holocene paleosols and colluvial sediments in northeast tibet qinghai province china properties dating and paleoenvironmental implications abstract colluvial deposits consisting of silts and loams were detected in several climatologically different areas of ne tibet 3200 3700 m a s l layering distinct organic content and low content of coarse matter as well as location in the relief revealed an origin from low energy slope erosion hillwash underlying and intercalated paleosols were classified as chernozems phaeozems regosols and fluvisols fifteen radiocarbon datings predominant on charcoal from both colluvial layers and paleosols yielded ages between 8988 66 and 3512 56 uncal bp natural or anthropogenic factors could have been the triggers of the erosional processes derived it remains unclear which reason was mainly responsible due to controversial paleoclimatic and geomorphic records as well as insufficient archaeological knowledge from this region determinations of charcoal and fossil wood revealed the holocene occurrence of tree species spruce juniper for areas which nowadays have no trees or only few forest islands thus large areas of ne tibet which are at present steppes and alpine pastures were forested in the past

spatial and temporal patterns of aeolian activities in the desert belt of northern china revealed by dune chronologies abstract as a part of the inqua project a global digital database and atlas of quaternary dune field and sand seas 337 age records from the desert dunes of china and 20 from mongolian dune fields have been compiled in the database this has opened the possibility of exploring and synthesizing the quaternary environmental changes in the asian mid latitudes dune fields directly from the on site aeolian sand archives this paper assessed the sand dune chronologies in terms of geographical distribution data quality and their implications for late quaternary palaeoenvironmental reconstructions the available ages are concentrated mainly in the last 20 ka and many are from the fields of stabilized dunes in the eastern portion of the desert belt in northern china the number of records and the ratio between the records of stable state and the total records could act as a proxy for the palaeoenvironmental interpretation the aeolian sand activities deciphered from the chronological data in the eastern portion of the desert belt in northern china show a reasonable correlation with the general global climatic curves at the glacial interglacial timescales the limited aeolian sand records from the glacial period however hamper the understanding of the detailed features e g forms and processes of the dune fields during glacial times in the last two millennia however there has not been any meaningful correlation between aeolian dune activity and climatic variation at the centennial time scales probably due to the complexity of the aeolian sand systems and human interventions extending the coverage of dune chronology both temporally and spatially is urgently needed for a full understanding of the environmental changes in the dune fields

palaeo moisture evolution in monsoonal central asia during the last 50 000 years abstract the late quaternary climate history of monsoonal central asia was inferred from 75 palaeoclimatic records which provide information about moisture conditions in the last 50 ka or part of this period wet conditions occurred during middle and late marine isotope stage 3 while the last glacial maximum lgm was characterized by dry climate conditions in the region a stepwise climate amelioration is suggested by the climate records following the lgm several climate signals of this period which were reported from high latitude ice core records are preserved in archives from monsoonal central asia as well during the early holocene high effective moisture was inferred from most records from the area dominated by the indian monsoon e g the tibetan plateau suggesting that holocene optimal climate conditions occurred there during this period in contrast areas which are dominated by the south east asian monsoon se monsoon and the westerlies in north western and north central china mongolia do not uniformly show an early holocene climate optimum for this area optimal conditions prevailed during the mid holocene these apparent contradictions can possibly be explained by the regional uplift and descent of air masses in the holocene during the early holocene strengthened insolation possibly caused an enhanced low level convergence over the tibetan plateau which led to the intensification of the summer monsoon the strong air uplift caused intensified precipitation and air divergence in the upper troposphere over the tibetan plateau the areas adjacent to the north therefore experienced an intensified descent of air masses and consequently increased aridity the majority of the palaeoclimatic records suggest reduced effective moisture since the late holocene in the region

palaeoenvironmental change recorded in the palaeodunefields of the western murray basin south australia new data from single grain osl dating this study is concerned with the reconstruction of the palaeoenvironmental history of southeastern australia for the last 300 ka by establishing a luminescence chronology of dune sand deposition in the western murray basin south australia in the study area vast fields of palaeodunes stabilised by vegetation provide evidence of past environmental change in total 98 samples were collected from dune sand layers at 13 different dune sections the time of their deposition was determined using optically stimulated luminescence dating of single quartz grains accounting for the impact of post depositional mixing by the use of a finite mixture model the oldest depositional phase demonstrates that dune sand layers of great antiquity are preserved in the western murray basin ranging up to at least 380 ka phases of substantial dune sand deposition were identified for the periods 18 38 ka and 63 72 ka older depositional phases also exist but are poorly resolved due to relatively large errors of the luminescence ages aeolian deposition during the last termination and the holocene is relatively limited with a slight clustering of ages at the time of the antarctic cold reversal and from 5 8 ka two modern ages give evidence of very recent dune sand deposition comparison with other palaeoclimate records from the region suggests that phases with high aeolian sedimentation coincide with more arid conditions and breaks in the dune record with more humid phases thus although dune records are often discontinuous and their interpretation in palaeoclimatic terms is not always straightforward the palaeodunes of the western murray basin show a good preservation of phases of aeolian activity and provide useful information for palaeoenvironmental reconstruction

determining soil moisture and sediment availability at white sands dune field new mexico from apparent thermal inertia data 1 determinations of soil moisture and sediment availability in arid regions are important indicators of local climate variability and the potential for future dust storm events data from the advanced spaceborne thermal emission and reflection aster radiometer were used to derive the relationships among potential soil erosion soil moisture and thermal inertia ti at the spatial scale of aeolian landforms for the white sands dune field between may 2000 and march 2008 land surface apparent thermal inertia ati data were used to derive an approximation of actual ti in order to estimate the wind threshold velocity ratio wtr the wtr is a ratio of the wind velocity thresholds at which soil erosion occurs for wet soil versus dry soil the aster derived soil moisture retrievals and the changes through time at white sands were interpreted to be driven primarily by precipitation but the presence of a perched groundwater table may also influence certain areas the sediment availability of dunes active playa surfaces and the margin of the alluvial fans to the west were determined to be consistently higher than the surrounding area the sediment availability can be primarily explained by precipitation events and the number of dry days prior to the data acquisition other factors such as vegetation and the amount of surface crusting may also influence soil mobility but these were not measured in the field this approach showed the highest modeled sediment availability values just days prior to the largest dust emission event at white sands in decades such an approach could be extended to a global monitoring technique for arid land systems that are prone to dust storms and for other regional land surface studies in the sahara

a quantitative approach to understanding dated dune stratigraphies attempts to reconstruct past changes in climate related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records in drylands as in other environments information on past forcing conditions is progressively modified degraded and removed from the available stratigraphic record by a series of filters involving changes in the primary forcing factors themselves geomorphological processes and the sampling dating procedures in this paper we describe a quantitative model that includes these effects and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions thicker preserved sedimentary records reflect periods of more intense aeolian activity localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences a preservation bias towards younger deposits is observed potentially leading to a continuum of accumulation that decays approximately in proportion to time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and or lower wind energy an asymmetry exists between the efficiency with which past drier and wetter episodes can be identified which relates to the time separation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to under sampling relevant to this is the effect of random dating errors statistical uncertainty which increasingly with age filter out higher frequency events from the record a new data treatment method termed accumulation rate variability provides an efficient proxy for accumulation rates and therefore the intensity of aeolian activity with significant improvements over existing date frequency methods the filtering problem discussed applies to all attempts at understanding the timing and nature of past events independent of the proxies and dating methods employed further explicit analysis of these issues would be beneficial copyright 2013 john wiley sons ltd

density of dry peridotite magma at high pressure using an x ray absorption method the density of a peridotite magma was measured up to 2 5 gpa and 2300 k using an x ray absorption method the method allowed measurement of the density of a peridotite melt under seven different conditions and clarified the pressure and temperature dependence of the density a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t 0 24 0 1 3 gpa its pressure derivative k 7 3 0 8 and the derivative of bulk modulus k t t p 0 0027 0 0017 gpa k at 2100 k the large bulk modulus and its pressure derivative of the peridotite melt compared with that of basaltic melt is consistent with previous results from sink float experiments

aeolian system responses to global change challenges of scale process and temporal integration aeolian sediment systems are extensive components of the earth s surface not just in today s active desert environments but in coastal locations and as presently stable loess and peri desert ergs all these systems are subject to potentially significant 21st century changes in dynamics due to global warming impacts on atmospheric circulation sediment moisture and vegetation cover but do we know enough in the critical areas of science to allow robust models of likely future dynamics to be developed since the establishment of modern aeolian science research has largely taken two divergent routes 1 small scale investigations of the processes of wind shear sediment entrainment and transportation and 2 landform and landscape analyses with bedform systems described and relationships to circulation explained an intermediate sedimentological route has generated attempts towards a more integrated understanding of system behaviour at a range of scales four recent developments provide the potential for more robust multiscale integrations of aeolian system behaviour these are 1 advances in empirical measurement that allow wind power and sediment flux relations to be better described 2 modelling of dune and dust dynamics and interactions with key controls 3 monitoring systems that allow high resolution observations of sediment flux variations to be recognized and aeolian deposit structures to be understood and 4 chronometric advances that permit the assessment of the frequency and drivers of dune system activity in the past we explore and analyse these methodological advances and their potential contribution to the multiscale integrations that are essential for better informed predictions of future global aeolian system dynamics considering whether the integration of these advances in reductionist and holistic elements of aeolian science represent an example of the effective application of the principles of earth system science copyright 2008 john wiley sons ltd

density of magmas at depth knowing the density of silicate liquids at high pressure is essential to answer questions relevant to the presence of magmas at depth whether that be in the present earth or in its earliest times during differentiation of the planet melts have unique physical and chemical properties which vary as a function pressure and chemical composition the focus here will be on in situ measurements of the density of magmas with a presentation of the available methods and of the main results obtained so far including why some magmas may be trapped at depth understanding the macroscopical physical properties of magmas requires an accurate microscopic structural description structural descriptions of compressed magmas are becoming more widely available from experiments and from theoretical calculations these structural inputs are used to understand the compression mechanisms at stake in the densification of magmas e g the collapse of voids coordination increase for the major cations and bond compressibility these densification processes profoundly affect not only the physical properties of the melt but also its chemical properties i e the way elements partition between the magma and a metallic melt or between the magma and crystals

climate driven changes to dune activity during the last glacial maximum and deglaciation in the mu us dune field north central china one significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind blown sand dunes the relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood however evidence of aeolian sand deposition during the last glacial maximum lgm is scarce in many mid latitude dune fields whereas abundant evidence exists for aeolian sand accumulation during the deglaciation i e after about 15 ka whether this contrast actually reflects changes in dune activity is still unclear making paleoclimatic interpretation uncertain comprehensive field investigation and luminescence dating in the mu us dune field north central china demonstrates that aeolian sands deposited during the lgm are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin the scarcity of lgm dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation increasing sand accumulation after 15 ka reflected by much more extensive preservation signals a change in sand supply relative to sand transportation through the dune field reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation the dunes however remained largely mobile as they were in the lgm similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid latitude dune fields imply broad climatic controls linked to the changes in high northern latitude forcing

shock compression of liquid silicates to 125 gpa the anorthite diopside join we determined the equation of state eos of three silicate liquid compositions by shock compression of preheated samples up to 127 gpa diopside di ca 2mg 2sio 6 at 1773 k anorthite an caal 2si 2o 8 at 1923 k and the eutectic composition di 64 an 36 at 1673 k were previously studied by shock compression to 38 gpa the new data extend the eos of each composition nearly to the earth s core mantle boundary the previously reported anomaly at 25 gpa for di 64 an 36 eutectic was not reproduced rather all data for this composition fit within error a straight line hugoniot in particle velocity vs shock velocity di also displays a linear hugoniot consistent with ultrasonic data and a third order finite strain eos the full anorthite data set is complex we examine a model with a transition between two structural states and a fourth order finite strain model excluding two points that may not display relaxed behavior we also report an experiment on room temperature solid di 64 an 36 aggregate that clearly demonstrates increase upon compression of the gruneisen parameter of this liquid much as experiment and theory have shown for forsterite and enstatite liquids we construct isentropes and isotherms from our hugoniots using mie gruneisen thermal pressure and evaluate the model of ideal mixing of volumes volume may mix almost linearly at high temperature but deviates strongly when calculated along an isotherm it remains difficult to reach a firm conclusion we compare the densities of liquids to lower mantle solids our results suggest that basaltic liquids rich in cao and al 2o 3 are notably denser than liquids in the mgo sio 2 binary and subject to uncertainties in the behavior of feo and in corrections for thermal pressure such liquids may be the most likely candidates for achieving negative buoyancy in the lowermost mantle

density of hydrous magma abstract magmas in the interior of the earth have been geophysically observed the generation of magmas is closely related to h2o because the water induced decrease in the melting temperature of mantle rocks is an essential process which forms hydrous magmas due to h2o incorporation into the molten rocks knowledge on physical properties of hydrous magmas such as density can give us better understanding of the magma behavior inside the earth the density of hydrous magma can be controlled by the partial molar volume of h2o v h 2 o and its pressure and temperature dependences the new compression behavior of v h 2 o using vinet equation of state is proposed based on compiled data since h2o is one of the most compressible oxides in the magma at lower pressure a rapid densification of hydrous magma can be observed at shallower mantle the dense hydrous magma can be gravitational stable above and below mantle transition zone

density of basaltic melt at high pressure and stability of the melt at the base of the lower mantle abstract we made density measurements of model morb and picritic melts up to about 15 gpa using the floating diamond method the compression behavior of the melts is fitted by the vinet equation of state and extrapolated to higher pressure a density crossover between the morb melt and the mantle peridotite is suggested at the base of the lower mantle thus the ultra low velocity zone in the d layer may be explained by the existence of gravitationally stabilized basaltic melt formed by melting of the accumulated slab materials this region might become unstable due to progressive melting of slab materials and or supply of volatiles

comment on the paper a test of the reliability of the rbsr dates for selected glauconite morphologies of the upper cretaceous navesink formation of new jersey by r l montag and d e seidemann the reliability of rb sr data on glauconite is a question which has not been very much investigated and every contribution to this subject will certainly be appreciated by all geochronologists interested in dating sediments however we have the strong feeling that by drawing a conclusion which seems very unlikely montag and seidemann 1 have not helped much in clarifying a situation which is already obscure enough due to lack of data the assumption which we consider improbable is the following that rb sr model age of glauconite could be drastically affected by preferential rb loss upon weathering we find the arguments presented unconvincing and think that other possibilities must be taken into account such as reworking a possibility considered by montag and seidemann themselves or the immatur i ty of glauconite a possibility not considered by them or the presence of non glauconitic detrital material in the samples analysed a possibility also not considered by them in our opinion alteration by weathering tends to cause a lowering of rb sr ages by preferential removal of a7sr d three points tend to support this contention 1 unpublished data obtained by one of us p p on glauconites from new jersey show a systematic tendency for weathered glauconite to yield rb sr ages which are too low while no case of the opposite was observed in cases of pervasive weathering as illustrated by the navesink formation the k ar ages may also be lowered 2 aside from these unpublished data unknown to the authors of the paper under discussion a lowering of rb sr ages also appears probable simply on the basis of the evident lowering of the k ar ages for the navesink formation indeed the conclusion of montag and seidemann according to which a 60 2 41 5 ma value corresponds to the true age of this late upper campanian lower maestrichtian formation see discussion in owens and sohl 2 is at variance with data given in references 3 4 5 6 7 8 9 and 10 in addition the well defined isochron as it is called by montag and seidemann in fig 1 of their paper and which corresponds to an age of 60 2 1 5 ma is defined by dark green lobate glauconites yielding almost exactly the same rb content 231 34 237 58 ppm this line is most probably a dark green lobate glauconitecarbonate mixing line and is the graphical representation of conventional apparent ages calculated with an initial sr isotope ratio of 0 7076 0 0009 of course it is by no means evident that if arra d is lost srra d should also be lost by the same agency although a priori this would also appear possible but that the agency i e chemical weathering should cause preferential ar versus k loss and rb versus sr loss is not at all probable why should rubidium behave like radiogenic argon and radiogenic strontium like potassium 2 it has been demonstrated in other cases that weathering causes a lowering of rb sr ages of

archean to recent aeolian sand systems and their sedimentary record current understanding and future prospects the sedimentary record of aeolian sand systems extends from the archean to the quaternary yet current understanding of aeolian sedimentary processes and product remains limited most preserved aeolian successions represent inland sand sea or dunefield erg deposits whereas coastal systems are primarily known from the cenozoic the complexity of aeolian sedimentary processes and facies variability are under represented and excessively simplified in current facies models which are not sufficiently refined to reliably account for the complexity inherent in bedform morphology and migratory behaviour and therefore cannot be used to consistently account for and predict the nature of the preserved sedimentary record in terms of formative processes archean and neoproterozoic aeolian successions remain poorly constrained palaeozoic ergs developed and accumulated in relation to the palaeogeographical location of land masses and desert belts during the triassic widespread desert conditions prevailed across much of europe during the jurassic extensive ergs developed in north america and gave rise to anomalously thick aeolian successions cretaceous aeolian successions are widespread in south america africa asia and locally in europe spain and the usa several eocene to pliocene successions represent the direct precursors to the present day systems quaternary systems include major sand seas ergs in low lattitude and mid latitude arid regions pleistocene carbonate and holocene modern siliciclastic coastal systems the sedimentary record of most modern aeolian systems remains largely unknown the majority of palaeoenvironmental reconstructions of aeolian systems envisage transverse dunes whereas successions representing linear and star dunes remain under recognized research questions that remain to be answered include i what factors control the preservation potential of different types of aeolian bedforms and what are the characteristics of the deposits of different bedform types that can be used for effective reconstruction of original bedform morphology ii what specific set of controlling conditions allow for sustained bedform climb versus episodic sequence accumulation and preservation iii can sophisticated four dimensional models be developed for complex patterns of spatial and temporal transition between different mechanisms of accumulation and preservation and iv is it reasonable to assume that the deposits of preserved aeolian successions necessarily represent an unbiased record of the conditions that prevailed during episodes of earth history when large scale aeolian systems were active or has the evidence to support the existence of other major desert basins been lost for many periods throughout earth history

age and origin of albian glauconites and associated clay minerals inferred from a detailed geochemical analysis abstract glauconitic grains are abundant in sandstones and siltstones from albian and cenomanian transition between lower and upper cretaceous formations of southeastern france morphological and crystal chemical data show that the green grains can be considered as glauconite s s with minute amounts of pyrite dolomite calcite and other clay minerals as grain coatings or crack fillings glauconite grains formed early during sedimentation generally from detrital chlorite biotite or clay particles and were found scattered together with other detrital mineral phases muscovite quartz in the silt in which porosity was considerably reduced afterwards by four stages of carbonate calcite dolomite cementation geochemical data especially the fe u and ce contents of the glauconitic grains strongly suggest increasing oxidizing conditions with time in the sedimentation environment the detailed geochemical analyses also allow the pristine glauconite grains to be distinguished from the other clay minerals occurring in the sequence this enabled k ar and rb sr dating of the glauconitic material which yields identical results of 97 9 0 4 and 97 9 3 5 ma respectively these dates point to a synsedimentary origin for the glauconites during the late albian about 97 98 ma the k ar data also indicate that the albian cenomanian boundary should be placed at 96 0 1 9 ma the similarity between the k ar and rb sr ages precludes any further significant pervasive recrystallization of these minerals during burial of the sequence either by heat flux or fluid flow the k ar study of the clay matrix from the same siltstones suggests synsedimentary precipitation of additional clay minerals probably together with the glauconite grains such as mixed layer illite smectite identified in the clay size fraction of the sedimentary succession

the k ar and 40ar 39ar methods revisited for dating fine grained k bearing clay minerals abstract the strengths and weaknesses of the two ar isotopic methods k ar and 40ar 39ar were evaluated on the basis of respective recent applications mainly on low temperature k bearing illite type clay minerals this review includes a presentation of basic analytical and technical aspects for both methods as well as a discussion of varied claims on the two methods and of requests about sample preparation and characterization whenever possible the advantages and weaknesses of each method were compared on coeval results obtained by both methods on the same mineral separates the comparative review examines stratigraphic dating of glauconites indirect dating of low temperature ore deposits dating of burial related illitization and dating of polyphased tectono thermal activity more specifically of fault gouges some pending questions such as the necessary encapsulation due to 39ar recoil and its restoration into step heating patterns are also raised together with the new potential of ar dating of nanometric illite crystals weakness of the k ar method is in its pioneering status that makes many believe that it is no longer accurate because of its traditional analytical aspects and of the k determinations leading to somewhat large uncertainties however precise evaluation of varied applications points to a k ar method having probably larger applicability in sedimentary to diagenetic environments than the 40ar 39ar method the drawbacks become less important if the method is applied to nanometer sized clay minerals in diagenetic to low grade metamorphic environments in this instance the extracted size fractions are generally homogeneous and the relative uncertainty given by the age calculations if mathematically justified can be reduced by duplicate analyses weakness of the 40ar 39ar method is in its basics such as the 39ar recoil the necessary encapsulation the reintegration of the 39ar into the step heating patterns and the meaning of the step heating patterns that are more suggestive of variable 39ar reservoirs created among the clay particles by irradiation than of meaningful geologic ages if the k ar method is the preferred method for dating diagenetic clay processes such as glauconitization illite crystal nucleation and growth or low temperature hydrothermal activities then the 40ar 39ar method has more potential in dating low temperature tectono thermal activities and in detailing mixtures of multi generation illite

density of high ti basalt magma at high pressure and origin of heterogeneities in the lunar mantle abstract the density of the apollo 14 black glass melt which has the highest tio 2 content of pristine mare glasses was measured to 4 8 gpa and 2100 k using an x ray absorption method a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t 0 9 0 1 2 gpa its pressure derivative k 0 16 0 3 4 and the temperature derivative of the bulk modulus k t t p 0 0030 0 0008 gpa k at 1700 k the high ti basalt magma is less dense than the lunar mantle below about 1 0 gpa therefore the high ti basalt magma produced in the hybridized source 100 200 km can ascend to the lunar surface the basalt formed at the higher pressure could not ascend but move downwards and solidify in the lunar mantle the solidified high ti basalt components can create chemical heterogeneities in the lunar mantle and can cause the low velocity anomalies observed seismologically

compositional effect on the pressure derivatives of bulk modulus of silicate melts abstract although the bulk moduli k t 0 of silicate melts have a relatively narrow range of values the pressure derivatives of the isothermal bulk modulus k t 0 can assume a broad range of values and have an important influence on the compositional dependence of the melt compressibility at high pressure based on the melt density data from sink float experiments at high pressures in the literature we calculate k t 0 using an isothermal equation of state eos e g birch murnaghan eos and vinet eos with the previously determined values of room pressure density 0 and room pressure bulk modulus k t 0 the results show that best estimates of k t 0 vary considerably from 3 to 7 for different compositions k t 0 is nearly independent of mg molar mg mg fe but decreases with sio 2 content hydrous melts have anomalously small k t 0 leading to a high degree of compression at high pressures for anhydrous melts k t 0 is 7 for peridotitic melts 6 for picritic melts 5 for komatiitic melts and 4 for basaltic melts

density of phonolitic magmas and time scales of crystal fractionation in magma chambers abstract understanding magmatic processes and their evolution in the earth s interior requires a better knowledge of silicate melts and their physical properties among them density is one of the most important to constrain the residence or ascent time of magma in the upper mantle and crust however the volumetric properties of volatile bearing and highly polymerized silicate melts are still poorly constrained due to scarce experimental data in this study the density of dry and hydrous 4 35 wt h2o phonolitic melt was measured in situ using the x ray absorption method in a paris edinburgh press at 0 73 3 1 gpa and 1484 1855 k calculated melt densities range from 2 49 0 02 to 2 66 0 03 g cm 3 and from 2 31 0 02 to 2 52 0 02 g cm 3 for the dry and hydrous compositions at depths of 30 to 100 km the results are used to calibrate the equation of state eos of phonolitic liquids for crustal and upper mantle conditions and to derive the partial molar volume of water a least squares fit of the p t data to a third order birch murnaghan eos yields v 0 28 10 0 74 0 10 cm 3 mol k t 14 6 3 0 3 2 gpa k 8 9 2 6 3 3 and 47 30 28 10 6 k for the dry melts and v 0 20 6 0 8 7 5 cm 3 mol k t 4 6 3 0 2 3 gpa k 5 5 0 5 6 1 and 135 115 114 10 6 k for the hydrous component at 1673 k combined with literature data our eos for water indicates that v h 2 o does not depend strongly on the silicate liquid composition at the investigated conditions crystal settling velocities in phonolitic liquids were calculated from the eos to constrain the time scales of crystal fractionation in magma chambers the high compressibility of phonolitic melts results in a small density contrast between nepheline and sanidine crystals and melt neph phon 0 13 0 27 g cm 3 and san phon 0 05 0 21 g cm 3 with corresponding settling times of about 380 and 510 yr km respectively for crystal sizes of 2 cm because of their higher density similar sized magnetite and augite only require about 31 and 100 yr km respectively the observed phenocryst populations in phonolitic magmas indicate that the residence time was sufficiently long to fractionate augite and magnetite but not sanidine and nepheline thus our density data combined with the phenocryst populations of the erupted lavas point to a residence time in the crust between a few tens to hundreds of years consistent with estimates from u th ra isotope compositions

regional grain size variations in aeolian sediments along the transition between tibetan highlands and north western chinese deserts the influence of geomorphological settings on aeolian transport pathways sediment distribution is investigated applying grain size analysis to 279 surface samples from the transitional zone between high mountains qilian shan and their arid forelands hexi corridor in north western china six main sediment types were classified medium scale 103 m geomorphological setting is carefully considered as it may play an important role concerning sediment supply and availability a tripartite distribution of sedimentological landscape units along the mountain to foreland transition is evident aeolian sediments e g loess and dune sands are widespread they are used to identify aeolian transport pathways the mu fs ratio 5 11 m 48 70 m among primary loess opposes the two grain size fractions being most sensitive to varying accumulation conditions the first fraction is attributed to long distance transport in high suspension clouds whereas the latter represents local transport in saltation mode the ratio shows strong correlation with elevation r2 0 77 thus it indicates a relatively higher far traveled dust supply in mountainous areas 3000 m above sea level a s l compared to the foreland the contribution of westerlies to high mountain loess deposits is considered likely hereby the influence of the geomorphological setting on grain size composition of aeolian sediments becomes apparent the contribution from distant dust sources is ubiquitous in the study area however the far distance contribution may be reduced by the availability of fine sand provided in low topography settings plain foreland areas support fine sand deflation from supplying river beds allowing the formation of sandy loess in foreland areas and intramontane basins in contrast high mountain topography inhibits strong sand deflation into loess deposits eastern parts of the hexi corridor show higher aeolian sand occurrence in contrast the western parts are dominated by gravel gobi surfaces this is attributed to higher sand supply in eastern parts provided by the badain jaran desert and fluvial storages as sand sources copyright 2014 john wiley sons ltd

holocene climate change inferred from stratigraphy and osl chronology of aeolian sediments in the qaidam basin northeastern qinghai tibetan plateau abstract paleoclimatic reconstruction based on aeolian sediments in the eastern qaidam basin qb has been hindered by the limited chronological data here we present 61 optically stimulated luminescence osl ages on the basis of these osl ages and the lithologic stratigraphy we propose the effective moisture index emi for aeolian sediments to reconstruct the effective moisture change based on the emi from twelve sections the effective moisture change moisture sources and relevant mechanisms for paleoclimatic change in the eastern qb are discussed the results indicate that 1 aeolian deposition started at least before 12 4 0 7 ka during the deglaciation the paleosols developed at the early and mid holocene and aeolian sand and loess accumulated at mid and late holocene 2 effective moisture history was hyper arid at 12 8 11 6 ka humid and variable at 11 6 8 3 ka moderately humid and stable at 8 3 3 5 ka and increasingly arid at 3 5 0 ka 3 the effective moisture change was mainly controlled by the asian summer monsoon asm which mainly followed the change of northern hemispheric summer insolation and the westerlies strengthened and increased the aridity in the qb when the asm shrank

k ca ages of authigenic sediments examples from paleozoic glauconite and applications to low temperature thermochronometry k ca ages of cambrian glauconites from the llano uplift central texas were determined in order to re evaluate the ability of the k ca system to constrain the timing of deposition of sedimentary packages all of the k ca ages presented here were found to be younger than their stratigraphic ages in addition to being too young the k ca ages are also highly variable ranging in age from silurian to permian the oldest subset of glauconite ages are in agreement with previously published rb sr ages from the same outcrop and provide further evidence for there having been a post depositional thermal or recrystallization event that reset both the rb sr and k ca systems the range of younger glauconite k ca ages is similar to the distribution of available apatite fission track ages for the llano basement k ca ages are interpreted as thermochronologic data reflecting partial retention of ca in thermally fluctuating basin conditions estimates of the closure temperature of ca in glauconite are found to be 60 90 c for cooling rates of 0 5 1 c my the k ca system is potentially useful as a low temperature thermochronometer with closure temperatures 100 c for glauconite

a test of the reliability of rb sr dates for selected glauconite morphologies of the upper cretaceous navesink formation of new jersey abstract glauconite samples from the navesink formation of new jersey were separated into different morphological groups each morphological type was dated using the rb sr method in an attempt to test the hypothesis that the mamillary and the lobate glauconite morphologies are more suitable than other morphologies for radiometric dating isochron dates of unaltered dark green lobate glauconites were found to be reliable indicators of the true age of the sedimentary rock weathering processes may drastically affect the87rb 87sr ratios of glauconite pellets by removal of rb from the glauconite this results in anomalously high apparent ages light green glauconites were shown to have suffered extensive rb loss and are hence inappropriate for dating a slightly altered dark green lobate glauconite appears to have suffered some rb loss x ray diffraction criteria were not always sufficient in indicating whether glauconite samples have remained closed systems with respect to87rb and87sr

geomorphological and palaeoclimate dynamics recorded by the formation of aeolian archives on the tibetan plateau abstract aeolian sediments are an important archive for palaeoclimate reconstructions on the tibetan plateau the accumulation of aeolian sediments and the formation of palaeosols are used as a proxy for dry and wet phases respectively during the last decade the number of osl optically stimulated luminescence ages of aeolian sediments has been rapidly increasing this study summarises the results from more than 300 individual osl ages despite the widespread occurrence of aeolian sediments on the tibetan plateau nearly all osl samples are located on the northeastern and the southern part in most regions the strongest accumulation occurred during the late glacial and in the early holocene this coincides with the strengthening of the asian summer monsoon on the tibetan plateau and wetter climate conditions after the relatively dry glacial times the development of a sufficient vegetation cover acting as a sediment trap seems to be an important requirement for the preservation of aeolian archives short dry periods like the younger dryas led to a more enhanced aeolian accumulation without destruction of previously formed archives in some regions the formation of palaeosols occurred mainly during the wet early and mid holocene but the number of ages is relatively small in contrast a second phase of aeolian accumulation during the late holocene was related to the weakening of the asian summer monsoon and drier climate conditions this indicates that the reaction of aeolian accumulation on the tibetan plateau depends on the previous climate state a comparison between the osl ages from aeolian sands and loess deposits yields a different timing of deposition of these two sediment types while the sand deposits in different basins resemble wet and dry phases loess deposits show no common signal between the analysed areas this indicates an influence of local factors such as varying source areas and erosive processes on the slopes in general the aeolian archives in the high mountain environment are governed by numerous factors besides the climatic influence

some fundamental considerations in the dating of glauconies a comment on a test of the reliability of rbsr dates for selected glauconite morphologies of the upper cretaceous navesink formation of new jersey by r l montag and d e seidemann in an attempt to understand the geochemical behaviour of rb and sr in glauconies see below used for dating purpose montag and seidemann 1 stated several hypotheses in contradiction with some facts generally known to the specialists in these difficult problems in their introduction these authors define the word glauconite as a mineral but unfortunately also use it to describe the green sedimentary pellets in which glauconitic minerals occur the term has unfortunately come to be used loosely to cover two concepts on the one hand a concept of facies something green usually in pelletal form lying in a marine sediment on the other hand a mineralogic concept which designates a mica 2 the two concepts cover diverse possibilities this duality of significance leads us amongst others 3 to propose to solve this confusion by using glaucony or pelletal glauconite for the facies and glauconitic minerals for the authigenic components of the green pellets 4 these glauconies may be more or less evolved and fundamentally contain two kinds of components 1 t h e inherited ones which originate from the initial substrate of glauconitization quartz mica clay calcareous debris 5 there is no glauconitization without this preliminary substrate 2 the authigenic ones which are the glauconitic minerals ranging from a smectitic end member component to a micaceous endmember only the latter should actually be named glauconite the suffix ite characterizes a mineral this is a convention other conventions are possible and we do not intend to impose a solution but it is certain that the confusion of the two concepts and withirl each concept the non recognition of their diversity can only lead to complete confusion in the application to geochronology ages of glauconies are not generally 10 20 younger than the age of sedimentation this old assumption was based on the study of deeply buried samples from north america which had been rejuvenated or on a biased time scale 6 numerous recent studies have shown that the main problems with the dating of giauconies are in chronological order 1 the zero time problem see tisserant and odin 7 and fig 1 2 possible influences from tectonic and deep burial 8 and 3 possible changes due to weathering 9 whatever the colour or the form the green pellets may lack reliability for geochronology due to the three main causes listed above if the light green pellets give apparent ages which are often different from the age of sedimentation it is well recognized today that this is not related to their colour but to the fact that either they are little evolved or that

asynchronous evolution of the indian and east asian summer monsoon indicated by holocene moisture patterns in monsoonal central asia abstract the numerical meta analysis of 92 proxy records 72 sites of moisture and or temperature change confirms earlier findings that the dominant trends of climatic evolution in monsoonal central asia since the last glacial roughly parallel changes in northern hemisphere summer insolation i e the period following the last glacial maximum was characterized by dry and cold conditions until 15 cal kyr bp followed by a warm wet period coincident with the bolling allerod warm period and terminated by a cold dry reversal during the younger dryas period after an abrupt increase at the start of the holocene warm and wet conditions prevailed until ca 4 cal kyr bp when moisture levels and temperatures started to decrease ordination of moisture records reveals strong spatial heterogeneity in moisture evolution during the last 10 cal kyr the indian summer monsoon ism areas northern india tibetan plateau and southwest china exhibit maximum wet conditions during the early holocene while many records from the area of the east asian summer monsoon indicate relatively dry conditions especially in north central china where the maximum moisture levels occurred during the mid holocene we assign such phenomena to strengthened hadley circulation centered over the tibetan plateau during the early holocene which resulted in subsidence in the east asian monsoonal regions leading to relatively dry conditions our observations of the asynchronous nature of the two asian monsoon subsystems on millennial time scales have also been observed on annual time scales as well as implied through the spatial analysis of vertical air motion patterns after strong ascending airflows over the tibetan plateau area that were calculated from ncep ncar reanalysis data for the last 30 years analogous with the early holocene the enhancement of the ism in a future warming world will result in an increase in the asynchronous nature of the monsoon subsystems this trend is already observed in the meteorological data from the last 15 years

lake level variations of qinghai lake in northeastern qinghai tibetan plateau since 3 7 ka based on osl dating abstract qinghai lake is the largest internally drained lake in china and its unique location makes it sensitive to climate changes late glacial climate changes associated with variation in qinghai lake levels have been intensively investigated for the past 40 years with particular attention paid to lake level fluctuation histories between the last interglacial and the holocene however the details of lake level fluctuations during the holocene are still unclear using both optically stimulated luminescence osl dating of quartz for 22 samples and infra red stimulated luminescence irsl of feldspars only for sample hyw1 whose irsl age is 37 15 years a total of 23 samples are dated from paleoshoreline deposits fluvial sediments and aeolian sands a total of 13 sections near the modern lake shore with ages from 37 15 to 3710 350 years these ages are used to reconstruct the lake level fluctuation history spanning the last 3700 years the results indicate that 1 the youngest irsl age of 37 15 years is in agreement with the independent age of 39 29 years suggesting that luminescence dating is able to date decadal samples for sediments from the study area 2 the lake experienced several oscillations imposed on an overall regressive trend during the past 3700 years 3 the dated paleoshoreline deposits are generally related to warm and wet periods suggesting that those shoreline deposits formed during cold and dry periods if any may have been modified by later transgressions 4 lake level fluctuations during the period of 3700 240 years ago are generally consistent with the climate conditions identified in other proxies with the highest lake level occurring about 1770 years ago and 5 after 240 years ago the lake level dropped more rapidly which is inconsistent with the proxy records showing a warmer and wetter phase

large scale controls on the development of sand seas in northern china abstract although sand seas are located in arid regions given that the proportions of dune areas vary greatly from region to region they are clearly influenced by other factors as well as aridity this paper discusses the distribution pattern and major features of sand seas and large fields of stabilized dunes in northern china and demonstrates the main influences on their development it appears that the availability of onsite loose sediments not wind strength is critical to the occurrence of the sand seas on a regional scale tectonic endorheic basins or areas of alluvial fans or forelands of mountain ranges are advantageous to the accumulation of fluvial sediments and thus are ideal locations of large sand seas in an arid climate the large dune fields currently stabilized by vegetation were active sand seas during the drier periods of the late pleistocene and early holocene the distribution patterns of chinese sand seas suggest that the height or size of the dunes in the sand seas are determined more by the availability of sands than any other potential factors as the sand seas in china account for a large portion of deserts in the middle latitudes of the northern hemisphere taklamakan is the second largest sand sea on earth knowledge of these sand seas past changes is important for understanding climatic changes in the terrestrial regions of mid latitudes

initiation and variation of the dune fields in semi arid china with a special reference to the hunshandake sandy land inner mongolia sedimentary sequences occurring in desert dunes reflect changes in desert systems and as such may contain signals useful for recognizing spatial and temporal changes of deserts and their response to regional or even global climate fluctuations geomorphological and palaeoenvironmental studies within the dune fields of the asian middle latitudes have provided some solid evidence for interpreting the history of these sand seas using the hunshandake otindag sandy land a sandy area covered primarily by stabilized dunes and located in the semi arid zone of eastern inner mongolia china fig 1 as an example we studied the initiation and variation in the dune landscape in the eastern portion of the desert belt in northern china on the basis of physical and biochemical indicators in the sediments and osl chronology we herein argue that this dune system in the middle latitudes of eastern asia is much younger than previously assumed and that it has responded sensitively to climate change during the late quaternary geological evidence from the sandy land suggests that most of the current dunes are of late pleistocene or even holocene age palaeosols intercalated in the aeolian sequences and their osl chronology show that the climate of the hunshandake was much wetter than today between 9 6 ka and 3 ka this resulted in stabilization of the dunes in the eastern and central portions of the sandy land epochs of reworking or stabilization of the dunes are broadly consistent with the fluctuations in northern hemisphere solar radiation although with an obvious time lag because the increase rate of annual precipitation was not sufficient to fully stabilize the dunes in more arid part of the region some active dunes persisted even during this long lasting wetter epoch we conclude that periods of holocene dune stabilization due to palaeosol formation varied along the climate gradients across the various sandy lands of northern china and in general it began earlier and lasted longer in the east than in the west the general nature of the sandy lands and their counterparts in the western portion of the desert belt during the lgm and mid holocene climate optimum is discussed in comparison with their current states

chinese loess record of monsoon climate during the last glacial interglacial cycle the thick loess paleosol succession of central china contains a detailed record of changes in east asian monsoon climate since the late miocene epoch the alternating loess paleosol stratigraphy closely resembles the marine oxygen isotope record implying that episodic dust deposition and pedogenesis are in phase with global ice volume fluctuations and controlled by variations in solar radiation reaching the land surface deposits equivalent to marine isotope stages mis 5 through 1 have been dated by 14c 10be luminescence and magnetic susceptibility and grain size models malan loess mis 4 2 decreases in thickness southeastward from 30 m in the western loess plateau to 5 m east of xi an downwind asian dust is found in japan the north pacific ocean and the greenland ice sheet where it has a chemical signature that points to a primary source in western china during glacial times the mean dust flux in the central loess plateau reached 0 35 mm year whereas in interglacial times it fell to 0 1 mm year times of high dust influx and reduced soil development coincided with strengthened winter monsoon conditions which are inferred from variations in loess grain size times of decreased dust accumulation and strong pedogenesis marked by high values of magnetic susceptibility represent times of strengthened summer monsoon conditions high frequency fluctuations in dust influx during deposition of the malan loess include peaks that likely correlate with north atlantic heinrich events the younger dryas oscillation is recorded in chinese eolian and organic deposits by a shift from cool humid late glacial conditions to cold and dry conditions followed by a return to milder humid climate at the beginning of the holocene warm moist climate associated with a strong summer monsoon characterized the first half of the holocene epoch when a widespread paleosol complex developed on the loess plateau increased dust deposition during the middle to late holocene marked a shift to cooler drier conditions

melting relations and the equation of state of magmas at high pressure application to geodynamics abstract the melting relations of mantle minerals together with the physical properties of silicate melts at high pressure have been extensively studied during the previous decade the melting relation of minerals and the equation of state of magmas are important properties for deducing the formation and differentiation of the earth and especially for elucidating the nature of the terrestrial magma ocean and the subsequent formation of the core mantle and crust of the earth because these magmas are compressible we expect that the olivine magma density crossover played an important role in controlling the geochemical characteristics of the primitive mantle after the magma ocean stage of the primordial earth the crystal magma density crossover is also expected to occur at the base of the upper mantle in the presence of volatiles and at the base of the lower mantle in the earth today the existence of dense magmas is consistent with seismological observations of low velocity regions existing at the base of the upper mantle beneath japan europe and the usa and the ultralow velocity zone ulvz at the core mantle boundary of the present earth

measurement of hydrous peridotite magma density at high pressure using the x ray absorption method abstract the density of hydrous peridotite magma containing 5 wt h 2 o was measured at pressures and temperatures up to 4 3 gpa and 2073 k respectively using the x ray absorption method a fit of pressure density temperature data to the high temperature birch murnaghan equation of state yields isothermal bulk modulus k t 8 8 1 9 gpa its pressure derivative k 9 9 3 6 and the temperature derivative of the bulk modulus k t t p 0 0022 0 0015 gpa k at 1773 k the small bulk modulus of the hydrous peridotite magma compared with that of the dry peridotite magma reflects the effect of water which is more compressible than the silicate melt the partial molar volume of h 2 o in magma under high pressure conditions was calculated and fitted using the vinet equation of state the isothermal bulk modulus was k t 2 4 1 0 gpa and its pressure derivative was k 5 7 1 5 at 1973 k

olivine flotation in mantle melt abstract molten komatiite and peridotite have been compressed in an octahedral multi anvil device up to 10 gpa densities of the melts were measured at pressure intervals in the range 7 to 10 gpa by observing sinking and floating san carlos olivines and synthetic forsterite marker spheres the multi anvil results for komatiite when combined with piston cylinder measurements done at 4 to 6 gpa and a calculated reference density at 105 pa yield a birch murnaghan isothermal bulk modulus of k1900c 26 gpa and pressure derivativek 4 25 the pressure of neutral buoyancy for olivine in komatiite is confirmed to be near 8 gpa as predicted in earlier work olivine flotation in the experimental komatiite commences at a pressure close to where the liquidus phase changes from olivine to denser garnet leading to the possibility of density driven crystal sorting during fractionation molten peridotite klb 1 shows an isothermal compression 2000 c of 0 065 g cm 3 gpa 1 in the interval 105 pa to 8 2 gpa the olivine liquid peridotite density crossover is predicted to lie between 9 and 11 gpa indicating that olivine flotation can operate at depths of 300 500 km in a molten peridotitic mantle

density of carbonated peridotite magma at high pressure using an x ray absorption method the density of carbonated peridotite magma was measured up to 3 8 gpa and 2100 k using an x ray absorption method a fit of the pressure density temperature data to the high temperature birch murnaghan equation of state yielded the isothermal bulk modulus k t0 22 9 1 4 gpa its pressure derivative k 0 7 4 1 4 and the temperature derivative of the bulk modulus k t t p 0 006 0 002 gpa k at 1800 k the bulk modulus of carbonated peridotite magma is larger than that of hydrous peridotite magma the partial molar volume of co 2 in magma under high pressure and temperature conditions was calculated and fit using the vinet equation of state the isothermal bulk modulus was k t0 8 1 1 7gpa and its pressure derivative was k 0 7 2 2 0 at 2000 k our results show that the partial molar volume of co 2 is less compressible than that of h 2 o suggesting that on an equal molar basis co 2 is more effective than h 2 o in reducing peridotite melt density at high pressure

high pressure equation of state of molten anorthite and diopside new hugoniot equation of state data for molten diopside at 1773 k and molten anorthite at 1923 k are reported to 38 and 35 gpa respectively the diopside data initial density 2 61 mg m 3 are described by a straight line fit to the shock velocity particle velocity results of u s 3 30 1 44 u p km s 1 and our preferred fit to the anorthite data initial density 2 55 mg m 3 is given by u s 2 68 1 42 u p km s 1 reduction of the data to a third order birch murnaghan isentrope assuming the gruneisen ratio times the density is a constant and the mie gruneisen equation of state gives k 0s 22 4 gpa and k s 6 9 for diopside for anorthite we calculate k 0s 17 9 gpa and k s 5 3 the present data for diopside are used to calculate the diopside solidus at high pressures we expect the solidus to be shallow above 10 gpa but the lack of data on the variation of either the gruneisen parameters of the liquid and crystal or the heat capacity and thermal expansion at elevated pressures makes extrapolation of fusion curves uncertain solidus temperatures of 2400 2500 k and 2560 2705 k for diopside are calculated at 10 and 20 gpa respectively the new data are combined with those of rigden et al 1988 for the di 0 64 a 0 36 eutectic composition to examine the degree to which such liquids mix ideally with respect to volume up to 25 gpa for the eutectic composition at 1400 c we calculate the volumes of the an and di mix nearly ideally to 25 gpa we find that the ratio of the partial molar volumes of the oxides in silicate melts to that of the crystal oxides at 1673 k and 1 atm is 1 0 0 1 for a wide range of oxide components for the low pressure tetrahedrally coordinated oxides e g sio 2 al 2o 3 fe 2o 3 the ratio is 1 3 with respect to oxides such as stishovite corundum and hematite in which the cations are octahedrally coordinated by oxygens if changes in coordination of al and si from tetrahedral at low pressures to octahedral at high pressures occur in melts they do so gradually over an interval of 40 gpa although 1 atm bulk moduli for a wide compositional range of silicate melts are similar the differences in integrated compression to mixed oxide like high pressure configurations are reflected mainly by variations in k t k t is found to vary inversely with fraction of network forming initially tetrahedrally coordinated cations e g al 3 si 4 thus k t which may be uncertain by 1 5 is estimated to vary from 7 for molten anorthite enstatite and diopside to 8 for molten ferrosilite to 10 for molten forsterite and to 11 for molten fayalite

palaeosol development in the chinese loess plateau as an indicator of the strength of the east asian summer monsoon evidence for a mid holocene maximum the interpretation of the stalagmite delta o 18 record from southern china as an indicator of east asian summer monsoon easm rainfall amount or intensity is strongly debated soil development in the chinese loess plateau clp situated in the modern summer monsoon domain has long been treated as a direct and reliable easm proxy in this study we compiled 81 loess and 229 palaeosol dates from 77 profiles across the clp and synthesized the data statistically in order to investigate the easm history during the holocene the resulting history of holocene loess deposition and palaeosol development demonstrates that 1 loess deposition decreased and palaeosol formation increased across the clp after 11 5 ka 1 ka 1000 cal yr bp revealing a gradually intensified easm during the early holocene 2 numerous palaeosols developed in the clp between 8 8 ka and 3 4 ka indicating a generally strong easm during the mid holocene 3 the number of palaeosol dates decreased rapidly at around 3 ka suggesting a sudden retreat of the easm in the late holocene these trends of easm evolution are broadly consistent with variations in aeolian sand activity in the four main sandlands the mu us otindag horqin and hulun buir sandlands along the modern monsoon fringe in northern china and are supported by a wide range of independent evidence in addition we also found that high loess deposition and stronger aeolian activity occurred at similar to 5 ka representing a weak easm event within the context of an overall strong mid holocene easm the strong mid holocene easm revealed by palaeosol development in the clp and aeolian sand activity in the sandlands in northern china contrasts with the early holocene easm maximum suggested by stalagmite delta o 18 data from southern china our results are compatible with the proposal that the stalagmite delta o 18 variations in china do not result from changes in easm rainfall amount or intensity but instead reflect changes in moisture source driven by variations in atmospheric oceanic circulation c 2014 elsevier ltd and inqua all rights reserved

the density of andesitic melts and the compressibility of dissolved water in silicate melts at crustal and upper mantle conditions abstract many magmatic processes including the extraction of partial melts fractional crystallization and buoyancy overpressure depend on the density of the silicate melt phase because of its low molecular weight water has a disproportionately large effect on melt density and accurate data on the effect of water on melt density is required to model density dependent processes however the volumetric properties of the hydrous component at crustal and mantle conditions remain debated in this study we determined the density of dry and hydrous 0 9 wt h2o haplo andesitic melts from 0 7 to 4 0 gpa and 1600 to 1930 k using the x ray absorption method in a paris edinburgh press to determine the partial molar volume of water at high pressure our in situ data were combined with atmospheric pressure data to derive the first experimental equation of state for andesitic melts valid for crustal and subduction zone conditions with k t 17 2 gpa and k 6 3 2 5 3 3 at 1273 k in addition the partial molar volume and compressibility of dissolved water in andesitic melts were derived from the in situ data with v 0 19 2 1 9 2 4 cm 3 mol k t 2 7 2 2 7 6 gpa and k 3 6 2 7 13 5 at 1273 k combined with available literature data for other melt compositions our results support a compositionally independent partial molar volume of water in silicate melts at least within the currently attainable precision of the in situ measurements this observation greatly simplifies the construction of future models for magma density

the effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach this paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement intensity of sand transport by wind and mass flux the experiment was carried out over a period of five weeks at greenwich dunes prince edward island canada in may and june 2002 moisture content was measured with a delta t moisture probe over a 50 m by 25 m grid established on the beach measurements of wind speed and direction were made with arrays of cup anemometers and a two dimensional sonic anemometer transport intensity was measured at a height of 2 4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal anemometers and saltation probes were sampled at 1 hz sand transport was measured with vertical integrating sand traps over periods of 10 20 minutes results show that where there is a considerable supply of dry sand the saltation system responds very rapidly 1 2 s to fluctuations in wind speed i e to wind gusts where sand supply from the surface is limited by moisture mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind mass flux increases with increasing fetch length and the relationship is described best by a power function further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance copyright 2007 john wiley sons ltd

static compression and olivine flotation in ultrabasic silicate liquid piston cylinder techniques have been used to observe static compressions of ultrabasic silicate liquids to 6 gpa and 2000 c compressions are measured by bracketing sinking and floating of olivine crystals of known density at run conditions komatiite peridotite and their liquid mixtures with fe2sio4 all show constant density changes with pressure of 0 07 g cm3 gpa along their liquidi these results confirm shock wave studies and ultrasonic studies which show weak compositional effects on compressibility of basic to ultrabasic silicate liquid the techniques converge in supporting the conjecture of stolper et al 1981 that ultrabasic silicate liquids may be denser than their equilibrium coexisting olivines and pyroxenes at high compressions the pressure of this density inversion is 7 8 gpa for the compositions studied olivine flotation provides an important constraint upon earth evolution models that include extensive melting during early differentiation it also provides a mechanism for concentrating high mg si olivine in the upper mantle without unduly perturbing other geochemical parameters a full evaluation of the physical and geochemical consequences is required at an early date