fertilizing potential of volcanic ash in ocean surface water the fertilization potential of newly erupted and well preserved ash from the 2000 hekla eruption in iceland was measured for the first time by flow through experiments as previously shown 1 the north atlantic ocean including the subarctic seas surrounding iceland is the largest net sink of the world s oceans for atmospheric co 2 owing to biological drawdown during summer 2 almost complete consumption of phosphate in chlorophyll rich areas of the north atlantic ocean might limit primary production and 3 in the southern pacific ocean and parts of the equatorial pacific ocean iron might limit primary production we found through laboratory experiments that volcanic ash exposed to seawater initially releases large amounts of adsorbed phosphate 1 7 mmol g 21 h 21 iron 37 0 mmol g 21 h 21 silica 49 5 mmol g 21 h 21 and manganese 1 7 mmol g 21 h 21 dissolution of acid aerosols adsorbed to the surface of the ash caused the high initial release of major and trace elements because of the instantaneous dissolution of adsorbed components when newly erupted volcanic ash comes in contact with the ocean surface water macronutrients and bioactive trace metals are released fast enough to become available to support primary production

mobilization of gold as a polymetallic melt during pelite anatexis at the challenger deposit south australia a metamorphosed archean gold deposit the challenger gold deposit in south australia is hosted by pelitic migmatites that underwent peak metamorphism at 7 5 1 5 kbars and at least 800 c nd model ages suggest a protolith age of 2900 ma zircon u pb and garnet sm nd dating indicates that peak metamorphism occurred at 2440 ma and that garnet was present during this event at this time in situ vapor absent melting affected the pelitic host rock indicating that peak metamorphism occurred without introduction of a foreign fluid or melt thus evidence indicating the presence of ore minerals during peak metamorphism implies a prepeak mineralization event this evidence includes the occurrence of invisible gold in lollingite but not in adjacent arsenopyrite and the presence of spherical gold sulfide inclusions in peak metamorphic garnet and other silicates textures developed between pyrrhotite lollingite arsenopyrite and gold the lack of silicate alteration minerals supports this conclusion experimental evidence is presented to support our interpretation that a gold rich polymetallic melt was mobilized into leucosomes synchronously with silicate melt during peak metamorphism visible gold is restricted to migmatitic leucosomes and to a lesser extent melanosomes large inclusions of gold with coexisting arsenopyrite pyrrhotite and bismuth are hosted within peak metamorphic silicate minerals and at grain boundaries trails of micrometric spherical inclusions of predominantly gold and bismuth propagate along annealed fractures from these larger inclusions we show that these gold sulfide inclusions represent the crystallized products of an immiscible polymetallic melt metamorphism of the challenger deposit resulted in partial melting of the pelitic host rock and formation of this gold rich melt these two melts were synchronously redistributed to accumulate as leucosomes during development of a stromatic migmatite formation of a polymetallic melt thereby enabled extensive mobilization of gold producing leucosomes enriched in gold this occurred because the immiscible metallic melt was physically entrained rather than chemically dissolved within the silicate melt gold rich shoots at challenger parallel the plunge of ptygmatically folded leucosomes that are shown to be parasitic to a larger scale fold geometry which appears to be structurally related to the ore shoots it is interpreted that concurrent migration of polymetallic and silicate melt allowed concentration of gold into a series of dilational structures which developed within the larger scale fold geometry challenger represents a new deposit type other deposits around the world such as renco and griffins find are hosted in granulite facies rocks but challenger is the first reported example of leucosome hosted gold in migmatites

igneous microstructures in migmatites clear differences between the microstructures of leucosomes and mesosomes occur in some nebulitic migmatites in the proterozoic arunta block central australia the leucosomes show crystal faces of k feldspar microcline microperthite cordierite andalusite and plagio clase against quartz indicating crystallization of a melt in contrast the mesosomes show predominantly polygonal grain shapes modified by 001 crystal faces of biotite and rare crystal faces in some porphyroblasts of garnet cordierite and orthopyroxene indicating re crystallization in the solid state the occurrence of abundant crystal faces in minerals such as feldspar cordierite and andalusite which typically grow crystal faces in magmas but generally not in metamorphic rocks is evidence of former melt therefore igneous microstructures can be preserved in leucosomes that have not undergone penetrative subsolidus deformation and recrystallization the cores of many of the crystals of cordierite and k feldspar have small locally oriented inclusions similar to those in the same minerals in the mesosomes these indicate that the cores remained solid during crystallization of the leucosome which produced inclusion free euhedral rims these crystals provide criteria for recognizing possible restite in granitoid magmas

productivity or preservation the factors controlling the organic matter accumulation in the late katian through hirnantian wufeng organic rich shale south china abstract the wufeng organic rich shale is widespread in the upper yangtze platform and it is one of the most advantageous shale gas producers in china its deposition commenced with the onset of the boda warming event in the late katian and terminated at the hirnantian glacial maximum the depositional mechanism of the wufeng formation was poorly understood owing to its relatively thin thickness being interpreted as the result of organic matter om accumulation in a shelf setting under anoxic conditions this study integrated detailed geochemical analyses based on the core samples from three boreholes which are located in the outer middle and inner shelf of the upper yangtze platform in order to investigate the depositional environments during the deposition of the wufeng formation geochemical redox proxies mo ef u ef and v cr and productivity proxies p baxs sixs indicate that the deposition of the wufeng formation was associated with four intervals wf1 to wf4 each characterized by its unique geochemical features related to sea level fluctuations black siliceous mudstones deposited during wf1 and wf2 are relatively organic lean due to low productivity less favorable preservation conditions and terrestrial dilution whereas black siliceous mudstone deposited during wf3 and wf4 is organic rich due to high paleoproductivity and conducive preservation conditions the geochemical proxies cd mo co x mn associated with the modern upwelling settings were replicated in the wufeng formation revealing that the outer shelf of the upper yangtze platform was dominated by persistent upwelling the upwelling driven primary productivity is considered as the first order control for the om enrichment at the outer shelf of the upper yangtze platform seasonal upwelling may influence the middle shelf of the upper yangtze platform where both primary productivity and preservation played essential roles in the om accumulation in contrast the om accumulation at the inner shelf was fundamentally driven by good preservation conditions

contrasting textures in metamorphic and anatectic migmatites an example from the scottish caledonides a method for the quantitative analysis of the spatial relations of minerals is described dispersed distributions are formed by annealing and destroyed in post tectonic migmatization aggregate distributions characterize solid state differentiation whereas leucosomes formed in systems of high fluid rock ratio in the examples studied anatectic melts show random distributions quantitative textural analysis can be used to indicate whether migmatization was post tectonic or earlier though caution is necessary if post migmatite cooling is slow or if there is some minor deformation more importantly it can be used to discriminate melt present from melt absent leucosomes this is exemplified by a suite of metamorphic and anatectic migmatites from the scottish caledonides the textural evolution of anatexites with increasing melt percentage is traced initial feldspar porphyroblastesis occurs by ostwald ripening via grain boundary melts subsequently ophthalmites develop with fabrics and chemistry inherited from the palaeosome at greater than 30 melt these inherited fabrics are wholly destroyed deformation prompts segregation into melanosome and leucosome resultant leucosomes contain no inherited crystals the scale of anatectic systems is fixed at the point at which segregation begins ophthalmites provide evidence for melt and crystal transfer beyond original palaeosome boundaries in contrast metamorphic migmatites are necessarily small scale systems because of diffusive constraints and melanosomes are invariably produced

the bangudae petroglyph in ulsan korea studies on weathering damage and risk prognosis the prehistoric bangudae petroglyph in the ulsan area represents an outstanding national treasure of the republic of korea since the construction of the sayeon dam the petroglyph with about two hundred carvings is periodically submerged by the sayeon reservoir the danger of increasing damage has resulted in intensive efforts to protect this cultural heritage diagnosis and risk prognosis studies were carried out results of petrographical studies monument mapping and in situ measurements are presented types degree and zonation of damage are evaluated the risk estimation derived from the studies confirms the necessity of preservation measures

remobilization of authigenic uranium in marine sediments by bioturbation uranium behaves as a nearly conservative element in oxygenated seawater but it is precipitated under chemically reducing conditions that occur in sediments underlying low oxygen bottom water or in sediments receiving high fluxes of particulate organic carbon sites characterized by a range of bottom water oxygen bwo and organic carbon flux ocf were studied to better understand the conditions that determine formation and preservation of authigenic u in marine sediments our study areas are located in the mid latitudes of the northeast pacific and the northwest atlantic oceans and all sites receive moderate 0 5 g cm2 kyr to high 2 8 g cm2 kyr ocf to the sediments bwo concentrations vary substantially among the sites ranging from 3 to 270 m a mass balance approach was used to evaluate authigenic u remobilization at each site within each region studied the supply of particulate nonlithogenic u associated with sinking particles was evaluated by means of sediment traps the diffusive flux of u into sediments was calculated from pore water u concentration profiles these combined sources were compared with the burial rate of authigenic u to assess the efficiency of its preservation a large fraction one third to two thirds of the authigenic u precipitated in these sediments via diffusion supply is later regenerated even under very low bwo concentrations 15 m bioturbating organisms periodically mix authigenic u containing sediment upward toward the sediment water interface where more oxidizing conditions lead to the remobilization of authigenic u and its loss to bottom waters

late ordovician global warming the boda event there is substantial evidence for mid ashgillian global warming before the latest ordovician hirnantian glaciation as shown by the movement of previously lower latitude benthic faunas such as trilobites and brachiopods to progressively higher latitudes and by an increase in endemic faunas at low latitudes this is shown by faunal dynamics on several paleocontinents and endorsed by published evidence of warmer water sediments from gondwana and elsewhere we term this global warming the boda event

carbon and phosphorus cycling in anoxic sediments of the saanich inlet british columbia abstract uncertainty currently exists about the removal of carbon c and phosphorus p from the oceanic reservoir especially in low oxygen settings in this paper the cycling of c and p is examined in sediments from the anoxic saanich inlet cored by ocean drilling program odp leg 169s in 1996 at two sites although c org p org ratios are high and increase with depth in the saanich inlet this effect is due largely to a remobilization of p from an organic matter sink to an authigenic sink reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting with the ultimate burial sink for the remobilized p being carbonate fluorapatite the effective c org p reactive molar ratio appears to be about 150 200 indicating some preferential loss of p compared to c during organic matter degradation but not approaching previously reported values of over 3000 in black shales reactive p accumulation rates in this basin range from 10 000 60 000 mol cm 2 kyr greatly exceeding the range of 500 8000 mol cm 2 kyr found in most continental margin settings including regions of modern phosphogenesis the initiation of marine sedimentation in the saanich inlet occurred after deglaciation and the high rates of p burial seen here may provide an end member example of the effects of sea level and margin sedimentation on the distribution of p within the marine p cycle

the scale invariant nature of migmatite from the oberpfalz ne bavaria and its significance for melt transport abstract four examples of migmatite from the moldanubian zone in western bohemia which formed during the late carboniferous display fractal patterns of melt bodies over more than 1 5 orders of magnitude net type migmatites have a fractal dimension of 1 80 1 85 in two orthogonal planes while that of a cross stromatic migmatite is 1 60 this fractal quality allows the migmatitic structures to be simply quantified and modelled for modelling purposes the net type migmatites are compared analogously to a menger sponge using a published theoretical model of magma flow in vertical channels it is shown that melt with viscosities less than 106 108 pa s can escape from the menger sponge under the influence of gravity alone

weathering damage evaluation of rock properties in the bunhwangsa temple stone pagoda gyeongju republic of korea the stone pagoda of the bunhwangsa temple in republic of korea was made of piling small brick shaped stones the majority of stone bricks are andesitic rocks with variable geneses rock properties of the pagoda roof suffer partial significant deterioration such as multiple peel offs exfoliation onion peel like decomposition cracks forming round lines and falling off stone pieces the stylobates and tabernacles at the four corners are composed of granitic rocks which are heavily contaminated by lichens and mosses some of these contamination marks show dark black or yellowish brown colors by inorganic secondary hydrates the four tabernacles and northern face of the pagoda body have been exposed to relatively high humidity which causes light gray efflorescence as stalactites between the northern and western sides of the body the efflorescences are composed of calcite gypsum and clay minerals the stone lion statues at the southeast and northeast corners are made of alkali granite while the others are lithic tuff total rock properties of the pagoda consist of 9 708 stone bricks among them 11 0 are fractured 6 7 are fallen off and 7 0 show considerable surface efflorescence which shows that the pagoda has been highly deteriorated by physical chemical and biological weathering the authors strongly suggest long term monitoring and comprehensive conservation researches

seismic anisotropy and shear wave splitting in lower crustal and upper mantle rocks from the ivrea zone experimental and calculated data to quantify the relationships between anisotropy s wave splitting and tectonics we determined the seismic properties of lower crustal and upper mantle rocks outcropping in the ivrea zone northern italy we obtained p and s wave seismic velocities by laboratory direct velocity measurements and or by calculations based on the modal compositions of the rocks the lattice preferred orientations lpos and the single crystal stiffness coefficients measured p and s wave velocities 6 0 7 5 km s 1 and 3 6 4 2 km s 1 are typical of the lower crust the p wave anisotropy is in the range 0 10 shear wave birefringence is in the range 0 0 0 6 km s 1 with typical values between 0 0 and 0 2 km s 1 in many cases the birefringence is clearly related to fabric elements foliation lineation mafic rocks such as anorthosite or pyroxene bearing gabbros exhibit low p wave anisotropies 5 and low shear wave birefringences less than 0 1 km s 1 in contrast the seismic properties of felsic rocks such as biotite bearing gneisses and mafic rocks such as amphibolites display high vp anisotropy 10 and strong birefringence 0 3 km s 1 biotite and amphibole preferred orientations clearly control seismic anisotropy and particularly shear wave splitting in these rocks maximum splitting is observed in directions parallel to the foliation with the fast split shear wave polarized parallel to the foliation plane to have an overview of the seismic properties of this lower crustal section at a broader scale we calculated from our data the anisotropic seismic properties of several hypothetical samples that are perhaps more representative of the regional anisotropy than each sample individually for instance the average lower crustal sample displays an anisotropy of 5 5 for p waves and a birefringence around 0 14 km s 1 for s waves propagating parallel to the foliation we observe little splitting for waves propagating at high angle to the foliation

correlation and correction factor between direct and indirect methods for the ultrasonic measurement of stone samples this study focused on analyzing and calculating the correction factor between direct and indirect methods for the ultrasonic testing of stone monuments using a customized transducer and couplant to achieve this goal the p wave velocity in 11 rock specimens including two artificially weathered samples was measured in a laboratory by applying both direct and indirect methods using an ultrasonic tester statistical interpretation of the results revealed that the indirect p wave velocities were always lower than the direct velocities with the correction factors between them differing by rock type the average correction factors produced by the indirect method were 1 50 in the medium to coarse grained granite sample 1 37 in fine grained granite 1 58 in fine grained diorite 1 38 in medium grained diorite 1 59 in sandstone and 1 71 in marble in addition the regression equation and coefficient of determination r 2 were acceptably high suggesting a sufficient relationship between the two variables for use in engineering this study will significantly contribute to improving the reliability of ultrasonic testing for weathering evaluation of a stone monument

paleoceanographic applications of trace metal concentration data abstract recent studies have identified a range of new applications of trace metal concentration data in the analysis of paleoceanographic systems in restricted anoxic marine systems trace metal toc ratios can provide insight into the degree of watermass restriction and estimates of deepwater renewal times in such systems secular changes in sediment trace metal ratios may provide evidence of the chemical evolution of basinal deepwaters in response to differential rates of trace metal removal to the sediment the degree of deepwater restriction in silled basins is generally controlled by eustatic elevations with higher lower sea levels resulting in lesser greater watermass restriction short term ca million year drawdown of the trace metal inventory of seawater has occurred repeatedly in conjunction with oceanic anoxic events which result in elevated rates of trace metal removal to widespread anoxic facies long term eon scale changes of the trace metal composition of seawater have occurred in response to secular changes in atmospheric oceanic redox conditions and their effects on trace metal cycling caution must be exercised in evaluating trace metal patterns in paleomarine systems however 1 hydrographic analyses based on trace metal toc relationships can be undertaken only on systems that had anoxic deepwaters and 2 the influence of redox variation on trace metal accumulation patterns outweighs that of hydrographic factors in some paleomarine systems

eclogites with a short lived granulite facies overprint in the moldanubian zone czech republic petrology geochemistry and diffusion modelling of garnet zoning the petrology and geochemistry of a newly discovered suite of high pressure garnet clinopyroxene bearing rocks from the monotonous series of the moldanubian zone of the bohemian massif southwest czech republic have been investigated three types common eclogites quartz kyanite clino zoisite eclogites and garnet hornblende clinopyroxenites are distinguished by petrography and geochemistry all underwent a significant degree of partial breakdown under granulite and amphibolite facies conditions during exhumation important features include the growth of orthopyroxene in breakdown domains after garnet and omphacite and anorthite spinel corundum exceedingly peraluminous sapphirine replacing kyanite garnet zoning and inclusion patterns support a prograde evolution from low pressures for at least some of the samples the post eclogite stage granulite facies overprint indicates that high temperatures prevailed during exhumation but preservation of zoning in some garnets and the results of diffusion modelling suggest that this overprint took place over a very short time scale the geochemical and petrological results allow characteristic differences to be recognized between these eclogites and metabasites found in other tectonic units of south bohemia and consequently the assigning of all high pressure rocks to a single now disrupted tectonic unit is a gross simplification that seriously misrepresents the tectono metamorphic history of the region

microbial sequestration of phosphorus in anoxic upwelling sediments organic phosphorus is removed from the ocean by its conversion to phosphorite laboratory incubations suggest that bacteria catalyse phosphorite formation and that the rate of conversion is greatest under anoxic conditions phosphorus is an essential nutrient for life in the ocean phosphorus burial regulates marine primary production1 2 phosphorus is removed from the ocean by sedimentation of organic matter and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite and ultimately phosphorite deposits3 4 bacteria are thought to mediate these processes5 but the mechanism of sequestration has remained unclear here we present results from laboratory incubations in which we labelled organic rich sediments from the benguela upwelling system namibia with a 33p radiotracer and tracked the fate of the phosphorus we show that under both anoxic and oxic conditions large sulphide oxidizing bacteria accumulate 33p in their cells and catalyse the nearly instantaneous conversion of phosphate to apatite apatite formation was greatest under anoxic conditions nutrient analyses of namibian upwelling waters and sediments suggest that the rate of phosphate to apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers we suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom water conditions expanding oxygen minimum zones are projected in simulations of future climate change6 potentially increasing sequestration of marine phosphate and restricting marine productivity

barium peaks at glacial terminations in sediments of the equatorial atlantic ocean relicts of deglacial productivity pulses in sediment cores recovered from oligotrophic settings of the western and eastern north equatorial atlantic ocean ceara rise and sierra leone rise distinct peaks of excess barium were detected at glacial interglacial transitions these ba maxima are unrelated to any other potential productivity proxy e g organic carbon carbonate or opal moreover they coincide with minima in organic carbon contents despite the lack of correlation between excess barium and organic carbon we ascribe these ba spikes to pulses of productivity that occurred during glacial interglacial transitions the discrepancy between barium and organic carbon in these transitional sediment intervals is attributed to the action of downward progressing oxidation fronts during deglacial nonsteady state depositional conditions the oxidation fronts were initiated due to the overall low sedimentation rates prevailing in the study areas and an increase in bottom water oxygen concentrations at the onset of enhanced nadw production during interglacial periods the fronts led to a very efficient oxidation of the organic carbon initially present leaving peaks in solid phase barium as relicts of these short time productivity events this assumption is supported by the depth arrangement of the solid phase peaks of ba fe and mn along the 6 5 oxygen isotope stage boundary in sediments of the ceara rise which show striking similarities to the distribution of these elements in oxidized sapropel intervals in eastern mediterranean sediments it remains unclear whether productivity was proportional to the magnitude of the baexcess maxima possibly higher dissolved ba concentrations in intermediate and deep waters during glacial interglacial transitions caused the precipitation of barite to increase out of proportion of the postulated deglacial productivity pulses

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

temporal and compositional differences between subsolidus and anatectic migmatite leucosomes from the quetico metasedimentary belt canada migmatites in the quetico metasedi mentary belt contain two types of leucosome 1 layer parallel leucosomes that grew during deformation and prograde metamorphism these are enriched in si02 sr and eu but depleted in ti02 fe203 mgo cs rb ree sc th zr and hf relative to the quetico metasediments 2 discordant leucosomes that formed after the regional folding events when metamorphic temperatures were at their peak these are enriched in rb ba sr and eu but display a wide range of lree th zr and hf contents relative to the quetico metasediments layer parallel leucosomes formed by a sub solidus process termed tectonic segregation this stress induced mass transfer pfocess began when the quetico sediments were deformed during burial and continued whilst the rocks were both stressed and heterogeneous sub solidus leucosome compositions are consistent with the mobilization of quartz and feldspar from the host rocks by pressure solution the discordant leucosomes formed by partial melt ing of the quetico metasediments possibly dur ing uplift of the belt the range of composition displayed by the anatectic leucosomes arises from crystal fractionation during leucosome emplacement some anatectic leucosomes pre serve primary melt compositions and have smooth ree patterns but those with negative eu anomalies represent fractionated melts and others with positive eu anomalies represent accumulations of feldspar plus trapped melt

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

the petrology of retrograded eclogites of the oberpfalz forest northeastern bavaria west germany abstract in the bavarian margin of the moldanubian basement of the bohemian massif retrograded eclogitic metabasites are found within cordierite gneisses associated with garnet free serpentinised peridotites the primary eclogite assemblage gar omph qz rut ky is rarely retained typically garnet pyr 12 37 alm 38 56 gro 14 29 is prograde zoned with thin retrograde rims and a kelyphitic corona of orthopyroxene plagioclase rare or mg hastingsite plagioclase an 60 common primary omphacitic clinopyroxene jd 25 35 is preserved within garnet groundmass omphacite jd 15 25 always showing an early exsolution of plagioclase is usually replaced by a vermicular di plag an 20 symplectite itself overgrown by a diablastic hastingsite plagioclase an 40 aggregate quartz is rimmed by hypersthene with an outer margin of diopside kyanite never preserved in the metabasites is altered anisochemically to a symplectite of hercynite anorthite commonly only anorthite aggregates remain geothermobarometric studies indicate equilibration around 710 c minimum pressure 15 kb for the primary eclogite assemblage the granulite facies overprint occurred at probably slightly higher temperatures but lower pressures with later retrogression into the amphibolite fades as mostly shown by the surrounding gneisses the p t t path preserved within these metabasic rocks is that expected from a region having undergone crustal thickening by subduction and crustal imbrication their present day surface exposure underlain by crust of normal thickness would indicate the presence of a basal thrust complex that has driven under the imbricate crustal pile aiding uplift and erosion a geometry confirmed by recent geophysical studies

the end ordovician glaciation and the hirnantian stage a global review and questions about late ordovician event stratigraphy abstract this paper proposes a global review of hirnantian event stratigraphy the hirnantian gssp in south china is tentatively correlated with latest ordovician strata from the peri gondwanan glacial regions problems of biostratigraphical correlation are highlighted at a worldwide scale the major biostratigraphically useful fossil groups graptolites chitinozoans brachiopods conodonts acritarchs are analysed and their limits for global correlation of the uppermost ordovician are discussed palaeobiogeographical disparities are invoked as the primary cause of the difficulty in establishing an effective late ordovician global biostratigraphical scheme as an alternative correlative tool the hice hirnantian isotopic curve excursion event is often put forward in the literature however carbon isotope chemostratigraphy shows like biostratigraphy some limits to the present state of knowledge no good independent biostratigraphical control of the hice exists in both shallow carbonate deposits and deeper shaly ones recent studies have also demonstrated inconsistencies between carbon isotopic signals obtained from organic 13corg and inorganic 13ccarb carbon species further complicating the use of the hice as an isochronous benchmark all of these difficulties for hirnantian event stratigraphy are discussed in detail in order to enable them to be overcome in the future precise late ordovician and early silurian event stratigraphies are essential for the understanding of the mechanisms linked to the first of the big five extinctions

sediment carbon nitrogen and phosphorus cycling in an anoxic fjord effingham inlet british columbia sediment geochemistry as well as benthic exchange of nutrients was investigated in effingham inlet a fjord located on the west coast of vancouver island in barkley sound the effect of bottom water oxygenation on sediment carbon nitrogen and phosphorus cycling was compared at sites overlain by oxic and anoxic bottom waters the sites separated by only 3 kilometers were similar in terms of key diagenetic parameters including mass accumulation rate and bulk sediment organic carbon content thus allowing a focus on diagenetic effects attributable to depositional oxygen availability benthic flux chamber incubations sulfate reduction rate measurements measurements of solid phase and pore water chemical profiles were compared for the sites these comparisons reveal that diagenetic processes in the site overlain by oxic waters act to retain more phosphorus in the sediment relative to the anoxic site differences in phosphorus benthic fluxes and burial between the two sites most likely result from differences in organic matter cycling under aerobic versus anaerobic conditions and are not strongly influenced by cycling of p associated with metal oxide phases

fracture development in paleozoic shale of chongqing area south china part one fracture characteristics and comparative analysis of main controlling factors abstract natural macro and micro fractures in the longmaxi shale lower silurian from yuye 1 well and the niutitang shale lower cambrian from yuke 1 well are characterized regional geological structural evolution and shale geochemistry including toc and mineral composition etc are analyzed the controlling factors of natural fractures in palaeozoic shale in the southeast of chongqing have been confirmed which have been analyzed qualitatively or semi quantitatively the results show that fractures are abundant in both the longmaxi shale and niutitang shale due to the multiphase strong tectonic movement in the southeast of chongqing therefore tectonic factors are the principal factors that control fracture development in the paleozoic shale of this region followed by the mineral composition of the shale vertically the mineral composition of shale in yuke 1 well has a high dispersion degree and a strong heterogeneity the dispersion coefficients of quartz and dolomite were 0 48 and 1 respectively therefore the development and distribution of fractures are controlled by quartz and dolomite content in the niutitang shale moreover the quartz content shows positive correlation with the fractures quantity and fractures are most abundant where dolomite content up to 64 7 while the mineral composition of shale in yuye 1 well has a low dispersion degree and a strong homogeneity in a vertical position the dispersion coefficients of quartz and plagioclase were 0 15 and 0 26 respectively which shows unconspicuous control effect for fractures therefore the development and distribution of fractures are mainly controlled by the toc content moreover the toc content shows positive correlation with the fractures quantity fractures are sealed by calcite quartz and pyrite although sealed fractures do not contribute to the permeability of the reservoir they are important planes of weakness that tend to be reactivated by hydraulically induced fractures sem images show that intergranular pore is connected by microfractures thereby the validity of porosity has been improved the mixed network of microfractures and micropore provide enhanced permeability or storage capacity for the reservoir

subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth evidence from biogeochemical experiments and satellite data volcanoes confront earth scientists with new fundamental questions can airborne volcanic ash release nutrients on contact with seawater thereby excite the marine primary productivity mpp and most notably can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood here we present results from biogeochemical experiments showing that 1 volcanic ash from subduction zone volcanoes rapidly release an array of nutrients co limiting algal growth in vast oceanic areas 2 at a speed much faster minute scale than hitherto known and that marine phytoplankton from low iron oceanic areas can swiftly within days utilize iron from volcanic sources we further present satellite data possibly indicating an increase of the mpp due to the seaward deposition of volcanic particulate matter our study supports the hypothesis that oceanic iron fertilization with volcanic ash may play a vital role for the development of the global climate

non destructive testing for the assessment of granite decay in heritage structures compared to quarry stone several types of granite found in two architectural heritage monuments were assessed with two non destructive portable techniques schmidt hammer rebound and ultrasound velocity vp similar assessments were conducted on the rock from which the granite was originally quarried for comparison the results obtained which revealed the existence of a direct correlation constitute a useful indication of decay particularly if the approximate dates of construction are known and conversely if they are not such stone assessments may provide a rough estimate of when the structure was built both of these convenient portable and non destructive techniques may be used as reliable indicators of the degree of stone decay

organic matter accumulation of late ordovician sediments in north guizhou province china sulfur isotope and trace element evidences abstract the organic rich upper ordovician sediments wufeng and guanyinqiao formations on the yangtze platform are considered to be one of the main source rocks here we present geochemical proxies including redox indicator s c ratios and sulfur isotopes and productivity indices toc mo and ba contents from nanbazi section in north guizhou province south china in order to investigate the mechanism of organic matter accumulation the geochemical data suggest a stagnant and anoxic environment predominated the yangtze sea during the wufeng period whereas ventilated and oxygenated marine conditions pervaded the yangtze sea during the guanyinqiao period variations in the concentration of toc mo and ba indicate that higher organic carbon export in the wufeng intervals than those in the guanyinqiao intervals these variations in redox and productivity during the late ordovician were associated with different mechanisms and forcing processes the abrupt change from anoxic to oxygenated condition at the beginning of the guanyinqiao was concomitant with the global glacial period likely resulted from the glacio eustatic sea level fall and subsequent circulation of cold dense oxygenated waters upon the shelf seabed the productivity variations were related to the change of nutrient supply which is consistent with volcanic activities and runoff to the yangtze sea redox changes together with primary productivity fluctuations could have played a significant role on the variation of organic matter accumulation during the late ordovician in south china

melting and diffusion processes in closed system migmatization estimated variations in mineral concentrations across leucosomes suggest that leucosomes are generated during anatexis by a diffusive exchange between the leucosome and the mesosome and not by the migration of melt from the mesosome however the presence of melt is a precondition for the diffusive exchange to take place initially a crack is formed due to shear stress the formation of a crack allows a diffusive exchange to take place through the melt which causes melting of minerals situated near the crack the diffusive exchange of material is less efficient in the mesosome where the melt is isolated at grain corners and edges the microcline enrichment of some granitic leucosomes is thought to be due to the diffusive depletion of the mesosome caused by growth of alkali feldspar during the consolidation of the migmatite in general it seems unnecessary to invoke concentrations of water in the leucosome or the intrusion of external fluids or magmas for migmatite formation

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

facies patterns and geography of the yangtze region south china through the ordovician and silurian transition abstract lithofacies and biofacies changes through the ordovician and silurian transition on the yangtze platform are coincident with stepwise mass extinctions recovery events global sea level changes and regional palaeogeographic configurations facies patterns through three intervals the late mid ashgill hirnantian and early rhuddanian indicate that black shale occupied most of the yangtze platform region during the late mid ashgill and early rhuddanian while the hirnantian possesses more diverse facies types the black shale was replaced by carbonate facies during the hirnantian coincident with a global sea level low stand biofacies changes from the late mid ashgill graptolitic to the hirnantian shelly facies were apparently signalled by gradual and diachronous existence of a mixed facies the manosia facies in the yangtze region however the biofacies change was abrupt from the hirnantian to the early rhuddanian when graptolitic facies occupied most areas on the yangtze platform leaving only a very narrow limited belt of shelly facies along the southern margin of the platform in northern guizhou the early rhuddanian unified biofacies pattern is a result of a global sea level rise which may be synchronized with a recovery bioevent of graptolites after hirnantian mass extinction

the emplacement of variscan ht metamorphic rocks linked to the interaction between gondwana and laurussia structural constraints in ne sardinia italy terra nova 22 369 377 2010 abstract the emplacement of variscan ht metamorphic rocks in sardinia italy occurred in a transpressive regime related to the oblique collision between gondwana and laurussia during the early visean c 340 ma bashkirian c 320 ma the restored directions of the main structural features in ne sardinia allow us to infer a ne sw oriented direction of shortening during this time as has been established for the french massif central and the maures tanneron massif which could lead to the exhumation of ht rocks by telescoping processes field evidence and finite strain analysis emphasize that the exhumation of ht metamorphic rocks could be driven by a restraining bend that developed in ne sardinia along dextral transpressive shear zones the tectonic model proposed in this paper allows us to conclude that crustal melt production usually attributed to extensional regimes can be related to compressional transpressional regimes

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

reconstruction of deformation and flow parameters from deformed vein sets abstract in any homogeneously deformed material sets of material lines with a similar stretch history occupy sectors with a scale and orientation that depend on finite strain area change rate and vorticity of the parent flow if the size and shape of these material line sectors are known they can be used to determine the sense of shear and to calculate deformation and flow parameters even if actual stretches along material lines are unknown in rocks which have undergone near homogeneous deformation on a large scale the orientation of sets of boudinaged folded and folded boudinaged or boudinaged folded veins can be used for such calculations a general theoretical background to the problem is presented and a mohr circle construction to carry out the deformation and flow analysis is introduced among other statements the theory predicts that shortened or folded boudins must develop in non coaxial monophase deformation with considerable area change in the plane of observation or in polyphase deformation

residence and redistribution of ree y zr th and u during granulite facies metamorphism behaviour of accessory and major phases in peraluminous granulites of central spain accessory minerals are thought to play a key role in controlling the behaviour of certain trace elements such as ree y zr th and u during crustal melting processes under high grade metamorphic conditions although this is probably the case at middle crustal levels when a comparison is made with granulite facies lower crustal levels differences are seen in trace element behaviour between accessory minerals and some major phases such a comparison can be made in central spain where two granulite facies terranes have equilibrated under slightly different metamorphic conditions and where lower crustal xenoliths are also found differences in texture and chemical composition between accessory phases found in leucosomes and leucogranites and those of melanosomes and protholiths indicate that most of the accessory minerals in melt rich migmatites are newly crystallized this implies that an important redistribution of trace elements occurs during the early stages of granulite facies metamorphism in addition the textural position of the accessory minerals with respect to the major phases is crucial in the redistribution of trace elements when melting proceeds via biotite dehydration melting reactions in granulitic xenoliths from lower crustal levels the situation seems to be different as major minerals show high concentration of certain trace elements the distribution of which is thus controlled by reactions involving final consumption of al ti phlogopite a marked redistribution of hree y zr between garnet and xenotime where present and zircon but also of lree between feldspars k feldspar and plagioclase and monazite is suggested

study of strain and partial melt transfer in a banded migmatite abstract an attempt is made to analyse in detail the strain and area change around the tip of a foliation parallel leucosome strain is determined in the mesosomes above and below the leucosome and the melanosome in both the xz foliation and lineation parallel and yz foliation parallel lineation perpendicular planes using the following methods march analysis of biotite orientation fabric fry method of zircon position fabric and r f method using cordierite grain outlines in addition march analysis of the orientation of sillimanite inclusions within the cordierite grains helps confirm the last method area change is measured by determining the population density of zircon around the leucosome in the xz plane the amount of material lost can account for the area gain in the leucosome and we suggest the sample at the observed scale was closed in terms of melt movement the results are used to construct tentative strain paths for the various components of the migmatite evidence suggests the leucosome was filled by true melt fluid deformation of the leucosome melt is demonstrated by the orientations of zircons

oxygen minimum zones omzs in the modern ocean in the modern ocean oxygen minimum zones omzs are potential traces of a primitive ocean in which archean bacteria lived and reduced chemical anomalies occurred but omzs are also keys to understanding the present unbalanced nitrogen cycle and the oceans role on atmospheric greenhouse control omzs are the main areas of nitrogen loss as n2 n2o to the atmosphere through denitrification and anammox and could even indirectly mitigate the oceanic biological sequestration of co2 it was recently hypothesized that omzs are going to spread in the coming decades as a consequence of global climate change despite an important omz role for the origin of marine life and for the biogeochemical cycles of carbon and nitrogen there are some key questions on the structure of omzs at a global scale there is no agreement concerning the threshold in oxygen that defines an omz and the extent of an omz is often evaluated by denitrification criteria which at the same time are o2 dependent our work deals with the identification of each omz the evaluation of its extent volume and vertical structure the determination of its seasonality or permanence and the comparison between omzs and denitrification zones at a global scale the co existence in the omz of oxic in its boundaries and suboxic even anoxic in its core conditions involves rather complex biogeochemical processes such as strong remineralization of the organic matter removal of nitrate and release of nitrite the quantitative omz analysis is focused on taking into account the whole water volume under the influence of an omz and adapted to the study of the specific low oxygen biogeochemical processes a characterization of the entire structure for the main and most intense omzs o2 10 mu m maximum zone the larger omz relative to the extent of denitrification zone suggests that the unbalanced nitrogen cycle on the global scale could be more intense than previously recognized and that evaluation of the omz from denitrification could underestimate their extent

suboxic trace metal geochemistry in the eastern tropical north pacific abstract we analyzed al ti fe mn cu ba cd u mo v and re in water column settling particulate and sediment 0 to 22 cm samples from the intense oxygen minimum zone omz of the eastern tropical north pacific near mazatlan mexico the goal was to determine how the geochemistry of these elements was influenced by suboxic water column conditions and whether the sediments have a unique suboxic geochemical signature the water column was characterized by a mn maximum reaching 8 nmol kg 1 at 400 m concentrations of cu ba cd mo re u and v were unaffected by the low o2 conditions and were comparable to those of the open ocean sinking particles were composed of lithogenic particles of detrital origin and nonlithogenic particles of biogenic origin al ti and fe were mostly at least 79 lithogenic about 75 of the mn was nonlithogenic significant amounts at least 58 of cu ba cd and mo were nonlithogenic sediment geochemistry varied across the continental shelf and slope cadmium u and re have prominent maxima centered at 310 m with 12 3 ppm 10 9 ppm and 68 3 ppb respectively at the core top high values of mo averaging 6 8 ppm and v averaging 90 ppm are seen in omz surface sediment additional down core enrichment occurs for all redox sensitive elements in the top 10 cm for u mo v and re surface sediments are a poor indicator of metal enrichment comparison of the nonlithogenic composition of sediments with sinking particles suggests that direct input of plankton material enriched in metals makes a significant contribution to the total composition especially for cd u and mo we evaluated re mo and cd u ratios as tracers for redox environments rhenium and mo concentrations and re mo ratios do not lead to consistent conclusions concurrent enrichments of re and mo are an indicator of an anoxic depositional environment in contrast high re mo ratios are an indicator of suboxic conditions cadmium is enriched in surface sediments while u has considerable down core enrichment the concentrations of cd and u and the cd u ratio do not follow patterns predicted from thermodynamics though the water column is suboxic these four redox sensitive elements indicate that the sediments are anoxic the implication for paleostudies is that a trace metal sediment signature that indicates anoxic conditions is not necessarily attributable to an anoxic water column

material characteristics and deterioration evaluation for the 13th century korean stone pagoda of magoksa temple this study focused on the quantitative deterioration evaluation for the magoksa temple stone pagoda of the thirteenth century in korea based on the deterioration map by precise observation and ultrasonic velocity measurements the stone pagoda is composed mainly of fine grained quartz diorite with some granodiorite used in the second story and dew bowl and the replacement stone for restoration in the basement is biotite granite the deterioration map and the 2d contour map projecting ultrasonic velocity showed that the most serious deterioration was to the north face of the pagoda which has about 81 2 deterioration rate and a low velocity range compared with the other directions thus it is required to prepare conservation schemes to reduce deterioration and reinforce the structure it is also required to carry out ground exploitation for calculation of load carrying strength and ground strength together with continuous structural monitoring the results will be important for the stable and long term conservation of the pagoda and will further serve to establish scientific conservation systems of stone cultural heritages in the future

the evolution of a precambrian arc related granulite facies gold deposit evidence from the glenburgh deposit western australia abstract gold deposits are rare in upper amphibolite to granulite facies environments known examples commonly attract debate about whether they formed under these conditions or instead represent metamorphosed metasomatic or superimposed retrograde mineralization the glenburgh gold deposit is located in the paleoproterozoic upper amphibolite to granulite facies glenburgh terrane in the southern gascoyne province of western australia gold at the glenburgh deposit is free and disseminated within quartz biotite garnet gneiss amphibolite and post gold quartz chlorite veins no clear association with a specific host lithology has been identified and mineralization does not have a visually distinct proximal alteration assemblage the rocks hosting the deposit represent a distinct sedimentary package that was deposited mineralized buried and metamorphosed all during arc magmatism features within the internal structure of gold grains such as high purity gold veinlets incoherent twinning and low silver content suggest the gold has been through post depositional processes such as metamorphism and deformation abundant sulfide minerals are interpreted to have formed by sulfidation of the host rock contemporaneously with gold mineralization and the presence of rounded sulfide inclusions within garnet porphyroblasts illustrates the presence of a sulfide phase prior to peak metamorphism geochronology of zircon and monazite constrains the timing of mineralization to be younger than c 2035 ma the maximum depositional age of the metasedimentary host rocks but older than c 1991 ma the peak of m1 metamorphism during the glenburgh orogeny these events were synchronous with arc magmatism rocks at the glenburgh deposit were likely deposited in a fore arc or accretionary wedge a favourable setting for porphyry cu mo au epithermal au polymetallic sn w skarn and orogenic au mineralization phase equilibria modelling of a pelitic migmatite constrains peak p t conditions to be 865 885 c 6 8 7 6 kbar consistent with elevated thermal gradients within the arc followed by conductive cooling of arc magmas partial melting during peak m1 metamorphism possible caused gold remobilization the lack of an alteration assemblage further suggests that the alteration assemblage and mineralization were recrystallized during deformation and metamorphism however increases in ca and k abundance and magnetic susceptibility decreases toward mineralization suggesting that they may constitute ore vectors

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

damage evaluation and conservation treatment of the tenth century korean rock carved buddha statues this study focuses on the lithological characterization quantitative deterioration assessment and conservation treatment of the tenth century rock carved buddha statues in korea the buddha statues were carved on light gray macrocrystalline biotite granite and features microcline phenocrysts and pegmatite patches the rock forming minerals are quartz plagioclase microcline and biotite showing micrographic and porphyritic textures feldspars and biotite in the host rock have been partly altered into sericite and chlorite by weathering the surface of the buddha statues is remarkably irregular due to granular disintegration and the differential weathering of the quartz and microcline in addition horizontal and vertical cracks in the host rock have promoted mechanical weathering biological colonization of the statues was serious and featured dark gray and yellowish green lichen dark green bryophyte and some plants the buddha statues were evaluated as the highly weathered rock by ultrasonic survey the lower parts under the influence of water and areas with severely broken surfaces showed a much more advanced weathering grade therefore scientific conservation treatment was carried out for the long term maintenance and conservation of the buddha statues after pretests dry wet and chemical cleanings were applied to the statues next joining of cracked parts and surface consolidating were executed finally the site environment was improved by installation of drain and trimming trees around the statues to ensure more stable long term conservation

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

physical and chemical response of zircons to deformation an investigation of u pb isotopic systematics in zircons from mylonitized henderson gneiss sinha and glover 1978 revealed that selected zircon fractions from the mylonite zone suffered total loss of radiogenic pb at 460 m y to further investigate the relationship between pb loss u gain and grain size reduction associated with increasing strain in the shear zone we have characterized the chemistry and morphology of zircons in the mylonitic rocks using both electron microprobe analysis and scanning electron microscopy

k ar geochronology of different tectonic units at the northwestern margin of the bohemian massif abstract the polymetamorphic moldanubian mo of the northeasthern margin of the bohemian massif has been thrust to the north onto the mainly paleozoic sedimentary saxothuringian of the fichtelgebirge fg these two units have undergone polyphase deformation and the last regional event to affect both units was a low pressure metamorphism in which temperatures decreased towards the north in contrast the nappe units of the erbendorf vohenstrauss zone zev and the erbendorf greenschist zone egz which partly cover the border of the moldanubian and the saxothuringian and the munchberg nappe pile mm which lies on the saxothuringian were in parts subjected to a late medium pressure metamorphic event the zev the egz the mo and the fg are intruded by late carboniferous granites conventional k ar analyses mainly of hornblendes and muscovites from the autochthonous fg and mo the units beneath the nappes have yielded exclusively carboniferous dates the oldest dates point to a regional cooling of the rocks which outcrop at the present day surface at about 330 320 ma i e at the early late carboniferous boundary the late carboniferous cooling history was largely governed by the thermal influence of the post kinematic granites 320 295 ma especially in the fg and the northern mo the high grade metamorphic rocks in the western part of the zev and in the upper three nappes of the mm mostly yield dates around 380 ma i e early devonian the results show a relatively wide scatter moreover biotites frequently appear to be older than the coexisting muscovites both observations indicate that the rocks underwent a later thermal influence whether some groups of older dates e g 400 ma are due to excess argon or to inherited argon is still open to discussion slightly scattered muscovite dates around 366 ma were obtained for the prasinite phyllite series one of the lower nappes of the mm a single hornblende from the egz gave the same age these two nappes have therefore probably been affected by a late devonian thermal and or tectonic event the muscovite dates obtained from the paleozoic bavarian lithofacies the lowermost nappe of the mm and the hornblende dates from the eastern part of the zev are indistinguishable from those of the autochthonous units fg and mo

predominance of stratified anoxic yangtze sea interrupted by short term oxygenation during the ordo silurian transition abstract the ordo silurian transition was a critical interval in geological history during which profound biotic climatic and oceanic changes occurred in order to explore the oceanic palaeoredox changes multiple geochemical proxies including ratios of s c fehr fet fep fehr and dop values are presented here from three sections wangjiawan western hubei sanjiaguan northern hunan and nanbazi northern guizhou across the ordo silurian boundary on the yangtze platform these palaeoredox data indicate a predominance of stratified anoxic ferruginous ocean on the yangtze block during this transition which was interrupted by a brief episode of oceanic oxygenation in the early hirnantian this oxygenation temporally coinciding with the end ordovician glaciation and global glacio eustatic sea level fall likely resulted from enhanced circulation of polar cold dense oxygen rich water onto the low latitude shelf the prior and subsequent longer term episodes of anoxic ocean particularly the later one which started in the late hirnantian occurred in parallel with the rapid climatic warming and sea level rise which could have slowed down oceanic circulation thereby enhancing oceanic stratification anoxia and organic preservation oceanic redox changes together with rapid climatic and sea level fluctuations were likely responsible for the stepwise massive demise of the ordo silurian biotic crisis

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

migmatite formation at subsolidus conditions an alternative to anatexis this contribution discusses the formation of stromatic high grade migmatites volume considerations require that most of the leucosome material is not added from outside the system a segregation mechanism is necessary except in those cases where the protolith of the migmatite already had a banded structure although partial melting is most often advocated to provide the segregation mechanism several arguments can be raised against high degrees of melting mineral compositions and even zoning patterns are similar in both mesosomes and leucosomes sufficient degrees of melting at reasonable temperatures require more than the available amounts of water the leucosomes do not always approximate to a minimum melt composition high degrees of melting cannot occur without an appreciable volume increase etc diffusion works as a segregation mechanism at low temperatures as diffusion rates increase exponentially with temperature diffusion must become still more important as a segregation mechanism at high temperatures a model is suggested based on the diffusion of components in response to the gradient x where 1 3 3i 1 i is the mean pressure in homogeneously strained rocks 3 is larger in rock parts rich in incompetent phases than in rock parts depleted in incompetent phases accordingly mechanically competent but chemically incompetent high volume phases like quartz and feldspars stressed in micadominated parts of a rock high migrate to parts of the rock that are depleted in mica low it is suggested that hornblende occurring in many leucosomes may be premigmatitic or early syn migmatitic and due to its mechanical competency it initiates the segregation diffusion occurs along grain boundaries and is enhanced by small amounts of intergranular fluid at the best semiquantitative estimates of diffusion rates and distances indicate that the process should work over geological times

chemical transport to the seafloor of the equatorial pacific ocean across a latitudinal transect at 135 w tracking sedimentary major trace and rare earth element fluxes at the equator and the intertropical convergence zone we have analyzed the major trace and rare earth element composition of surface sediments collected from a transect across the equator at 135 w longitude in the pacific ocean comparing the behavior of this suite of elements to the caco3 opal and corg fluxes which record sharp maxima at the equator previously documented at the same sampling stations enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial pacific seafloor the 1 1 high biogenic source at the equator associated with equatorial divergence of surface water and upwelling of nutrient rich water and 2 2 high aluminosilicate flux at 4 n associated with increased terrigenous input from elevated rainfall at the intertropical convergence zone itcz of the tradewinds are the two most important fluxes with which elemental transport is affiliated the biogenic flux at the equator transports ca and sr structurally bound to carbonate tests and mn primarily as an adsorbed component trace elements such as cr as pb and the rees are also influenced by the biogenic flux at the equator although this affiliation is not regionally dominant normative calculations suggest that extremely large fluxes of ba and p at the equator are carried by only small proportions of barite and apatite phases the high terrigenous flux at the itcz has a profound effect on chemical transport to the seafloor with elemental fluxes increasing tremendously and in parallel with ti normative calculations however indicate that these fluxes are far in excess of what can be supplied by lattice bound terrigenous phases the accumulation of ba is greater than is affiliated with biogenic transport at the equator while the p flux at the itcz is only 10 less than at the equator this challenges the common view that ba and p are essentially exclusively associated with biogenic fluxes many other elements including mn pb as and rees also record greater accumulation beneath the itcz than at the equator thus adsorptive scavenging by terrigenous paniculate matter or phases intimately associated with them appears to be an extremely important process regulating elemental transport to the equatorial pacific seafloor these findings emphasize the role of vertical transport to the sediment and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes

migmatite structures in the central gneiss complex boca de quadra alaska migmatite structures in the coast plutonic metamorphic complex are well exposed in the inlet of boca de quadra southeast alaska two types of anatectic migmatites are present patch migmatites formed by in situ melting and subsequent crystallization of melt diktyonitic migmatites comprise a discontinuous veined network of leucocratic material in which leucosomes enclose boudins of host rock the margins of these boudins show the development of both melanosomes and shear band fabrics strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 20 27 this volume decrease is attributed to melt extraction into the adjacent fracture filling leucosomes thus diktyonitic migmatites formed by shear induced segregation of partial melt whereas in patch migmatites the lack of shear stresses inhibited melt segregation the variable structural style of anatectic migmatites in boca de quadra is not related to host rock composition but may be due to differences in the amount of differential stress during migmatization these in turn may be controlled by host rock strength and or diachroneity of migmatization and deformation determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels

experimental deformation of partially melted granitic aggregates abstract the effects of varying amounts of partial melt on the deformation of granitic aggregates have been tested experimentally at conditions 900 c 1500 mpa 10 4 to 10 6 s where melt free samples deform by dislocation creep with microstructures approximately equivalent to those of upper greenschist facies experiments were performed on samples of various grain sizes including an aplite 150 m and sintered aggregates of quartz albitemicrocline 10 50 and 2 10 m water was added to the samples to obtain various amounts of melt 1 15 in the aplite 1 5 in the sintered aggregates optical and tem observations of the melt distribution in hydrostatically annealed samples show that the melt in the sintered aggregates is homogeneously distributed along an interconnected network of triple junction channels while the melt in the aplites is inhomogeneously distributed the effect of partial melt on deformation depends an melt amount and distribution grain size and strain rate for samples deformed with 1 melt all grain sizes exhibit microstructures indicative of dislocation creep for samples deformed with 3 5 melt the 150 m and 10 50 m grain size samples also exhibit dislocation creep microstructures but the 2 10 m grain size samples exhibit abundant tem scale evidence of dissolution precipitation and little evidence of dislocation activity suggesting a switch in deformation mechanism to predominantly melt enhanced diffusion creep at natural strain rates melt enhanced diffusion creep would predominate at larger grain sizes although probably not for most coarse grained granites the effects of melt percentage and strain rate have been studied for the 150 m aplites for samples with 5 and 10 melt deformation at 10 6 s squeezes excess melt out of the central compressed region allowing predominantly dislocation creep conversely deformation at 10 5 s produces considerable cataclasis presumably because the excess melt cannot flow laterally fast enough and a high pore fluid pressure results for samples with 15 melt deformation at both strain rates produces cataclasis presumably because the inhomogeneous melt distribution resulted in regions of decoupled grains which would produce high stress concentrations at point contacts at natural strain rates there should be little or no cataclasis if an equilibrium melt texture exists and if the melt can flow as fast as the imposed strain rate however if the melt is confined and cannot migrate a high pore fluid pressure should promote brittle deformation