vegetation and climate change since 14 810 14c yr b p in southeastern uruguay and implications for the rise of early formative societies abstract this article presents a combined pollen and phytolith record of a 1 70 m sediment core from the wetlands of india muerta 33 42 s 53 57 w in the lowland pampa grasslands of southeastern uruguay six 14c dates and the pollen and phytolith content of the samples permitted the recognition of four distinct climatic periods between 14 850 14c yr b p and the present the late pleistocene period between ca 14 810 and ca 10 000 14c yr b p was characterized by drier and cooler conditions indicated by the presence of a c3 dominated grassland these conditions prevailed until the onset of the warmer and more humid climate of the holocene around 9450 14c yr b p the early holocene between around 10 000 and 6620 14c yr b p was characterized by the establishment of wetlands in the region as evidenced by the formation of black peat the increase in wetland taxa and the replacement of c3 pooideae by c4 panicoideae grasses during the mid holocene around 6620 14c yr b p began a period of environmental change characterized by drier climatic conditions which resulted in the expansion of halophytic communities in the flat low lying areas of the wetlands of india muerta about 4020 14c yr b p a massive spike of amaranthaceae chenopodiaceae coupled with a radical drop in wetland species indicates another major and more severe period of dryness after ca 4000 14c yr b p a decrease of halophytic species indicates the onset of more humid and stable climatic conditions which characterized the late holocene the findings reported in this article substantially improve our knowledge of the late glacial and holocene climate and vegetation in the region the data provide a detailed record of the timing and severity of mid holocene environmental changes in southeastern south america significantly the mid holocene drying trend coincided with major organizational changes in settlement subsistence and technology of the pre hispanic populations in the region which gave rise to early formative societies this study also represents the first combined pollen and phytolith record for southeastern south america reinforcing the utility of phytoliths as significant indicators of long term grassland dynamics

a multi proxy approach to paleoenvironmental changes in the southwestern rio de la plata area argentina during late pleistocene abstract in the southwestern margin of the rio de la plata argentina mining works have uncovered deposits that correspond to the last glacio eustatic cycle

experimental study of mineral equilibria in the system k2o li2o al2o3 sio2 h2o hf at 300 to 600 c and 100 mpa with application to natural greisen systems we present the results of experimental studies on mineral and phase transformations in the model system k 2 o li 2 o al 2 o 3 sio 2 h 2 o hf at 300 to 600 c and 100 mpa using the method of univariant assemblages the phase diagrams involve equilibrium curves among topaz andalusite muscovite pyrophyllite alf 3 and k n alf 3 n built from our experiments which have allowed us to determine the topaz stability field topaz is stable in solutions with hf concentrations from 3 10 3 to 8 10 1 m and with kf concentrations lower than 7 5 10 3 m as temperature increases topaz becomes stable at higher hf concentrations application of the results to the akchatau greisen w mo deposit provides an explanation of the observed zonation as a manifestation of metasomatic processes and imposes constraints on the mechanism and conditions of formation of the akchatau deposit as well as on the compositions of the f rich fluids participating in the greisenization

a multi proxy study of holocene environmental change recorded in alluvial deposits along the southern coast of the pampa region argentina analyses of fossil records of molluscs stable isotopes of carbon and oxygen diatoms and palynomorphs from alluvial deposits at arroyo claromeco in the southern pampa region of argentina provide an integrated reconstruction of rapid holocene environmental change related to marine and palaeoclimate influences the major events recorded include i disturbances produced by marine influences in close proximity to the coast before ca 7700 cal a bp ii a short term decrease in salinity associated with freshwater influx between ca 7700 and 7400 cal a bp in response to eustatic adjustment as sea level rose iii an increasing input of marine water related to the holocene sea level highstand and greater evaporative conditions between 7400 and 6450 cal a bp and iv evaporative processes linked to a pronounced climatic variability that triggered changes in water chemistry during the last ca 6000 cal a bp concurrently with the late holocene sea level fall a comparison of coastal and continental stable isotope records from the pampa region reveals that evaporation and a negative precipitation evaporation p e ratio balance strongly influenced water chemistry in the coastal region and was as important an influence as marine water during the period of maximum sea level highstand copyright 2014 john wiley sons ltd

holocene vegetation changes along the southeastern coast of the argentinean pampa grasslands in relation to sea level fluctuations and climatic variability palynological analysis of alluvial sequences from arroyo claromeco abstract here we present palynological records from alluvial deposits in four outcrop sequences along the lower reaches of arroyo claromeco buenos aires province argentina 38 50 s latitude 60 05 w longitude these data indicate development of soils and grasslands with associated halophytic vegetation in the higher elevations of the floodplains between ca 7200 and 6000 14 c yr bp ca 8000 and 7000 cal yr bp at lower elevations halophytic saltmarsh vegetation was replaced by wetland communities sedges in response to a sea level highstand at 6500 14 c yr bp ca 7400 cal yr bp soils were buried by expanding wetlands at ca 6000 14 c yr bp a trend that persisted until ca 3400 14 c yr bp ca 3700 cal yr bp over this interval we observe repeated fluctuations between grassland and halophytic vegetation in response to variations in water level and physical chemical conditions resulting from desiccation or flooding events these variations are caused by hydrologic variability in a subhumid dry climatic mean state channel incision occurred between ca 3400 and 2500 14 c yr bp ca 3700 3200 cal yr bp concurrent with sporadic and intermittent sediment deposition at higher elevations of the floodplain the pollen record from the paleochannel infilling indicate grasses accompanied by halophytic taxa between ca 2500 and 800 14 c yr bp 3200 and 700 cal yr bp deposited in a shallow brackish to fresh water body the palynological spectra from sediments deposited sporadically at higher elevations show halophytic vegetation and a trend toward wetland desiccation followed by development of psammophytic communities after ca 1100 14 c yr bp the tops of the alluvial sequences are covered by sand dunes whose modern spectra are characterized by psammophytic vegetation along with exotic tree taxa our results and inferences are consistent with previous studies and provide more detailed insights into the impacts of holocene sea level and climatic variations aspects that are relevant for the coastal pampa grasslands under various scenarios in a warming world

the relationship between emergence of mound builders in se uruguay and climate change inferred from opal phytolith records abstract the strong correspondence between the spatial arrangement of archaeological sites and wetland environments is one of the main axes of the merin lagoon basin archaeology without implying a deterministic simplification from the epistemological point of view the cultural and environmental history of the region hold evidence suggesting a more complex scenario where cultural responses to climate change were not so mechanical or direct as previously argued the relationship between paleoclimate and prehistoric mound builders development between 7 0 and 0 6 ka 14 c bp was studied in se uruguay paleoclimatic data were inferred from the phytolith record of three lagoon sediment cores four paleoclimatic periods were identified according to temperature humidity changes the first period dated at 7 0 4 5 ka 14 c bp was characterized by a warm humid climate between 4 5 and 3 5 ka 14 c bp the onset of a cool dry climate was inferred a hiatus between 3 5 and 2 6 ka 14 c bp was identified in the third period 2 5 1 2 ka 14 c bp similar climate conditions to those of the present were inferred finally the period 1 2 and 0 6 ka 14 c bp was characterized by warmer and wetter conditions than those of the present according to these data it was determined that mounds were first observed during the transition from warm humid to cool dry conditions but the complexity of the mounds increased after the full establishment of cool dry conditions with the inception of warm humid conditions an increased number of mounds was observed in the plains located close to the merin lagoon littoral the mounds showed lower density and height than those recorded for the cool dry period this behavioral modification in mound construction was explained because of the paleoenvironmental change

fluid inclusion evidence for immiscibility in magmatic differentiation abstract after a brief review of recent work on melt inclusions in diamond and in normal magmatic environments the nature of the fluid inclusion evidence for various stages of magmatic immiscibility is summarized during magmatic differentiation by crystal fractionation from originally low volatile content silicate melts yielding normal plutonic rocks through hydrous silicate melts yielding pegmatites to late stage water rich fluids yielding quartz veins and ore deposits the composition of the residual liquid changes drastically in some geologic environments this change in composition of the residual liquid may be continuous with no phase change in the fluid part of the system under most natural conditions however it is far more likely to have one or more stages in the evolution during which globules of a separate new immiscible fluid phase exsolve the term immiscibility is used here in its more general sense to refer to the existence at equilibrium of two or more non crystalline polycomponent solutions fluids differing in properties and generally in composition i believe that the great bulk of the magmatic inclusions that are being studied today have come about through the intervention of one or more such stages of immiscible fluid separation i e magmatic differentiation by fluid immiscibility examples include silicate melt dense co2 fluid silicate melt sulfide melt silicate melt silicate melt silicate melt low density vapor i e vesiculation and as presented in more detail in this paper various stages of silicate melt hydrous saline melt aqueous fluid co2 fluid immiscibility generally only parts of these stages are recorded by the trapping of fluid inclusions and the interpretation of the inclusion record is commonly ambiguous and difficult particularly that stage between hydrous silicate melts and the hydrous saline melts and aqueous solutions responsible for many ore deposits the ambiguity results mainly from problems of inclusion origin and nonrepresentative trapping within any given individual inclusion thus the probability of trapping of only one vs various amounts of two immiscible fluids or of trapping solid phases along with the fluid present severe difficulties in addition there is the almost universal superposition of various stages of trapping of fluids within any given sample these problems can only be approached by very careful petrography and analysis of optimum material combined with field data and experimental p v t x studies of pertinent systems completely unequivocal statements of the course of evolution of the fluids in such natural systems may never be possible

elasticity of mgsio3 in the ilmenite phase abstract the single crystal elastic moduli of the ilmenite phase of mgsio 3 have been determined from brillouin spectroscopy they are c 11 472 c 12 168 c 33 382 c 13 70 c 44 106 c 14 27 c 66 152 and c 25 24 in gpa these elastic properties are consistent with a structural mechanical model where the silicon octahedra are very stiff under compression and shear this latter property yields an unexpectedly high shear modulus for the magnesium silicate ilmenite as compared with analogue compounds the further transformation to perovskite will probably be associated with a significant increase in elastic properties since the strong silicon polyhedra form a structural network in this phase the transformation of spinel and stishovite to ilmenite is associated with a slight density increase and a slight decrease in acoustic velocities this transformation will probably not produce a seismic discontinuity even if it does occur in the earth s mantle

source and partitioning of b and sn in the cornubian batholith of southwest england abstract emplacement of the variscan s type cornubian batholith initiated the formation of the historical world class sn and cu deposits and extensive tourmalinisation of southwest england the hypothesis is tested that the sn and tourmaline mineralisation were wholly formed by magmatically derived hydrothermal fluids with no requirement for a contribution from the stripping of country rocks by circulating hydrothermal fluids from simple geochemical modelling sufficient sn concentrations to match those in the main 90 of granite outcrop biotite granites average of 23 mg kg and to produce the large sn deposits can be derived by partial melting of pre granite southwest england crust at geologically realistic levels of partial melting 30 fractionation 10 to 50 and melt aqueous fluid partitioning assumed to be 6 wt of the mass of the granite batholith in contrast insufficient b 700 mg kg or b concentrations found in many of the granites we conclude that tourmaline in the biotite granites was formed from magmatically derived hydrothermal fluids which emanated as a result of first and possibly second boiling an additional source of b for the hydrothermal fluids may have been the devolatilisation of stoped blocks of country rock mudstones these findings provide fundamental constraints on the evolution of the cornubian batholith which is used as a model for a large number of sn provinces worldwide

radiocarbon dating of soil organic matter radiocarbon ages of soil organic matter are evaluated with a model which incorporates the dynamics of the14c content of soil organic matter measured14c ages of soil organic matter or its fractions are always younger than the true ages of soils due to continuous input of organic matter into soils differences in soil c dynamics due to climate or soil depth will result in significantly different14c signatures of soil organic matter for soils of the same age as a result the deviation of the measured14c age from the true age of soil formation could differ significantly among different soils or soil horizons our model calculations also suggest that14c ages of soil organic matter will eventually reach a steady state provided that no climatic or ecological perturbations occur once a soil or a soil horizon has reached a steady state 14c dating of soil organic matter will provide no useful information regarding the age of the soil however for soils in which steady state has not been reached it is possible to estimate the age of soil formation by modeling the measured14c contents of soil organic matter radiocarbon dating of buried soils could in general overestimate the true age of the burial by as much as the steady state age of the soil or soil horizon

the composition of hypersaline iron rich granitic fluids based on laser icp and synchrotron xrf microprobe analysis of individual fluid inclusions in topaz mole granite eastern australia abstract high temperature 550 c hypersaline 50 wt salts fluid inclusions representative of the earliest hydrothermal fluids associated with the sn w cu pb zn mineralised mole granite of eastern australia are well developed in topaz from the fielders hill locality methods based on inductively coupled plasma emission spectroscopy following laser ablation and on synchrotron x ray fluorescence microanalysis are described and applied to the semiquantitative point analysis of these inclusions crushleach analysis provides further information as well as highlighting the importance of point methods when several generations of inclusions are present the laser icp results confirm the dominance of fe k and na in these early high temperature fluids the mean fe k na atomic ratios 0 95 0 79 1 00 are entirely in agreement with published experimental data on the composition of chloride brines in equilibrium with synthetic granite at magmatic temperatures and support the view that these fluids are direct products from a cooling granite magma a number of trace and minor elements have also been detected in the inclusions these include ca mg li b be ba sr and several of the ore metals order of magnitude estimates of the ore metal contents of these fluids based on combined xrf microprobe and laser icp analysis are in the percent range for fe mn and zn in the range from several hundred to several thousand ppm in the case of sn cu and pb and less than 600 ppm for mo and w these results have important implications for ore genesis in granitic environments and point to the very high ore carrying potential of high temperature hypersaline chloride rich brines exsolved from cooling granite magmas

pedosedimentary and palaeoenvironmental significance of a holocene alluvial sequence in the southern pampas argentina a representative section of the holocene alluvial record of the southern pampas argentina com prises a sequence of clastic sediments a diatomite and two palaeosols detailed macro and micromorphological descriptions provide the basis for the reconstruction of its pedosedimentary history combining the pedosedi mentary reconstruction with palaeoecological data allows a detailed overview of alluvial landscape development and associated palaeoenvironmental change in the region during the holocene the early holocene shift from a subhumid dry to humid climate was marked initially by a diminution in clastic sedimentation the development of the puesto callejon viejo soil and then re establishment of fluvial aggradation with a dominance of bioclastic sedimentation loess inputs increased during the mid holocene as the climate reverted to subhumid dry and temporary subaerial exposure of the sediments led to the formation of the puesto berrondo soil more variable environmental conditions followed with natur

stability of anhydrous phase b experimental studies and implications for phase relations in subducting slab and the x discontinuity in the mantle 1 we have experimentally determined the equilibrium boundary of the reaction forsterite fo periclase per anhydrous phase b anh b at 900 1600 c and we used the retrieved gibbs free energy of formation of anh b to calculate the stability field of anh b stishovite sti with respect to the mg2sio4 polymorphs the results suggest the possibility of the reaction sequence wadsleytite anh b sti ringwoodite with increasing pressure at temperature below 600 c this might lead to an eye shaped splitting of the 410 km discontinuity within the interior of a sufficiently cold slab such as would prevail in a 140 myr old slab subducting at an angle of 60 with a rate of 14 cm yr e g tonga the equilibrium boundary of anh b sti with respect to the wadsleyite and ringwoodite has respectively positive and negative slope in the p t space the reaction of fo per to anh b seems to offer a viable explanation of the so called x discontinuity that has been observed at 275 345 km depth in several subcontinental and subduction zone environments it is suggested that periclase could form locally by the dissolution of silica in mantle fluid or precipitate from a hydrous melt that became enriched in mgo due to the incongruent melting of olivine at pressures of 6 8 gpa

liquidus equilibria in the system k2o na2o al2o3 sio2 f2o 1 h2o to 100 mpa ii differentiation paths of fluorosilicic magmas in hydrous systems we investigated phase equilibria in the six component system na2o k2o al2o3 sio2 f2o 1 h2o at 100mpa to characterize differentiation paths of natural fluorine bearing granitic and rhyolitic magmas topaz and cryolite are stable saturating solid phases in calcium poor systems at 100mpa the maximum solidus depression and fluorine solubility in evolving silicic melts are controlled by the eutectics haplogranite cryolite h2o at 6408c and 4 wt f and haplogranite topaz h2o at 6408c and 2 wt f topaz and cryolite form a binary peralkaline eutectic at 6608c 100mpa and fluid saturation the low temperature nature of this invariant point causes displacement of multiphase eutectics with quartz and alkali feldspar towards the topaz cryolite join and enables the silicate liquidus and cotectic surfaces to extend to very high fluorine concentrations more than 30 wt f for weakly peraluminous and subaluminous compositions the differentiation of fluorine bearing magmas follows two distinct paths of fluorine behavior depending on whether additional minerals buffer the alkali alumina ratio in the melt in systems with micas or aluminosilicates that buffer the activity of alumina magmatic crystallization will reach either topaz or cryolite saturation and the system solidifies at low fluorine concentration in leucogranitic suites precipitating quartz and feldspar only the liquid line of descent will reach topaz or cryolite but fluorine will continue to increase until the quaternary eutectic with two fluorine bearing solid phases is reached at 5408c 100mpa and aqueous fluid saturation the maximum water solubility in the haplogranitic melts increases with the fluorine content and reaches 12 5 0 5 wt h2oat the quartz cryolite topaz eutectic composition a continuous transition between hydrous fluorosilicate melts and solute rich aqueous fluids is not documented by this study our experimental results are applicable to leucocratic fluorosilicic magmas in multicomponent systems however the presence of calcium may severely limit enrichment of fluorine by crystallization of fluorite

earth mineralogical model gibbs free energy minimization computation in the system mgofeosio2 abstract a thermodynamic database which is consistent with most available phase equilibrium experiments and calorimetric and physical measurements on the solids in the system mgo feo sio 2 is established for the phases with the compositions mg fe sio 3 garnet perovskite pyroxene and ilmenite mg fe 2 sio 4 olivine and phases sio 2 stishovite and coesite and mg fe o periclase and wustite the data are systematized by using the high temperature birch murnaghan equation of state which includes the pressure and temperature dependent bulk modulus k and temperature dependent thermal expansion of the solids the systematized thermodynamic data contains heat capacity c p data which is internally consistent with the data on k volume and temperature such a systematized database is used to calculate by the method of minimization of gibbs free energy the mineralogical composition of the peridotitic pyrolitic and chondritic mgo feo sio 2 mantles the model corresponds closely to the seismological prem preliminary earth reference model in predicting the major seismic discontinuities however such discontinuities resulting from reactions or phase transformation are not as sharp as the seismic ones calculated adiabatic geothermal gradient starting at 6 gpa and 1500 k reaches a temperature of 2046 k at the core mantle pressure 135 gpa in a pyrolite mantle the model earth parameters in the lower mantle are prem parameters in bracket k s 308 306 to 687 656 gpa 70 69 to 121 118 km 2 s 2

kinetics of the olivine ringwoodite transformation and seismic attenuation in the earth s mantle transition zone abstract in regions of the mantle where multi phases coexist like at the olivine wadsleyite ringwoodite transitions the stress induced by the seismic waves may drive a mineralogical reaction between the low to high pressure phases a possible source of dissipation in such a situation the amount of attenuation critically depends on the timescale for the phase transformations to reach equilibrium relative to the period of the seismic wave here we report synchrotron based measurements of the kinetics of the olivine to ringwoodite transformation at pressure temperature conditions of the co stability loop for iron rich olivine compositions both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries transformation time data show an increase of reaction rates with temperature and iron content and have been fitted to a rate equation for interface controlled transformation g k 0 t exp n x fa exp h a p v r t 1 exp g r r t where x fa is the fayalite fraction the exponential factor n 9 7 ln k 0 9 1 m s 1 x fa 1 and h a 199 kj mol assuming v 0 cm 3 mol including these new kinetic results in a micro mechanical model of a two phase loop ricard et al 2009 we predict q k 1 and q 1 significantly higher than the prem values for both body waves and normal modes this attests that the olivine wadsleyite transition can significantly contribute to the attenuation of the earth s mantle transition zone

a petrologic assessment of internal zonation in granitic pegmatites abstract cameron et al 1949 devised the nomenclature and delineated the patterns of internal zonation within granitic pegmatites that are in use today zonation in pegmatites is manifested both in mineralogy and in fabric mineral habits and rock texture although internal zonation is a conspicuous and distinctive attribute of pegmatites there has been no thorough effort to explain that mineralogical and textural evolution in relation to the zoning sequence presented by cameron et al 1949 or in terms of the comprehensive petrogenesis of pegmatite bodies pressure temperature and whole rock composition this overview of internal zonation within granitic pegmatites consists of four principal parts 1 a historic review of the subject 2 a summary of the current understanding of the pegmatite forming environment 3 the processes that determine mineralogical and textural zonation in pegmatites and 4 the applications of those processes to each of the major zones of pegmatites based on the concepts presented in london 2008 the fundamental determinates of the internal evolution of pegmatite zones are 1 the bulk composition of melt 2 the magnitude of liquidus undercooling prior to the onset of crystallization 3 subsolidus isothermal fractional crystallization by which eutectic or minimum melts fractionate by sequential non eutectic crystallization 4 constitutional zone refining via the creation of a boundary layer liquid chemically distinct from but continuous with the bulk melt at the crystallization front and 5 far field chemical diffusion the long range and coordinated diffusion of ions particularly of alkalis and alkaline earths through melt

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

a review of late quaternary inland dune systems of south america east of the andes abstract inland dune systems of south america occur in a variety of environmental settings under different climatic conditions from humid subhumid to semiarid arid this contribution provides the state of the art on dune research of inland systems east of the andes tropical northern 10 n 10 s including the dune fields of llanos del orinoco and the amazonian basin are mainly formed from parabolic blowout or deflation basins and linear dunes developed on river floodplains aeolian activity was reported to occur near the late pleistocene holocene boundary in llanos del orinoco over the last 17 ka in the branco river basin and 32 6 ka in the negro river basin both in the amazonian region in general the attributed aeolian origin is controversial the morphology difficult to determine and the chronology still extremely limited and rather debatable in some cases the southern tropical region 10 s 22 s includes aeolian systems situated across the extensive lowlands of the gran chaco and those located in fluvial basins related to the cratonic brazilian shield sao francisco river pantanal and mato grosso the oldest barchanoid barchan ridges at the gran chaco were dated 36 33 ka and subsequent aeolian sand accumulation occurred at 18 ka 14 12 ka 10 9 ka and mid to late holocene times parabolic dunes at the sao francisco river floodplain show an oldest episode generated between 28 and 11 ka followed by eolian activity during the early to mid holocene no chronological data is available for the linear and lunette dunes described at the pantanal linear ridges were distinguished in the upper parana river mato grosso with associated sand accumulation at different intervals of the holocene the last reviewed region is the andean piedmont and western pampas at subtropical eastern south america comprising a large variety of dune morphologies barchan barchanoid linear parabolic transverse and lunette dunes deflation basins and sand sheets luminescence ages suggest the occurrence of aeolian activity intervals during late glacial times and the holocene the general understanding on the dynamic of south american dune systems is hampered by the paucity of chronological information and the representativeness of some dune records whether they reflect local or regional environmental conditions is still a matter of discussion in several areas that need further studies

chemical variation and significance of tourmaline from southwest england tourmaline is a common and locally abundant mineral in all products of the granite magmatism and associated hydrothermal activity in southwest england particularly in the county of cornwall tourmaline of magmatic origin is homogeneous and is marked by high fe mg high f and high al in the place of divalent cations r2 site the substitution of al for divalent cations such as mg and fe super 2 is charge compensated by a deficit of alkalies and protons in other structural sites tourmaline compositions from the granites clearly reflect the sequence of increased differentiation among the magma types with biotite granites as the least evolved and topaz granites as the most evolved in contrast tourmaline of hydrothermal origin within granites displays fine scale compositional zonation with a general tendency toward more magnesian compositions nearer the schorl dravite solid solution i e little or no al in the r2 site metasomatic tourmaline precipitated in the surrounding pelitic and mafic rocks also possesses fine scale zonation and generally reflects the compositions of the host rocks in addition tourmaline formed in the country rocks has a higher proportion of fe super 3 to fe super 2 which presumably indicates a higher oxidation state of fluids in the metamorphic rocks than in the granites this variation may correlate with the mobilization of tin from the granites and its consequent deposition as cassiterite in the host rocks the abundance of magmatic tourmaline is limited by the initial fe mg content of the magmas to not more than a few modal or weight percent although they contain tourmaline the biotite granites are not the most likely sources of boron for voluminous late stage tourmalinization magmas that contained only tourmaline or no fe mg minerals at all such as the those that formed the topaz granites may have been sources of large quantities of boron the most intense areas of tourmalinization do surround the small stocks and sheets of topaz microgranite high concentrations of tourmaline for example in hydrothermal veins and breccias appear to require mixing of two different chemical reservoirs one a source of boron the magmas or fluids

fluid fluid interactions in magmatic hydrothermal ore formation hydrothermal ore deposits have provided some of the first geological evidence for the interaction of multiple fluids in the earth s interior including fluid mixing as well as fluid phase separation physical evidence comes from veins and breccias documenting the impact of fluids in breaking rocks and creating fracture permeability for ore formation as a result of the fluid expansion that is commonly associated with phase separation between melts and multiple fluids chemical evidence of fluid fluid interaction includes the precipitation of minerals in veins as a result of fluid boiling or mixing between chemically contrasting fluids fluid inclusions record interactions of multiple fluids especially in magmatic hydrothermal ore deposits and associated igneous rocks fig 1 in recent years fluid inclusions have contributed to a more quantitative understanding of the role of fluid fluid interactions since new microanalytical techniques allow determination of element concentrations in all types of fluids from low density vapor through aqueous and hypersaline liquids to hydrous salt melts roedder 1984 samson et al 2003 figure 1 geological evidence for fluid phase separation in ore forming magmatic hydrothermal systems a bonanza grade gold 1 wt that was precipitated together with fine grained pyrite in a fluidized breccia resulting from instantaneous boiling and expansion of magmatic fluids ascending from an underlying andesite porphyry intrusion the breccia consists of adularia sericite altered clasts of sedimentary wall rock s and nodules of originally colloidal pyrite with bright specks of gold p g both cemented by roscoelite r vanadium rich muscovite and late calcite c zone vii ore body porgera papua new guinea ronacher et al 2004 b bladed manganocalcite the characteristic habit of calcite precipitated from aqueous epithermal fluids as a result of the ph change following loss of co2 to a separating vapor phase madan bulgaria kostova et al 2004 c growth band in a euhedral quartz

silica hydrate preserved with δ18o rich quartz in high temperature hydrothermal quartz in the high sulfidation copper gold deposit at el indio chile quartz microcrystals from the el indio au ag cu deposit chile preserve a rare glimpse into the high temperature evolution of silica here we show for the first time that aggregates of euhedral quartz microcrystals preserve cryptocrystalline cores that contain silica hydrates opal and moganite we propose that these phases are metastable remnants of progressive dehydration from a precursor silica hydrate phase evidence for sequential dehydration to from silica hydrate to quartz silica hydrate opal moganite quartz is provided by shrimp 18o microanalytical data that show oscillatory isotopic zoning from 3 6 to 16 2 18o 0 5 coupled with k and al variations we estimate that the precursor silica hydrate deposited between 480 680 c and contained 32 63 wt h2o silica hydrate is metastable with respect to quartz and forms during rapid deposition of silica at high silica supersaturation a consequence of rapid expansion of magmatic fluid into the fracture array that hosts the el indio copper gold deposit modern understanding of ore forming fluids in hydrothermal ore deposits is largely underpinned by the assumption that quartz and its included fluids faithfully record depositional conditions the discovery of silica hydrate affects the paragenetic and geochemical interpretation of quartz and included fluids quartz matured from silica hydrate would record pseudo primary fluid inclusions such that homogenization temperatures record retrograde rather than depositional conditions while 18o data may bias fluid provenance interpretation within sub volcanic systems

a fluid inclusion investigation of ore formation in a tin mineralized granite new england new south wales primary fluid inclusions have filling temperatures from 550 degrees to more than 620 degrees c and salt contents of 54 to 65 wt percent daughter crystals in multiphase inclusions were mostly halite and other chlorides above a temperature of 400 degrees c the hydrothermal solutions were two phase fluid inclusion measurements and chemical analyses indicate two stages of hydrothermal activity in stage one in which heat was dispersed but not dissolved salts the temperature decreased by 200 degrees c while the salt content increased in stage two dissolved salts were dispersed more rapidly than heat and fluid inclusion evidence indicates a decreasing incidence of vapor in the hydrothermal system formation of major fractures occurred at the transition from stage one to stage two of hydrothermal activity fracturing accelerated condensation of vapor and mixing of magmatic brine and ground water most of the tin and tungsten ores were precipitated during the decrease in salt content of the concentrated brine modified journal abstract

a mineralogical model for density and elasticity of the earth s mantle 1 we present a thermodynamic model of high pressure mineralogy that allows the evaluation of phase stability and physical properties for the earth s mantle the thermodynamic model is built from previous assessments and experiments in the five component cfmas system cao feo mgo al2o3 sio2 including mineral phases that occur close to typical chemical models of the mantle and reasonable mantle temperatures in this system we have performed a system gibbs free energy minimization including pure end member phases and a nonideal formulation for solid solutions solid solutions were subdivided into discrete pseudocompounds and treated as stoichiometric phases during computation of chemical equilibrium by the simplex method we have complemented the thermodynamic model with a model of shear wave properties to obtain a full description of aggregate elastic properties density bulk and shear moduli that provide a useful basis for the consideration of seismic and geodynamic models of the earth s mantle the thermodynamic model described here is made available for research and training purposes through a web interface http www earthmodel org we examine its validity in light of experiments from mineral physics and briefly discuss inferences for mantle structure

quaternary mammalian faunas of the pampean region abstract knowledge of the fossil mammals from the pampean region of argentina has greatly increased in recent years to analyze the patterns of change in regional climates and environments through the quaternary the fossil record of land mammals was used two principal factors affected mammalian diversity in the pampean region during the pleistocene glaciations and the climatic environmental and sea level changes associated with them and the large numbers of north american taxa that immigrated to south america from the pliocene the regional climatic conditions changed from being warm and wet to being colder drier and more seasonal during the pleistocene as a consequence of glacial cycles cold and dry conditions were interrupted by relatively short warmer and wetter periods several pulses of expansion and contraction of steppes and subtropical forests are recorded this change in habitat produced the provincialism that has characterized the mammal faunas from the pampean region finally the most notable characteristic of the quaternary mammal fauna of south america is the almost complete extinction of large mammals during the latest pleistocene earliest holocene the evidence presented here is most consistent with a model that explains megafaunal extinction through climatic fluctuations as it appears that only a few species of large mammals survived until the holocene nevertheless a human presence could have accelerated the process of extinction

implications from inclusions in topaz for greisenisation and mineralisation in the hensbarrow topaz granite cornwall england textural and geochemical studies of inclusions in topaz from greisens in the hensbarrow topaz granite stock st austell cornwall are used to constrain the composition of fluids responsible for late stage greisening and mineralisation the topaz contains an abundant and varied suite of inclusions including aqueous liquid vapour l v quartz zinnwaldite albite k feldspar muscovite ilmenorutile apatite columbite zircon varlamoffite sn fe o oh 2 and qitianlingite fe 2 mn 2 2 nb ta 2w 6o10 primary l v inclusions in topaz show relatively high th mainly 300 to 500 c and a narrow range of salinities 23 30 wt nacl equivalent compared with those in greisen quartz 150 450 c 0 50 wt nacl equivalent textures indicate that topaz formed earlier than quartz and the fluid inclusion data are interpreted as indicating a cooling of the hydrothermal fluids during greisenisation mixing with meteoric waters and a decrease in pressure causing intermittent boiling the presence of early formed albite and k feldspar as inclusions in the topaz is likely to indicate that the greisen forming fluid became progressively more acid during greisenisation the most distinctive inclusions in the topaz are wisp and bleb shaped quartz 50 m in size which show textural characteristics indicating former high degrees of plasticity they often have multiple shrinkage bubbles at their margins rich in sn fe mn s and cl and more rarely contain euhedral albite k feldspar stannite or pyrrhotite crystals up to 40 m in size the quartz inclusions show similar morphologies to inclusions in topaz from quartz topaz rocks elsewhere which have been interpreted as trapped silicate melt their compositions are however very different to those expected for late stage topaz normative granitic melts from their textural and chemical characteristics they are interpreted as representing crystallised silica colloid probably trapped as a hydro gel during greisenisation there is also evidence for the colloidal origin of inclusions of varlamoffite in the topaz these occurrences offer the first reported evidence in natural systems for the formation of colloids in high temperature hydrothermal fluids their high ore carrying potential is suggested by the presence of varlamoffite and the occurrence of stannite pyrrhotite and sncl within the quartz inclusions

vegetational history of the late glacial holocene transition in the grasslands of eastern argentina abstract palynological records from eight sites located in the eastern plains of argentina from the humid pampa in the east to the xerophytic woodland dry pampa ecotone in the west allow a regional reconstruction of the vegetation of late glacial holocene transition fossil pollen records were interpreted in terms of palaeoenvironmental information using the modern pollen vegetation climate relationship as an analogue although an exact analogue does not exist today late glacial vegetation consisted mostly of psammophytic steppe in large areas of the central and south western pampa grassland which in the south west is associated with a shrub steppe suggesting subhumid dry to semi arid climatic conditions the replacement of dry steppe by humid grassland and the rapid evolution of pond environments during the early holocene starting during the late glacial holocene transition suggests a shift towards subhumid to humid climate conditions the late glacial holocene transition is indicated in the pollen records by repeated abrupt changes in the proportions and concentrations of some taxa such as brassicaceae asteraceae and carduus type in the modern vegetation they represent species of common occurrence in human induced disturbance habitats suggesting an environment that was subject to frequent natural disturbance such as rapid and repeated flooding episodes that inundated the depressions along the valley floodplains caused by unusual rainfall events some species of carduus may have been native and not introduced by the europeans suggesting that late glacial vegetation of the pampa grasslands may account for the abundance of ruderal species of special interest is the presence of myrtaceae in some pollen assemblages between 11 000 and 9000 yr b p at present myrtaceae are not part of the natural vegetation in the pampa grassland their presence in the fossil pollen records may be interpreted as local deposition instead of extra regional origin myrtaceae formed part of the psammophytic steppe and after late glacial holocene transition they disappeared from the regional flora perhaps due to the climatic change that occurred at the beginning of the holocene it is the most significant cause of extending the area of some pampa grassland taxa but it may have reduced the area for others of the late glacial vegetation at least myrtaceae were probably not able to adapt to the new habitats and hence disappeared from the regional flora at the pleistocene holocene transition although other plants may have disappeared as well these cannot be identified because pollen from these plants cannot be differentiated morphologically during the late glacial holocene transition communities with no modern counterparts probably formed and disappeared

thermal expansion of wadsleyite ringwoodite hydrous wadsleyite and hydrous ringwoodite abstract the thermal expansions of wadsleyite ringwoodite hydrous wadsleyite and hydrous ringwoodite have been determined by high temperature powder x ray diffraction at ambient pressure wadsleyite and ringwoodite persist up to 700 c and their thermal expansion coefficients are measured as 34 0 5 10 6 and 30 7 6 10 6 k 1 respectively values that are slightly larger than those measured by j phys earth 27 1979 53 j phys earth 28 1980 273 hydrous wadsleyite and hydrous ringwoodite were dehydrated at 450 and 400 c respectively below their dehydration temperatures their thermal expansion coefficients are 30 1 14 10 6 and 27 3 9 10 6 k 1 respectively which are slightly lower than those of their anhydrous forms using the present results combined with the previous thermoelastic data the seismic velocity contrast at the 410 km discontinuity has been calculated for both dry and wet mantle if a pyrolite composition is assumed a hydrous mantle transition zone better explains seismic constraints

indium mineralisation in sw england host parageneses and mineralogical relations abstract the sw england ore region contains significant amounts of indium in in early permian granite related skarn and lode parageneses and to a lesser extent triassic epithermal crosscourse veins ore parageneses that predate granite emplacement devonian and lower carboniferous sedimentary exhalative and vein parageneses are largely devoid of in cadmium cd and gallium ga occur widely in all sulphide bearing parageneses across the region with sphalerite concentrations locally reaching 1 74 wt cd and 1750 ppm ga indium displays a strong affinity to sulphide bearing magmatic hydrothermal parageneses it occurs in silicate sulphide skarns polymetallic sulphide lodes and sulphide bearing portions of greisen bordered sheeted vein systems and quartz tourmaline lodes across the region magnetite silicate skarns and quartz tourmaline lodes that are devoid of sulphide in contrast were comparatively unfavourable for in precipitation the highest in concentrations are found in mineral lodes associated with the carnmenellis and st agnes granites which are the districts that had the highest historical production of sn total in concentrations in these areas locally exceed 430 ppm while concentrations elsewhere are systematically below 200 ppm the principal in hosts are chalcopyrite sphalerite and stannite group minerals with local concentrations within cassiterite and tennantite surprisingly chalcopyrite accounts for the majority of the in budget throughout the region although concentrations are highest in sphalerite and stannite group minerals sphalerite locally contains up to 1 42 wt in chalcopyrite has up to 2200 ppm and stannite group minerals up to 6800 ppm no in was detected in lollingite arsenopyrite rutile haematite magnetite tourmaline biotite chlorite galena bornite chalcocite or pyrrhotite scattered concentrations in pyrite relate to impurities rather than incorporation by solid solution roquesite and possibly dzhalindite or native in formed locally where in bearing chalcopyrite or sphalerite has been replaced by bornite and quartz the in partitioning between sphalerite and chalcopyrite varies broadly between 1 1 and 10 1 sporadic in was included in triassic crosscourse veins as a result of interactions between migrating cacl2 rich basinal brines and earlier formed granite related parageneses the interactions involved at least two distinct components 1 incorporation of clasts of magmatic hydrothermal veins in crosscourse veins during faulting and 2 dissolution and re precipitation of magmatic hydrothermal vein minerals in crosscourse fluids local concentrations reach 140 ppm in the magmatic hydrothermal parageneses in sw england are comparable to the south china tin belt mount pleasant as well as erzgebirge krusne hory magmatic hydrothermal fluids associated with peraluminous granites have developed a variety of skarn greisen lode and veins parageneses by interactions with their host rocks and contained fluids crosscourse epithermal mineralisation occurred as in was transported by cacl2 rich basinal brines in a similar manner as in bearing veins in the west shropshire ore field

stability of majorite mg fe sio3 at high pressures and 1800 c abstract phase relations in the system mgsio 3 fesio 3 were studied experimentally up to a pressure of 24 gpa at 1800 c alumina free tetragonal garnet exists in the pressure range from 16 to 23 5 gpa the compositional range of the tetragonal garnet phase extends from pure mgsio 3 to mg 0 76 fe 0 24 sio 3 at 18 2 gpa and 1800 c the sequence of the phase transitions in mg rich part of this system at 1800 c is clinopyroxene 17gpatetragonal garnet 22 5gpailmenite 23gpamg perovskite the lattice constants of tetragonal garnet increase with increasing iron content from a 11 517 0 002aandc 11 435 0 003afor mgsio 3 toa 11 543 0 002a and c 11 476 0 003a for mg 0 76 fe 0 24 sio 3 cubic garnet was not observed in the pressure and temperature range studied in this work the alumina free tetragonal garnet observed in this study may exist in the harzbergite layer in the descending slab

thermal diffusivity and conductivity of olivine wadsleyite and ringwoodite to 20 gpa and 1373 k abstract we present results of lattice thermal diffusivity measurements on mg0 9fe0 1 2sio4 olivine and its high pressure polymorphs wadsleyite and ringwoodite under mantle conditions we used the angstrom method on cylindrical samples in multianvil apparatus at pressures up to 20 gpa and temperatures up to 1373 k because of the fine polycrystallinity of the specimens 30 40 m or less there is strong scattering absorption of light and suppression of radiative transport so that the lattice vibrational component is the dominant heat transfer mode lattice thermal conductivities were calculated from the thermal diffusivity results using heat capacity and equation of state data olivine thermal conductivities are consistent with previous results obtained at 1 atm e g j am ceramic soc 38 1954 107 j geophys res 77 1972 6966 science 283 1999 1699 thermal conductivity increases by approximately 30 at the transition from olivine to wadsleyite corresponding to the 410 km discontinuity and a further but smaller increase may occur at the transition from wadsleyite to ringwoodite for each of these phases lattice conductivity closely follows a t 1 2 dependence on temperature t phys rev 119 1960 507 j geophys res 79 1974 703 brown 2002 if such a dependence applies to other silicates and complex crystals there should be a useful way to estimate conductivities at high temperatures from room temperature measurements

late pleistocene mollusc assemblages and inferred paleoenvironments from the andean piedmont of mendoza argentina abstract this paper is focused on the paleoecological analysis of a mollusc succession cropping out on the right margin of la estacada stream in the andean piedmont of mendoza argentina 33 28 s 69 03 w the stratigraphic section mainly composed of fine sands interbedded with levels of silty clays and organic matter records the interval between 35 2 35 5 14c ka b p and 31 5 31 6 14c ka b p the mollusc succession is represented by freshwater and land snails biomphalaria peregrina planorbidae lymnaea viator lymnaeidae succinea meridionalis succineidae rotadiscus amancaezensis charopidae and radiodiscus sp aff radiodiscus quillajicola charopidae the dominance of semi aquatic and hygrophilous land snails suggests the development of a vegetated shallow water body probably a damp habitat occasionally submerged with four main stages of evolution related to fluctuating water levels the abundance of shells together with the stable isotope composition of carbonate shells of l viator 13c and 18o and the presence of radiodiscus sp aff radiodiscus quillajicola and r amancaezensis suggest relatively warm and wet conditions based on its radiocarbon chronology and the paleoecological reconstruction the studied section is recording a mild interval corresponding to an interstadial marine isotope stage 3 of the last glacial cycle

petrogenesis of tourmaline granites and topaz granites the contribution of experimental data abstract fluorine and boron are generally only minor components of granitic rocks but may be found highly concentrated in certain tourmaline granites and topaz granites up to 1 wt b2o3 and 3 2 wt f respectively studies of various examples of these granite types which occur as small bodies emplaced at shallow levels p lithostatic textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures below 700 c and that a fluid phase may have been present during the crystallization interval both granites varieties are peraluminous co up to 5 characterized by the presence of white micas lithium micas or muscovite aluminium silicates and other al rich minerals garnet cordierite boron and fluorine are hosted by tourmaline schorl rich member of the schorl dravite series topaz and mica respectively these granites have low ca fe mg and ti contents each the crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine both elements act as a flux enabling boron and fluorine enriched melts to persist to temperatures as low as 650 c at 1 kbar in addition the effect of increasing fluorine content displaces the minimum in q ab or at ph2o 1 kbar toward the albite apex plots of fluorine rich topaz granites coincide with this trend suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures boron rich granites plot near the low ph2o minima in qz ab or suggesting that boron has less of an influence on minimum melt compositions the low temperatures of crystallization permits phases such as muscovite or andalusite topaz and two alkali feldspars to crystallize directly from f and b enriched melts at low pressures in addition the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt vapour interaction

predominance of arid climates indicated by mammals in the pampas of argentina during the late pleistocene and holocene abstract south american climates during the pleistocene and holocene are poorly known especially in the lowlands east of the andean ranges however there is relatively good biostratigraphic and climatic information for the late lujanian and platan local ages latest pleistocene to holocene of the pampas region most of the climatic data from the pampean area are based on land mammal assemblages pollen records and geology contrasting with north american faunal associations there are many non analogue assemblages in the holocene of the pampean area the climate was arid and relatively cold during most of the early lujanian however several relatively wet and warm events are suggested by the presence of subtropical mammals and evidence of tchernozoid paleosoils the late lujanian is well represented by the fossiliferous sediments of the la chumbiada and guerrero members of the lujan formation ca 30 000 and 21 000 13 000 yr b p respectively cropping out in stream valleys in the buenos aires province mammal assemblages suggest a change from a temperate to a cool climate from the la chumbiada member to the guerrero member the latter representing the last glacial maximum the lower portion of the eolian la postrera formation has been dated at 11 000 8000 yr b p this section was deposited on basin divides under dry and cool conditions the mammal association was similar to that of the gueffero member and includes the last megaherbivore mammals in south america e g megatherium americanum mammals occurring in platan beds usually indicate dry but not cool conditions warm and probably wetter conditions were detected in continental beds deposited synchronously with a mid holocene marginal marine ingression ca 7000 6000 yr b p a holocene non analogue assemblage of subtropical mammals and dry cold indicators occurred at latitude 38 30 s at ca 2000 yr b p subtropical mammals that require wetter conditions have been migrating southwards in the pampean region since 1500 1000 yr b p eolian sediments in the la postrera formation dated ca 440 yr b p yielded an arid to semiarid mammal assemblage which could relate to the little ice age period remarkably most of the present day manual biocenoses and climatic conditions in the pampas seem to have been recently established paleogeographic maps for the last glacial maximum and the mid holocene are also provided

colloidal gold and silica in mesothermal vein systems some of the textural features of mesothermal gold quartz veins may be best explained by the initial precipitation of amorphous silica gel colloid which subsequently crystallizes to quartz this can occur in brittle ductile shear zones where a significant fluid pressure drop occurs during stick slip failure such a process rapidly supersaturates the hydrothermal fluid with respect to amorphous silica which precipitates instead of quartz owing to favorable kinetics depressurization also commonly leads to fluid unmixing and destabilization of soluble gold complexes however the presence of colloidal silica can stabilize gold colloid allowing further transport of particulate gold in suspension in the hydrothermal fluid silica gel would be highly unstable under mesothermal conditions and would undergo rapid syneresis and crystallization to form quartz solid impurities would tend to be expelled toward grain boundaries this model can account for the primary anhedral aggregate textures typical of mesothermal quartz veins the concentration of gold along grain boundaries and the formation of discrete gold nuggets and the rare occurrence of low order silica polymorphs and relict spheroidal structures the transport of gold in colloidal form may be one reason for the frequently consistent bulk grade distribution in gold quartz vein systems over many hundreds of metres in some cases kilometres of depth in addition the formation of charged colloidal particles may help to explain the attraction of gold grains to specific mineral surfaces

spinel elasticity and seismic structure of the transition zone of the mantle there is continuing debate about whether the upper mantle is chemically stratified and whether the seismic discontinuity at 400 km depth represents a chemical boundary a phase change of the mg fe 2sio4 component from the phase olivine to the p phase or a combination of both recent developments in high pressure synthesis1 2 and ultrasonic interferometry3 4 have made possible measurements of elastic wave velocities in small poly crystalline samples of high pressure phases by combining our new acoustic measurements on the spinel phase of mg2 sio4 with existing data for the and phases we present here velocity profiles for the m2sio4 component of the mantle where m represents mg or fe to depths of about 600 km we find it to be unlikely that any seismologically observable velocity discontinuity at about 520 km depth can be attributed to this component although the contrast in impedance the product of density and velocity might be sufficient for the transformation to be observed in long period seismic reflection studies at near normal incidence5 the velocity gradients in the transition zone particularly for shear waves are steeper than would be expected for simple adiabatic compression of likely mantle compositions suggesting that alternative explanations including chemical heterogeneity and anelastic relaxation need to be explored

the structure and sharpness of mg fe 2sio4 phase transformations in the transition zone abstract to calculate accurately the pressure interval and mineral proportions i e yields across the olivine to wadsleyite and wadsleyite to ringwoodite transformations requires a detailed knowledge of the non ideality of fe mg mixing in these mg fe 2 sio 4 solid solutions in order to constrain the activity composition relations that describe non ideal mixing fe mg partitioning experiments have been conducted between magnesiowustite and mg fe 2 sio 4 olivine wadsleyite and ringwoodite as a function of pressure at 1400 c using known activity composition relations for magnesiowustite the corresponding relations for the three polymorphs were determined from the partitioning data in all experiments the presence of metallic iron ensured redox conditions compatible with the earth s transition zone the non ideality of the mg fe 2 sio 4 solid solutions was found to decrease in the order w wadsleyite femg w ringwoodite femg w olivine femg these partitioning data were used along with published phase equilibria measurements for the mg 2 sio 4 and fe 2 sio 4 end member transformations to produce an internally consistent thermodynamic model for the mg 2 sio 4 fe 2 sio 4 system at 1400 c using this model the pressure interval of the olivine to wadsleyite transformation is calculated to be significantly smaller than previous determinations by combining these results with fe mg partitioning data for garnet the widths of transition zone phase transformations in a peridotite composition were calculated the olivine to wadsleyite transformation at 1400 c in dry peridotite was found to occur over a pressure interval equivalent to approximately 6 km depth and the mineral yields were found to vary almost linearly with depth across the transformation this transformation is likely to be even sharper at higher temperatures or could be significantly broader in wet mantle or in regions with a significant vertical component of mantle flow the entire range of estimated widths for the 410 km discontinuity 4 35 km could therefore be explained by the olivine to wadsleyite transformation in a peridotite composition over a range of quite plausible mantle temperatures and h 2 o contents the wadsleyite to ringwoodite transformation in peridotite mantle was calculated to take place over an interval of 20 km at 1400 c this transformation yield was also found to be near linear

density profiles of oceanic slabs and surrounding mantle integrated thermodynamic and thermal modeling and implications for the fate of slabs at the 660 km discontinuity abstract we have calculated the mineralogical properties of the earth s mantle and the lithological units constituting the subducting oceanic slabs within a wide range of p t conditions within the cao feo mgo al2o3 sio2 system except for the basalt top layer of a slab for which the system is extended to include na2o the mineralogical data are then converted using the appropriate p v t relations to bulk densities the calculated adiabatic density vs depth profile of the mantle between 200 and 725 km depths is in good agreement with geophysical and experimental data the density data of the different compositional units are combined with calculated thermal structures for a variety of slab mantle systems to construct equilibrium density profiles as a function of depth the mean equilibrium densities of the slabs within the transition zone 400 660 km depth are found to be 0 04 0 05 g cm3 greater than those of the ambient mantle within the same depth interval for the entire upper mantle density differences between slabs and ambient mantle are slightly less but the slabs still remain denser than the latter at 670 km depth slabs have lower density than the ambient lower mantle because of the commencement of perovskite forming reactions within the mantle and displacements of these reaction boundaries to higher pressures within the slabs as a consequence of their negative p t slopes if perovskite forming reactions within slabs are hindered for kinetic sluggishness then neutral buoyancy would be achieved when the slabs have penetrated 100 km into the lower mantle however using the available data on the kinetics of spinel to perovskite plus periclase reaction we conclude that the reaction would go to completion in a peru type young slab 41 myr and very likely also in a tonga type old slab 110 myr before these penetrated 100 km into the lower mantle thus slabs should always remain negatively buoyant and therefore continue to subduct through the lower mantle once it penetrates through the 660 km discontinuity despite a negative buoyancy force a slab could deflect at the top of the lower mantle 660 km because of factors resisting subduction namely viscosity jump low dip angle slab roll back and metastable persistence of olivine in cold slabs if published scale model experiments represent realistic approximations of the factors affecting plate subduction then according to our density data any slab with a dip angle of 40 50 would bend at the 660 km discontinuity if there is a viscosity jump of at least by a factor of 10 and trench migration the basalt top layer of a slab is denser than other slab components and the ambient mantle at all depths to 660 km and therefore should continue to sink into the lower mantle especially if a slab directly penetrates the 660 km barrier instead of peeling off in the transition zone to form a perched eclogite or piclogite layer as previously proposed the harzburgite layer which is sandwiched between denser basalt and lherzolite layers faces greater resistance to subduction especially in a young slab and thus could significantly contribute to the deformation of a slab near the 660 km discontinuity

sound velocities and elastic properties of fe bearing wadsleyite and ringwoodite the sound velocities and single crystal elastic moduli of phase wadsleyite and phase ringwoodite of mg fe 2sio4 with fe fe mg ratios of 0 075 and 0 09 respectively have been determined at ambient conditions by brillouin spectroscopy both compressional and shear wave aggregate velocities decrease with increasing fe content in both phases but the magnitude of this decrease is different for the two phases the adiabatic bulk modulus ks of fe bearing mg2sio4 ks 170 2 gpa is indistinguishable from that of the mg end member within experimental uncertainty whereas ks of mg fe 2sio4 increases rapidly with increasing iron content the shear moduli of both phases decrease with increasing fe content our measurements indicate that the velocity and impedance contrasts between olivine and mg fe 2sio4 are independent of fe content for mg rich compositions but the contrast for the mg fe 2sio4 transition increases significantly with increasing fe content the new data support a previous estimate of 40 10 for the olivine content of the upper mantle and suggest that less than 50 mg fe 2sio4 is sufficient to account for the observed impedance contrasts at depths of both 410 km and 520 km unless the effect of fe on elastic properties is accounted for it is difficult to account for both the 410 and 520 km discontinuities with a single olivine content

single crystal elasticity of ringwoodite to high pressures and high temperatures implications for 520 km seismic discontinuity abstract the single crystal elastic moduli of spinel structured mg 0 91 fe 0 09 2 sio 4 ringwoodite were measured to 16 gpa at room temperature and to 923 k at ambient pressure by brillouin spectroscopy a third order finite strain equation of state yields pressure derivatives of 4 1 2 and 1 3 1 for the adiabatic bulk modulus k s and shear modulus respectively the pressure derivatives of aggregate elastic moduli for all three polymorphs and of mg fe 2 sio 4 in the mg rich end are equal within the mutual experimental uncertainties with k s p t 4 1 4 3 and p t 1 3 1 4 a linear decrease of the elastic moduli and sound velocities with temperature adequately describes the data the temperature derivatives of k s and are 0 021 and 0 016 gpa k respectively an extrapolation of our data to transition zone pressures and temperatures indicates that the shear and compressional impedance contrasts associated with mg fe 2 sio 4 mg fe 2 sio 4 transition are sufficient to produce a visible discontinuity at 520 km depth even with only a moderate 30 50 amount of olivine moreover the partitioning of fe between mg fe 2 sio 4 and mg fe 2 sio 4 and majoritic garnet will produce a relatively sharp seismic discontinuity in the order of 10 15 km even when the latent heat of reaction is taken into account the visibility of the discontinuity in regional and global studies could be inhibited by large topography that would accompany any local variations in temperature or fe content the high v p contrasts observed in some localities are difficult to explain by the transition and are suggestive of a chemical boundary this is consistent with chemical heterogeneity in the transition zone probably related to subduction one of the possible explanations for high velocity contrasts near 520 km is a buried moho a boundary between garnetite former oceanic crust and mg fe 2 sio 4 enriched former peridotite layers

mechanism and kinetics of the α β transition in san carlos olivine mg1 8fe0 2sio4 the mechanism and kinetics of the a b transformation in san carlos olivine a mg1 8fe0 2sio4 containing ca 526 wt ppm h2o were studied in situ by time resolved synchrotron x ray diffraction xrd in the range 12 5 14 5 gpa and 870 1150 k time series of xrd spectra reveal the early formation of an intermediate phase that further transforms to wadsleyite b phase this intermediate phase may be either a metastable ringwoodite g phase or the disordered spinelloid phase proposed in the pseudomartensitic reaction model both microstructural and kinetic data suggest that the transformation rates are controlled by growth processes after the early saturation of nucleation sites along olivine grain boundaries growth rates in the range 1 7 10 12 2 1 10 9 m s 1 are estimated by fitting the transformation time data to the cahn rate equation and define an activation enthalpy for growth ha 204 55 kj mol compared to the previous studies performed on pure forsterite mg2sio4 these new kinetic results point out an increase of transformation rates with the iron content hence the persistence of a metastable olivine wedge to depths 660 km might be restricted to even colder and or dryer subduction zones than previously estimated

dry and humid phases in the highlands of southern brazil during the last 34 000 years and their influence on the paleoenvironments of the region abstract the palynology of the last 34 000 years was determined for a sedimentary profile from a bog in sao francisco de paula rio grande do sul eastern plateau using radiocarbon dates profile 29 19 05 s 50 08 18 w this is a rare older palynological sequence studied in the quaternary of southern brazil between 34 300 and 28 000 bp the records suggest a cold and semi arid climate with rarefied vegetation that was dominated by sparse grassland the araucaria forest probably in refuges between 28 000 and 23 500 bp a cold and humid climate was clearly detected at the last glacial stage the vegetation generally developed with a grassland dominion and a water reservoir was in the study site between 23 500 and 12 000 bp cold and semi arid climate promoted the reduction of grassland and the local water reservoir began to be filled by sediment between 12 000 and 10 000 bp the rise in temperature and humidity resulted in the development of regional vegetation and the araucaria forest probably expanded a little from the refuges herbaceous marsh dominated the study site between 10 000 and 7500 bp an elevated temperature and dry conditions promoted a general decrease in vegetation cover between 7500 and 3000 bp a progressive increase in humidity permitted the development of local and regional vegetation and the arborous pioneers migrated from the refuges with the expansion of forest taxa such as araucaria angustifolia bertol kuntze there was the beginning and expansion of the bogs from 6000 bp onward the grassland decreased after 4000 bp probably due to the forest cover the records indicate a high regional humidity after 3000 bp which is favorable to araucaria forest however the temperature elevation during this phase probably reduced the reproductive capacity of the araucaria forest taxa resulting in a lower rate of expansion on the grassland the same factor probably reduced the regional bogs from 2000 bp onward

paleolimnological record of the pampean plains argentina as a natural archive of south american hydroclimatic variability since the lgm to the current warm period abstract laguna mar chiquita lmc 30 54 s 62 51 w is a highly variable and shallow saline lake located in the pampean plains of argentina the paleolimnological record of lmc contains information on the environmental variability that occurred in a large area of southern south america since the last glacial maximum lgm until the present as inferred from the diatom assemblages sedimentary features and geochemical proxies prolonged intervals of high and lowstands have caused variations in water salinity trophic state and sedimentary processes this is the first paleolimnological reconstruction covering the hydroclimatic variability that occurred over the last 25 000 cal yr bp in the argentinean pampean region results are in accordance with well known global climatic phases the late pleistocene record is characterized by a scenario dominated by lowstands hypersaline and oligotrophic lake conditions radiocarbon ages 25 000 19 000 cal yr bp indicate that the onset of the record is coeval with the lgm later a progressive lake water level increase was registered at 17 000 cal yr bp which can be assigned to the heinrich stadial 1 a shift toward comparatively drier conditions identified in the record between 14 700 and 13 000 cal yr bp can be chronologically related to the antarctic cold reversal the transition from the late pleistocene to the holocene 13 500 10 500 cal yr bp is recorded by highstand phases while the early holocene record is characterized by high to intermediate water levels the hydrological reconstruction corresponding to the mid holocene is characterized by alternating phases of high lowstands the onset of the late holocene record is marked by the development of dry conditions and thus lowstand phases while around 1300 cal yr bp a distinct water lake level increase is recognized this humid phase ascribed to the medieval climatic anomaly is followed by the record of lowstands between 500 and 1000 cal yr bp being coeval with the little ice age the uppermost part of the record of lmc encompasses the current warm period showing a marked shift towards high lake water level conditions the hydrological variability registered in the paleolimnological record highlights the importance of laguna mar chiquita as an outstanding paleoclimate sensor of hydroclimatic variations for a large area of south eastern south america

stable isotope analyses on the last 30 ka molluscan fauna from pampa grassland bonaerense region argentina abstract fossil and living shells of terrestrial and freshwater molluscs collected from various sites in the bonaerense and patagonia regions of argentina were analysed for their stable isotope content as a possible tool for palaeoclimatic and palaeoenvironmental reconstruction the oxygen isotope composition of calcareous shell from freshwater samples was interpreted in terms of a change in moisture condition and the related evaporative effect on surficial bodies of water linked to a climatic shift the carbon isotope composition mainly records changes in biological productivity interpretation of the isotopic composition of the land snail carbonate is more complex and worldwide data from living shells have been used to decipher to some extent the palaeoenvironmental record contained in their isotopic composition overall the interpretations deduced from isotopic data of land snails as well as from nearby freshwater molluscs are quite comparable the isotopic data suggest that arid conditions occurred between 35 and 15 ka b p and warmer conditions around 35 25 ka b p a shift toward a new phase comparable with the present meteorological and climatic situation probably began around 9 ka b p and it was linked to some short but severe climatic fluctuations thus suggesting that high climatic stress characterised this period moreover a trend toward slightly arid conditions is suggested by isotopic data possibly sometimes after 5 ka the differences arising from the geographical location and the short duration of each single series studied still hamper an extensive interpretation of the isotopic data

landscape evolution and climate changes in the late pleistocene holocene southern pampa argentina evidence from palynology mammals and sedimentology abstract the landscape evolution of the southwestern part of buenos aires province southern pampa is a good example for the understanding of continental deposits in arid semiarid regions in buenos aires province the last 9 3 ma record is described as sequences composed of alternating loess and palaeosol units indicating climatic fluctuations between arid and cold loess deposition and warm and humid intervals palaeosol development the present drainage system flows across the early pliocene middle pleistocene stratigraphic units the stratigraphy and evolutionary history are analyzed using sequence stratigraphic criteria the interpretation of the climatic evolution of the area is based on pollen and mammal mainly rodents records the late pleistocene sediments reflect arid to semiarid conditions the late pleistocene holocene transition is characterized by development of palaeosols the early holocene pollen records reflect the development of a vegetation community characteristic of coastal dunes sea level was still lower than today temperature and humidity reached its maximum during the mid holocene when the high diversity and abundance of marine dinocysts and acritarchs indicate a transgression this event is associated with the gramineous steppe in the continent reflecting more temperate or local humid conditions and with brazilian mammal fauna this relative rise of sea level lead to flooding the riverbeds producing deposition of gray muddy facies approximately at 3000 years bp the marine influence ended in the area after 2610 years bp psammophytic herbaceous steppe development as well as mammals suggests arid to semiarid conditions an interval of higher humidity is inferred at approximately 2000 years bp based on the development of gramineous steppe communities a relative rise of temperature may be inferred by the southward expansion of the brazilian mammal fauna

fluvial connectivity and climate a comparison of channel pattern and process in two climatically contrasting fluvial sedimentary systems in south africa abstract the aim of this research was to investigate the dynamics of valley formation sediment delivery and channel pattern in two climatically contrasting fluvial sedimentary systems in south africa each system comprised a network of headwater valley fills and floodplains underlain by sedimentary karoo supergroup rocks that are intersected by resistant dolerite dykes and sills the seekoei river floodplain and gordonville valley fill site in the great karoo however experience less than half the annual precipitation of the nsonge river floodplain and hlatikhulu valley fill in the kwazulu natal drakensberg foothills furthermore rainfall is more variable in the karoo despite climatic differences headwater valley fills were geomorphically similar in contrast floodplains in the two regions were vastly different even when the same downstream control a resistant dolerite intrusion crossing the drainage line was considered upstream of a dolerite dyke the nsonge river is highly sinuous and located in a wide floodplain that has been carved by lateral planation of the underlying bedrock in comparison the seekoei river located upstream of a dolerite sill is discontinuous and characterized by floodouts and avulsing distributaries that undergo periods of bedrock incision followed by infilling it is likely that this disparity is caused by the inability of infrequent unsustained flows to develop meanders and thus adjust the channel planform to changes in discharge sediment load and valley slope flow variability thus exercises a strong control on channel pattern and causes floodouts in headwater settings and the semi arid karoo floodplain as a result sediment transport in the seekoei river is likely to be episodic and net retention of sediment in the semi arid floodplain is greater than in the sub humid nsonge river floodplain where sediment depth is limited

fractionation of li be ga nb ta in sn sb w and bi in the peraluminous early permian variscan granites of the cornubian batholith precursor processes to magmatic hydrothermal mineralisation this study was supported by the european regional development fund and european social fund as part of the convergence funding for cornwall and the isles of scilly supporting a phd for bs combined universities in cornwall project number11200nco5 and the european union horizon 2020 project 641650 fame the la icp ms work was supported by a grant from the natural environment research council nerc ne l001896 1 the cornwall heritage trust are thanked for providing additional funds for analysis the natural history museum london uk are thanked for loan of samples from collection bm 2004 p14 specimen numbers 1 7 8 10 21 23 24 30 and 31 and thin sections p11849 p11851 p11864 p12400 and p12399 samples gg6 gg15 gg28 and gg44 from the study of darbyshire and shepherd 1994 came from peter floyd university of keele steve pendray sharon uren and joe pickles assisted with the sample preparation and analysis at camborne school of mines sam hammond assisted with la icp ms analysis at the open university de lank carnsew and castle an dinas quarries richard scrivener nick leboutillier and ben thompson imerys are thanked for help with sampling karel breiter and one anonymous reviewer are thanked for their generous and constructive comments which have helped to improve the manuscript

late pleistocene sea level variations derived from the argentine shelf 1 neritic littoral marine sedimentary deposits from the argentine shelf provide a record of late pleistocene sea level variation sediments interpreted to reflect the last glacial maximum low stand are 150 m below present using a simple airy isostatic model for hydroisostatic compensation and correcting for a minor tectonic component yields a local eustatic sea level lowering of 105 m at the last glacial maximum the deglacial sea level curve records two rapid sea level rises consistent with mwp1 a and 1 b as documented by the barbados coral based sea level curve comparison with relative sea level variations predicted by the ice4g vm2 viscoelastic model have highlighted a deficiency in the model s predicted sea level history for this region detailed data model comparisons of late pleistocene sea level variations are necessary in the face of climate change induced sea level perturbations to determine regional and or systematic biases in the treatment of lithosphere viscosity and accurate predictions of future sea level

brillouin scattering and x ray diffraction of san carlos olivine direct pressure determination to 32 gpa the single crystal elastic moduli of san carlos olivine mg 0 9fe0 1 2sio4 were determined at seven pressures between 2 5 and 32 5 gpa by brillouin spectroscopy in a diamond anvil cell the unit cell volume was also determined at each pressure and ambient pressure by single crystal x ray diffraction the shear elastic moduli exhibit non linear pressure dependencies in particular a non linear dependence is required for the elastic modulus c55 above 10 gpa aggregate bulk and shear moduli were determined from hashin shtrikman averages of the individual constants pressures were determined by fitting the bulk modulus reuss bound and volume data to a third order eulerian finite strain equation and integrating the results are compared to independent pressure measurements made using the ruby fluorescence scale the ruby measurements yield pressures that are in good agreement with the brillouin results on average the ruby fluorescence measurements produce pressures that are larger than the brillouin determinations by 1 6 1998 elsevier science b v all rights reserved

albite rich silica depleted metasomatic rocks at emuford northeast queensland mineralogical geochemical and fluid inclusion constraints on hydrothermal evolution and tin mineralization late paleozoic fluorine rich granites and their host metasediments in the emuford district of the herberton tin field contain small zones of intense albitization that host cassiterite mineralization sodium metasomatism was accompanied by hydrothermal leaching of granite quartz to form vuggy albite rocks episyenites vugs created by quartz dissolution were filled in by hydrothermal minerals including albite k feldspar and or muscovite and cassiterite late phases are dominated by quartz and fluorite swarms of parallel veinlets crosscut the albitized zones these veinlets were formed by repeated fracturing in response to local fluid over pressures they contain infill mineralogy similar to the vugs and probably formed at least partly contemporaneously with vug infill due to the overprinting at various scales of alteration vug infill and vein formation stages chemical changes associated with episyenite formation are only qualitatively constrained however the mineralogical and textural features of the alteration zones suggest that most major and trace elements had substantial mobility during their formation major chemical changes associated with episyenite formation include leaching of sio 2 k 2 o rb and ba with introduction of na 2 o and minor sr during vug and vein filling stages there was an introduction of sio 2 al 2 o 3 na 2 o k 2 o cao f and sn the erratic behavior of ree is probably related to the growth of fluorite and minor accessory phases zircon monazite xenotime with preferential enrichment of heavy ree in rocks with the highest fluorine concentrations fluid inclusion study indicates that vug and vein filling stages of the hydrothermal evolution involved two types of fluids a high salinity fluid 30 50 equiv wt nacl of probable magmatic origin and homogenization temperatures up to 428 degrees c was associated with vug filling in the granite hosted deposits a lower salinity fluid 5 15 equiv wt nacl containing variable amounts of co 2 and having homogenization temperatures between 160 degrees and 420 degrees c was associated with veinlet formation in the granite hosted deposits and with vein and cavity filling in the metasediment hosted deposit this lower salinity fluid may represent a condensed vapor phase derived from boiling of the magmatic fluid or may be a mixture of magmatic and meteoric components the close association of albitization and quartz dissolution suggests a genetic link between the two processes it is proposed that exchange of na for k in the fluorine rich hydrothermal fluids caused a substantial increase in quartz solubility and led to quartz dissolution in the albitized rocks

megafauna extinction in south america a new chronology for the argentine pampas abstract the megafauna extinction in south america was one of the most profound events with the loss of 50 genera 83 three orders disappeared notoungulata proboscidea litopterna as did all large xenarthrans but how this fits into global extinction is uncertain mainly due to the lack of chronological resolution in recent years there has been an increase in the number of radiocarbon dating at archeological and paleontological sites but this information varies greatly from area to area in south america and few data can be considered to constitute a taxon date the timing of the late pleistocene extinction in the pampas is poorly established most taxa only appear in the biostratigraphic context and many reported 14 c dates do not meet rigorous criteria for accepting dates including reports suggesting survival of megafauna into the holocene in the present paper we evaluate the published radiocarbon dates in the pampas and present 20 new radiocarbon dates for paleontological sites in order to establish a more accurate extinction window for the key taxa these new dates are sufficiently robust to assess correspondences among last appearance records of megafauna first appearance records of humans and the younger dryas to holocene climatic transition in the argentine pampas these results highlight the need for greater effort in taxa selection for dating

contrasting fluid behavior during two styles of greisen alteration leading to distinct wolframite mineralizations the echassieres district massif central france abstract the echassieres district of central france hosts diverse magmatic and magmatic hydrothermal deposits of rare metals mostly related to the well known beauvoir granite tungsten mineralization crops out at three distinct wolframite occurrences the two most important of which are related to two distinct magmatic bodies emplaced ca 335 and 310 ma monnier et al 2019 the mineralization occurred at 335 ma formed during a hydrothermal episode marked by precipitation of topaz replacing quartz in a stockwork system and as veinlets in the surrounding schist fluid inclusions in topaz and quartz display similar features i e all have low salinity contain significant amount of licl display constant liquid vapor ratios and homogenized within a narrow temperature range th 380 c no evidence for fluid pressure variations was observed and temperature decrease is considered to be the main cause for wolframite deposition the younger w mineralization is related to greisenizing fluids that altered the beauvoir granite and generated several quartz topaz and apatite veins all greisen related fluid inclusions display low salinity however th are spread from ca 190 to 400 c and several populations exhibit heterogeneous liquid vapor ratios while others consist of only vapor rich fluid inclusions respectively these populations are interpreted to have been trapped during boiling or flashing vaporization of the fluid in contrast with the other regional veins flashing was particularly intense in the mazet veins which host the bulk of the last wolframite generation consequently it is proposed that flashing is the key factor that triggered w precipitation this work highlights the role of two physical parameters pressure and temperature whose variations played a preponderant role on wolframite mineralization it documents in depth an example of greisen fluid evolution providing critical information on w behavior in orthomagmatic fluids and on greisen related rare metal deposits

laser ablation icp aes for the determination of metals in fluid inclusions an application to the study of magmatic ore fluids abstract the laser ablation icp aes l icp aes technique is an effective method for the multielement analysis of individual fluid inclusions recent tests on synthetic fluid inclusions and improvements in data processing suggest that the method is valid for the analysis of a range of alkali alkali earth and transition metals in single large inclusions 30 m of moderate to high salinity 20 wt nacl equiv the system involving a small perspex ablation chamber a 1 j ruby laser focussed through an optical microscope and a conventional icp aes instrument is discussed and applied to natural fluid inclusions in quartz from two contrasting types of magmatic hydrothermal mineralization samples were selected from the san pedro cu au porphyry system new mexico usa and the sn w cu mineralized dartmoor granite of southwest england variable salinity high temperature fluid inclusions in hydrothermal quartz from both environments display similarly high concentrations and ratios of na k ca and fe the ore metals cu zn and mn but not sn mo w were detected in inclusions from both environments the estimated combined concentrations of up to 3 wt show that these three elements are major components of these fluids a method has been devised to estimate the confidence intervals of the measured concentration ratios the confidence intervals obtained show that the analytical uncertainty for an inclusion is much less than the natural geochemical variation between inclusions so that geologically useful information can be obtained a trend of increasing salinity with decreasing na and k and increasing ca and fe contents is observed in inclusions from san pedro consistent with the continuous evolution of a magmatic aqueous phase exsolved from a low pressure melt during crystallization in contrast the combined compositional and microthermometric data for samples from lee moor dartmoor suggest that a magmatic aqueous phase evolved from fe k rich to na ca rich compositions during cooling and was periodically diluted by meteoric fluids

late quaternary vegetational and climatic changes in the pampa grassland of argentina abstract the vegetation and climate of the pampa grassland argentina during the late quaternary are reconstructed from pollen recovered from dated stratigraphic sections from arroyo walls and from archaelogical excavations prior to 10 500 yr b p herbaceous psammophytic steppe existed in the central part of the pampa grassland while xerophytic woodland associated with psammophytic and halophytic steppe occurred in the southwestern part of the pampa these types of vegetation and the continental conditions that prevailed in the area of the present day coast 38 s indicate subhumid dry climate and annual precipitation 100 mm lower than present a subsequent change toward a vegetation characteristic of ponds swamps and foodplains or toward environments with locally more effective moisture occurred ca 10 500 yr b p suggesting annual precipitation close to modern levels or a higher availability of water in the central part of the pampa grassland this type of vegetation existed until 8000 yr b p when it was replaced by grassland communities that lasted until 7000 yr b p in the southwestern part of the pampa grassland this vegetation developed before 7000 yr b p and persisted until ca 5000 yr b p sea level higher than the present ca 6200 yr b p is consistent with sharp modification of the vegetation and development of local halophytic communities dominant at 38 s a return to subhumid dry conditions occurred after 5000 yr b p the late holocene vegetation is characterized by pollen assemblages similar to the psammophytic and halophytic communities of the southern pampa grassland associated with communities with more edaphic conditions at the same time at 38 s a sea level regression is suggested by the dominance of fresh water pollen assemblages and micropaleontological remains the trend toward humid temperate conditions ca 1000 yr b p suggested by vertebrate remains characteristic of temperate and humid conditions as well as a very short but dry episode during the 18th century suggested by the geology are not clearly evidenced in the pollen sequences vegetational and climatic changes are explained by the latitudinal shifts and changes in intensity of the southern atmospheric circulation and changes in sea level

isothermal compressibility of hydrous ringwoodite and its relation to the mantle discontinuities high pressure x ray diffraction experiments of hydrous ringwoodite containing 2 8 0 2 wt h2o have been carried out by using x rays from a synchrotron radiation source with a diamond anvil cell under hydrostatic pressure up to 6 gpa the isothermal bulk modulus k0 was determined to be 148 1 gpa with the pressure derivative k 0 fixed to 5 using the birch murnaghan equation of state this value is almost 80 of that of anhydrous ringwoodite the relations of the bulk modulus and zero pressure volumes v0 with h2o content are estimated within the solid solution range combining the present results with recent seismological data the nature of the 520 km and 660 km seismic discontinuities is discussed

thermodynamically consistent decompression implications for lower mantle composition estimates of the composition of the lower mantle are commonly obtained by a process of adiabatic decompression in which zero pressure mantle parameters are determined with a least squares fit of an equation of state to mantle densities we show that this procedure may lead to biased estimates of the zero pressure density and compressibility of the mantle the bias can be eliminated or minimized by subjecting the equation of state fit to a thermodynamic constraint at zero pressure such inversions provide equations of state that are compatible with the lower mantle as well as the thermal properties of selected mineral models we used this method to evaluate assemblages containing mg fe sio3 perovskite and mg fe o with fe fe mg ratios as high as 0 2 thermodynamic systematics were used to place bounds on the anderson gruneisen parameter s for perovskite we find a fairly large range of acceptable models for the composition of the lower mantle they range from uppermantle like compositions to assemblages that are enriched in both si and fe relative to the upper mantle however a pure perovskite lower mantle whether enriched in fe or not seems improbable small fe enrichments of the order of 1 given density contrasts across the 670 km discontinuity that are probably insufficient to prevent convective mixing of the upper and lower mantles we therefore suggest that unless the mantle is homogeneous in its major oxide components the lower mantle is likely to be enriched in fe by at least several percent

paleoenvironments in the paso otero locality during late pleistocene holocene pampean region argentina an interdisciplinary approach the recently excavated paso otero 4 site is located within the paso otero archaeological locality necochea district pampean region the site is characterized by the presence of a great variety of archaeological materials and a rich and complex stratigraphic record which allows use of an interdisciplinary approach the objective of this paper is to present the results of the geoarchaeological palynological phytolith and diatom analyses in order to reconstruct the paleoenvironmental conditions for the final late pleistocene through holocene these lines of research allow inference of paleoenvironmental and palaeoclimatic conditions on both local and regional scales at the site the rio salado member unit 2 where the archaeological deposit is buried underwent sudden and fluctuating changes in water availability conditions although the setting was basically characterized by calm depositional processes within and along the margins of interconnected lagoons paleoclimatic reconstructions indicate the existence of abrupt climatic changes throughout the sequence early holocene human occupations took place under regionally temperate warm climates while the end of the middle holocene witnessed cold and arid or cold temperate climates in general terms paleoenvironmental conditions inferred for paso otero 4 are in accordance with regional reconstructions proposed for the pampas

high temperature phase equilibria in a solar composition gas abstract using recent additions to thermochemical data on minerals and information on their solid solution behavior new equilibrium phase diagrams have been computed in a system of solar gas composition si al mg ca fe ni ti na k c h o s n in the pressure and temperature ranges of 1 to 10 6 bar and 1153 to 1773 k respectively these calculations show that fe ni alloy condenses before all silicates included here except melilite down to a pressure of 2 10 4 bar below which plagioclase and clinopyroxene condense first orthopyroxene condenses next followed by ilmenite pressure temperature variation of the chemical composition of melilite clinopyroxene orthopyroxene metal alloy and plagioclase may be used for cosmothermometry and cosmobarometry for equilibrium assemblages the major transition from the refractory oxides and melilite the meteorite inclusion assemblage to an assemblage of fe ni alloy olivine plagioclase and pyroxenes planet forming takes place within a narrow interval of pressure and temperature small fluctuations of either pressure or temperature across this narrow region result in drastic changes in types and modes of minerals which may explain the wide mineralogical varieties of meteorites

colloidal transport of gold and silica in epithermal precious metal systems evidence from the sleeper deposit nevada bonanza vein gold ore from the sleeper deposit nevada was deposited at a depth of less than 500 m and exhibits a characteristic texture of alternating colloform bands of fine grained quartz and bands of opaline silica containing abundant electrum textural evidence indicates that the quartz bands recrystallized from a gel like amorphous precursor whereas the gold rich bands were deposited originally as amorphous precipitate formed by the coagulation of colloidal silica and gold particles gold and silica precipitated initially as colloidal particles at deeper levels in the hydrothermal system and were mechanically transported upward by the hydraulic action of the ore forming fluids coagulation of the colloidal particles may have been caused by solution cooling or boiling and catalyzed by hydrated polycationic al 3 aqueous species transport of gold as colloidal particles in epithermal systems indicates that at least in some instances higher gold content is possible than in true solution a gold enriched ore fluid appears necessary to explain the origin of the bonanza grade ore at the sleeper mine and the colloidal gold transport process locally might have played a role in the genesis of the more common disseminated epithermal precious metal deposits

single crystal elasticity of β mg2sio4 to the pressure of the 410 km seismic discontinuity in the earth s mantle the complete set of elastic stiffness coefficients of a single crystal of mg2sio4 in the modified spinel wadsleyite structure are reported at eight pressures from ambient to 14 gigapascals gpa all moduli vary linearly with pressure within the resolution of the data third order birch murnaghan equation fits to aggregate elastic moduli yield values of 170 2 gpa and 4 3 0 2 for the adiabatic bulk modulus and its first pressure derivative and 115 2 gpa and 1 4 0 2 for the shear modulus and its pressure derivative these data together with previous results for mg2sio4 enable us to make the first in situ determination of the velocity increase due to the transition at the pressure 13 8 gpa of the 410 km discontinuity the room temperature velocity increase at the transition pressure is 9 8 for compressional waves and 12 4 for shear waves

the origins of late stage rocks in the st austell granite a re interpretation the origin of the granite varieties present in the st austell granite body biotite granite megacrystic and non megacrystic lithium mica granite fluorite granite is discussed in the light of new petrographic chemical and experimental evidence there were essentially two stages of magmatic activity the first represented by the intrusion of several phases of biotite granite the second by a later intrusion of non megacrystic lithium mica granite which crystallized from a volatile rich residual differentiate of the biotite granite magma both intrusions suffered hydrothermal alteration which primarily involved at least two stages of exchange of components via a single aqueous fluid phase within the non megacrystic lithium mica granite topaz and lithium mica were among the first phases to break down releasing f and li to this aqueous phase f was locally fixed as fluorite removing ca derived from the host biotite granite from the fluid and giving rise to pockets of fluorite granite apart from losing ca from plagioclase the biotite granite gained li expressed as lithium rich mica resulting in an aureole of megacrystic lithium mica granite surrounding the second intrusion at least one pervasive hydrothermal system using joints and grain boundaries as fluid pathways may have been in existence water rock interaction during fluid circulation is believed to have modified considerably the composition of predominantly meteoric water to give rise to the hydrothermal fluid responsible for greisening and mineralization within its sphere of influence the alteration phenomena initiated by the proposed hydrothermal system may have culminated in the formation of the major kaolinite deposits currently worked in the area

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

elastic properties of hydrous ringwoodite sound velocities and single crystal elastic moduli of hydrous mg 2 sio 4 ringwoodite containing 2 3 wt h 2 o have been measured by brillouin spectroscopy at ambient conditions the aggregate elastic moduli vrh averages are k s 165 8 5 gpa and 107 4 3 gpa for the adiabatic bulk modulus and shear modulus respectively although the aggregate elastic moduli and acoustic velocities of hydrous ringwoodite are smaller than those of anhydrous ringwoodite by about 10 and 3 6 respectively our results indicate that water has a smaller effect on the elastic moduli and velocities of ringwoodite than implied by previous studies our new results are consistent with systematic relationships between changes in the elastic properties and density that accompany the hydration of mineral phases

first direct evidence for natural occurrence of colloidal silica in chalcedony hosted vacuoles and implications for ore forming processes different forms of abundant silica e g quartz and chalcedony are closely associated with many types of ore deposits in igneous metamorphic and sedimentary environments occurrence of quartz and metal bearing minerals together strongly indicates that silica is an important component in hydrothermal fluids transporting and concentrating economic metals to the ore grade however chemical and physical characteristics of such ore forming media remain debated understanding of the environment in which chalcedony forms is largely hampered by the lack of chalcedony hosted fluid inclusions our study reports for the first time fortuitously preserved large sized up to 150 m fluid inclusions in chalcedony from the gonchak deposit of optical calcite in the early triassic basalts belonging to the siberian large igneous province the application of microthermometric methods scanning electron microscopy with cathodoluminescence and laser raman spectroscopy to the fluid inclusions and their host chalcedony recognized the formation of chalcedony from a colloidal suspension the fluid inclusions represent a gel like saline aqueous fluid that is residual after precipitation of spherulitic chalcedony aggregates with numerous h2o bearing and h2o poor layers we propose that the colloidal nature of fluids forming chalcedony lends strong support to the natural existence of experimentally predicted silicothermal fluids such fluids can be instrumental in mobilizing and transporting large quantities of both silica and nano and micro particles of ore minerals followed by efficient separation of the latter from coagulating silica gel into ore rich zones and bodies

environmental history since 11 000 14c yr b p of the northeastern pampas argentina from alluvial sequences of the lujan river abstract sedimentological malacological and pollen analyses from 14c dated alluvial sections from the lujan river provide a detailed record of environmental changes during the holocene in the northeastern pampas of argentina from 11 200 to 9000 14c yr b p both sedimentary and biological components suggest that the depositional environment was eutrophic alkaline and freshwater to brackish shallow water bodies without significant water circulation during this time bioclastic sedimentation was dominant and the shallow water bodies reached maximum development as the climate became more humid suggesting an increase in precipitation short term fluctuations in climate during the last stage of this interval may have been sufficient to initiate changes in the water bodies as reduction of the volume alternated with periods of flooding the beginning of the evolution of shallow swamps in the wide floodplain or huge wetlands was contemporaneous with a sea level lower than the present one from 9000 and 7000 14c yr b p mesotrophic alkaline brackish probably anoxic swamps existed between 7000 and 3000 14c yr b p anoxic calcareous swamps were formed with subaerial exposure and development of the puesto berrondo soil 3500 2900 14c yr b p a trend to a reduction of water bodies is recorded from 9000 to ca 3000 14c yr b p with a significant reduction after ca 7000 14c yr b p a shift to subhumid dry climate after 7000 14c yr b p appears to be the main cause during this time an additional external forcing toward higher groundwater levels was caused by holocene marine transgression causing changes in the water bodies levels the climate became drier during the late holocene ca 3000 yr b p when clastic sedimentation increased under subhumid dry conditions flood events increased in frequency during this time from ca a d 1790 to present the pollen record reflects widespread disturbance of the vegetation during the european settlement

the melting of al bearing perovskite at the core mantle boundary abstract we have investigated the melting temperature of al bearing perovskites including ca al al si o 3 and mg al al si o 3 as well as mgsio 3 and casio 3 at high pressure conditions using empirical melting equation this study indicates that the incorporation of 25 mol al 2 o 3 into casio 3 decreases its melting temperature at the core mantle boundary cmb from 5900 to 4400 k a less dramatic effect is calculated for al 2 o 3 in mgsio 3 with a decrease in melting temperature from 5500 to 5200 k at the cmb compared to the liquidus of pyrolite in the deep mantle estimated from the experimental observations of zerr et al 1998 ca al perovskite provides a more probable source of the partial melt proposed to exist in the d region

an investigation into thermodynamic consistency of data for the olivine wadsleyite and ringwoodite form of mg fe 2sio4 abstract we have performed a thermodynamic analysis to determine the internal consistency of state of the art experimental data for olivine wadsleyite and ringwoodite solid solutions the analysis has been carried out between 200 and 2200 k and 0 and 20 gpa we conclude that the volume pressure temperature data of wadsleyite and ringwoodite show very large inconsistencies which hamper the accurate prediction of bulk sound velocities in the transition zone to within tomographic accuracy owing to the compositional effect in two phase regions thermodynamic properties crucial for geodynamic modeling differ up to an order of magnitude relative to values in single phase regions at conditions prevailing in the earth s transition zone thermal expansivity in the olivine wadsleyite two phase region is 23 times larger than that in the olivine region for the wadsleyite ringwoodite two phase region thermal expansivity is 6 times larger than that in the wadsleyite region it may be anticipated that this differential thermal expansivity significantly affects future geodynamic model calculations

late quaternary palaeosol records from subtropical 38 s to tropical 16 s south america and palaeoclimatic implications abstract loess and palaeosols in the subtropical lowlands of south america 23 38 s have a large potential to serve as archives of late quaternary environmental and climate changes at present mean annual precipitation generally decreases from n to s and from e to w though with a complex seasonal pattern with austral summer rainfall related to the monsoonal circulation and with austral winter rainfall related to the se trades in this paper we present results of multiproxy geochemical analyses from three representative eolian alluvial soil profiles along a s n transect aiming at the reconstruction of past climate changes i profile chasico at the southern border of the subtropics 38 s ii d4 in misiones at the northern border of the subtropics 27 s and for comparison iii laguna sucuara in the savannas of the bolivian lowlands 16 s our results show that before 16 ka bp conditions were likely very cold and dry except for in d4 loess or soils are not preserved due to rather scarce vegetation cover and resultant deflation in chasico accumulation of sands directly overlying the tertiary starts only during the late glacial indicating increasing temperatures and increased monsoonal precipitation coinciding with the tauca wet phase on the altiplano in d4 a palaeosol is preserved below the late glacial sediments and the deflation hiatus this palaeosol is dated to 40 ka bp and documents an earlier but less intensive southward reaching phase of monsoonal precipitation inca huasi on the altiplano whereas the seasonality during the late glacial seems to have been very pronounced conditions for organic matter production and preservation became much more favourable at chasico and d4 during the early holocene we suggest that extra tropical winter precipitation played a more important role than before and than today between 7 5 and 3 ka bp the expansion of c4 plants along the s n transect suggests increasing aridity probably due to a weakening of the extra tropical circulation in combination with a relatively weak monsoonal circulation only after 3 ka bp climate became more humid again due to the re strengthening of the monsoon

crustal melts below 400 c we propose that the internally zoned li bearing tin mountain pegmatite in the harney peak granite pegmatite system of the black hills south dakota crystallized from fluid rich compositionally complex melts at 400 350 c the low crystallization temperatures resulted from the combined fluxing effects of li b p h 2 o and carbonate anions the presence of hydrous silicate melts at temperatures of 350 c is revealed by microthermometric data on primary fluid inclusions cogenetic with crystallized melt inclusions mineral assemblages of the crystallized melt inclusions and chemistry of bulk fluid leachates indicate that the melts and fluids contained significant amounts of li and na as carbonates and or borates that acted as powerful fluxes the low temperatures give a new perspective on the stability of silicate melts in the crust

late quaternary paleoenvironments and paleoclimatic conditions in the distal andean piedmont southern mendoza argentina abstract the andean piedmont of mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology this paper is focused on the san rafael plain srp environment situated in the distal andean piedmont of mendoza 34 30 s and reports the sedimentology and osl chronology of two representative exposures of late quaternary deposits including their paleoenvironmental and paleoclimatic significance eleven facies including channel floodplain fluvio aeolian interaction and reworked pyroclastic and aeolian deposits were described and grouped into two facies associations fa1 and fa2 fa1 was formed by unconfined sheet flows minor channelized streams and fluvial aeolian interaction processes fa2 was interpreted as aeolian dune and sand sheet deposits osl chronology from the srp sedimentary record indicates that between ca 58 39 ka and ca 36 24 ka mis 3 aggradation was governed by ephemeral fluvial processes fa1 under generally semiarid conditions during mis 2 the last glacial maximum ca 24 12 ka a major climatic shift to more arid conditions is documented by significant aeolian activity fa2 that became the dominant sedimentation process north of the diamante atuel fluvial system the inferred paleoenvironmental conditions from the srp sections are in broad agreement with regional evidence

paleoenvironments and faunal extinctions analysis of the archaeological assemblages at the paso otero locality argentina during the late pleistocene early holocene abstract paso otero archaeological locality pampean region argentina has provided detailed paleoenvironmental reconstructions and faunal assemblages from the pleistocene holocene transition and early holocene this time span is represented by paso otero 5 c 10 450 10 200 14 c bp 12 593 11 353 cal bp and paso otero 4 c 9900 7700 14 c bp 10 667 7982 cal bp palaeoenvironmental studies have been carried out on the basis of data derived from geoarchaeological sedimentary palynofacies pollen diatoms and silica microremains unlike other areas of the pampean region bone assemblages from paso otero include high representation and diversity of taxa in this paper paleoenvironmental reconstructions and faunal assemblages from both sites are integrated in order to discuss the consistency of the inferences derived from the two lines of evidence its contribution to the paleoecological scenarios and to faunal extinctions it is suggested that not only hunting pressure but the mere presence of humans was a factor in ecosystem disturbance and is the most parsimonious explanation for the process of extinction

experimental determination of the effect of h2o on the 410 km seismic discontinuity abstract due to the high solubility of h 2 o in the mineral wadsleyite it has been recognized that the presence of h 2 o in the mantle could influence the pressure and pressure interval of the olivine to wadsleyite phase transformation that is generally considered to be the cause of the 410 km seismic discontinuity we have performed multianvil experiments in the mg 2 sio 4 h 2 o system in order to quantify the expansion of the wadsleyite stability field as a result of the presence of h 2 o at 1200 c we find that the wadsleyite stability field expands to lower pressures by approximately 1 gpa under h 2 o rich fluid saturated conditions at 1400 c the expansion is approximately 0 4 gpa and no expansion can be detected at 1600 c a thermodynamic model based on recent h 2 o solubility measurements and crystallographic observations predicts an expansion of the wadsleyite stability field that is in good agreement with the experimental results when these results are combined with phase relations in the mg 2 sio 4 fe 2 sio 4 system it can be shown that significant effects on the pressure and pressure interval of the olivine to wadsleyite transformation i e on the depth and width of the 410 km discontinuity are only expected at lower than ambient mantle temperatures 2 o concentrations that are substantially greater than 0 2 wt areas of the mantle where the 410 km discontinuity appears to occur over a depth interval of over 20 km can only be explained if the temperature in these regions is at or below 1200 c and water concentrations are close to the level where olivine would become h 2 o saturated i e 0 5 wt the presence of ferric fe in the mantle however may also play a role in the broadening of the 410 km discontinuity that is as yet unquantified

new late pleistocene megafaunal assemblage with well supported chronology from the pampas of southern south america abstract late pleistocene outcrops exposed in buenos aires province argentina represent one of the most informative sources about the paleoecology of south american megafauna however there are no records of an accurately dated carnivore herbivore taphocenosis this paper presents preliminary results of a recent excavation at the margins of the salado river on sediments attributed to the lujan formation late pleistocene early holocene the fossiliferous strata consist of greenish brown sandy clays deposited in a small paleopond environment that was filled by fluvial sediments exhibiting abundant organic matter gypsum and carbonate concretions fieldwork yielded an association of extinct large sized mammals that include the horse hippidion principale the saber tooth cat smilodon populator at least one adult and one juvenile associated specimen a giant ground sloth megatherium americanum and the glyptodont doedicurus clavicaudatus four 14 c dates were performed on organic matter 12 100 100 14 c bp a femur of s populator 13 400 200 14 c bp and a cervical vertebra of hippidion principale 12 860 120 14 c bp and a pelvis of d clavicaudatus 12 380 190 14 c bp situating the site within 12 500 and 13 500 years approximately remarkably some of the recovered specimens exhibit conspicuous bone modifications furrows pits punctures striations and crenulated margins attributed to the activity of a medium large carnivore the association between bones of herbivore mammals with conspicuous modifications produced by a large carnivore and the presence of cub and adult remains of smilodon link this felid with at least part of the excavated association

first insights on the metallogenic signature of magmatic fluids exsolved from the active magma chamber of vesuvius ad 79 pompei eruption abstract fluid inclusions hosted in sanidine from xenoliths representing the crystallization front of the ad 79 magma chamber of vesuvius offer a rare opportunity to track the composition of magmatic fluids exsolving at the peripheral part of a growing k alkaline magma chamber disrupted by an explosive eruption this work demonstrates that the exsolving magmatic fluids have a complex composition taking in evidence the great capability of metal transport by means of these solutions inclusions are particularly enriched in zn mo w sb bi tl and pb metals display two different positive correlations 1 pb zn tl bi 2 mo w the different trends may reflect the different complexing agent for these elements probably chloride for pb zn tl bi and probably hydroxy for mo w the occurrence of a silicothermal component in these fluids may furthermore favor the metal transport of these solutions this is probably a major previously underestimated process in the enrichment of some metals in magmatic hydrothermal systems this hypothesis may challenge conventional ideas on fluid phase mass transport of components by means of magmatic hydrothermal fluids and should be taken into account in future works on these topics