadjusted counterparts internal validation suggests improvements are more modest with bootstrapped prediction errors rmsep up to 10 lower when tested on a short core from devils lake north dakota which has a historical record of salinity dissolution adjusted models infer higher values compared to unadjusted models during peak salinity of the 1930s 1940s dust bowl but nonetheless significantly underestimate peak values site specific factors at devils lake associated with effects of lake level change on taphonomy preservation and re working implied by dissolution data may override model improvements incorporating dissolution dissolution adjusted salinity models are also applied to a 150 year sediment record from spiritwood lake north dakota which suggests that this lake has a damped and lagged response to major regional climate forcing of salinity during the dust bowl at this site dissolution data also suggest different taphonomic behaviour of taxa related to their seasonal patterns of growth and sedimentation thus dissolution data can improve models and aid interpretation of sedimentary profiles as records of limnological ecological and environmental change filtered by taphonomy

quantification of the biogenic silica dissolution in southern ocean sediments abstract a transfer function has been established to quantify the dissolution of diatom silica in southern ocean sediments the relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box core tops each representative of a modern diatom species sediment assemblage the amount of dissolved silica was measured for each experiment the resulting data set of species abundances 42 samples containing 32 diatom species and 2 silicoflagellate genera was added to the modern data base of diatom species distributed over the southern ocean 124 core tops q mode factor analysis individualizes four factors explaining 83 of the variance the first three factors are controlled by surface water properties mostly temperature the fourth factor is the only one correlated with loss of silica in the reference samples r 0 900 we quantified the dissolution factor using this correlation superficial sediments of the southeast indian ocean are characterized from low to high latitudes by a decrease in silica loss by dissolution from 50 to 10 from the subantarctic zone 40 s to around 55 s followed by an increase of silica loss to values larger than 60 between 63 and 68 s application of the dissolution factor in two cores from the southern ocean 44 and 55 s shows enhanced opal dissolution during the last glaciation particularly during emiliani s stage 3 from 40 000 to 30 000 yr b p

geotechnical characterization of limestones employed for the reconstruction of a unesco world heritage baroque monument in southeastern sicily italy a detailed laboratory characterization of limestones employed for the reconstruction of saint nicholas cathedral a unesco world heritage monument in southeastern sicily is presented herein with the purpose of achieving a complete knowledge on the behavior of such rocks under stress whose engineering geological aspect had not been investigated before for scientific purposes specimens were sampled at three sites where this rock is quarried from two lithofacies of the same geological formation and are similar to other limestone varieties quarried worldwide and employed as construction material although slight differences between the samples occur at a macroscopic scale geotechnical tests highlighted relevant differences from the physical and mechanical points of view in order to look for one or more factors responsible of such dissimilarities a statistical analysis was carried out and interesting outcomes were achieved with the help of a microscopic analysis of the specimens moreover attention was paid on the modes of failure of tested specimens under compression whose attitude was described and correlated to selected properties of the rock results have both a practical implication because of the employment of this rock type as engineering material worldwide and a scientific relevance due to the peculiar behavior that such rock offered under stress

influence of a fault system on rock mass response to shaft excavation in soft sedimentary rock horonobe area northern japan abstract this paper focuses on the stress field that produced a fault system in the horonobe area of japan and considers the relationship between the fault system and the rock mass response to shaft excavation in soft sedimentary rocks in this area hydraulic fracturing investigations in boreholes and tectonic plate movements indicate that the major horizontal principal stress is oriented e w however during shaft excavation the greatest convergence in the shaft was oriented nne ssw therefore it is necessary to understand the influence of the fault system on the rock mass response to shaft excavation we performed a fault slip analysis of faults in the shaft wall and reconstructed the paleostress field that produced the fault system the maximum horizontal principal stress was oriented mainly nne ssw and the minimum horizontal principal stress was oriented mainly wnw ese these directions are similar to the directions of maximum and minimum convergence in the shaft respectively the results show that a fault system can affect the rock mass response to shaft excavation in soft rock and it is considered that the rock mass deformation is controlled by the fault system in addition it may be possible to assess and predict the rock mass behavior by focusing on paleostress field that produced the fault system