co2 emissions related to the yellowstone volcanic system 2 statistical sampling total degassing and transport mechanisms a stratified adaptive sampling plan was designed to estimate co2 degassing in yellowstone national park and was applied in the mud volcano thermal area the stratified component of the sampling design focused effort in thermal areas and the adaptive component in high flux regions yet neither sampling technique biased the estimate of total degassing both diffuse soil fluxes up to 30 000 g m 2d 1 and emission rates from thermal vents up to 1 7 108 mol yr 1 were measured in thermal areas soil fluxes observed in most nonthermal regions were similar to values reported for conifer forests 15 g m 2 d 1 however through adaptive sampling high flux vegetated sites were identified in mud volcano that likely would not have been found if sampling was focused in obvious thermal or altered regions a simple model applied to flux measurements suggests that 40 of the analyzed measurements were dominated by possible advective transport and 30 by diffusive transport isotopic signatures of soil co2 generally suggest a deep origin 13c 2 3 to 0 0 in thermal areas and biogenic origin 13c 20 5 in nonthermal low flux areas vent emissions accounted for 32 63 of the total degassing observed at mud volcano 2 4 to 4 0 109 mol yr 1 the largest source of error in the estimation of total degassing factor of 2 resulted because the population distribution of thermal feature emissions was indeterminate total co2 emissions at mud volcano are comparable to other hydrothermal regions worldwide suggesting that the yellowstone volcanic system is likely a large contributor to global volcanic metamoohic hydrothermal vmh emissions

half graben versus large offset low angle normal fault importance of keeping cool during normal faulting 1 we study the effect of temperature in the crust on the style of faulting during the extension of a model lithosphere two distinct fault patterns are seen depending on whether the brittle layer thickness hl is greater or less than a critical value hc for a thin layer hl hc a rift develops with multiple faults bounding an evolving set of grabens numerical results show that the value of hc depends on how the thermal structure and therefore the thickness distribution of the lithosphere evolve during extension in the region where the displacement occurs along the fault the brittle lithosphere thins and we show that this promotes development of multiple faults in models with heat transfer only by rock motion and conduction the advective thinning effect can greatly reduce hc with rift velocities greater than 1 cm yr 1 hc is reduced by a factor of 5 to unreasonably small values however inclusion of simulated hydrothermal cooling increases hc this allows large offsets to develop in model lithospheres with brittle layers of order 10 km thick extension of layers thicker than 10 km tends to produce a rift with multiple graben structures finally we compare the result of a simplified analytic model of extension to data we find that the style of faulting seen in a variety of continental rifts is broadly consistent with our model predictions

carbon dioxide discharged through the las canadas aquifer tenerife canary islands carbon dioxide is one of the first gases to escape the magmatic environment due to its low solubility in basaltic magmas at low pressures the exsolved co2 gas migrates towards the surface through rock fractures and high permeability paths if an aquifer is located between the magmatic environment and the surface a fraction of the co2 emitted is dissolved in the aquifer in this paper an estimation of the water mass balance and the co2 budget in las canadas aquifer tenerife canary islands is presented magmatic co2 is transported by groundwater and discharged through man made sub horizontal drains or galleries that exist in this island and by the flow of groundwater discharged laterally towards other aquifers or to the ocean in addition the pco2 at the gallery mouth or entrance and at the gallery bottom internal and deepest discharge point where the gallery starts are calculated and mapped the total co2 advectively transported by groundwater is estimated to range from 143 to 211 t co2 d 1 considering that the diffuse soil emission of co2 for the same area is 437 t d 1 the diffuse dissolved co2 flux ratio varies between 2 and 3 the high dissolved inorganic carbon content of groundwater explains the ability of this low temperature hydrothermal water to dissolve and transfer magmatic co2 at volcanoes even during quiescence periods

a physical explanation of the relation between flank uplifts and the breakup unconformity at rifted continental margins rift flank uplifts and the breakup or postrift unconformity are characteristic features of many rifted passive or atlantic type continental margins but are not predicted as primary features of simple lithospheric stretching models the explanations that have been proposed for their origin remain controversial either because they call upon special circumstances or because they are difficult to test plane strain finite element models are used in this paper to explore the dynamics of lithospheric necking during rifting and rupture the results agree with the conceptual interpretation that uplift of the rift boundaries to form flank mountains and uplift of the basin responsible for the breakup unconformity are related consequences of regional isostatic compensation of mass that is redistributed during the necking and rupture phases although the amplitudes of these uplifts depend on the model parameter values the relations between and relative signs of these two effects appear to be fundamental the explanation we propose may have been missed in recent studies because there has been a tendency to concentrate on kinematic stretching models which assume local isostatic equilibrium through out the rifting process such an approach is predicated on the assumption that the lithosphere has an insignificant strength or flexural rigidity during extension which is not true if our explanation is correct

diffuse volcanic degassing and thermal energy release from hengill volcanic system iceland we report the first detailed study of spatial variations on the diffuse emission of carbon dioxide co2 and hydrogen sulfide h2s from hengill volcanic system iceland soil co2 and h2s efflux measurements were performed at 752 sampling sites and ranged from nondetectable to 17 666 and 722 g m 2 day 1 respectively the soil temperature was measured at each sampling site and used to evaluate the heat flow the chemical composition of soil gases sampled at selected sampling sites during this study shows they result from a mixing process between deep volcanic hydrothermal component and air most of the diffuse co2 degassing is observed close to areas where active thermal manifestations occur northeast flank of the hengill central volcano close to the nesjavellir power plant suggesting a diffuse degassing structure with a ssw nne trend overlapping main fissure zone and indicating a structural control of the degassing process on the other hand h2s efflux values are in general very low or negligible along the study area except those observed at the northeast flank of the hengill central volcano where anomalously high co2 efflux and soil temperatures were also measured the total diffuse co2 emission estimated for this volcanic system was about 1 526 160 t day 1 of which 453 t day 1 29 7 are of volcanic hydrothermal origin to calculate the steam discharge associated with the volcanic hydrothermal co2 output we used the average h2o co2 mass ratio from 12 fumarole samples equal to 88 6 range 9 4 240 2 as a representative value of the h2o co2 mass ratios for hengill fumarole steam the resulting estimate of the steam flow associated with the gas flux is equal to 40 154 t day 1 the condensation of this steam results in thermal energy release for helgill volcanic system of 1 07 1014 j day 1 or to a total heat flow of 1 237 mwt

precursory diffuse co2 and h2s emission signatures of the 2011 2012 el hierro submarine eruption canary islands 1 on october 12 2011 a submarine eruption began 2 km off the coast of la restinga south of el hierro island co2 and h2s soil efflux were continuously measured during the period of volcanic unrest by using the accumulation chamber method at two different geochemical stations hie01 and hie07 recorded co2 and h2s effluxes showed precursory signals that preceded the submarine eruption beginning in late august the co2 efflux time series started increasing at a relatively constant rate over one month reaching a maximum of 19 gm 2d 1 one week before the onset of the submarine volcanic eruption the h2s efflux time series at hie07 showed a pulse in h2s emission just one day before the initiation of the submarine eruption reaching peak values of 42 mg m 2 d 1 10 times the average h2s efflux recorded during the observation period since co2 and h2s effluxes are strongly influenced by external factors we applied a multiple regression analysis to remove their contribution a statistical analysis showed that the long term trend of the filtered data is well correlated with the seismic energy we find that these geochemical stations are important monitoring sites for evaluating the volcanic activity of el hierro and that they demonstrate the potential of applying continuous monitoring of soil co2 and h2s efflux to improve and optimize the detection of early warning signals of future volcanic unrest episodes at el hierro continuous diffuse degassing studies would likely prove useful for monitoring other volcanoes during unrest episodes

soil co2 flux in hydrothermal areas of the tatun volcano group northern taiwan abstract we measured soil co2 flux in the representative hydrothermal areas of the tatun volcano group tvg to better understand the volcano s dynamic nature and to estimate its soil co2 degassing output results show that the average soil co2 fluxes obtained at da you keng dyk geng tze ping gtp she haung ping shp and tatun natural park tnp were 128 g m 2 d 1 518 g m 2 d 1 420 g m 2 d 1 and 25 g m 2 d 1 respectively the range is comparable to other active volcanic hydrothermal areas in the world along with liu huang ku lhk where the soil co2 flux is known the total soil co2 output from measured areas is evaluated at 82 t d 1 furthermore a first total soil co2 output from the whole hydrothermal areas of the tvg is roughly estimated at 113 t d 1 which includes 15 t d 1 mantle contribution considering the mantle derived co2 flux and h2o co2 ratio of fumarolic gas thermal energy associated with the diffuse degassing at the tvg hydrothermal area is estimated at 8 2 mw carbon 13c and helium 3he 4he isotopic ratios of soil samples of the studied areas ranged from 4 4 to 6 7 and 2 45 to 6 98 ra respectively the extent of air involvement in the soil degassing system as constrained by the helium and carbon isotopic compositions provides essential information for depicting regional degassing features of the hydrothermal areas

helium emission at cumbre vieja volcano la palma canary islands abstract we report herein the results of three soil helium surveys undertaken at cumbre vieja volcano la palma island canary islands helium content analyses at the surface environment of the volcano were carried out in the summers of 2002 2003 and 2004 to estimate the diffusion contribution of helium emission soil porosity was estimated indirectly from the granulometry data measured on a previous soil survey carried out in 1997 helium enrichments in the soil layer with respect to the air concentration measured on cumbre vieja indicate a strong structural control in the degassing processes of the volcano and the excess helium seems to be emitted mainly along both n s and n w rifts of the volcano 4 he flux values calculated following a pure diffusive model ranged between non detectable values and 1 0 mg m 2 d 1 in 2002 2003 and 2004 surveys total 4 he emission rate at cumbre vieja was estimated in the range of 18 38 kg d 1 isotopic composition of helium measured in soil gases along the n s volcanic rift of cumbre vieja showed small contributions of morb type helium increasing towards the southern part of the volcano a 3 he 4 he ratio of 9 95 0 12 r a was measured at a cold spring geothermal sample showing a 7 2 contribution of plume type helium 3 he emission results in the range of 0 6 0 7 mol yr support the hypothesis of contemporary degassing at cumbre vieja coming from magmas stored at different depths under la palma island

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

pinpointing deep geothermal upflow in zones of complex tectono volcanic degassing new insights from aluto volcano main ethiopian rift the project was financed in the framework of the volkswagen foundation s postdoctoral fellowships for african researchers in the engineering sciences reference 90017

modes of extensional faulting controlled by surface processes we investigate the feedbacks between surface processes and tectonics in an extensional setting by coupling a 2 d geodynamical model with a landscape evolution law focusing on the evolution of a single normal fault we show that surface processes significantly enhance the amount of horizontal extension a fault can accommodate before being abandoned in favor of a new fault in simulations with very slow erosion rates a 15 km thick brittle layer extends via a succession of crosscutting short lived faults heave 10 km using simple scaling arguments we quantify the effect of surface mass removal on the force balance acting on a growing normal fault this leads us to propose that the major range bounding normal faults observed in many continental rifts owe their large offsets to erosional and depositional processes

carbon dioxide degassing by advective flow from usu volcano japan magmatic carbon dioxide co2 degassing has been documented before the 31 march 2000 eruption of usu volcano hokkaido japan six months before the eruption an increase in co2 flux was detected on the summit caldera from 120 september 1998 to 340 metric tons per day september 1999 followed by a sudden decrease to 39 metric tons per day in june 2000 3 months after the eruption the change in co2 flux and seismic observations suggests that before the eruption advective processes controlled gas migration toward the surface the decrease in flux after the eruption at the summit caldera could be due to a rapid release of co2 during the eruption from ascending dacitic dikes spreading away from the magma chamber beneath the caldera

anomalous soil co2 degassing in relation to faults and eruptive fissures on mount etna sicily italy the relationships between soil gas emissions and both tectonic and volcano tectonic structures on mt etna have been studied the investigation consisted of soil co2 flux measurements along traverses orthogonal to the main faults and eruptive fissures of the volcano anomalous levels of soil degassing were found mainly in coincidence with faults whereas only 49 of the eruptive fissures were found to produce elevated co2 soil fluxes this result suggests that only zones of strain are able to channel deep gases to the surface according to this hypothesis several previously unknown structures are suggested based on our geochemical data new structural maps of different areas of etna are proposed the soil co2 fluxes observed in this study are higher than those measured in a 1987 study and they are consistent with the higher level of volcanic unrest during the current study

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

radon and helium in soil gases at canadas caldera tenerife canary islands spain abstract the spatial distribution of soil radon was investigated at canadas caldera tenerife in two surveys carried out in the summers of 1992 and 1995 by using particle sensitive cellulose nitrate films track etch and emanometry respectively soil helium was studied at several transects crossing different structural features of the area radon concentration measured by track etch ranged from 1 0 to 1990 pci l while that measured by emanometry ranged from 0 1 to 618 pci l soil helium concentration varied from 5250 to 15 560 ppb with an average value of 6197 ppb the spatial distribution of soil radon correlates quite closely with structural features fractures emission centers etc where the main geothermal manifestations fumaroles steam ground and high subsurface temperature and gas contents also occur areas showing high soil rn concentrations occur at the summit of teide roques de garcia caldera rim and south and east off side of the caldera high soil helium anomalies correlate well spatially with those of radon especially at the summit of teide where relatively high 3 he 4 he isotopic ratios occur suggesting a deep contribution for these emanations data indicate that radon and helium are supplied mostly from a deep source with a minor contribution from u and th rich shallow rocks and soils

measurements of 220rn and 222rn and co2 emissions in soil and fumarole gases on mt etna volcano italy implications for gas transport and shallow ground fracture this work was funded by the istituto nazionale di geofisica e vulcanologia s g m n and by the dipartimento per la protezione civile italy projects v3 6 28 etna m n and v5 08 diffuse degassing in italy s g and nsf ear 063824101 k w w s

linking gas fluxes at earth s surface with fracture zones in an active geothermal field the percolation of fluids is of utmost relevance for the utilization of underground resources however the location and occurrence of fractures are not always known and important characteristics of faults such as stress state and permeability are commonly uncertain using a case study at the brady s geothermal field in nevada usa we demonstrate how permeable fractures can be identified and assessed by combining fault stress models with measurements of diffuse degassing and emanations at earth s surface areas of maximum gas emissions and emanations correspond to fault segments with increased slip and dilation tendency and represent a fingerprint of the geothermal system at depth thus linking gas fluxes with fault stress models serves as a measure of the connectivity between surface and subsurface

elevated carbon dioxide flux at the dixie valley geothermal field nevada relations between surface phenomena and the geothermal reservoir abstract in the later part of the 1990s a large die off of desert shrubs occurred over an approximately 1 km 2 area in the northwestern section of the dixie valley dv geothermal field this paper reports results from accumulation chamber measurements of soil co 2 flux from locations in the dead zone and stable isotope and chemical data on fluids from fumaroles shallow wells and geothermal production wells within and adjacent to the dead zone a cumulative probability plot shows three types of flux sites within the dead zone locations with a normal background co 2 flux 7 g m 2 day 1 moderate flux sites displaying excess geothermal flux and high flux sites near young vents and fumaroles a maximum co 2 flux of 570 g m 2 day 1 was measured at a location adjacent to a fumarole using statistical methods appropriate for lognormally distributed populations of data estimates of the geothermal flux range from 7 5 t day 1 from a 0 14 km 2 site near the stillwater fault to 0 1 t day 1 from a 0 01 km 2 location of steaming ground on the valley floor anomalous co 2 flux is positively correlated with shallow temperature anomalies the anomalous flux associated with the entire dead zone area declined about 35 over a 6 month period the decline was most notable at a hot zone located on an alluvial fan and in the sg located on the valley floor gas geochemistry indicates that older established fumaroles along the stillwater fault and a 2 year old vent in the lower section of the dead zone discharge a mixture of geothermal gases and air or gases from air saturated meteoric water asmw stable isotope data indicate that steam from the smaller fumaroles is produced by 100 c boiling of these mixed fluids and reservoir fluid steam from the senator fumarole sf and from shallow wells penetrating the dead zone are probably derived by 140 c to 160 c boiling of reservoir fluid carbon 13 isotope data suggest that the reservoir co 2 is produced mainly by thermal decarbonation of hydrothermal calcite in veins that cut reservoir rocks formation of the dead zone is linked to the reservoir pressure decline caused by continuous reservoir drawdown from 1986 to present these reservoir changes have restricted flow and induced boiling in a subsurface hydrothermal outflow plume extending from the stillwater fault southeast toward the dv floor we estimate that maximum co 2 flux in the upflow zone along the stillwater fault in 1998 was roughly seven to eight times greater than the pre production flux in 1986 the eventual decline in co 2 flux reflects the drying out of the outflow plume

diffuse surface emanations as indicator of structural permeability in fault controlled geothermal systems abstract diffuse degassing processes provide valuable information on geothermal reservoir characteristics not only in the context of monitoring but also for exploration purposes areas with increased gas emissions can be indicative of major upflow zones from the reservoir through deep reaching permeable fault zones these fault zones may act as preferential target areas for geothermal production drillings in this study it is successfully demonstrated that diffuse degassing measurements can be used for the detection and characterization of permeable structural elements the combination of following techniques has been applied at the brady s geothermal system in the basin and range province nevada usa accumulation chamber method for carbon dioxide and hydrogen sulfide measurements alpha spectroscopic measurements of radon and thoron activity concentrations and gamma spectroscopic measurements of selected nuclides

origin and quantification of diffuse co2 and h2s emissions at crater hills yellowstone national park abstract we characterized volatile emissions based upon diffuse soil degassing measurements and fumarolic gas chemistry at crater hills a thermally altered area adjoining the sour creek resurgent dome that is located within the yellowstone caldera the objective of this study was to investigate the source and flux of co2 and h2s gases to improve our understanding of both the total emissions and origin of the spatial distribution the total emission of co2 estimated using the sequential gaussian simulation method sgs was 66 to 109 t day 1 with 95 confidence which is an underestimation due to the 1 inability to measure a high flux area on a steep slope and 2 absence of measurements from fumarole and hot pool emissions based on gas chemistry data obtained for a fumarole at crater hills in 2007 the proportion of co2 calculated to be derived from magma would be at least 38 but could be as high as 50 the spatial distribution of prominent geothermal features with the highest gas flux are broadly consistent with the regional fault pattern and therefore likely reflect the pattern of blind faults and or fractures covered by overlying alluvium the estimated emission of h2s was 0 39 t day 1 based on the linear correlation between h2s and co2 the heat output was also estimated to be 35 mw with an average heat flux of 100 w m 2 based upon co2 h2o heat relations

soil co2 degassing on mt etna sicily during the period 1989 1993 discrimination between climatic and volcanic influences wide variations were measured in the diffuse co2 flux through the soils in three selected areas of mt etna between august 1989 and march 1993 degassing of co2 from the area of zafferana etnea s venerina on the eastern slope of the volcano has been determined to be more strongly influenced by meteorological parameters than the other areas the seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between co2 flux values and those of air temperature the filtered data appear to have variations temporally coincident with those from the other areas thus suggesting a common and probably deep source of gas the highest fluxes measured in the two most peripheral areas may correlate well with other geophysical and volcanological anomalous signals that preceded the strong eruption of 1991 1993 and that were interpreted as deep pressure increases anomalous decreases in co2 fluxes accompanied the onset and the evolution of that eruption and have been interpreted as a sign of upward migration of the gas source the variations of co2 flux at the 1989 se fracture have also given interesting information on the timing of the magmatic intrusion that has then fed the 1991 1993 eruption

diffusive helium emissions as a precursory sign of volcanic unrest significant increases in helium emissions from the soil and 3 he 4 he ratios in groundwater on el hierro island canary islands spain were observed prior to the 2011 2012 submarine eruption off the coast of the island the changes of diffusive helium emissions rate were observed one month prior to the submarine eruption onset 12 october 2011 and the major increase preceded increases in seismic energy release during the volcanic unrest measured 3 he 4 he ratios in groundwaters from a well in el hierro island increased from 2 3 r a to 7 2 r a r a 3 he 4 he ratio in air 1 month prior to the eruption onset and reached a peak of 8 2 r a indicating a dominant magmatic contribution to the dissolved gases in ground waters 3 he 4 he values and diffusive helium emission studies have been extremely important for forecasting the onset of the volcanic unrest and subsequent volcanic eruption an aseismic exsolution of magmatic gases from magma bodies beneath el hierro island through fractures and vertical permeability structures increased the diffusive helium emission rate prior to episodes of seismic energy release associated with the volcanic unrest

soil gas co 2 ch 4 and h 2 distribution in and around las canadas caldera tenerife canary islands spain abstract diffuse degassing of co 2 ch 4 and h 2 was investigated at the surface environment of canadas caldera canary islands during the gas survey carried out in the summer of 1995 soil co 2 concentration varied significantly from atmospheric levels to 30 while soil ch 4 and h 2 contents ranged from 5 to 851 ppm and from 0 5 to 620 ppm respectively soil co 2 ch 4 and h 2 distribution suggests that high diffuse degassing at canadas caldera is volcanic structurally controlled anomalous soil h 2 concentrations were identified at the summit of teide and outside caldera boundaries where the most recent eruption of tenerife island occurred 13 c co 2 data showed a magmatic mixed magmatic biogenic and biogenic origin while a biogenic origin is suggested for soil ch 4 at canadas caldera and its surroundings by coupling the co 2 3 he ratio with the 3 he 4 he ratio of fumarolic gas samples from the summit of teide we propose three possible sources for carbon morb type organic carbon and carbonate

the late ordovician granitoids in the east kunlun orogenic belt northwestern china petrogenesis and constraints for tectonic evolution of the proto tethys ocean petrology whole rock geochemistry in situ zircon u pb ages and lu hf isotopic data are reported for granodiorite and monzonitic granite samples from the harizha region in the eastern section of the east kunlun orogenic belt the results of the la icp ms zircon dating indicate that the granodiorite and monzonitic granite were emplaced at 447 9 3 0 ma and 443 8 3 5 ma respectively i e in the late ordovician early paleozoic periods the granodiorite is characterized by relatively high mgo 4 52 5 91 wt sr 541 712 ppm cr 218 357 ppm ni 56 7 80 7 ppm and v 66 8 94 7 ppm with low y 10 40 13 60 ppm and yb 1 05 1 45 contents this results in elevated mg 65 68 sr y 39 78 58 84 and la yb n 10 21 18 30 ratios common features for adakitic high mg andesite hma the granodiorite is metaluminous to weakly peraluminous and high k calc alkaline in composition in addition the granodiorite is enriched in light rare earth elements lree and large ion lithophile elements liles rb k sr and pb u and nd and depleted in high field strength elements hfses nb ta zr hf ti and p the zircon grains from the granodiorites have ehf t values of 5 5 to 4 7 with two stage hf model ages tdm2 ranging from 0 92 to 1 71 ga these features suggest that the granodiorites were formed by mixing processes of crustal melts and magma from a metasomatized mantle in a subduction setting the monzonitic granite possesses high normative corundum values 2 34 4 10 wt is strongly peraluminous a cnk ratios of 1 16 1 32 with minor mineral muscovite with high k calc alkaline affinity furthermore enrichments in large ion lithophile elements rb k and pb u th and nd depletions in high field strength elements nb ta and ti and ba and p and mainly right inclined ree patterns with negative eu anomalies exhibits an s type granite affinity the magmatic zircons from the monzonitic granite yielded ehf t values between 4 9 and 2 7 corresponding to two stage hf model ages of 1 60 1 73 ga therefore this study suggests that the monzonitic granite magma was derived from crustal material metagreywacke in a syn collision setting subsequently by combining these findings with the previous research results this study propose that a transverse diachronism closure model which entailed an earlier on the sides later in the middle in an east west direction in the east kunlun orogenic belt for the proto tethys ocean s evolution process

ascent and emplacement of buoyant magma bodies in brittle ductile upper crust 1 the emplacement of silicic magma bodies in the upper crust may be controlled by density such that there is no buoyancy to drive further ascent or temperature such that surrounding rocks are too cold to deform significantly over geological timescales evidence for the latter control is provided by negative gravity anomalies over many granitic plutons conditions of diapir ascent and emplacement in this case are studied with a numerical model for deformation and heat transport allowing for ductile elastic and brittle behavior a large strain formulation is used to solve for temperature stress strain and strain rate fields as a function of time for a range of diapir sizes density contrasts and background geotherms the method allows for large viscosity contrasts of more than 6 orders of magnitude and determines the dominant deformation mechanism depending on the local values of temperature strain and strain rate emplacement depth and final deformation characteristics depend on diapir size and buoyancy small diapirs less than about 5 km in diameter cannot reach shallow crustal levels and do not involve brittle deformation in the ductile regime the diapir flattens significantly upon emplacement due to stiff roof rocks and to the free surface above late stage deformation proceeds by horizontal spreading with little upward displacement of roof rocks and is likely to be interpreted as ballooning large diapirs more than about 5 km in diameter rapidly rise to shallow depths 1 5 km and induce brittle faulting in the overlying rocks in this regime buoyancy forces may lead to faulting in roof rocks in this case late stage ascent proceeds by vertical intrusion of a plug of smaller horizontal dimensions than the main body buoyant diapirs keep on rising after solidification long after the relatively short lived high temperature magmatic stage this may account for some phases of late caldera resurgence in extinct volcanic systems

kinematics of the northern walker lane an incipient transform fault along the pacific north american plate boundary in the western great basin of north america a system of dextral faults accommodates 15 25 of the pacific north american plate motion the northern walker lane in northwest nevada and northeast california occupies the northern terminus of this system this young evolving part of the plate boundary offers insight into how strike slip fault systems develop and may reflect the birth of a transform fault a belt of overlapping left stepping dextral faults dominates the northern walker lane offset segments of a w trending oligocene paleovalley suggest 20 30 km of cumulative dextral slip beginning ca 9 3 ma the inferred long term slip rate of 2 10 mm yr is compatible with global positioning system observations of the current strain field we interpret the left stepping faults as macroscopic riedel shears developing above a nascent lithospheric scale transform fault the strike slip faults end in arrays of n striking normal faults suggesting that dextral shear diffuses into extension in the great basin coeval extension and dextral shear have induced slight counterclockwise fault block rotations which may ultimately rotate riedel shears toward the main shear zone at depth thus facilitating development of a throughgoing strike slip fault

soil efflux and total emission rates of magmatic co2 at the horseshoe lake tree kill mammoth mountain california 1995 1999 abstract we report the results of eight soil co 2 efflux surveys by the closed circulation chamber method at the horseshoe lake tree kill hltk the largest tree kill on mammoth mountain the surveys were undertaken from 1995 to 1999 to constrain total hltk co 2 emissions and to evaluate occasional efflux surveys as a surveillance tool for the tree kills hltk effluxes range from 1 to 10 000 g m 2 day 1 grams co 2 per square meter per day they are not normally distributed station efflux rates can vary by 7 35 during the course of the 8 to 16 h surveys disturbance of the upper 2 cm of ground surface causes effluxes to almost double semivariograms of efflux spatial covariance fit exponential or spherical models they lack nugget effects efflux contour maps and total co 2 emission rates based on exponential spherical and linear kriging models of survey data are nearly identical similar results are also obtained with triangulation models suggesting that the kriging models are not seriously distorted by the lack of normal efflux distributions in addition model estimates of total co 2 emission rates are relatively insensitive to the measurement precision of the efflux rates and to the efflux value used to separate magmatic from forest soil sources of co 2 surveys since 1997 indicate that contrary to earlier speculations a termination of elevated co 2 emissions at the hltk is unlikely anytime soon the hltk co 2 efflux anomaly fluctuated greatly in size and intensity throughout the 1995 1999 surveys but maintained a n s elongation presumably reflecting fault control of co 2 transport from depth total co 2 emission rates also fluctuated greatly ranging from 46 to 136 t day 1 metric tons co 2 per day and averaging 93 t day 1 the large inter survey variations are caused primarily by external meteorological processes operating on time scales of hours to days the externally caused variations can mask significant changes occurring at depth a striking example is the masking of a degassing event generated at depth and detected by a soil gas sensor network in september 1997 while an efflux survey was in progress thus occasional efflux surveys are not an altogether effective surveillance tool for the hltk and making them effective by greatly increasing their frequency may not be practical

soil gases in geothermal prospecting two case histories sabatini volcanoes and alban hills latium central italy studies were conducted to test the effectiveness of soil gas surveying for locating permeable zones in buried carbonate reservoirs and to locate the presence of possible gasoeus haloes linked to active geothermal systems two surveys were conducted in the sabatini volcanoes and alban hills areas each area is characterized by a thermal anomaly and a scarcity of surface manifestations in the former area co2 h2 he and ch4 in soil gases were determined in the latter total helium in about 1000 soil gas samples and in about 400 water samples was determined in both cases anomalous concentrations of the gases were found mainly according to fault or fracture systems therefore it seems possible to utilize the distribution of the gases in these zones as indicators of deep permeability

evaluation of results from the fourth and fifth iavcei field workshops on volcanic gases vulcano island italy and java indonesia abstract the major purpose of field workshops on volcanic gases organized by the iavcei commission on the chemistry of volcanic gases is the collection and analysis of volcanic gas discharges with the aim to develop and improve techniques for the geochemical surveillance of active volcanoes the fourth and fifth workshops were held at vulcano island italy in 1991 and on java island indonesia in 1994 respectively gas samples were collected from four gas vents by nine groups at vulcano and from eight gas vents by eight groups on java the quality e g scatter of the data of most of the results reported from these two workshops is sufficient to permit a broad chemical classification of the discharge and meaningful thermodynamic interpretation in most cases the majority of the data for individual gas vents cluster closely around the median values suggesting that the median values are the best estimates of chemical composition there is however also a considerable scatter of the analytical data and this scatter warns us to not rely too heavily on a single analytical value in particular on a value for ch4 and co because analytical data for these species often show a wide scatter this warning is particularly relevant for chemical monitoring of volcanic activity further improvement of the sampling and analytical techniques as well as more detailed comparison of the techniques is required to reduce such uncertainty in order to interpret the volcanic activity and hydrothermal conditions

sealing capacity of clay cap units above the cerro pabellon hidden geothermal system northern chile derived by soil co2 flux and temperature measurements abstract cerro pabellon is a hidden high enthalpy geothermal system reservoir temperature up to 250 c located in the pampa apacheta northern chile where the first geothermal power plant in south america is currently operating a fumarolic field located on the summit of apacheta volcano about 3 5 km w of pampa apacheta is the only evidence of the presence of a degassing magma connected to the surface co 2 soil flux and temperatures on a grid of 400 points were measured to understand the absence of any other thermal manifestations more than 90 of the measured co 2 flux values were below background estimated at 1 35 g m 2 day 1 whereas the associated soil temperatures mean value 19 4 c carried out at 10 cm depth were related at least partially to an endogenous though weak thermal anomaly no spatial correlation was observed between soil co 2 flux and temperature measurements suggesting a minimal role played by the volcano tectonic structures in the circulation of geothermal fluids soil temperature gradients measured on a grid of 85 points in the active fumarolic field where acid waters and magmatic gases are discharged revealed the only strong thermal anomaly temperatures up to 83 c of the area the thick argillic clay cap 300 m located above the geothermal reservoir has a pivotal role in preventing the resurgence of fluids whereas an efficient interaction between the rising magmatic fluids and the liquid dominated reservoir favours acidic gas scrubbing processes thus allowing the ascent of a steam depleted in magmatic compounds this steam interacts with the shallower discontinuous aquifer s below pampa apacheta with the consequent nearly complete dissolution of co 2 and h 2 s and heating of the shallow groundwater this results in low co 2 fluxes and extended slight thermal anomaly at the surface finally an integrated conceptual model using our results and available geological mineralogical geochemical and geophysical data of the cerro pabellon hidden geothermal system is presented with the aim of providing criteria for geothermal exploration of similar high enthalpy geothermal systems in the andes that also exhibit a lack of thermal surface features

controls of sedimentation in the malawi rift valley central africa abstract the malawi rift is the southermost classic rift valley trough in the cenozoic african rift valley system much of its floor is flooded by lake malawi which is approximately 570 km long 60 km across and up to 500 m deep this rift basin is a potentially useful analogue of many economically important ancient sedimentary troughs rift valley structures are extremely important in controlling both the distribution of sediments in the basin as a whole and also details of sedimentation on a local scale on the basin wide scale an important association between the type of rift boundary structure and amount of rift floor subsidence is recognised this association appears to apply to several section of the african rift system pre rift topography is major control on the position of major rivers and their deltas or turbidite fans along the basin margin the area of pre rift drainage network captured in the course of rift movements is a significant factor in the hydrologic budget of the basin climate is however the dominant control on the hydrologic budget and at present the basin is flooded to overflow level prevailing winds are important in beach ridge and back beach aeolian dune development climatic conditions produce thermal stratification of the lake with an oxic epilimnion down to 250 m depth overlying an anoxic hypolimnion the oxic bottom waters in the shallower parts of the lake appear to promote iron precipitation in the sediments