low heat flux and large variations of lithospheric thickness in the canadian shield 1 ten new heat flux determinations have been made using measurements in 22 mining exploration boreholes located at latitudes higher than 51 n in the canadian shield they provide data in poorly sampled regions near the core of the north american craton where one expects the lithosphere to be thickest the new heat flux values are all smaller than 34 mw m 2 and are among the lowest recorded so far in the shield for all the new sites there is no relationship between heat flux and heat production in surface rocks in the canadian shield heat flux variations occur at wavelengths 100 km and are mostly of crustal origin local averages in two 250 250 km windows located on archean areas at high latitudes on either side of james bay are 29 mw m 2 and 31 mw m 2 the lowest values found so far at this scale in the canadian shield s wave traveltime delays derived from tomographic models provide the additional constraints needed to resolve differences of deep lithospheric thermal structure there is no significant correlation between average surface heat flux and traveltime delays within the canadian shield confirming that variations of the surface heat flux are mostly of crustal origin traveltime delays cannot be explained by variations in crustal heat production only and require variations of heat supply to the lithosphere and or radiogenic heat production in the lithospheric mantle these variations are associated with changes of lithospheric thickness that may be as large as 80 km the heat flux at the base of the superior lithosphere is constrained to be 11 2 mw m 2

18o exchange between steam and carbon dioxide in volcanic and hydrothermal gases implications for the source of water abstract the oxygen isotopic compositions of h 2 o and co 2 from 31 fumaroles from different volcanoes vesuvio campi flegrei vulcano and etna in italy soufriere of guadeloupe in lesser antilles prove that 18 o exchange between co 2 and steam is fast enough in natural gas phases to allow rapid isotopic reequilibration within a wide temperature range 100 1000 c the isotopic composition of h 2 o discharged by volcanic hydrothermal fumaroles is affected by isotopic reequilibration along with cooling of the gas phase and this secondary process must be taken into account when interpreting the origin of the water from isotopic data the use of corrected 18 o values computed considering the overall oxygen isotopic composition of the h 2 o co 2 system is therefore compulsory to overcome interpretative biases as an example we apply this method to 100 600 c fumaroles at vulcano crater whose isotopic composition is reinterpreted considering the effects of 18 o exchange between co 2 and h 2 o in contrast to most previous interpretations the corrected isotopic values for h 2 o clearly show that the vulcano system is fed by a two component mixture of magmatic water with a typical andesitic composition and either 18 o shifted seawater or magmatic steam partly condensed within the volcanic ground with minor contribution of local meteoric water the possible additional effects of isotopic reequilibration involving other o and h bearing gas species in volcanic fluids such as so 2 h 2 s hcl hf and h 2 have been also considered the influence of so 2 upon the isotopic composition of h 2 o is subordinate with respect to that of co 2 whereas significant shifts in deuterium composition are expected from hydrogen isotopic exchanges in the h 2 o h 2 s hcl hf h 2 gas system

what can we learn about crustal structure from thermal data thermal data represent a valuable remote sensing aid in studying crustal evolution heat flow q results from the heat loss by the cooling earth and from the heat production a of the radiogenic elements brought to the upper crust by magmatic intrusives heat flow is often observed to be linearly related to heat production the slope of this relation or thermal depth d has been used to infer a global upward enrichment in heat producing elements this thermal depth has been equated with the thickness of granites but such an interpretation has not been confirmed everywhere the depth to which granitic plutons are rooted can be computed from the inversion of gravity data it averages 7 2 km and is much smaller than the thermal depth granulite facies rocks are assumed to be present in the lower crust on the basis of seismic and geochemical data these rocks are generally depleted or initially poor in radiogenic elements u th k it is suggested that the thermal depth reflects the depth to the depleted layer in continental regions and that it corresponds to the granulitic layer in most places worldwide thermal and seismic data support this relationship although surface heterogeneities introduce complications thermal data can therefore be used to constrain the structure of the crust and its evolution through time

genesis of fumarolic emissions as inferred by isotope mass balances co2 and water at vulcano island italy we have developed a quantitative model of co2 and h2o isotopic mixing between magmatic and hydrothermal gases for the fumarolic emissions of the la fossa crater vulcano island italy on the basis of isotope balance equations the model takes into account the isotope equilibrium between h2o and co2 and extends the recent model of chemical and energy two end member mixing by nuccio et al 1999 as a result the h2o and co2 content and the d 18o and 13c isotope compositions for both magmatic and hydrothermal end members have been assessed low contributions of meteoric steam added at a shallow depth have been also recognized and quantified in the fumaroles throughout the period from 1988 to 1998 nonequilibrium oxygen isotope exchange also seems to be occurring between ascending gases and wall rocks along some fumarolic conduits the 13cco2 of the magmatic gases varies around 3 to 1 vs peedee belemnite pdb following a perfect synchronism with the variations of the co2 concentration in the magmatic gases this suggests a process of isotope fractionation because of vapor exsolution caused by magma depressurization the hydrogen isotopes in the magmatic gases 1 to vs standard mean ocean water smow as well as the above 13cco2 value are coherent with a convergent tectonic setting of magma generation where the local mantle is widely contaminated by fluids released from the subducted slab magma contamination in the crust probably amplifies this effect the computed isotope composition of carbon and hydrogen in the hydrothermal vapors has been used to calculate the d and 13c of the entire hydrothermal system including mixed h2o co2 vapor liquid water and dissolved carbon we have computed values of about 10 vs smow for water and 2 to 6 5 vs pdb for co2 on these grounds we think that mediterranean marine water dh2o 10 feeds the hydrothermal system it infiltrates at depth throughout the local rocks reaching oxygen isotope equilibrium at high temperatures interaction processes between magmatic gases and the evolving seawater also seem to occur causing the dissolution of isotopically fractionated aqueous co2 and providing the source for hydrothermal carbon these results have important implications concerning fluid circulation beneath vulcano and address the more convenient routine of geochemical surveillance

the role of radiogenic heat production in the thermal evolution of a proterozoic granulite facies orogenic belt eastern ghats indian shield abstract the eastern ghats belt egb is a deeply eroded proterozoic orogenic belt juxtaposed against the archaean dharwar bastar singhbhum cratons in the indian shield the tectono metamorphic history of this belt is broadly similar to the grenvillian orogenic belts the egb exposes dominantly the granulite facies rocks such as charnockites khondalites and migmatitic gneisses with less abundant intermediate to mafic granulites the granulites are intruded by small plutons of granites syenites and anorthosites the northern and southern parts of the belt negb and segb have distinct crustal histories but 1600 1000 550 ma old tectono metamorphic events are common to both the belts in this research we attempt to understand the present day and past thermal state of this orogen on the basis of our radioelement k u and th measurements at 562 sites using in situ gamma ray spectrometry with other geological and geophysical constraints the dominant rock types of the negb and segb have similar radioelement abundances 3 k 3 ppm u and 30 ppm th and heat production heat production of charnockites gneisses khondalites and intermediate granulites of the negb is 2 9 2 8 2 9 and 1 1 w m 3 respectively in the segb they are 2 7 2 5 2 8 and 0 6 w m 3 respectively and the mafic granulites are the lowest in heat production 0 3 w m 3 on the basis of the heat production data and crustal petrologic models we show that the crustal contribution of the negb and segb is 54 and 45 mw m 2 respectively which are broadly in good agreement with the available surface heat flow data thermal models of the present day egb crust indicate that the temperature at the moho is 550 c radioelements and heat production of the eastern ghats granulites are higher than the other granulite belts in the indian shield the crustal radiogenic heat contribution and moho temperatures of the egb are higher than the adjoining archaean cratons this could also be responsible for the development of inverted metamorphic isograds in the tectonic boundary between the egb and the adjoining cratons during a collisional orogenic event at about 550 ma ago

temperature and rheological properties of the mantle beneath the north american craton from an analysis of heat flux and seismic data 1 we combine heat flux data and seismic velocity models for the north american lithosphere to derive constraints on thermal conditions and deformation mechanisms in the underlying convecting mantle local heat flux averages that are not affected by shallow crustal heat production contrasts allow calculation of reliable lithospheric geotherms and uncertainty ranges for consistency with the seismic data the mantle potential temperature beneath north america must lie within a 1290 c 1450 c range close to that for the oceanic mantle sampled at mid ocean ridges the heat flux at the base of the lithosphere varies laterally from 11 3 mw m 2 beneath the 250 km thick archean core of the superior province to 15 3 mw m 2 beneath the thinner younger appalachians province it is shown that the most likely cause of such rates of heat supply into the north american continent is small scale convection in an unstable boundary layer beneath the rigid mechanical lithosphere this allows useful constraints on the mantle rheological properties we show that the most likely deformation mechanism is dislocation creep in wet mantle rocks ranges for the mantle temperature water content and rheological parameters could be tightened very significantly once strong constraints are obtained on radiogenic heat production in the lithospheric mantle

genesis and evolution of the fumaroles of vulcano aeolian islands italy a geochemical model a geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of vulcano island is proposed a pressurized biphase liquid vapor reservoir at the depth of about 2 km is hypothesized energy and mass balance sheets controlp t conditions in the system p t must vary along a boiling curve of brine as liquid is present the co2 content in the steam is governed by the thermodynamic properties of the fluids in the h2 nacl co2 system on the assumption that oxygen fugacity in the system is between the hm fmq oxygen buffers observed so2 h2s co2 co co ch4 ratios in the fumarolic gases at the fossa crater appear in equilibrium with a temperature higher than that observed such as may exist at depth the more reduced gas phases present on the sea side may result from re equilibrium processes in shallower aquifers the suggested model would help in monitoring changes in volcanic activity by analyzing fumarolic gases

chronology of the youfang site and its implications for the emergence of microblade technology in north china abstract the youfang paleolithic site located in the eastern nihewan basin hebei province china was discovered in 1984 however the microblade assemblages which were excavated from the site lacked reliable chronological data in this study an optical dating technique was applied to nine samples from late pleistocene eolian sequences at the site the ages of three samples from artifact bearing deposits were in the range of ca 26 29 ka with depths between 2 1 m and 2 9 m obtained with medium grained quartz corresponding to marine isotope stage 3 mis3 these displayed evidence of a longer term climate trend in which the climate became gradually warmer and more humid the sample from the upper culture layer was dated to 26 4 2 1 ka five samples taken from the lower culture layer yielded ages between ca 28 ka and 43 ka the results suggest that human occupation at the youfang site ranged from ca 26 ka to 29 ka indeed the nihewan basin yields the oldest microblade site in northern high latitudes 40 n and offers a unique opportunity to study the emergence and characteristics of microblade technologies in northeast asia nevertheless extensive archeological field surveys and excavations are still needed to understand further the developmental process of microblade technologies in the region

seismic properties of rock samples from the pikwitonei granulite belt god s lake domain crustal cross section manitoba laboratory measurements of compressional and shear wave velocity to confining pressures of 600 mpa for a suite of representative samples collected from the pikwitonei granulite belt and god s lake domain an archean crustal cross section in the northwestern superior province provide the basis of comparison of these terranes with the seismic characteristics of archean lower crust we found that felsic rocks in the pikwitonei granulite belt and god s lake domain which make up the bulk of these terranes have a similar average compressional wave velocity of 6 5 km s at 600 mpa indicating that felsic rocks show little velocity change across the amphibolite granulite facies transition compressional wave velocities for mafic rocks from each terrane are between 7 1 and 7 3 km s apparent poisson s ratio ranges from 0 24 to 0 26 and 0 26 to 0 28 for felsic and mafic rocks respectively these velocity data compare favorably with data for similar lithologies from the kapuskasing uplift using the relative abun

long time variation of soil co2 fluxes at the summit crater of vulcano italy here we report the first continuous data of geochemical parameters acquired directly from the active summit crater of vulcano this approach provides a means to better investigate deep geochemical processes associated with the degassing system of vulcano island in particular we report on soil co2 fluxes from the upper part of vulcano a closed conduit volcano from september 2007 to october 2010 large variations in the soil co2 and plume so2 fluxes order of magnitude coinciding with other discontinuous geochemical parameters co2 concentrations in fumarole gas and physical parameters increase of shallow seismic activity and fumarole temperatures have been recorded the results from this work suggest new prospects for strengthening geochemical monitoring of volcanic activity and for improving the constraints in the construction of a geochemical model this being a necessary condition to better understand the functioning of volcanic systems

the shuidonggou site complex new excavations and implications for the earliest late paleolithic in north china the initial late paleolithic said to appear between 40 and 30 kya in eastern asia is defined by the appearance of many innovations these archaeological indicators include the appearance of more refined stone tool making techniques e g include the appearance of blade and microblade technology complex hearth construction use of pigments and personal ornamentation as well as worked faunal implements such as bone and antler tools we report here new findings from a multidisciplinary research project conducted at the shuidonggou choei tong keou site complex in northern china a series of localities that date from the initial late paleolithic to the neolithic six new localities sdg7e12 were discovered and five localities sdg2 previously identified and sdg7e9 and 12 were excavated yielding more than 50 000 stone artifacts fauna ostrich eggshell beads and hearths dating results suggest that human occupation of the shuidonggou area occurred during the late pleistocene to middle holocene w32 000e6000 bp some sites are characterized by small irregular flakes casually retouched tools modified or informally retouched tools i e non standardized tools with sporadic retouch which was not well controlled and small numbers of blades or no blades others lithic assemblages are dominated by blades and microblades at two sites higher quality or exotic raw materials were exploited but at the majority of sites locally available river cobbles were used in addition to blades microblades and hearths more than 80 finely perforated and polished ostrich eggshell beads mostly colored with red ochre were recovered from three sites several worked bone needles and an awl were also uncovered from the youngest site sdg12 in deposits dating to c 13 000 cal bp the implications for the initial appearance of the late paleolithic in china and movement of modern human populations into north china are discussed

thermal properties of granulite facies rocks in the precambrian basement of finland and estonia abstract we present results of heat production thermal conductivity and p wave velocity measurements of 252 rock samples from five granulite facies areas in finland and estonia these compositionally mainly intermediate archaean and palaeoproterozoic metamorphic rocks have relatively high heat production values mean values averaged by areas range from 0 57 to 2 24 w m 3 the lowest values are in the varpaisjarvi area which is the oldest and most mafic and where the highest metamorphic pressure occurred 8 11 kbar whereas the highest heat production is found in the turku granulite belt where the metamorphic pressure was 4 6 kbar the heat production decreases with the increase of the metamorphic pressure however a general numerical relationship cannot be presented because of considerable variations in heat production data there is no significant difference in the metamorphic temperatures of the studied granulites and therefore no dependence on temperature is found further our data suggest no relationship between heat production and p wave velocity the mean thermal conductivity of granulites varies from 3 0 to 3 5 w m 1 k 1 slightly elevated thermal conductivity values in the varpaisjarvi and lapland granulite areas can be attributed to higher sillimanite and quartz contents respectively

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

thermophysical properties of the earth s crust in situ measurements from continental and ocean drilling knowledge of the variation of thermal conductivity and heat production with depth is critical to understanding the thermal state of the crust continental and oceanic drill holes provide unique opportunities for the calibration of empirical and theoretical models relating crustal thermal properties to physical and chemical properties these calibrations are based on more than 30 000 well log measurements of acoustic velocity both compressional and shear density porosity radioelement concentrations k u th and major element chemistry al si ca fe s mg na in formations ranging in age from 5 to 620 ma and in composition from granitic to gabbroic the mineralogical data available from induced gamma ray spectroscopy logs when combined with known mineral thermal conductivities in a model for the thermal conductivity of a crystalline aggregate enable the in situ application of a laboratory estimation technique and yield continuous conductivity profiles however mineralogy based conductivity models cannot account for the anisotropic conductivity observed in foliated metamorphic rocks a phonon conduction model which utilizes acoustic velocity and bulk density measurements is accurate within 15 in both isotropic and anisotropic formations of the upper continental crust and in oceanic crustal layers 2c and 3 in oceanic crustal layers 2a and 2b however the effects of fracturing on compressional and shear velocities lead to inaccurate results the heat flow heat production relationship which provides one method of determining subsurface heat production has well documented limitations allis 1979 and rybach and buntebarth 1982 1984 on the basis of laboratory measurements have proposed quantitative relationships between heat production and rock compositional and physical properties the well log k u and th data indicate that heat production can be predicted from compositional data within a factor of 2 or 3 predictions of heat production from acoustic velocity and bulk density measurements are only accurate to within an order of magnitude three factors account for these results 1 the natural variability of velocity and density for a given rock composition 2 the tendency of u and th to associate with secondary rather than primary minerals and 3 u and th redistribution through fluid flow and metamorphism thus seismic velocity based heat production profiles can at best be taken as first order estimates which may misrepresent the complexity of the continental crust however the correlation of formations of known heat production with subsurface structures when combined with a suite of existing techniques for estimating heat production may lead to more accurate results

timing of glaciation during the last glacial cycle evaluating the concept of a global last glacial maximum lgm abstract it has long been known that mountain glaciers and continental ice sheets around the globe reached their respective maximum extent at different times during the last glacial cycle often well before the global last glacial maximum lgm c 23 19 ka which is formally defined by peaks in global sea level and marine oxygen isotope records however there is increasing evidence from around the world that it was not only mountain glaciers which were asynchronous with the global lgm but also some regions of the large continental glaciers the barents kara ice sheet in northern eurasia together with a majority of ice masses throughout asia and australasia reached their maximum early in the last glacial cycle a few thousand years before the global lgm period the east antarctic ice sheet also reached its maximum extent several millennia before the global lgm in numerous mountainous regions at high mid and low latitudes across the world glaciers reached their maximum extent before marine isotope stage mis 2 in mis 5 4 and 3 this is in contrast to most sectors of the laurentide ice sheet the cordilleran ice sheet the se sector of the fennoscandinavian ice sheet and the alpine ice sheet in central europe which appear to have reached their maximum close to the global lgm in mis 2 the diachronous maximum extents of both mountain glaciers and continental ice sheets during the last glacial cycle means that the term and acronym last glacial maximum lgm has limited chronostratigraphical meaning when correlating glacial deposits and landforms

the distribution of radiogenic heat production as a function of depth in the sierra nevada batholith california geochemical analyses and geobarometric determinations have been combined to create a depth vs radiogenic heat production database for the sierra nevada batholith california this database shows that mean heat production values first increase then decrease with increasing depth heat production is 2 aw m 3 within the 3 km thick volcanic pile at the top of the batholith below which it increases to an average value of 3 5 aw m 3 at 5 5 km depth then decreases to 0 5 1 aw m 3 at 15 km depth and remains at these values through the entire crust below 15 km below the crust from depths of 40 125 km the batholith s root and mantle wedge that coevolved beneath the batholith appears to have an average radiogenic heat production rate of 0 14 aw m 3 this is higher than the rates from most published xenolith studies but reasonable given the presence of crustal components in the arc root assemblages the pattern of radiogenic heat production interpreted from the depth vs heat production database is not consistent with the downward decreasing exponential distribution predicted from modeling of surface heat flow data the interpreted distribution predicts a reasonable range of geothermal gradients and shows that essentially all of the present day surface heat flow from the sierra nevada could be generated within the 35 km thick crust this requires a very low heat flux from the mantle which is consistent with a model of cessation of sierran magmatism during laramide flat slab subduction followed by conductive cooling of the upper mantle for 70 m y the heat production variation with depth is principally due to large variations in uranium and thorium concentration potassium is less variable in concentration within the sierran crust and produces relatively little of the heat in high heat production rocks because silica content is relatively constant through the upper 30 km of the sierran batholith while u th and k concentrations are highly variable radiogenic heat production does not vary directly with silica content d 2005 elsevier b v all rights reserved

the heat flow heat generation relationship implications for the nature of continental crust abstract the apparent linear relationship between surface heat flow q and heat generation a is usually interpreted in terms of heat flow provinces i e terrains that have a common tectonothermal history and a uniform mantle component of heat flow the slope d of the linear regression of heat flow on heat generation is an indication of the thickness of the upper heat producing layer for many terrains d is numerically similar to the depth of a major mid crustal transition zone these observations are modelled by a two layer crust consisting of an upper layer approximately 10 15 km thick of variable heat generation underlain by a layer about 20 km thick in which heat generation is lower and more uniform than that in the upper layer the model is well able to simulate q a regression parameters for different sets of real data it is also consistent with other geological and geophysical observations the higher and more variable heat generation of the upper layer is consistent with ideas concerning removal of heat producing elements from the lower layer during amphibolite to granulite metamorphism and their redistribution into the upper crust further redistribution of heat producing elements may occur in zones of hydrothermal circulation whose depth is a function of stress pressure and temperature and which may migrate vertically in response to stress changes during uplift and erosion large scale metamorphism to granulite facies has been postulated as one mechanism for stabilisation of continental crust in the late archaean it is shown however that redistribution of heat producing elements in such a process would have only a small effect on crustal geotherms so that partitioning of heat production was not a major factor in the crustal stabilisation

genesis of chlorine and sulphur in fumarolic emissions at vulcano island italy assessment of ph and redox conditions in the hydrothermal system chlorine and sulphur bearing compounds in fumarole discharges of the la fossa crater at vulcano island italy can be modelled by a mixing process between magmatic gases and vapour from a boiling hydrothermal system this allows estimating the compounds in both endmembers magma degassing cannot explain the time variation of sulphur and hcl concentrations in the deep endmember which are more probably linked to reactions of solid phases at depth before mixing with the hydrothermal vapours based on the p t conditions and speciation of the boiling hydrothermal system below la fossa the hcl and stot contents in the hydrothermal vapours were used to compute the redox conditions and ph of the aqueous solution the results suggest that the haematite magnetite buffer controls the hydrothermal fo2 values while the ph has increased since the end of the 1970s the main processes affecting ph values may be linked to na ca exchanges between evolved seawater feeding the boiling hydrothermal system and local rocks while na is removed from water calcium enters the solution undergoes hydrolysis and produces hcl lowering the ph of the water the increasing water rock ratio within the hydrothermal system lowers the ca availability so the aqueous solution becomes less acidic seawater flowing towards the boiling hydrothermal brine dissolves a large quantity of pyrite along its path in the boiling hydrothermal system dissolved sulphur precipitates as pyrite and anhydrite and becomes partitioned in vapour phase as h2s and so2 these results are in agreement with the paragenesis of hydrothermal alteration minerals recovered in drilled wells at vulcano and are also in agreement with the isotopic composition of sulphur emitted by the crater fumaroles

investigation of the he solubility in h2oâco2 bearing silicate liquids at moderate pressure a new experimental method we have designed the first available experimental method capable to investigate the solubility of inert gases in h2o co2 bearing silicate melts in a large range of pressures the method overcomes the difficulties imposed by the physical state of volatiles at room conditions experiments were done by using an internally heated pressure vessel where sealed capsules containing the sample are introduced the peculiarity of the method consists in the capability of loading in accurately known proportions even lower than ppm volatiles in a gaseous state at room conditions gas is loaded as a weighed amount of a gas bearing glass which was previously prepared by using the same gas as a pressure medium of a superliquidus experimental run by analyzing the gas concentration in the prepared glass the glass itself can be used as a gas source we applied this method in order to investigate the helium solubility in silicate melts having dissolved volatile mixtures mostly composed of h2o and co2 in a range of pressure suitable to provide useful information regarding pre eruptive magma degassing our results indicate that helium solubility is strongly affected by the h2o content in silicate liquid displaying an increase by about a factor three as a consequence of the addition of 3 wt h2o to the melt taking into account the physical mechanism of he dissolution the sites of the silicate melt structure where noble gases can be accommodated drastically increase by adding modest aliquots of h2o the influence of dissolved co2 on helium solubility is not certain although few signs would suggest an opposite effect with respect to h2o at least in basalt melts on the basis of the obtained results we could reasonably expect that the helium behavior during the degassing of h2o co2 bearing magmas is sensibly different with respect to a h2o co2 free silicate liquid therefore the effect of the major volatiles on noble gas solubility in magmas should be taken into account in the investigation of several geological processes such as magma genesis ascent and degassing or mantle evolution

the influence of second scale convection on the thickness of continental lithosphere and crust abstract the effect of sublithospheric convection on the thickness and structure of the continental lithosphere is studied in numerical models assuming different rheologies newtonian non newtonian and temperature and pressure dependent heat fluxes and heating modes bottom versus internal heating the stagnant regions near the top of the models are identified with the lithosphere we distinguish a seismic and thermal lithosphere controlled by temperature an elastic lithosphere controlled by viscosity and a mechanical lithosphere controlled by strain rate strong lateral thickness undulations with a thick lithosphere above the downwelling regions and a thin lithosphere above the upwelling regions develop the thickness of the elastic lithosphere is about two thirds of the mechanical lithosphere while the ratio of the elastic to the thermal lithosphere varies between 0 4 and 0 8 the time dependence of some models with internal heating and a surface heat flow of 20 mw m 2 is characterized by long periods of the order of 1 ga close to steady state and short periods 100 ma of changing cell patterns and lithospheric thicknesses models showing thick lithospheric roots suggest that the mantle beneath some old shields may be associated with cold slowly downwelling convective flow rather than being firmly attached to the lithosphere the missing gravity and topography signals from such regions can be explained by elastic bending of the lithosphere and by dynamic adjustment of the moho observed lithospheric thickness variations in europe and their minimum to maximum spacing agree well with the models suggesting sublithospheric convection to be the cause compared to other observed features thickness undulations of the lithosphere seem to provide the strongest indications for sublithospherical convection relatively low viscosities in the lower crust may lead to a long term decoupling of surface topography from moho topography and mantle dynamics the moho depth is capable of adjusting to mantle stresses within relaxation times of the order of 100 ma while surface topography may flatten out such a mechanism may be important in regions with a deep moho such as fennoscandia or with a shallow moho such as the pannonian basin neither region showing a pronounced surface topography

heat flow and heat generation in the archaean dharwar cratons and implications for the southern indian shield geotherm and lithospheric thickness abstract we report terrestrial heat flow density measurements from 11 new sites in the archaean eastern and western dharwar cratons of the southern indian shield the new values together with already published data have yielded a mean heat flow of 40 3 4 s d mw m 2 n 11 for the eastern dharwar craton which is a predominantly gneiss granite terrain the mean heat flow in the archaean supracrustal belts of western dharwar craton which is a granite greenstone terrain is 31 4 1 s d mw m 2 n 4 the observed difference in surface heat flow between the two cratons is ascribed to differences in radiogenic heat production in upper crustal layers inferred to be related to different crust forming processes it has been argued that low heat production appears to be an inherent characteristic of the crust similar to that of the western dharwar craton which evolved during the early archaean and suffered depletion of the lithophile elements of its lower crust prior to the late archaean radiogenic heat production measurements were carried out on borehole core samples for one heat flow site sortur and data have been compiled from the literature on three other sites and on a variety of rocks of the southern indian shield heat flow and radiogenic heat production for sortur when combined with the published data define a linear relation r 0 97 with a slope of 11 5 km and an intercept of 23 mw m 2 the thickness of the thermal lithosphere beneath the dharwar cratons is over 200 km thereby indicating beneath the cratons the existence of deep continental roots a concept which is also supported by teleseismic p wave travel time data the geothermal data has clearly demonstrated that the archaean dharwar cratons of the indian landmass are associated with low mean surface heat flow 37 7 mw m 2 reduced heat flow moho heat flux 12 17 mw m 2 and a cool and thick lithosphere all characteristics of many archaean early proterozoic terrains of other shields it is inferred that the thermal structure of the south indian lithosphere is identical with that of other cratons

the evolution of a dynamic geological system the support of a gis for geochemical measurements at the fumarole field of vulcano italy abstract the island of vulcano aeolian arc southern italy has displayed several periods of volcanic unrest since the end of the last eruption 1890 we report here results obtained from a long term survey concerning variations of both the steam output and the exhaling surface area at the summit crater fumarolic field of la fossa the field measurements analysed in a geographical information system gis show a highly dynamic volcanic system in which deep variations in the geochemistry and the temperature of the released fluids were accompanied by fluctuations in the mass output of steam and the topography of the crater field the use of a gis facilitated digitized reconstructions of maps of the crater field in addition to analysis of the steam flux data the fumarolic field expanded its surface area from 50 m 2 in 1983 to more than 2400 m 2 in 1995 accompanied by an increase in steam output from 152 to about 1400 tonnes per day the possibility that the observed phenomena are related to volcano tectonic activity and to magma uprising is taken into consideration

bone needle fragment in lgm from the shizitan site china archaeological evidence and experimental study an eyed bone needle fragment found in shizitan 29 site shanxi province dated to ca 23 26 ka cal bp is one of the early needles with a precise stratigraphic context and date among the open air palaeolithic sites in north china although the needle was found broken based on microwear observation and experiments in making and using bone needles we conclude that it had been used for sewing further archaeological evidence including a sandstone needle shaping stone drilling tools perforated ornaments and microscopic evidence of thread support the presence of a bone needle at the shizitan 29 site it was the same type as the bone needles used in siberia during the late pleistocene and the use of needles at shizitan was one of the strategies for making warm clothes to adapt to the coming of the last glacial maximum lgm 24 000 18 000 cal bp

the episodic and abrupt geochemical changes at la fossa fumaroles vulcano island italy and related constraints on the dynamics structure and compositions of the magmatic system abstract herein we report on the chemical and isotopic c h o and he compositions of the fluids from la fossa crater fumaroles of vulcano from 1999 to 2010 consistent with records obtained since the end of the 1980s our data show that the geochemical features of the fumarole system have experienced several episodes of remarkable change each lasting no more than a few months typical signatures of these short term anomalies are large increments in co 2 n 2 and he concentrations coupled to increased 13 c 12 c isotopic ratios but their meaning remains widely debated within a model of fumarolic fluids based on mixing between hydrothermal and magmatic endmembers we have developed a novel approach to constrain chemical he co 2 and n 2 he and isotopic 13 c 12 c d h and 3 he 4 he ratios of the magmatic endmember during the short term anomalies although much of the geochemical variability in fumaroles results from changes in mixing proportions the magmatic fluid unquestionably shows significant variations in time the magmatic he co 2 n 2 he 13 c 12 c and 3 he 4 he values throughout 1988 1996 differed from those feeding the anomaly at the end of 2004 early clues of the new magmatic fluid appeared in 1998 1999 far from any short term anomaly whereas new and old magmatic fluids coexisted after 2004 we quantitatively prove that the detected geochemical changes are consistent with the degassing path of a magma having a latitic composition and suggest the presence of two magma ponding levels at slightly different pressures where bubble melt decoupling can occur the different he isotope compositions at these levels suggest low hydraulic connectivity typical of a complex reservoir with dike and sill structures in this framework the short term geochemical anomalies are probably due to gas accumulation at the top of magma bodies followed by massive escape or activation of new degassing levels in the reservoir for which the stress field almost certainly plays a key role such a scenario explains the observed increases in both fumarole output and shallow high frequency seismicity due to increased pore pressure during the anomalies while being consistent with the concomitant absence of any deep seismicity or ground deformation eventually related to magma movement

isotopic variation of the hydrothermal system on vulcano island italy the isotopic and chemical composition of thermal waters and the isotopic composition of high temperature fumarolic steam at vulcano island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water seawater is not a component in this system the isotopic values of the fumaroles indicate a local magmatic composition of 7 to 8 18o and 5 to 15 d the high d values of this vapor may reflect contamination of the magma by connate water the isotopic and chemical composition of water from well w2 indicates the existence of geothermal fluid formed by mixing of hcl and so2 bearing condensates of volcanic origin with groundwater with subsequent evolution via water rock interaction the estimated isotopic composition of the geothermal water is 18o 1 and d 5 local shallow seismic events result in a temporary increase in fracture permeability enabling the mixing of magmatic vapor with groundwater or geothermal water tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles

geochemical evidence for mixing between fluids exsolved at different depths in the magmatic system of mt etna italy abstract a 4 year geochemical survey of some fumaroles at the voragine summit crater of mt etna was performed in combination with synchronous monitoring of peripheral gas emissions at the base of the volcano this was the first geochemical study at mt etna to have included the abundances of ar he and c isotopes once the effects of postmagmatic shallow processes were identified and quantitatively removed the he ar co 2 systematics of the voragine crater fumaroles and peripheral gas emissions described the same degassing path combining the carbon isotope composition with information about noble gases provided evidence that the crater fumaroles are fed from a two endmember mixture composed of a deep member coming from pressures between 200 and 400 mpa depending on time and a shallower one exsolved at 130 mpa similar mixing processes probably also occur in gases from peripheral vents the simultaneous assessment of 13 c co2 and he ar values of crater fumaroles over time has identified simple changes in the mixing proportion between the two endmembers and moreover periods during which the exsolution pressure of the deep fluid increased these periods seem to be linked to pre eruptive phases of the volcano the identified open system degassing processes are indicative of efficient bubble melt decoupling at depth whereas the mixing process requires a convective transfer of the deeply exsolved fluids toward shallower levels of magma where further vapor is exsolved in agreement with the most recent geophysical and petrological data from mt etna these observations allow inferences about a deep portion of the plumbing system 5 to 12 km b s l comprising sill like reservoirs connected by small vertical structures and a main reservoir at 2 3 km b s l that is probably fluxed by magmatic volatiles

heat flow and structure of the lithosphere in the eastern canadian shield twenty two new determinations of heat flow and radiogenic heat production in the superior and grenville provinces of the canadian shield are presented the new data and previously published measurements strongly constrain the thermal structure of the eastern canadian shield in the abitibi greenstone belt heat flow gradually increases from 29 mw m 2 near the grenville front to 44 mw m 2 east of the kapuskasing uplift this heat flow variation is interpreted in terms of crustal thickening and increased thickness of a tonalitic layer with average heat production of about 1 1 w m 3 this interpretation based on estimated heat production of major rock types in the region is consistent with crustal models derived from recent seismic reflection and refraction studies it also leads to an estimate of about 12 mw m 2 for the mantle heat flow beneath the area the average heat flow in the grenville province 41 10 mw m 2 is the same as that of the superior province this similarity and the lack of significant variation of heat flow across the grenville front indicate that the crust on both sides of the front has similar heat production and thus composition in the western part of the grenville province heat flow reaches high values in the vicinity of the boundary between the allochtonous polycyclic and monocyclic belts where enriched granitic plutons are found in the crystalline terranes in the central part of the grenville province heat flow and heat production are related to each other the parameters of the linear heat flow heat production relationship qr 30 2 in mw m 2 and d 7 1 1 7 km are close to those of the much younger appalachian province implying that the higher appalachian heat flow is due solely to higher heat production in the upper crust the data provide no evidence for variation of mantle heat flow between the superior grenville and appalachian provinces whose tectonic ages range between 2700 and 400 ma the small value of the mantle heat flow about 12 mw m 2 implies that the depth to the 450 c isotherm which controls the effective elastic thickness of the lithosphere is very sensitive to crustal heat production

steam output from fumaroles of an active volcano tectonic and magmatic hydrothermal controls on the degassing system at vulcano aeolian arc the results from measurements of extensive parameters steam output and exhaling surface area taken at the crater fumarolic field of vulcano island aeolian arc southern italy are reported along with a detailed description of the measuring method the steam emission rate increased by 1 order of magnitude during the observation time 1983 1995 while its concentration in the released gases was only slightly changed during the same period the total exhaling surface expanded from 50 m2 to more than 2400 m2 and evolved following preferential trends that coincide with the main tectonic structures of the island the observed peaks in steam output show a positive correlation with episodes of volcanic activity unrest the temporal increase of steam output and the observed development in the exhaling surface areas are consistent with a volcano tectonic triggering of the exhaling activity particularly the peaks in the steam output are interpreted as a consequence of degassing from an active magma slowly moving toward the surface

a heat production model of a shield area and its implications for the heat flow heat production relationship the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust to constrain thermal models of the crust we measured heat production and thermal conductivity in rocks from this terrain using standard gamma ray spectrometry and divided bar techniques these data when used in a two dimensional model of shield crust show that estimates of surface heat flow and surface heat production yield the well known linear relationship between surface heat production and surface heat flow observed for heat flow provinces this demonstrates that determinations of heat production with depth based on inversion of the linear heat production heat flow relationship are non unique

radioelement concentrations in the deep profile through precambrian basement of the vredefort structure the vredefort basement granite in south africa forms the core of an undomed and overturned sequence of precambrian strata slawson 1976 proposed that the granite core has also been overturned exposing to view a thick section through the archean crust incrasing in depth toward the center of the dome profiles across the vredefort basement provide an opportunity for studying the distribution of u th and k with depth in the upper and middle crust detailed radioelement concentration profiles across the granitic basement showed that 1 the central part of the basement core is depleted in th and u relative to the perimeter and the concentration of th and u falls off regularly from the basement margin inward 2 the distribution of the radioelements and the distribution of heat production with depth over the outer 8 km are consistent with an exponential depth function 3 the felsic rocks of the central basement are characterized by high k u and th u ratios and the ratios k u k th and th u increase from the margin inward and 4 mafic granulites which occur in the central regions of the dome have normal k u k th and th u ratios high grade metamorphic environment resulted in the depletion of bothmore u and th relative to k in the greater proportion of the felsic rocks from the central regions of the vredefort basement depletion of u was far greater than that of th the normal th u k u and k th ratios in mafic rocks in close proximity to the felsic rocks suggest that mineral assemblages have a strong control on the behavior of the radioelements during regional metamorphism in the vredefort basement less

environmental reconstruction and dating of shizitan 29 shanxi province an early microblade site in north china global cooling during the last glacial maximum lgm posed significant challenges to peoples living in northern eurasia using micromorphology pollen and non pollen palynomorphs npp and faunal analyses this study reconstructs the local paleoenvironmental contexts of repeated ephemeral occupations at shizitan 29 in shanxi province north china across the lgm from ca 28 to 18 ka cal bp followed by a gap until a final occupation ca 13 5 ka cal bp among the significant finds at shizitan 29 are remains of 285 hearths and a rich lithic assemblage that contains the earliest radiocarbon dated evidence for microblades in china appearing first in layer 7 the environmental data show that the low mountains and tributary river valleys of the yellow river in the loess plateau provided abundant sources of water and food in spite of environmental fluctuations microblade producing groups repeatedly visiting this locality survived severe climate change by making use of fire selective herbivore hunting processing plant foods with grinding stones and symbolic ornamentation such as ostrich shell beads npp data also indicate the potential presence of flax and other fiber processing the shizitan 29 data demonstrate how humans adapted to challenging local conditions throughout the lgm allowing them to stay within this northerly region without migrating to warmer southern latitudes

seismic events at vulcano italy during 1988 1992 abstract a classification of seismic events is proposed that originate on vulcano aeolian islands southern tyrrhenian sea and adjacent regions into four broad classes 1 shocks that exhibit single peaked spectra 2 typical earthquakes with distinct p and s phases 3 irregular shaped events with ill defined to undetectable s phases and 4 long period events with dominant frequency peak less than 2 hz a hypothesis is put forward that the shocks occurring within the volcanic cone of la fossa are mainly related to intense fumarolic activity of high temperature more than 650 c in october 1992 estimation of seismic energy release within two distinct sectors one including la fossa cone the other external to it during 1988 1992 has been developed in order to evaluate the level of seismic activity of the system over the time here analysed the rate of seismic energy density release at la fossa was 4 71 1014 erg km 2 yr 1 that is significantly larger than that of the surrounding areas furthermore the energy partition estimate indicates that within la fossa seismic energy release associated with rock failure processes is on the whole about 3 6 times larger than that of fluid driven shocks the latter appear to be concentrated at rather shallow depths 400 1000 m where geochemical analyses and geothermal surveys indicate the sealing action of hydrothermal minerals estimated b values of the gutenberg richter magnitude frequency relation range between 0 81 0 27 and 1 45 0 29 within la fossa whereas a value around 1 6 has been calculated for the external sector the comparison between data presented in this paper and those from recent geophyical and geochemical investigations shows that appreciable increments in the rate of seismicity are accompanied with significant modifications in the chemistry of fumarolic gases and in the ground deformation pattern recorded at the base of the active cone

bubble plumes generated during recharge of basaltic magma reservoirs co2 is relatively insoluble in basaltic magma at low crustal pressures it therefore exists as a gas phase in the form of bubbles in shallow crustal reservoirs over time these bubbles may separate gravitationally from the magma in the chamber as a result any new magma which recharges the chamber from deeper in the crust may be more bubble rich and hence of lower density than the magma in the chamber using scaling arguments we show that for typical recharge fluxes such a source of low viscosity bubble rich basalt may generate a turbulent bubble plume within the chamber we also show that the bubbles are typically sufficiently small to have a low reynolds number and to remain in the flow we then present a series of analogue laboratory experiments which identify that the motion of such a turbulent bubble driven line plume is well described by the classical theory of buoyant plumes using the classical plume theory we then examine the effect of the return flow associated with such bubble plumes on the mixing and redistribution of bubbles within the chamber using this model we show that a relatively deep bubbly layer of magma may form below a thin foam layer at the roof if as an eruption proceeds there is a continuing influx at the base of the chamber then our model suggests that the bubble content of the bubbly layer may gradually increase this may lead to a transition from lava flow activity to more explosive fire fountaining activity the foam layer at the top of the chamber may provide a flux for the continual outgassing from the flanks of the volcano ryan am geophys union geophys monogr 91 1990 and if it deepens sufficiently it may contribute to the eruptive activity vergniolle and jaupart j geophys res 95 1990 2793 3001

multiparametric approach in investigating volcano hydrothermal systems the case study of vulcano aeolian islands italy seismic activity ground deformation and soil and fumarole temperatures acquired during 2004 2007 at vulcano aeolian islands are analysed and the time relations among the different time series are discussed changes in temperature of fumarolic gases took place during four anomalous periods november 2004 march 2005 october 2005 february 2006 august october 2006 july december 2007 at the same time as an increasing number of volcano seismic events in particular the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440 c and from 20 to 90 c respectively the maximum daily number of volcano seismic events was 57 reached during the second anomalous period this seismicity characterised by focal depth generally lower than 1 km below sea level b s l and composed of different kinds of events associated to both resonance and shear failure processes is related to the shallow dynamics of the hydrothermal system during the analysed period very few volcano tectonic earthquakes took place and tilt recordings showed no sharp or important changes in light of such observations the increases in both temperature and volcano seismic events number were associated to increases in the release of gas from a deep and stable magma body without magma intrusions within the shallow hydrothermal system indeed a greater release of gas from depth leads to increased fluid circulation that can promote increases in volcano seismic events number by both fracturing processes and resonance and vibration in cracks and conduits the different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body finally all the observed variations together with the changing temporal distribution of the different seismic event kinds suggest that the hydrothermal system at vulcano can be considered unsteady and dynamic

is there a relationship between seismic velocity and heat production for crustal rocks abstract several investigators proposed an empirical relationship between heat production and seismic velocity for rocks typical of the continental crust these relationships could allow for indirect resolution of the distribution of heat producing elements with depth new heat production data for rock samples from the pikwitonei granulite domain and the sachigo granite greenstone subprovince of the superior province do not follow these relationships indicating that heat production cannot be reliably predicted from seismic velocity these two parameters are not likely to be related as velocity depends upon the major mineral constituents of rocks whereas heat production results from radiogenic components concentrated in both major and trace minerals in rocks

high radiogenic heat production in the kerala khondalite block southern granulite province india in situ radioelemental k u and th analysis and heat production estimates have been made at 59 sites in the kerala khondalite block kkb of the southern granulite province sgp of india together with the in situ analyses on granulites and gneisses previously reported from 28 sites and heat production estimated from the published geochemical analyses on granites and syenites of the kkb the new data set allows good characterization of heat production for the major granulite facies rocks and granitoids of the kkb garnet biotite gneisses are characterized by high levels of th and u with mean values of 60 and 3 ppm respectively khondalites leptynites and charnockites have slightly lower levels of th 23 20 and 22 ppm respectively and u 2 9 2 4 and 0 9 ppm respectively the mean k u th abundances for the granites leucogranites and granitic gneisses ranges from 3 9 to 4 3 2 6 to 4 3 ppm 22 to 50 ppm respectively and for the syenites 4 8 2 ppm and 5 7 ppm mean radiogenic heat production values for garnet biotite gneiss khondalite leptynite and charnockite are 5 5 2 7 2 4 and 2 2 w m 3 respectively for the granites leucogranites granitic gneisses and syenites it is 2 6 3 4 4 6 and 1 4 w m 3 respectively heat production of granulite facies rocks which are the most abundant rocks in kkb correlate well with th but less with u suggesting that variation is caused by th and u bearing accessory minerals such as monazite and zircon the high heat production of the kkb granulites are in contrast to the low heat production of the late archaean granulites of the northern block nb of the sgp which are highly depleted in radioelements and also the granulites of madurai block mb that have higher radioelemental abundances than in the granulites of the nb the high heat production of the kkb granulites could be due to the nature of protoliths and or metasomatism associated with neoproteroic to pan african alkaline magmatic activity represented by alkali granite and syenite carbonatite emplacements and emplacement of pegmatites

ground deformation induced by geothermal processes a model for la fossa crater vulcano island italy 1 since the last eruption in 1888 1890 volcanic activity at vulcano island aeolian archipelago italy has been limited to fumarolic degassing concentrated near the active cone of la fossa crater in the northern sector of the island during the period 1990 1996 edm and leveling data indicate a deflation and contraction focused on the la fossa cone we jointly inverted these data sets using for volume change both a spherical mogi 1958 source and an ellipsoid as defined by davis 1986 the best fitting source for the 1990 1996 deflation is a shallow subvertical prolate ellipsoid positioned roughly under the crater our model is consistent with increased activity in a shallow hydrothermal system supported by observations of water evaporation testified by the increase of steam emission and temperature at crater fumaroles the fluid loss from a shallow geothermal reservoir is the most likely cause of the subsidence recorded at la fossa cone during the same period this clear linkage between the deformation signals and hydrothermal activity has important implications in the hazard assessment and monitoring of the vulcano activity

radioactive element distribution in the archean granulite terrane of jequie bahia brazil the radioactive element distribution in the archean granulite facies rocks of jequie brazil has been determined the k rb ratios show a large spread with majority of the values falling within the normal field k rb 300 the th u ratios fall into two groups one group with values in the range of 1 7 to 2 6 whereas the other group show th u values greater than 7 7 to 25 these distributions can be explained on the basis of the presence of accessory minerals apatite and zircon the relatively high concentrations of the radioactive and other elements in jequie granulites probably represents the relict primary geochemical character little modified during metamorphism the radiogenic heat production data for the area are calculated and using the measured regional heat flow value from nearby area an estimate of the relative thickness of the continental lithosphere is made using the model developed by oxburgh 1981

the significance of shuidonggou locality 12 to studies of hunter gatherer adaptive strategies in north china during the late pleistocene the effect of rapid climate change during the late upper paleolithic on hunter gatherers is attested by a variety of signals in the archaeological record one of these the spread of the microblade technology in north china shows a particularly close relationship with climate change the appearance of microblades and functionally related bone and ground stone technology at sdg12 is particularly revealing of this late pleistocene adaptive diversification in north china sdg12 and other records suggest that microblade technology flourished in harsh environments that demanded high residential mobility that in addition to their use in hunting weaponry microblades were used in manufacturing the sophisticated cold weather clothing required for winter mobility is shown by the presence of bone needles and a bone knife handle slotted to accept microblades the sdg12 fauna and ground stone indicate an attendant shift from a more large game dominated to a more plant and small game dominated diet that included net hunting and demanded a variety of production tasks that included net making spinning and extensive stone boiling to maximize nutrient returns and as a step in manufacturing we suspect these changes are the root cause of subsequent changes in social structure

a stratigraphical basis for the last glacial maximum lgm abstract the last glacial maximum lgm is widely used to refer to the episode when global ice volume last reached its maximum and associated sea levels were at their lowest however the boundaries of the interval are ill defined and the term and acronym have no formal stratigraphical basis this is despite a previous proposal to define it as a chronozone in the marine records on the basis of oxygen isotopes and sea levels spanning the interval 23 19 or 24 18 ka and centred on 21 ka in terrestrial records the lgm is poorly represented since many sequences show a diachronous response to global climate changes during the last glacial cycle for example glaciers and ice sheets reached their maximum extents at widely differing times in different places in fact most terrestrial records display spatial variation in response to global climate fluctuations and changes recorded on land are often diachronous asynchronous or both leading to difficulties in global correlation however variations in the global hydrological system during glacial cycles are recorded by atmospheric dust flux and this provides a signal of terrestrial changes whilst regional dust accumulation is recorded in loess deposits global dust flux is best recorded in high resolution polar ice core records providing an opportunity to define the lgm on land and establish a clear stratigraphical basis for its definition on this basis one option is to define the global lgm as an event between the top end of greenland interstadial 3 and the base onset of greenland interstadial 2 spanning the interval 27 540 23 340 ka greenland stadial 3 this corresponds closely to the peak dust concentration in both the greenland and antarctic ice cores and to records of the global sea level minima this suggests that this definition includes not just the coldest and driest part of the last glacial cycle but also the peak in global ice volume the later part of the lgm event is marked by heinrich event 2 which reflects the onset of the collapse of the laurentide at c 24 ka together with other ice sheets in the north atlantic region a longer and later span for the lgm may be desirable although defining this in chronostratigraphical terms is problematic whichever formal definition is chosen this requires the contribution of the wider quaternary community

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

time space variation of volcano seismic events at la fossa vulcano aeolian islands italy new insights into seismic sources in a hydrothermal system we investigated the relationship between volcano seismic events recorded at la fossa crater of vulcano aeolian islands italy during 2004 2006 and the dynamics of the hydrothermal system during the period of study three episodes of increasing numbers of volcano seismic events took place at the same time as geothermal and geochemical anomalies were observed these geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids three classes of seismic events long period high frequency and monochromatic events characterised by different spectral content and various similarity of the waveforms have been recognised these events clustered mainly below la fossa crater area at depths of 0 5 1 1 km b s l were space distributed according to the classes based on their features we can infer that such events at vulcano are related to two different source mechanisms 1 fracturing processes of rocks and 2 resonance of cracks or conduits filled with hydrothermal fluid in the light of these source mechanisms the increase in the number of events at the same time as geochemical and geothermal anomalies were observed was interpreted as the result of an increasing magmatic component of the hydrothermal fluids implying an increase of their flux indeed such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids increased pore pressures gave rise to fracturing processes while the increased fluid flux favoured resonance and vibration processes in cracks and conduits finally a gradual temporal variation of the waveform of the hybrid events one of the subclasses of long period events was observed likely caused by heating and drying of the hydrothermal system

heat flow and crustal thermal structure in the late archaean closepet granite batholith south india the late archaean closepet granite batholith in south india is exposed at different crustal levels grading from greenschist facies in the north through amphibolite and granulite facies in the south along a 400 km long segment in the dharwar craton two areas pavagada and magadi located in the main mass of the batholith best represent the granitoid of the greenschist and amphibolite facies crustal levels respectively heat flow estimates of 38 mw m 2 from pavagada and 25 mw m 2 from magadi have been obtained through measurements in deep 430 and 445 m and carefully sited boreholes measurements made in four boreholes of opportunity in pavagada area yield a mean heat flow of 39 4 s d mw m 2 which is in good agreement with the estimate from deep borehole the study therefore demonstrates a clear cut heat flow variation concomitant with the crustal levels exposed in the two areas the mean heat production estimates for the greenschist facies and amphibolite facies layers constituting the main mass of the batholith are 2 9 and 1 8 w m 3 respectively the enhanced heat flow in the pavagada area is consistent with the occurrence of a radioelement enriched 2 km thick greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented in the magadi area the crustal heat production models indicate similar mantle heat flow estimates in the range 12 14 mw m 2 consistent with the other parts of the greenstone granite gneiss terrain of the dharwar craton

heat flow in the trans hudson orogen of the canadian shield implications for proterozoic continental growth fourteen new heat flow and radiogenic heat production measurements have been obtained in the paleo proterozoic trans hudson orogen of the canadian shield this orogen which consists of several distinctive belts corresponds to a pulse of crustal growth through island arc magmatism between 1 9 and 1 8 ga the data now available include 17 previously published measurements heat flow variations that are related to the history of magmatism and internal differentiation of the belts provide constraints on the crustal assemblages in the different belts of the orogen the average and standard deviation of heat flow values for the entire orogen 425 11 mw m 2 are identical to those of the older superior province and of the younger grenville province for the orogen as a whole heat flow is weakly correlated to the heat production of surface rocks high heat flow values are found in the thompson belt consisting of metasedimentary rocks deposited on the ancient continental margin of the superior craton there the accumulation of sediments derived from older and differentiated continental upper crust has resulted in significant concentrations of rdioelements in large volumes of rocks the heat flow is low in the belts that expose juvenile proterozoic crust consisting mostly of arc related volcanic rocks in the flin flon snow lake belt the average heat flow is the same as the average of the orogen the low heat production and the lack of correlation between heat flow and heat production suggest that the supracrustal volcanics exposed a t the surface are thin and rest on a basement richer in radioelements in the lynn lake belt the heat flow is significantly lower than the average for the orogen although the surface heat production is not low the heat flow data require a thin 10 kin surface layer overlying the mid and lower crust depleted in ra dioelements around the town of lynn lake heat flow is consistently low over a distance of m40 kin the coincidence between this cold spot and anomalously thick crust suggests that deep crustal roots may be preserved because of the stronger rheology implied by the low temperatures the evolution of the trans hudson orogen exemplifies the interplay between the processes generating rocks of evolved composition which require crustal thickening and those forming normal continental crust with average thickness which require crustal flow and soft crustal rheology

a preliminary reconstruction of the paleoecological and paleoclimatic history of the chinese loess plateau from the application of biomarkers abstract this study provides a preliminary reconstruction of paleoecological and paleoclimatic history over the central chinese loess plateau clp during the last 8 1 ma based on biomarker records from the earliest of the chaona stratigraphic section throughout the section we found variations in n alkane and n alkan 2 one distributions and dramatic changes in six other biomarker proxies 1 n alkanes c27 c29 c31 c33 ratios 2 n alkanes c27 c31 ratios 3 cpi carbon preference index values for cpi h alk 4 values for cpi h ket 5 n alkane mean chain lengths acl alk and 6 n alkan 2 ones c29 c31 ratios the c29 n alkanes dominate the red clay sediments with little variability indicating that trees dominated the clp and that the climate was relatively stable and less variable during the 8 1 2 6 ma period in contrast the c31 n alkanes dominate the loess paleosol sediments and biomarkers vary with relatively greater amplitude and higher frequency indicating that grasses dominated the clp and the climate was more arid and variable these biomarker records chronicle a drying and cooling trend on the clp since 4 ma these records can be further divided into four stages with boundaries around 5 6 3 8 and 2 6 ma indicating that the clp vegetation and climate experienced four evolutionary phases broadly consistent with those inferred from other available proxy data

30 000 year old wild flax fibers a unique finding of wild flax fibers from a series of upper paleolithic layers at dzudzuana cave located in the foothills of the caucasus georgia indicates that prehistoric hunter gatherers were making cords for hafting stone tools weaving baskets or sewing garments radiocarbon dates demonstrate that the cave was inhabited intermittently during several periods dated to 32 to 26 thousand years before the present kyr b p 23 to 19 kyr b p and 13 to 11 kyr b p spun dyed and knotted flax fibers are common apparently climatic fluctuations recorded in the cave s deposits did not affect the growth of the plants because a certain level of humidity was sustained

thermal regime of the lithosphere in the canadian shieldthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geothermal studies were conducted within the framework of lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the canadian shield one of the main conclusions is that in the shield the variations in surface heat flow are dominated by the crustal heat generation horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements different methods constrain the mantle heat flow to be in the range of 12 18 mw m 2 most of the heat flow anomalies high and low are due to variations in crustal composition and structure the vertical distribution of radioelements is characterized by a differentiation index di that measures the ratio of the surface to the average crustal heat generation in a province determination of mantle temperatures requires the knowledge of both the surface heat flow and di mantle temperatures increase with an increase in surface heat flow but decrease with an increase in di stabi

rethinking the origin of microblade technology a chronological and ecological perspective abstract there are four hypotheses on the origin of microblade technology in north china i that it originated from siberia before the last glacial maximum ii that it emerged in siberia after the last glacial maximum iii that it developed from the long narrow flakes produced by the long established knapping tradition in north china and iv that it had multi regional origins among which a microblade industry may have emerged from the bipolar technology in northern china based on archaeological data from siberia mongolia the japanese archipelago korean peninsula and north china it is reasonable to say that the technological groundwork of siberia was more substantial and the initial microblade technology appeared in siberia earlier than in the other areas microblade technology was involved in core preparation systematic knapping soft hammer and indirect pressure flaking techniques which were all present in the blade technology in siberia but hardly ever evidenced in the traditional flaking technology systems in north china it is well accepted that the microblade technology was closely related the high mobility of foragers to live in harsh environments the climatic fluctuations of the last glacial in siberia were more severe than in low latitudes and placed greater subsistence pressure on hunter gatherers in siberia the advantages of the initial microblade technology in dealing with these hostile circumstances encouraged foragers to employ and develop it and finally generated its widespread use during the upper paleolithic through human migration and cultural transmission in northeast asia and north america

sapphirine bearing granulites from the sipiwesk lake area of the late archean pikwitonei granulite terrain manitoba canada sapphirine occurs in the orthopyroxene cordierite and feldspar sillimanite granulites in the sipiwesk lake area of the pikwitonei granulite terrain manitoba 97 40 w 55 05 n the orthopyroxene cordierite granulites have extremely high al2o3 24 5 wt and mgo 24 6 wt contents and contain sapphirine up to 69 2 wt al2o3 aluminous orthopyroxene up to 8 93 wt al2o3 cordierite spinel phlogopite and corundum sapphirine forms coronas mantling spinel and corundum corona sapphirine is zoned and its composition varies through the substitution mg fe mn si 2 al as a function of the phases with which it is in contact textural and chemical relationships of sapphirine with coexisting phases indicate that spinel cordierite reacted to form orthopyroxene sapphirine under conditions of increasing pressure moreover decreasing core to rim variation of al2o3 in orthopyroxene porphyroblasts suggests decreasing temperature during sapphirine formation on the basis of experimentally determined p t stability of the assemblage enstatite sapphirine cordierite and the al content of hypothetical fe2 free orthopyroxene associated with sapphirine and cordierite metamorphic temperatures and pressures are estimated to be 860 890 c and 3 0 11 2 kbar

density temperature and rheological models for the southeastern canadian cordillera implications for its geodynamic evolution two dimensional density temperature and rheological models are constructed for a 350 km northeast trending transect of the southeastern canadian cordillera all models highlight several major physical differences between foreland and hinterland lithosphere significant features of the density model are the presence of an anomalously low density 3 10 103 kg m 3 layer with a maximum thickness of 12 km beneath the moho in the hinterland the similar densities of the monashee terrane and the cratonic crust of the foreland and an increase in crustal thickness beneath the southern rocky mountain trench the temperature model shows steeper gradients and higher moho temperatures beneath the hinterland than beneath the foreland in the rheological model the hinterland is characterized by a thin brittle upper crust beneath which the entire lithosphere is hot weak and ductile in contrast the foreland is composed of a thick brittle upper crust with an additional brittle zone in the upper mantle the

exposed cross sections through the continental crust implications for crustal structure petrology and evolution abstract the continental crust is exposed in cross section at numerous sites on the earth s surface these exposures which appear to have formed by obduction along great faults during continental collision may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle from an examination of five complexes which meet these criteria it is concluded that the most prominent layering in the crust is not compositional but metamorphic the lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks respectively post metamorphic granitic intrusions are common at intermediate to shallow levels position of discontinuities in refraction velocity where present commonly correspond to changes in composition or metamorphic grade with depth the continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by cocorp field observations coupled with geochemical data indicate a complex evolution of the lower crust which can include anatexis multiple deformation polymetamorphism and reworking of older crustal material the complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments

radiogenic heat production in the continental crust abstract the thermal structure and evolution of continents depend strongly on the amount and distribution of radioactive heat sources in the crust determining the contribution of crustal rocks beneath a superficial layer is a major challenge because heat production depends weakly on major element composition and physical properties such as seismic wavespeed and density enriched granitic intrusives that lie at the current erosion level have a large impact on the surface heat flux but little influence on temperatures in the deep crust many lower crustal rocks that are poor in heat producing elements are restites from ancient orogenic events implying that enrichment of the upper crust was achieved at the expense of deeper crustal levels for the same total heat production concentrating heat sources in an upper layer acts to reduce temperatures in the lower crust thereby allowing stabilization of the crust the present day structure of the crust is a consequence of orogeny and should not be adopted for thermal models of the orogenic event itself this review summarizes information extracted from large data sets on heat flow and heat production and provides estimates of crustal stratification and heat production in several geological provinces analysis of global and regional data sets reveals the absence of a positive correlation between surface heat flow and crustal thickness showing that the average crustal heat production is not constant differences of heat flow between geological provinces are due in large part to changes of crustal structure and bulk composition collating values of the bulk crustal heat production in a few age intervals reveals a clear trend of decrease with increasing age this trend can be accounted for by radioactive decay indicating that thermal conditions at the time of crustal stabilization have not changed significantly for the average crustal thickness of 40 km moho temperatures are near solidus values at the time of stabilization suggesting an intrinsic thermal control on crustal thickness and heat production distribution crustal thickening by more than about 10 km above this mean value induces changes of gravitational potential energy that exceed the strength of the lithosphere for several provinces where strong constraints on heat production are available it is shown that prior to intracrustal fractionation only modest amounts of thickening were needed to generate the conditions of ultra high temperature metamorphism the tell tale signature of crustal heat production is anatectic and metamorphic events that lag the cessation of orogenic activity by several tens of million years crustal heat production is decreasing with time because it is due to the radioactive decay of uranium thorium and potassium its rundown is responsible for the secular cooling of lithospheric roots at a typical rate of about 100 k gy 1 implying complex thermal interactions with a convecting mantle that is not cooling at the same rate

radioelements and heat production of an exposed archaean crustal cross section dharwar craton south india the dharwar craton dc in south india exposes a tilted f30 km thick crustal section equivalent to upper middle and lower archaean continental crust the dc is composed of poly magmatic metamorphic terrains such as the western dharwar craton wdc and eastern dharwar craton edc whose contact is marked by the closepet granite batholith cg in situ gamma ray spectrometric analysis has been carried out to measure k u and th abundance at 1023 sites covering all major rock formations of the dc the data show that the greenschist and amphibolite facies tonalite trondhjemite granodioritic ttg gneisses of the wdc are poorer in radioelements compared to granodioritic gneisses of the edc similarly the wdc granites of the amphibolite facies region have lower abundance indicating their derivation from a depleted lower crust which had suffered an earlier crustal differentiation the elemental data on the gneisses in the wdc and edc do not show a difference between the greenschist and amphibolite facies but there is a marked depletion in the granulite facies the depletion reaches a maximum in the high p granulites in the southernmost part of the dc the elongate cg is an i type calc alkaline metaluminous granite which exposes a f12 km thick batholith where k is remarkably uniform but u and th show several fold increase with decreasing crustal levels heat production was calculated from the radioelemental data for estimating the radiogenic heat contribution of crust to heat flow we arrive at a present day crustal configuration comprising four northerly dipping metamorphic facies layers greenschist amphibolite metasomatized granulite and depleted granulite gross heat production of each layer is computed from heat production of constituent rocks and their abundance the crustal contribution is found to decrease from greenschist to granulite facies regions from 23 to 18 mw m 2 in the wdc 27 to 7 mw m 2 in the edc surface heat flow and the crustal contribution models indicate that mantle heat flow of the wdc is lower 7 10 mw m 2 compared to the edc 17 24 mw m 2 in the greenschist and amphibolite facies regions high mantle heat flow of 29 mw m 2 beneath the depleted granulite facies region of the edc appears anomalous in the dharwar craton

environmental change and human activity in the northeastern part of the north china plain during early mis 2 abstract marine isotope stage 2 mis 2 the coldest and the longest glacial during the last glacial period was an important interval for the development and evolution of microlithic cultures the zhaocun site located in the northeastern part of the north china plain is not only the first late paleolithic site discovered in the southern piedmont of the yan mountains but also an important representative of late pleistocene strata and fossil fauna in north china however there have been few studies of the upper cultural layer at the site which have focused on the development of paleolithic culture especially the microlithic technology in the context of environmental changes moreover no absolute age determinations are available here we present a study of the paleoenvironmental record of the zhibuchang profile at the zhaocun site during the interval of 27 6 23 6 cal kyr bp we conducted a stratigraphic study based on pollen and grain size analyses of 78 samples from the profile and obtained 7 ams 14c dates during 27 6 26 6 cal kyr bp the regional vegetation was relatively diverse meadow steppe dominated by artemisia and asteraceae the climate although colder and drier than today was the warmest record within the studied profile and was relatively favorable for human beings from 26 6 cal kyr bp with the onset of the last glacial maximum the climate became colder and more variable with two extreme climatic events occurred at 26 2 25 5 cal kyr bp and 24 3 23 6 cal kyr bp respectively a cold wet event from 26 2 to 25 5 cal kyr bp led to a drastic decline in local biodiversity which would have resulted in food shortages for human beings in addition previous areas available for human activities were gradually flooded due to the rising river level forcing the relocation of human beings and resulting in the termination of the cultural layer a cold dry event from 24 3 to 23 6 cal kyr bp which may correspond to north atlantic heinrich event 2 caused a further deterioration of the environment for human beings and may be a major cause of the absence of microlithic cultural remains on the northeastern part of the north china plain during late mis 2

isotopic and elemental partitioning of boron between hydrous fluid and silicate melt the fractionation of b and its isotopes between aqueous fluid and silicate melt has been studied from 550 to 1100 c and 100 500 mpa fluid melt partition coefficients are 1 for rhyolite melt this shows that b is not always strongly extracted from melts into hydrous fluids boron isotopic fractionation is large compared with the carbon and oxygen stable isotopic systems especially at high t and is most simply explained by differences in coordination trigonal vs tetrahedral among coexisting phases combined with earlier measurements on illite water 300 350 c b isotopic fractionation defines a temperature dependent trend from 300 to 1100 c because of the large magnitude and apparent low sensitivity to bulk composition b isotopic fractionation can be readily applied to studies of diagenesis hydrothermal alteration of planetary bodies subduction zone processing and arc magma generation and magma chamber evolution

the paleolithic site of longwangchan in the middle yellow river china chronology paleoenvironment and implications the longwangchan paleolithic site situated on the yellow river terraces in the hukou area shaanxi province china was found in 2003e2004 and two areas localities 1 and 2 of the site were excavated in 2005e2008 abundant stone artifacts including microliths a grinding stone fragment and a shovel with some animal bones and shells were recovered from locality 1 in this study the cultural deposits from locality 1 were dated using radiocarbon and optical dating techniques and the sediment properties of the deposits were analyzed the results show that the age of the deposits ranges from 29 to 21 ka and most of them were deposited between 25 ka and 29 ka this indicates that corresponds to late marine isotope stage mis 3 and early mis 2 during the human occupation period the climate in this area became colder and drier sediments from beds where the grinding slab and the shovel were found were dated to w25 ka which is the oldest among the grinding stones found in china the microliths and the grinding stone are important evidence for an incipient socio economic process that eventually led to the regional transition from hunting foraging to farming

imaging and modelling the subsurface structure of volcanic calderas with high resolution aeromagnetic data at vulcano aeolian islands italy in this paper we present a magnetic model of the subsurface structure of vulcano island based on high resolution aeromagnetic data three profiles across the most intense magnetic anomalies over the piano and fossa calderas were selected for the magnetic modelling which was constrained by structural and volcanological data previous geophysical models paleomagnetic data and borehole stratigraphy obtained from two deep wells the interpretation of the magnetic sources represents a significant contribution to the understanding of the piano and fossa calderas underlying structure providing us with evidence of the lateral discontinuity between them at depth we propose that the positive magnetic anomalies in the piano caldera area are caused by a the remnants of an early submarine volcano b an outcropping dyke swarm related to the feeding system of the primordial vulcano phase beneath mt saraceno and c the presence of a non outcropping dyke system intruded along a ne sw oriented intra caldera fault beneath the eastern part of the piano caldera offshore to the west the magnetic anomaly map suggests the presence of a submarine volcanic structure not revealed by bathymetric data which could represent the eruptive centre the presence of which has been indirectly deduced from the outcrop of eastern dipping lavas on the western seashore magnetic modelling of the fossa caldera points to the presence of a highly magnetized cone like body inside the fossa cone centred beneath the oldest crater rims we interpret this body as a pile of tephritic lavas emplaced in an early phase of activity of the fossa cone suggesting that the volume of mafic lavas that erupted at the beginning of the construction of the fossa edifice was more significant than has previously been deduced furthermore the presence of a magnetized body inside the fossa cone implies that high temperatures are contained in very limited spaces do not affect its bulk inner structure and are restricted to fumarolic conduits and vents in addition structures beneath the western and northern part of the fossa caldera are revealed to have null or low magnetization which can be ascribed to the presence of pyroclasts and hyaloclastites in this area as well as to a large volume of hydrothermally altered materials this suggests that the hydrothermal system with a very limited extension at present affected a larger area in the past especially beneath the western part of the caldera

isotope composition of rain water well water and fumarole steam on the island of vulcano and their implications for volcanic surveillance abstract water samples from eight wells in the vulcano porto area and fumarole steam from the crater of vulcano southern italy were collected at monthly intervals over a two year period from february 1987 to january 1989 samples of bulk precipitation were also collected in three points at vulcano porto and vulcano piano island of vulcano and castroreale tyrrhenian coast of sicily again at monthly intervals the weighted mean isotopic composition of rain water on vulcano is d 32 and d 18 o 6 4 results for well waters tend to support the existence of at least two water bodies one of purely meteoric water and the other of brackish thermal water an intermediate water body probably the result of mixing of the other two was also recognized the isotope composition of fumarolic steam from the crater suggests the mixed contribution of both sea and rain waters although mixing is not the only process occurring the existence of a deep marine brine body is inferred characterized by d and 18o values more positive than those of mediterranean sea water a close relationship indicating common source effects is shown by temporal isotopic variations at some wells and the fumarolic steam wich may be used for volcano survey at distance from the active crater

the effect of lateral deformation on heat flow heat production relations deformation that takes place following the fractionation of heat producing elements can cause the relationship of surface heat flow and heat production to deviate from a simple linear trend lateral transport by low angle normal faulting or thrust faulting may place the near surface rocks above rocks with different thermal properties even for a simple model the relationships can be complex but some constraints can be placed on the vertical distribution of heat generation and layer thickness measurements at many sites in a province could produce an overall linear trend of surface flux and heat production departures from linearity may be found at sites that were disturbed transported following the latest cycle of radioelement fractionation the amount of departure from linearity is a function of the thickness of the transported layer and the thermal properties of underlying layers

crustal heterogeneities and the thermal structure of the continental crust the observed linear relationship between surface heat flow q0 and the radiogenic heat production of near surface rocks a0 discovered almost two decades ago has been a primary tool used to infer the distribution of heat production in the continental crust recent evidence on the nature of compositional heterogeneities in the continental crust has led us to reexamine the q0 a0 relationship and the likely implications for the thermal structure of the lower continental crust numerical simulations of crustal thermal models indicate that some interpretations derived from this relation may be flawed in particular the length scale determined from the q0 a0 function normally thought to describe the depth distribution of crustal heat sources is significantly affected by the horizontal scale of crustal heterogeneity as a consequence most estimates of lower crustal heat flow and lower crustal temperatures obtained using heat flow data with the q0 a0 relationship are overestimates this overestimation is proportionally largest in areas of low mantle heat flux such as cratons where basal heat flux may be overestimated by more than a factor of two

a global analysis of heat flow from precambrian terrains implications for the thermal structure of archean and proterozoic lithosphere previous studies of heat flow from precambrian terrains have yielded two different relationships a global temporal relationship between heat flow and tectonic age and a regional spatial relationship between heat flow and the proximity of archean cratons we analyze heat flow from tectonically stable precambrian terrains worldwide to address questions associated with these two heat flow patterns 1 is the spatial relationship a global pattern 2 do the two heat flow relationships have a common underpinning in answer to the first question our data analysis reveals a widespread spatial pattern between heat flow and the proximity of archean cratons which is characterized by low heat flow in archean cratons and proterozoic terrains adjacent to cratonic margins and higher heat flow in proterozoic terrains that are more than a few hundred kilometers from a craton to address the second question we examine three previous interpretative models of precambrian heat flow 1 simple cooling of a thermal boundary layer 2 thicker lithosphere in archean terrains than in proterozoic and 3 greater heat production in proterozoic crust than in archean model 1 predicts essentially no change in heat flow in terrains older than 1 5 ga and therefore does not likely provide a common underpinning for the precambrian heat flow patterns models 2 and 3 when combined with the special structural configuration of sutures can independently yield both the spatial and temporal heat flow distributions and thus alone or together may be considered candidates to explain the precambrian heat flow patterns however thermal models of the lithosphere in which the heat flow patterns are explained entirely by variations in crustal heat production cannot satisfy constraints on upper mantle temperatures beneath archean cratons derived from xenolith thermobarometry the thermobarometry constraints can be satisfied by models in which differences in lithospheric thickness are the principal factor controlling the surface heat flow distributions if the heat flow patterns result primarily from variations in lithospheric thickness then a different temporal heat flow relationship for precambrian terrains can be proposed one in which heat flow varies inversely with the age of stabilization of the lithosphere

boron isotopic variations in fumarolic condensates and thermal waters from vulcano island italy implications for evolution of volcanic fluids abstract temporal variation in the isotopic composition of boron has been monitored in fumarolic condensates collected over an extended time period 1970 1996 from la fossa crater volcano island we also report comparative boron isotopic data for representative vulcano lavas and for shallow hydrologic samples seawater wells thermal springs from the north flank of la fossa combined with concurrent chemical and isotopic 18o d data for the fumaroles these results indicate that the fumarolic fluids record mixing relations between three distinct fluid end members 1 a dominantly magmatic fluid em1 2 a mixture of modified seawater with magmatic fluid em2 and 3 an aqueous fluid produced from seawater by extensive wall rock reaction evaporation and boiling af differences between the latter two end members are most clearly accentuated on the basis of the boron isotopic data long term compositional variations for crater fumaroles were dominated by em1 af mixing between 1979 88 with progressive decrease in em1 contribution with time and by em2 af mixing between 1988 96 the exact spatial distribution of these fluid reservoirs remains unclear but all must have been present throughout the monitoring period to account for the observed variations moreover the combined b o h data seem to preclude important contributions from shallow meteoric reservoirs marked short term variations in 11b closely coincide with episodes of local seismicity which presumably triggered reorganization of hydrothermal circulation patterns gradual variations over periods up to 3 4 years are associated with relatively low seismicity during which fluid circulation was likely influenced by effects of mineral precipitation on permeability of the hydrologic system

relationships between diffuse co2 emissions and volcanic activity on the island of vulcano aeolian islands italy during the period 1984 1994 measurements of co2 flux from the ground were periodically carried out on the island of vulcano aeolian islands italy between 1984 and 1994 three high flux areas were identified at the foot of the volcanic cone la fossa either inside or very close to the main village effect of the choice of the sampling grid was evaluated a different sampling grid resulted in similar distribution patterns but with different co2 fluxes therefore the absolute estimate of the total flux from the investigated area includes a large degree of uncertainty but repeated measurements with permanent sampling sites are accurate and can detect small changes no correlation of the flux with atmospheric parameters was found at sites with high fluxes some periods characterized by high co2 fluxes were observed and a close correlation was found between the gas emissions from the ground and other geochemical and geophysical parameters such as temperature chemical composition steam and so2 flux from fumaroles seismic energy release and ground deformations the results show that major temporal variations of diffuse co2 flux are related to variations in volcanic activity

heat production and thermal conductivity of rocks from the pikwitonei sachigo continental cross section central manitoba implications for the thermal structure of archean crust the pikwitonei and sachigo subprovinces of central manitoba provide a cross sectional view of the superior province crust in cross section the upper to mid level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses both of which are intruded by granitoid plutons this crustal structure persists downward into the granulite facies where keels of the greenstone belts can be found to constrain thermal models of the crust we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma ray spectrometry and divided bar techniques large vertical and lateral heterogeneities in heat production in the upper crust are evident heat production is high in granites and metasedimentary rocks intermediate in tonalite gneisses and low in the portions of greenstone belts dominated by mafic meta igneous rocks in the deeper granulite facies rocks heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high grad

contribution of metapelitic sediments to the composition heat production and seismic velocity of the lower crust of southern new mexico u s a abstract granulite xenoliths erupted at kilbourne hole maar were recently extracted from the lower crust of southern new mexico garnet and sillimanite bearing quartzofeldspathic xenoliths had pelitic protoliths and were probably emplaced in the lower crust by tectonic underplating at a lower proterozoic subduction zone thus the kilbourne hole metapelitic xenoliths illustrate the potential role of tectonosedimentary processes at convergent margins in determining the ultimate composition of the crust average p wave velocities for metapelitic xenoliths from kilbourne hole are 7 km s at 6 kbar like those of mafic metagabbros and anorthosites however in contrast to mafic lithologies the major element composition of the representative pelitic paragneiss rpp described in this paper is relatively siliceous and like that of average upper crust except for depletions of u and cs the trace element characteristics of the rpp are like those of pelitic sediments and are 3 10 times higher than those typically estimated for the lower crust the heat production of the rpp is high 1 0 w m3 as are those of many granulite and amphibolite grade metapelites in general portions of the lower crust in which sediments are present may be high in light ion lithophile and rare earth element abundances heat production 18o and87sr 86sr moreover the high pb contents and unradiogenic pb isotope signatures of metapelites provide an important reservoir for unradiogenic pb in the earth as a whole

heat flow in the bastar craton central indian shield implications for thermal characteristics of proterozoic cratons measurements of surface heat flow density in various lithologies from the central parts of the proterozoic bastar craton of the central indian shield have yielded heat flow values ranging from 51 to 64 mw m 2 with a mean value of 56 mw m 2 standard deviation 6 1 mw m 2 these values are considerably higher than in the archaean and archaean to early proterozoic cratons of many precambrian shields but are compatible with the heat flow data from the proterozoic gawler craton central australian shield it is inferred that 1 the contrast in surface heat flow between the archaean and proterozoic cratons is a consequence of the difference in the radiogenic heat production in their upper 10 20 km thick crustal layers and 2 the proterozoic cratons as these could also have enclaves of basic archaean rocks show a wide range of surface heat flow values controlled mainly by the varying amounts of upper crustal radiogenic heat source

three dimensional vp and vp vs models of the upper crust in the friuli area northeastern italy summary 3 d images of p velocity and p t os velocity ratio have been produced for the upper crust of the friuli area northeastern italy using local earthquake tomography the data consist of 2565 p and 930 s arrival times of high quality the best fitting v p and v p v s 1 d models were computed before the 3 d inversion v p was measured on two rock samples representative of the investigated upper layers of the friuli crust the tomographic v p model was used for modelling the gravity anomalies by converting the velocity values into densities along three vertical cross sections the computed gravity anomalies were optimized with respect to the observed gravity anomalies the crust investigated is characterized by sharp lateral and deep v p and v p v s anomalies that are associated with the complex geological structure high v p v s values are associated with highly fractured zones related to the main faulting pattern the relocated seismicity is generally associated with sharp variations in the v p v s anomalies the v p images show a high velocity body below 6 km depth in the central part of the friuli area marked also by strong v p v s heterogeneities and this is interpreted as a tectonic wedge comparison with the distribution of earthquakes supports the hypothesis that the tectonic wedge controls most of the seismicity and can be considered to be the main seismogenic zone in the friuli area

heat production in the continental crust part i data converted from seismic velocities and their attempted interpretation abstract when using the simple exponential distribution of radiogenic heat production a with depth z a z a o exp z d the statistical analysis of a large number of heat production profiles converted from the observed seismic velocity vs depth profiles and the experimental knowledge of the relationship between seismic velocity and heat production disclosed certain relations between the logarithmic decrement d value and heat flow tectonic age and crustal thickness the d valuein this respect characterizes the depth rate of the differentiation of the heat production in all tectonic units the d parameter decreases with depth as the next step the more complicated distribution law a z a o exp z d a was applied where a characterizes the quantity of removed heat sources by the processes accompanying the crustal evolution such as remelting metamorphosis leaching by underground waters etc all parameters a o a and d are constant within each particular tectonic province and parameter d does not depend on depth contrary to the former law the amount of removed heat sources a reflects the initial concentration of heat sources and is higher in young tectonic terranes in areas of high heat flow and in regions of thin crust