dryline on 19 june 2002 during ihop part i airborne doppler and leandre ii analyses of the thin line structure and convection initiation the evolution and finescale structure of a dryline that initiated a line of thunderstorms is presented both the along line variability and mean vertical structure were examined using data collected by an airborne doppler radar and a water vapor differential absorption lidar dial the initiation of convection appeared to result from the diurnally induced easterly flow in the maritime air east of the dryline that typically develops late in the day this flow increased the low level convergence and allowed rising parcels of air to reach the level of free convection the along line variability was largely attributed to numerous misocyclones distorting the thin line of radar reflectivity by advecting dry moist air across the dryline south north of the misocyclone the misocyclones also influenced the location of the updrafts with most of the peak values positioned north of the circulations as a result these updrafts were fortuitously positioned in regions of high mixing ratio where the first convective cells initiated

finescale vertical structure and dynamics of some dryline boundaries observed in ihop abstract several radar fine lines all with a humidity contrast were sampled in the central great plains during the 2002 international h2o project ihop this study primarily uses aircraft and airborne millimeter wave radar observations to dynamically interpret the presence and vertical structure of these fine lines as they formed within the well developed convective boundary layer in all cases the fine line represents a boundary layer convergence zone this convergence sustains a sharp contrast in humidity and usually in potential temperature across the fine line the key question addressed herein is whether at the scale examined here 10 km the airmass contrast itself in particular the horizontal density virtual potential temperature difference and resulting solenoidal circulation is responsible for the sustained convergence and the radar fine line for the 10 cases examined herein the answer is affirmative

the behavior of trace elements during the chemical evolution of the h 2 o b and f rich granite pegmatite hydrothermal system at ehrenfriedersdorf germany a sxrf study of melt and fluid inclusions detailed melt and fluid inclusion studies in quartz hosts from the variscan ehrenfriedersdorf complex revealed that ongoing fractional crystallization of the highly evolved h2o b and f rich granite magma produced a pegmatite melt which started to separate into two immiscible phases at about 720 c 100 mpa with cooling and further chemical evolution the immiscibilty field expanded two conjugate melts a peraluminous one and a peralkaline one coexisted down to temperatures of about 490 c additionally high salinity brine exsolved throughout the pegmatitic stage along with low density vapor towards lower temperatures a hydrothermal system gradually developed boiling processes occurred between 450 and 400 c increasing the salinities of hydrothermal fluids at this stage below the late hydrothermal stage is dominated by low salinity fluids using a combination of synchrotron radiation induced x ray fluorescence analysis and raman spectroscopy the concentration of trace elements mn fe zn as sb rb cs sr zr nb ta ag sn ta w rare earth elements ree and cu was determined in 52 melt and 8 fluid inclusions that are representative of distinct stages from 720 c down to 380 c homogenization temperatures and water contents of both melt and fluid inclusions are used to estimate trapping temperatures thus revealing the evolutionary stage during the process trace elements are partitioned in different proportions between the two pegmatite melts high salinity brines and exsolving vapors concentrations are strongly shifted by co ncomitant crystallization and precipitation of ore forming minerals for example pegmatite melts at the initial stage 700 c have about 1 600 ppm of sn concentrations in both melts decrease towards lower temperatures due to the crystallization of cassiterite between 650 and 550 c tin is preferentially fractionated into the peralkaline melt by a factor of 2 3 while the last pegmatite melts are low in sn 64 ppm at 500 c early hydrothermal fluids become again enriched with about 800 ppm of sn at the boiling stage a sudden drop in late hydrothermal fluids 23 ppm of sn at 370 c results from precipitation of another cassiterite generation between 400 and 370 c zinc concentrations in peraluminous melts are low some tens of parts per million and are not correlated with temperature in coexisting peralkaline melts and high t brines they are higher by a factor of 2 3 zinc continuously increases in hydrothermal fluids 3 000 ppm at 400 c where the precipitation of sphalerite starts the main removal of zn from the fluid system occurs at lower temperatures similarly melt and fluid inclusion concentrations of many other trace elements directly reflect the crystallization and precipitation history of minerals at distinctive temperatures or temperature windows

origine des substances dissoutes dans les eaux des sources thermales et des forages de la region asal ghoubbet republique de djibouti abstract from a chemical and sr isotopic study of hot fluids from the asal area republic of djibouti we conclude that the fluids result from basalt seawater interaction associated with variable evaporation some spring waters result from a mixing between geothermal water and seawater or asal lake water in contrast with previous studies dissolution from evaporitic rocks appears unimportant the negative boron anomaly in the fluids from the boreholes suggests the presence of a vapour dominated subsystem in the asal geothermal field

experimental evidence for a protracted enrichment of tungsten in evolving granitic melts implications for scheelite mineralization the solubility of scheelite in evolved granitic magmas qz ab or an system with minor feototal tio2 and cao added was studied experimentally at 200 mpa 750 850 c and relatively oxidizing condition logfo2 nno 2 3 where nno is ni nio oxygen buffer water saturated granitic melts have been equilibrated with seeds of scheelite crystals the resulted wo3 contents in the melts vary only slightly from 0 21 to 0 32 wt wo3 over the investigated temperature and compositional range 0 7 to 1 4 wt cao but tends to increase with increasing temperature and decreasing cao concentration one important message conveyed from the study is that wo3 concentrations at scheelite saturation are more dependent on temperature in evolved ca poor melts than in ca rich melts natural granitic rocks associated with scheelite mineralization and associated melt inclusions hosted in quartz have much lower w contents than the experimental melts equilibrated with scheelite this implies that enrichment of tungsten w at magmatic stages is not sufficient to produce significant scheelite mineralization and confirms the important role of w mobilization by magmatic hydrothermal fluids in the formation of scheelite deposits

hydrothermal activity in the northern tanganyika rift east africa abstract hydrothermal fluids from sub lacustrine and sub aerial sites were sampled in the north tanganyika rift during the 1991 tanganydro expedition two types of hydrothermal end member fluids a na hco 3 type and a na cl type have been identified within the sample set the na hco 3 hydrothermal fluids are emitted at the level of the sub lacustrine pemba and sub aerial kabezi and mashuzi sites which are located in the northernmost bujumbura sub basin the na cl hydrothermal fluid vents at the level of the sub lacustrine cape banza field on the southeastern edge of the ubwari ridge the two types of hydrothermal fluids display isotopic and chemical evidence of interaction with magmatic volatiles the magmatic effects are strongest in the fluid discharging on the pemba hydrothermal field where abundant co 2 bubbling accompanies fluid emission the 13 c values of the co 2 gas sampled at pemba and at cape banza indicate a magmatic origin the pemba fluid shows the highest alkalinity and boron content and the lowest ph of the hydrothermal end member fluids and it has equilibrated at depth at the highest temperature 214 7 c in addition the sulfide mineralizations associated with the pemba hydrothermal vents are enriched in as and tl which similarly to b can be transported as volatiles in magmatic fluids the northern tanganyika na hco 3 fluids are similar to the na hco 3 fluid of the geothermal system of lake bogoria in the eastern branch of the east african rift and they can be compared with the na hco 3 hydrothermal water that is inferred to flow into lake kivu the cape banza na cl fluids may derive from the mixing between meteoric water and a deep seated basement brine similar to the ones found in old continental shields such as the canadian shield the high equilibrium temperatures and the geochemistry of the north tanganyika rift hydrothermal fluids suggest that degassing magmatic bodies are present at depth in the area these magmatic bodies may be either the southern expression of the south kivu magmatism or a more recent activity not yet expressed as surface volcanism the hydrothermal sites are located along major active rift bounding faults which can be associated with deep and strong seismicity as in the case of the pemba field such deep fractures may have favoured the uprise of the magmatic bodies that are the source of heat and volatiles to the hydrothermal systems the circulation of hydrothermal fluids within the tanganyika lacustrine sedimentary pile could play an important role in the maturation of the organic matter enclosed in the lake sediments and the subsequent oil generation and migration

the triple point on 24 may 2002 during ihop part i airborne doppler and lase analyses of the frontal boundaries and convection initiation an analysis of the initiation of deep convection near the triple point between a cold front and dryline is presented high spatial resolution doppler wind syntheses combined with vertical cross sections of mixing ratio q and aerosol scattering ratio retrieved from a lidar flying over the triple point provide an unprecedented view of the initiation process the doppler wind synthesis revealed variability along the dryline similar to the precipitation core gap structure documented for oceanic cold fronts vertical cross sections through the dryline suggest a density current like structure with the hot and dry air being forced up and over the moist air double thin lines associated with moisture gradients were also resolved the vertical profile of retrieved q approximately perpendicular to the dryline showed a pronounced jump in the depth of the moisture layer across the triple point analyses of dropsonde data show the existence of virtual potential temperature v gradients across the cold front and the dryline although the vertical velocity was strong at the triple point deep convection initiated 50 km to the east the location where convection first developed was characterized by a prominent aerosol and moisture plume reduced static stability and the largest potential instability an internal gravity wave may have provided the lift to initiate convection

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

tungsten solubility in evolved granitic melts an evaluation of magmatic wolframite abstract a variety of parameters that potentially control the solubilities of synthetic hubnerite mnwo4 and ferberite fewo4 in haplogranitic melts rich in fluxing compounds have been determined at 200 mpa in order to test the hypothesis that wolframite can occur as a magmatic mineral the melts considered representative of highly evolved pegmatites contain 1 1 1 7 and 2 02 wt of li2o p2o5 and b2o3 respectively although the molar al na k ratio is one if li is considered to be an alkali element the molar al na k li asili of the melt is 0 88 and the melt is peralkaline hubnerite and ferberite solubilities at 800 c are strongly controlled by melt composition they are much lower in subaluminous melt asili 1 05 than in peralkaline melt by contrast hubnerite and ferberite solubilities are nearly independent of the fluorine content of the melt for up to 8 wt f hubnerite and ferberite solubilities at 800 c are also nearly independent of oxygen fugacity over a log f o 2 range of approximately ni nio 3 to ni nio 2 which implies that the predominant oxidation state of tungsten in the melts is 6 even at moderately reduced conditions a series of experiments on haplogranitic melt rich in fluxing compounds with 0 and 6 wt f at 850 650 c shows that temperature strongly influences hubnerite solubility e g the solubility product of hubnerite k sp hub in the melts with 6 wt f decreases from 71 0 7 9 10 4 mol2 kg2 at 850 c to 4 4 2 3 10 4 mol2 kg2 at 650 c our experimental results show that ferberite solubilities are much higher than those of hubnerite with the same composition of melt but the mn fe and w concentrations in natural melt inclusions indicate that these melts were undersaturated with wolframite at 800 c however flux rich melts crystallize at lower temperatures in nature and the occurrence of natural magmatic wolframite was evaluated by comparing experimental solubility product values extrapolated to 500 c with wolframite activities at these temperatures magmatic wolframite is unlikely in flux rich peralkaline melts but by contrast flux rich subaluminous to peraluminous melt inclusions appear to have been saturated with wolframite at approximately 500 c because of the strong temperature dependence of wolframite solubility the dominant effect of fluxing compounds is to lower the solidus temperature of the melt

airborne pseudo dual doppler analysis of a dryline outflow boundary intersection abstract on 3 june 1995 as part of the verification of the origins of rotation in tornadoes experiment vortex the electra doppler radar eldora onboard the national center for atmospheric research ncar electra aircraft made possible a high resolution examination of clear air motions in the texas panhandle in and around the intersection of the dryline and a surface baroclinic boundary a location commonly referred to as the triple point the eldora observations as well as conclusions drawn from analyses of these data are presented and discussed a transverse secondary circulation associated with the dryline is visualized through analyses of the eldora data typical values of rising and sinking air are found to be 2 m s 1 and 2 3 m s 1 respectively these vertical velocities are approximately the same as those indicated by in situ data collected onboard the electra because the maximum in rising motion is found at the western edge of the dewpoint gradient and because the low level relative airfl

a high resolution modeling study of the 24 may 2002 dryline case during ihop part i numerical simulation and general evolution of the dryline and convection abstract results from a high resolution numerical simulation of the 24 may 2002 dryline convective initiation ci case are presented the simulation uses a 400 km 700 km domain with a 1 km horizontal resolution grid nested inside a 3 km domain and starts from an assimilated initial condition at 1800 utc routine as well as special upper air and surface observations collected during the international h2o project ihop 2002 are assimilated into the initial condition the initiation of convective storms at around 2015 utc along a section of the dryline south of the texas panhandle is correctly predicted as is the noninitiation of convection at a cold front dryline intersection triple point located farther north the timing and location of predicted ci are accurate to within 20 min and 25 km respectively the general evolution of the predicted convective line up to 6 h of model time also verifies well mesoscale convergence associated with the confluent flow around the dryline is shown to produce an u

fluid fractionation of tungsten during granite pegmatite differentiation and the metal source of peribatholitic w quartz veins evidence from the karagwe ankole belt rwanda abstract the identification of a magmatic source for granite associated rare metal w nb ta and sn mineralisation in metasediment hosted quartz veins is often obscured by intense fluid rock interactions which metamorphically overprinted most source signatures in the vein system in order to address this recurrent metal sourcing problem we have studied the metasediment hosted tungsten bearing quartz veins of the nyakabingo deposit of the karagwe ankole belt in central rwanda the vein system 992 2 ma is spatiotemporal related to the well characterised b rich f poor g4 leucogranite pegmatite suite 986 10 ma to 975 8 ma of the gatumba gitarama area which culminated in nb ta sn mineralisation muscovite in the nyakabingo veins is significantly enriched in granitophile elements rb cs w and sn and show alkali metal signatures equivalent to muscovite of less differentiated pegmatite zones of the gatumba gitarama area pegmatitic muscovite records a decrease in w content with increasing differentiation proxies rb and cs in contrast to the continuous enrichment of other high field strength elements nb and ta and sn this is an indication of a selective redistribution for w by fluid exsolution and fluid fractionation primary fluid inclusions in tourmaline of these less differentiated pegmatites demonstrate the presence of medium to low saline h 2 o nacl kcl mgcl 2 complex salt e g rb cs fluids which started to exsolve at the g4 granite pegmatite transition stage laser ablation inductively coupled plasma mass spectrometry shows significant tungsten enrichment in these fluid phases 5 500 ppm fractional crystallisation has been identified previously as the driving mechanism for the transition from g4 granites less differentiated biotite biotite muscovite towards muscovite pegmatites and eventually columbite tantalite mineralised pegmatites the general absence of tungsten mineralisation in this magmatic suite including the most differentiated columbite tantalite mineralised pegmatites of the gatumba gitarama area emphasises the efficiency of fluid saturation to extract crystal melt incompatible tungsten from the differentiating melt phase fluid melt crystal partitioning calculations support the concept of a magmatic hydrothermal fluid source for tungsten and constrain the range of permissible crystal melt and fluid melt partition coefficients together with realistic values for water solubility in the parental g4 granitic melt consequently we propose that for highly differentiated b rich f poor granite systems fluid saturation started prior to or at the granite pegmatite transition stage resulting in apical to peribatholitic tungsten veins systems that are paragenetically older than the final pegmatite stage

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

finescale vertical structure of a cold front as revealed by an airborne doppler radar abstract in the afternoon of 24 may 2002 a well defined and frontogenetic cold front moved through the texas panhandle detailed observations from a series of platforms were collected near the triple point between this cold front and a dryline boundary this paper primarily uses reflectivity and doppler velocity data from an airborne 95 ghz radar as well as flight level thermodynamic data to describe the vertical structure of the cold front as it intersected with the dryline the prefrontal convective boundary layer was weakly capped weakly sheared and about 2 5 times deeper than the cold frontal density current the radar data depict the cold front as a fine example of an atmospheric density current at unprecedented detail 40 m the echo structure and dual doppler inferred airflow in the vertical plane reveal typical features such as a nose a head a rear inflow current and a broad current of rising prefrontal air that feeds the accelerating front to rear current over the head the 2d cross fro

lake bogoria hot springs kenya geochemical features and geothermal implications abstract many boiling springs and fumaroles are present along the shores of lake bogoria which is a closed basin alkaline saline lake typical of african rifts two different geothermal waters both of na hco3 type have been recognized the first discharged by the boiling springs located along the western shores of the lake comes from a shallow steam heated thermal aquifer its temperature is close to 100 c as indicated by chalcedony solubility while the chloride content of these waters is slightly higher than 200 mg l 1 the second recognizable in the southernmost boiling springs is representative of a deeper and hotter geothermal reservoir the occurrence of mixing and boiling processes complicates the interpretation of geochemical data nevertheless a chloride content of about 660 mg l 1 an equilibrium temperature close to 170 c and a high carbon dioxide partial pressure at least 10 20 bar have been estimated for the deep geothermal reservoir

kinematic and moisture characteristics of a nonprecipitating cold front observed during ihop part i across front structures abstract a wide array of ground based and airborne instrumentation is used to examine the kinematic and moisture characteristics of a nonprecipitating cold front observed in west central kansas on 10 june 2002 during the international h2o project ihop this study the first of two parts is focused on describing structures in the across front dimension coarsely resolved observations from the operational network and dropsondes deployed over a 200 km distance centered on the front are combined with higher resolution observations from in situ sensors doppler radars a microwave radiometer and a differential absorption lidar that were collected across a 40 km swath that straddled a 100 km segment of the front the northeast southwest oriented cold front moved toward the southeast at 8 10 m s 1 during the morning hours but its motion slowed to less than 1 m s 1 in the afternoon in the early afternoon the cold front separated cool air with a northerly component flow of 2 4 m s 1 from a 10 km wide ban

iridium bearing sublimates at a hot spot volcano piton de la fournaise indian ocean sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites piton de la fournaise poas momotombo etna ardoukoba and erta ale they have been analysed for ir and other volatile elements se as cu au ag pb tl by means of instrumental neutron activation analysis inaa and proton induced x ray emission pixe among the investigated volcanoes only piton de la fournaise is found to release detectable amounts of iridium ir in piton de la fournaise sublimates is associated with f minerals this confirms its gaseous transport as a volatile fluoride compound iridium seems to be preferentialy released by hot spot type volcanoes and its detection in piton de la fournaise sublimates provides a positive argument in favour of a volcanic hypothesis to explain the ktb events

three dimensional numerical modeling of convection produced by interacting thunderstorm outflows part i control simulation and low level moisture variations abstract the klemp wilhelmson three dimensional numerical cloud model is used to investigate cloud development along intersecting thunderstorm outflow boundaries the model initial environment is characterized by a temperature and moisture profile typically found in strong convective situations and the initial wind field is prescribed by a constant unidirectional shear 2 9 m s 1 km 1 from 0 8 to 8 9 km with a constant wind everywhere else the wind shear vector is perpendicular to the line containing the two initial outflow producing clouds which are spaced 16 km apart and are triggered by thermal impulses centered at the top of the boundary layer the dynamics of the outflow collision are documented using time dependent kinematic air parcel trajectories and thermodynamic data we find that ambient air in the outflow collision region is literally squeezed out of the way as the two outflows collide some of this air is lifted to saturation triggering two convective clouds the upshear member of the

analysis of convergence boundaries observed during ihop_2002 abstract an analysis of six convergence boundaries observed during the international h2o project ihop 2002 is presented the detailed kinematic and thermodynamic structure of these boundaries was examined using data collected by an airborne doppler radar and a series of dropsondes released by a jet flying at 500 mb the former and latter platforms were able to resolve the meso and meso scale circulations respectively convection initiated on three of the days while no storms developed in the regions targeted by the mobile platforms on the other days referred to as null cases the airborne radar resolved the finescale structure of four drylines a cold front and an outflow boundary on the six days horizontal profiles through radar detected thin lines revealed bell shaped distributions and there appeared to be a seasonal dependence of the peak values of radar reflectivity the echo profiles through the fine line in may were in general greater than those plotted for the june cases there was

melt inclusions in quartz from an evolved peraluminous pegmatite geochemical evidence for strong tin enrichment in fluorine rich and phosphorus rich residual liquids abstract we have investigated the magmatic evolution of a late stage f and p rich pegmatite forming aluminosilicate liquid and the geochemical controls on magmatic mineralizing processes by remelting totally crystallized melt inclusions in quartz and analyzing the quenched glass by epma and sims the quartz phenocrysts were sampled from a pegmatite that occurs in a variscan granite genetically associated with cassiterite and wolframite mineralized greisen veins at the ehrenfriedersdorf sn w deposit central erzgebirge se germany the melt inclusion compositions imply that the pegmatite forming liquid achieved extreme levels of chemical differentiation it contained high abundances of sn f p li rb cs nb ta and be and abnormally low concentrations of ca y sr and ree for a granite and it was strongly peraluminous the molar al 2 o 3 cao na 2 o k 2 o ranged from 1 3 to 2 0 fractions of the pegmatite forming liquid were extremely enriched in p 2 o 5 f al 2 o 3 and the molar abundances of f p in the glasses correlate strongly with moles of network modifying al ions implying that the bulk liquid included f p and al bearing complexes formation of these complexes reduced the activities of f p and al in bulk liquid suppressed the crystallization of magmatic topaz and p rich minerals and allowed the liquid to become enriched in these constituents some fractions of the ehrenfriedersdorf aluminosilicate liquid contained 1000 2000 ppm sn these levels of sn enrichment were up to 2 orders of magnitude greater than that ever reported for nonmineralized metaluminous and peraluminous igneous materials and are consistent with some experimentally derived sn solubilities in cassiterite saturated granitic liquids at geologically relevant pressures and temperatures this concordance implies that cassiterite could have crystallized directly from this highly evolved p and f rich peraluminous granitic liquid without the involvement of hydrothermal fluids

fractionation vs magma mixing in the wangrah suite a type granites lachlan fold belt australia experimental constraints abstract the wangrah suite granites lachlan fold belt australia reflect different stages of differentiation in the magmatic history of an a type plutonic suite in this study we use experimentally determined phase equilibria of four natural a type granitic compositions of the wangrah suite to constrain phases and phase compositions involved in fractionation processes each composition represents a distinct granite intrusion in the wangrah suite the intrusions are the danswell creek dcg wangrah wg eastwood eg and dunskeig granite dg ordered from most mafic to most felsic by increasing sio2 and decreasing feototal experimental investigation show that the initial water content in melts from dcg is between 2 3 wt h2o if the dcg is viewed as the parental magma for the wangrah suite then 1 fractionation of magnetite orthopyroxene and plagioclase 20 wt of the dcg composition leads to compositions similar to that of the eg 2 further fractionation of plagioclase quartz k feldspar and biotite 40 wt from the eg composition leads to the dg composition these fractionation steps can occur nearly isobarically and are confirmed by bulk rock ba sr rb and zr concentrations in contrast the generation of the most abundant wg composition cannot be explained by fractional crystallisation from the dcg at isobaric conditions because of the high k2o content of this granite magma mixing could be the process to explain the chemical distinctiveness of the wangrah granite from all the other granites of the wangrah suite

variscan silicic magmatism and related tin tungsten mineralization in the erzgebirge slavkovský les metallogenic province integration of geochemical mineralogical isotopic and geochronological data with geodynamic considerations suggests that the variscan granites in the erzgebirge slavkovsk les domain originated from repeated melting events and were emplaced over a period of about 40 ma 330 290 ma several lines of evidence exist supporting the idea that erzgebirge granites assigned to different types biotite granites two mica granites strongly peraluminous p rich li mica granites and slightly peraluminous p poor granites are in most cases not genetically related via continuous fractional crystallization from a common magmatic reservoir the genesis of the slavkovsky les granites however might be discussed in terms of an uninterrupted fractionation series geological models of sn w deposits based upon geochemical and structural results imply that the main ore depositional events followed immediately the emplacement and solidification processes of melt via fluid melt immiscibility breccia pipe formation and or pervasive rock fluid interactions

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

the role of boundary layer convergence zones and horizontal rolls in the initiation of thunderstorms a case study abstract the initiation of thunderstorms is examined through a combined observational and modeling case study the study is based on doppler radar aircraft mesonet balloon sounding and profiler and photographic data from the convection initiation and downburst experiment cinde conducted near denver colorado the study examines the initiation of a line of thunderstorms that developed along a preexisting quasi stationary boundary layer convergence line on 17 july 1987 the storms were triggered at the intersection of the convergence line with horizontal rolls where enhanced updrafts were present the primary effect of the convergence line was to deepen the moist layer locally and provide a region potentially favorable to deep convection the critical factor governing the time of storm development was apparently related to the attainment of a balance between horizontal vorticity in the opposing flows on either side of the convergence line the effect was to cause the updrafts in the convergence line

hydrothermal vents in lake tanganyika east african rift system sublacustrine hydrothermal vents with associated massive sulfides were discovered during april 1987 at pemba and cape banza on the zaire side of the northern basin of lake tanganyika east african rift system new investigations by a team of ten scuba divers during the multinational france zaire germany and burundi tanganydro expedition august october 1991 found hydrothermal vents down to a depth of 46 m along north trending active faults bounding the tanganyika rift on the western side temperatures from 53 to 103 degrees c were measured in hydrothermal fluids and sediments veins of massive sulfides 1 10 cm thick pyrite and marcasite banding were found associated with vents at the pemba site at cape banza active vents are characterized by 1 70 cm high aragonite chimneys and there are microcrystalline pyrite coatings on the walls of hydrothermal pipes hydrothermal fluid end members show distinctive compositions at the two sites the pemba end member is a nahco sub 3 enriched fluid similar to the nahco sub 3 thermal fluids form lakes magadi and bogoria in the eastern branch of the rift the cape banza end member is a solution enriched in nacl such brines may have a deep seated basement origin as do the uvinza nacl brines on the eastern flank ofmore the tanganyika basin geothermometric calculations have yielded temperatures of fluid rock interaction of 219 and 179 degrees c in the pemba and cape banza systems respectively abundant white or reddish brown microbial colonies resembling beggiatoa mats were found surrounding the active vents thermal fluid circulation is permitted by opening of cracks related to 130 degrees n normal dextral faults that intersect the north south major rift trend the sources of heat for such hydrothermal systems may relate to the existence of magmatic bodies under the rift which is suggested by the isotopic composition of carbon dioxide released at pemba and cape banza 21 refs 2 figs less

observations of the finescale structure of a dryline during vortex 95 abstract the three dimensional finescale structure of a dryline observed over the texas panhandle during the verification of the origins in tornadoes experiment vortex on 6 may 1995 is presented high resolution observations documenting dryline evolution were collected from midafternoon while it moved slowly eastward until late afternoon as it retrogressed back to the west dryline variability in the horizontal along line direction was revealed by airborne doppler radar observations from the national center for atmospheric research electra doppler radar and ground based measurements from the nearby wsr 88d at amarillo texas this variability was created as the dryline interacted with horizontal convective rolls forming west of the dryline the rolls intersected the dryline at periodic locations creating radar reflectivity and vertical velocity maxima more importantly clouds initiated at these intersection points additional dryline variability was generated through the interaction of the low level fl

initiation of convective storms at radar observed boundary layer convergence lines abstract the origin of 653 convective storms occurring over a 5000 km2 area immediately east of the colorado rocky mountains from 18 may to 15 august 1984 was examined seventy nine percent of the 418 storms that initiated within the study area occurred in close proximity to radar observed boundary layer convergence lines this percentage increased to 95 when only the more intense storms 60 dbze were considered colliding convergence lines initiated new storms or intensified existing storms in 71 of the cases a new storm took a median time of 24 min to grow to 30 dbz following line collision the convergence lines ranged in length between ten and several hundred kilometers both radar and mesonet stations indicated that the primary convergence was concentrated in a zone 0 5 to 5 km in width these lines were characterized on doppler radar as thin lines of enhanced reflectivity between 0 and 20 dbze and as a line of strong radial or azimuthal gradient in doppler velocity these lines were observed ev

observations of convection initiation failure from the 12 june 2002 ihop deployment abstract observations of the development of cumulus convection which reached depths of several kilometers but failed to develop into sustained precipitating cumulonimbus clouds an event the authors term convection initiation failure are presented from the 12 june 2002 international h2o project ihop case the investigation relies heavily on remote and in situ data obtained by mobile truck borne doppler radars mobile mesonets mobile soundings and stereo cloud photogrammetry data collection was focused in northwestern oklahoma near the intersection of an outflow boundary and dryline thunderstorms developed along the dryline during the late afternoon approximately 40 km east of the domain intensively observed by the ground based observing systems farther west within the region of dense observations analyzed herein cumulus congestus clouds formed along an outflow boundary multiple doppler wind syntheses revealed that the boundary layer vertical velocity field was dominated by thermals rather t

a modeling study of the dryline abstract results of a modeling study of the 24 may 1989 dryline are presented a nonhydrostatic two dimensional version of the colorado state university regional atmospheric modeling system csu rams is used to deduce the impact of east west variability of soil moisture and vegetation on convective boundary layer evolution and dryline formation the effects of the initial moisture and wind fields and the impact of the coriolis force on the model results are also examined model output is compared with special airborne and sounding observations of the 24 may dryline several findings of an earlier observational study of the 24 may dryline are supported in the present study the modeled drylines are broadly comparable to the observed dryline with respect to the following properties 1 width 10 km 2 strong horizontal moisture and virtual potential temperature gradients 4 g kg 1 10 km and 2 k 10 km 3 strong horizontal convergence updraft w e shear of n s wind component 8 10 4 s 1 1 m s 1 10 m

the triple point on 24 may 2002 during ihop part ii ground radar and in situ boundary layer analysis of cumulus development and convection initiation abstract cumulus formation and convection initiation are examined near a cold front dryline triple point intersection on 24 may 2002 during the international h2o project ihop a new lagrangian objective analysis technique assimilates in situ measurements using time dependent doppler derived 3d wind fields providing output 3d fields of water vapor mixing ratio virtual potential temperature and lifted condensation level lcl and water saturated i e cloud volumes on a subdomain of the radar analysis grid the radar and lagrangian analyses reveal the presence of along wind i e longitudinal and cross wind i e transverse roll circulations in the boundary layer bl a remarkable finding of the evolving radar analyses is the apparent persistence of both transverse rolls and individual updraft vertical vorticity and reflectivity cores for periods of up to 30 min or more while moving approximately with the local bl wind satellite cloud images and single camera ground photogrammetry imply tha

mild hydrothermal alteration of immature organic matter in sediments from the bransfield strait antarctica surface sediments in the eastern bransfield strait antarctica were piston ccored to reconfirm previously observed hydrothermal alteration at depth 3 6 m subbottom the bransfield basin is still actively rifting with concomittant slow advection of fluids through the sediments covering the the back arc spreading axis and mild thermal alteration near the sea bed of the immature marine organic matter bitumen products from hydrothermally enhanced alteration are superimposed over the endogenous lipids which had undergone normal diagenesis for example the total hydrocarbbon yields are enhanced in the gray facies and had to a lesser degree in the red beds the cpi for the n alkanenes c25 c33 is about 2 for all samples with no major n alkane generation observed due to hydrothermal activity in altered zones the biomarker signature changes thus confirming some thermal stress however the steroid distributions are controlled more by iputs from source organisms nevertheless chemical reactions have occurred and include dehydration of sterols to sterenes isomerization of triterpenes and sterenes rearrangement of sterenes to diasterenes and reductive processes generating phytane from phytol via phytenes polynuclear aromatic hydrocarbons comprise the parent pah with significant amounts of alkylated homologs and aromatic terpenoid hydrocarbons these compounds are probably derived from disseminated coal in the sediments and not from hydrothermal activity such a source would also explain the n alkane distribution thus hydrothermal activity induced by the intrusion of a volcanic plug dike in the study are caused accelerated diagenesis of immature organic matter with simulataneous migration of volatile products in the sediments

mineralogical evidence for two magmatic stages in the evolution of an extremely fractionated p rich rare metal granite the podlesi stock krusne hory czech republic have the oh f sites fully occupied by fluorine also accessory the podlesi granite stock in the western krusne hory erzgebirge phosphates were formed during late magmatic crystallization of the mountains czech republic represents an extremely fractionated strongly p f enriched residual melt thus the mineralogical data strongly peraluminous fand p rich rare metal granite system of reflect the presence of two crystallization events within the dyke late variscan age the stock studied in drill core of 300 m length granite and pegmatite the presence of two melts parental and is formed by albite protolithionite topaz granite stock granite residual the latter strongly enriched in phosphorus has been also depth 50 300 m and shows geochemical and textural zoning the confirmed by study of melt inclusions in quartz from samples of stock granite is rich in p 0 5 wt f 0 5 1 2 wt rb the stock granite in its dyke bearing uppermost part mineral melt 1000 ppm li 500 1000 ppm and cs 100 150 ppm inclusion and whole rock chemical data from all rock types provide and poor in ti mg fe ca sr ba zr and rare earth elements evidence for two stages of granite evolution namely crystallization ree within the uppermost part of the stock depth 57 115 m from parental and residual melts this means that in addition to the stock granite is intercalated with albite zinnwaldite topaz dyke the granites in beauvoir france and argemela portugal the granite layers of 0 5 7 m thickness and a few thin flat dykes of podlesi stock is another well documented example of a two stage pegmatite the dyke granite and pegmatite are even more enriched evolution of a p rich granite system in p 1 wt p2o5 f 1 0 1 5 wt and rb up to 3000 ppm and are also rich in nb up to 100 ppm and ta up to 50 ppm the chemical data for the rock forming minerals show distinct differences between the stock granite and the dyke granite and pegmatite no chemical zoning of the rock forming minerals either from the upper rapidly cooled or from the lower slowly

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

the dryline on 22 may 2002 during ihop ground radar and in situ data analyses of the dryline and boundary layer evolution abstract on the afternoon and evening of 22 may 2002 high resolution observations of the boundary layer bl and a dryline were obtained in the eastern oklahoma and texas panhandles during the international h2o project using overdetermined multiple doppler radar syntheses in concert with a lagrangian analysis of water vapor and temperature fields the 3d kinematic and thermodynamic structure of the dryline and surrounding bl have been analyzed over a nearly 2 h period the dryline is resolved as a strong 2 4 g kg 1 km 1 gradient of water vapor mixing ratio that resides in a nearly north south oriented zone of convergence maintained through frontogenesis the dryline is also located within a gradient of virtual potential temperature which induces a persistent solenoidally forced secondary circulation initially quasi stationary the dryline retrogrades to the west during early evening and displays complicated substructures including small wavelike perturbations that travel from south to north at nea

columbite solubility in granitic melts consequences for the enrichment and fractionation of nb and ta in the earth s crust the behaviour of niobium and tantalum in magmatic processes has been investigated by conducting mnnb2o6 and mnta2o6 solubility experiments in nominally dry to water saturated peralkaline aluminium saturation index a s i 0 64 to peraluminous a s i 1 22 granitic melts at 800 to 1035 c and 800 to 5000 bars the attainment of equilibrium is demonstrated by the concurrence of the solubility products from dissolution crystallization mn doped and nb or ta doped experiments at the same pressure and temperature the solubility products of mnnb2o6 ksp nb and mnta2o6 ksp ta at 800 c and 2 kbar both increase dramatically with alkali contents in water saturated peralkaline melts they range from 1 2 10 4 and 2 6 10 4 mol2 kg2 respectively in subaluminous melt a s i 1 02 to 202 10 4 and 255 10 4 mol2 kg2 respectively in peralkaline melt a s i 0 64 this increase from the subaluminous composition can be explained by five non bridging oxygens being required for each excess atom of nb5 or ta5 that is dissolved into the melt the ksp nb and ksp ta also increase weakly with al content in peraluminous melts ranging up to 1 7 10 4 and 4 6 10 4 mol2 kg2 respectively in the a s i 1 22 composition columbite tantalite solubilities in subaluminous and peraluminous melts a s i 1 02 and 1 22 are strongly temperature dependent increasing by a factor of 10 to 20 from 800 to 1035 c by contrast columbite tantalite solubility in the peralkaline composition a s i 0 64 is only weakly temperature dependent increasing by a factor of less than 3 over the same temperature range similarly ksp nb and ksp ta increase by more than two orders of magnitude with the first 3 wt h2o added to the a s i 1 02 and 1 22 compositions whereas there is no detectable change in solubility for the a s i 0 64 composition over the same range of water contents solubilities are only slightly dependent on pressure over the range 800 to 5000 bars the data for water saturated sub and peraluminous granites have been extrapolated to 600 c conditions at which pegmatites and highly evolved granites may crystallize using a melt concentration of 0 05 wt mno 70 to 100 ppm nb or 500 to 1400 ppm ta are required for manganocolumbite and manganotantalite saturation respectively the solubility data are also used to model the fractionation of nb and ta between rutile and silicate melts predicted rutile melt partition coefficients increase by about two orders of magnitude from peralkaline to peraluminous granitic compositions it is demonstrated that the nb2o5 ta2o5 activity coefficient ratio in the melt phase depends on melt composition this ratio is estimated to decrease by a factor of 4 to 5 from andesitic to peraluminous granitic melt compositions accordingly all the relevant accessory phases in subaluminous to peraluminous granites are predicted to incorporate nb preferentially over ta this explains the enrichment of ta over nb observed in highly fractionated granitic rocks and in the continental crust in general

observations of the sea breeze front during cape part ii dual doppler and aircraft analysis abstract the three dimensional kinematic structures of offshore and onshore flow sea breeze fronts observed during the cape experiment are shown using high resolution dual doppler and aircraft data the fronts interact with horizontal convective rolls hcrs that develop within the convective boundary layer nearly perpendicular intersections between the hcrs and sea breeze front were observed during the offshore flow case close to the front the hcr axes were tilted upward and lifted by the frontal updrafts consequently a deeper updraft was created at the intersection points providing additional impetus for cloud development furthermore clouds forming at periodic intervals along the ncrs intensified as they propagated over the front during the onshore flow case the hcr orientation was nearly parallel to the front extended sections of the front merged with the hcrs this process strengthened the front and is explained as the merger of like sign vortices associated with both the front and hcrs

tracing metal sources in peribatholitic hydrothermal w deposits based on the chemical composition of wolframite the example of the variscan french massif central abstract we present a complete dataset for major minor and trace elements in wolframite fe mn wo4 based on the example of several peribatholitic hydrothermal w deposits located in the variscan french massif central fmc the wolframite samples were characterized down to the micrometer scale by combining scanning electron microscopy observations and in situ chemical analysis by electron probe microanalyzer and laser ablation inductively coupled plasma mass spectrometry most samples are fe dominated wolframites and are characterized by variable fe fe mn values for the studied deposits from 0 36 to 0 86 without significant alteration features wolframites present intracrystalline variations for concentrations of several minor and trace elements principally for nb ta and sn which reflect growth zoning the minor and trace element compositions of the different wolframite samples show at first order similar enrichments in ta nb sn zn and in as well as depletions in lree li th ti zr hf pb v co and mg compared to the upper continental crust second order compositional variations are observed between the studied deposits which can be separated in four main regional geochemical groups this work highlights that the chemical composition of wolframite is controlled by both the crystallochemical parameters and the composition of the primary hydrothermal fluid the regional variations observed in the geochemical signatures of wolframite reflect local variations in the composition of the hydrothermal fluid i e variable metal sources therefore this suggests that the minor and trace element contents in wolframite likely represent direct markers of the source of the hydrothermal fluid and ultimately of the metals the comparison between the trace element compositions of wolframite with the compositions of regional granitic rocks and worldwide shales suggests that evolved peraluminous granites represent the main source of metals in peribatholitic hydrothermal w deposits from the fmc whereas metasedimentary rocks have a limited to no influence on the metal budget

fractionation of metaluminous a type granites an experimental study of the wangrah suite lachlan fold belt australia abstract crystallisation experiments were performed on two metaluminous a type granite compositions ab412 and ab422 from the wangrah suite a representative a type granite suite from the lachlan fold belt south eastern australia ab412 is more mafic than ab422 and zircon saturation temperatures are 897 and 843 c respectively experiments were performed at 200 mpa f o 2 between nno and nno 1 05 in a temperature range between 700 and 900 c for various melt h 2 o contents experimental results were compared to the natural phase compositions to constrain the water content of the melt and the phases involved in fractionation processes in the wangrah suite with decreasing temperature fe ti oxide orthopyroxene and plagioclase are the first phases to crystallise followed by biotite the orthopyroxene stability is mainly restricted to temperatures above 750 c hornblende is only stable in the less evolved composition if the water content of the melt is at least 4 5 wt h 2 o the initial water content in the more mafic melt ab412 was between 2 and 3 wt h 2 o although orthopyroxene is not observed in the natural assemblages of the wangrah suite it has influenced the early fractionation of the wangrah suite granites mass balance calculations show that composition ab422 can be obtained after the crystallisation of 4 7 wt iron rich orthopyroxene plus 8 5 wt plagioclase from ab412

highly fractionated jurassic i type granites and related tungsten mineralization in the shirenzhang deposit northern guangdong south china evidence from cassiterite and zircon u pb ages geochemistry and sr nd pb hf isotopes abstract the shirenzhang tungsten deposit is a classic wolframite quartz vein type deposit located in northern guangdong province eastern segment of the nanling w sn polymetallic belt the ore veins controlled by the nw striking fault system are mainly hosted in the ordovician metasedimentary rocks and can also be found with less amount in the cupola of the concealed granitic stock displaying a typical five floor vertical zonation proposed by the chinese geologists the concealed granitic stock mainly comprises two intrusive facies the porphyritic biotite granite g1 in the outer zone and the medium to fine grained monzogranite g2 in the inner zone in this paper we report new cassiterite u pb ages and pb isotopes of sulfides for the shirenzhang tungsten deposit combined with new zircon u pb ages and hf isotopes elemental geochemistry and sr nd pb isotopes of the concealed granitic rocks with aims to elucidate the origin of the ore related granites and the link between the tungsten mineralization and granitic magmatism la icp ms zircon u pb dating gives the weighted mean ages of 164 2 ma for g1 and 162 4 ma for g2 respectively cassiterite from the wolframite bearing quartz vein and the drusy quartz vein yield the weighted mean ages of 164 2 ma and 160 2 ma respectively these ages suggest that both the granitic intrusion and related w sn mineralization in the shirenzhang deposit were initiated during the late jurassic ca 160 ma the shirenzhang granitic rocks are weakly peraluminous highly fractionated i type granites detailed elemental and isotopic data demonstrate that the granitic rocks were derived from partial melting of the paleoproterozoic basement rocks at a relatively shallow depth of 30 km triggered by underplating of basaltic magma and underwent extensive fractional crystallization of hornblende biotite feldspar and monazite and or allanite a continental arc setting induced by northwesterly subduction of the paleo pacific plate is suggested for the genesis of the shirenzhang i type granites the comparable pb isotopic compositions of feldspar and sulfides imply that the lead in the ore veins was of magmatic origin integrating the spatial temporal relationship between the ore veins and the concealed granitic rocks with the pb isotopes from the sulfides and granites we suggest that the tungsten mineralization is genetically linked with the concealed granitic rocks in the shirenzhang deposit fractional crystallization and melt fluid interaction may play an important role on the formation of the granite related tungsten mineralization

meteoric water basalt interactions ii a field study in n e iceland the compositions of rain snow melt spring and geothermal waters from the rift zone of n e iceland can be explained by seaspray addition chemical fractionation at the seawater air interface burning of fossil fuel farming activities purification by partial melting of snow and ice dissolution of basalts and buffering by alteration minerals the dissolution of the rocks appears to be incongruent during solute acquisition spring compositions move through the stability fields of kaolinite and smectite to the laumontite and illite fields all but four of the springs are undersaturated with respect to calcite silica concentrations are compatible with the solubility of basaltic glass the reactions reflected in the spring waters appear to have taken place sealed off from atmospheric co2 after initial saturation the geothermal waters which are recharged by the spring waters are depleted in mg and ca but enriched in carbon and sulfur with respect to dissolution of primary rocks expressions are derived relating dissolution rates of rocks age of groundwaters physical properties of groundwaters and mass transfer the characteristic rock particle radii in the cold water aquifers range from 0 2 to 2 cm and the characteristic crack openings are of the order 0 04 to 0 4 cm using laboratory studies on the icelandic lavas as a guide the residence times of the cold waters in the aquifers can be estimated at 60 days to 4 years the average active surface area of the aquifers enclosing 1000 g of spring water is of the order of 0 6 to 6 m2 and these 1000 g of water have reacted with 0 1 to 1 g of basaltic rocks the same mass of thermal water has interacted with 100 to 300 g of unaltered rocks

the synoptic regulation of dryline intensity abstract to investigate the role of synoptic scale processes in regulating the strength of the dryline a dataset is constructed of all drylines occurring within the west texas mesonet wtm during april may and june of 2004 and 2005 in addition dewpoint and wind data were collected from stations on the western morton mort and eastern paducah padu periphery of the wtm domain 230 km across generally oriented east west across the typical location of the dryline in west texas drylines were characterized by two variables the difference in dewpoint between mort and padu hereafter dryline intensity and the difference in the eastward component of the wind between mort and padu hereafter dryline confluence a high degree of correlation existed between the two variables consistent with a strong role for dryline confluence in determining dryline intensity some cases departing from the strong correlation between these variables represent synoptically quiescent drylines whose strength is likely

analysis of a dryline during ihop implications for convection initiation abstract a detailed analysis of a dryline that formed on 22 may 2002 during the international h2o project ihop is presented the dryline was classified as a null case since air parcels lifted over the convergence boundary were unable to reach the level of free convection preventing thunderstorms from forming a secondary dryline associated with a distinct moisture discontinuity developed to the west of the primary dryline the primary dryline exhibited substantial along frontal variability owing to the presence of misocyclones this nonlinear pattern resembled the precipitation core gap structure associated with cold fronts during one of the analysis times although the misocyclones were positioned within the gap regions radar refractivity has been recently shown to accurately retrieve the low level moisture fields within the convective boundary layer however its use in forecasting the initiation of convection has been restricted to qualitative interpretations this study introduces the total derivati

finescale radar observations of the 22 may 2002 dryline during the international h2o project ihop abstract the dryline has long been associated with the development of severe thunderstorms in the southern plains during the spring and early summer months the propagation and structure of the dryline are closely tied to surface processes that are neither well understood nor well resolved with current observational capabilities as a result there are often large errors in forecasts of dryline position and structure improvements in radar technology have allowed for better observations of the dryline in recent years here very finescale radar observations taken with the university of massachusetts amherst umass mobile w band radar during an international h2o project ihop double dryline event on 22 may 2002 in the oklahoma panhandle are presented the observations are placed in the context of the dryline secondary circulation which describes flow in a plane normal to the dryline the narrow half power beamwidth of the antenna on the w band 0 18 permitted the measurements of channels of upward 8

a case study of severe storm development along a dryline within a synoptically active environment part ii multiple boundaries and convective initiation abstract a dryline that occurred on 16 may 1991 within a synoptically active environment is examined in detail using research aircraft radar surface satellite and upper air observations the work focuses on multiple boundaries in the dryline environment and initiation of tornadic storms in two along line areas aircraft measurements in the boundary layer reveal that both the east west extent of moisture gradients and the number of regions containing large moisture gradients vary in the along dryline direction aircraft penetrations of thinlines observed in clear air return from radar reveal that all thinlines are associated with convergence and a moisture gradient and that more distinct thinlines are associated with stronger convergence however significant moisture gradients are not always associated with either thinlines or convergent signatures convective clouds on this day formed at the dryline rather than significantly east of the dryline the three thunderstorm cells that occurred in east cen

kinematic observations of misocyclones along boundaries during ihop during the international h2o project mobile radars collected high resolution data of several 0 5 2 kmwide vertically oriented vortices or misocyclones along at least five mesoscale airmass boundaries this study analyzes the properties of the misocyclones in three of these datasets 3 10 and 19 june 2002 to verify findings from finescale numerical models and other past observations of misocyclones and to further the understanding of the role that they play in the initiation of deep moist convection and nonsupercell tornadoes misocyclones inflect or disjoint the swath of low level convergence along each boundary to varying degrees depending on the size of their circulations when several relatively large misocyclones are next to each other the shape of low level convergence along each boundary is arranged into a staircase pattern mergers of misocyclones are an important process in the evolution of the vorticity field as a population of small vortices consolidates into a smaller number of larger ones additionally merging misocyclones may affect the mixing of thermodynamic fields in their vicinity when the merger axis is perpendicular to the boundary misocyclones interact with linear and cellular structures in the planetary boundary layers pbls of the air masses adjacent to each boundary cyclonic low level vertical vorticity generated by both types of structures makes contact with each boundary and sometimes is incorporated into preexisting misocyclones intersections of either type of pbl structure with the boundary result in strengthened pockets of low level convergence and typically strengthened misocyclones

petrogenesis of jurassic tungsten bearing granites in the nanling range south china evidence from whole rock geochemistry and zircon u pb and hf o isotopes abstract the nanling range nlr is the largest tungsten metallogenic province in china and perhaps in the world the tungsten mineralization is believed to be related to jurassic granitic magmatism however the petrogenesis of these granites and their relation to the tungsten mineralization are still debated whole rock geochemical and sr nd hf isotopic data and zircon in situ u pb ages and hf o isotopes are reported for w bearing granitic intrusions from the southern jiangxi province in the nlr in order to constrain their magmatic sources and petrogenesis the nlr granites include biotite granites two mica granites and garnet muscovite granites sims and la icpms u pb dating of zircons and monazites give emplacement ages of 161 154 ma for these rocks the granites are metaluminous to strongly peraluminous with high sio 2 72 3 wt and high k 2 o 3 7 wt petrographic and geochemical features show that they are highly fractionated i type granites the biotite granites are enriched in light rare earth elements lrees relative to heavy rees have weakly negative eu anomalies and are depleted in nb ba p and ti in contrast the two mica and garnet bearing muscovite granites have tetrad type ree patterns with strongly negative eu anomalies and are extremely depleted in ba nb sr p and ti magmatic garnets are mainly almandine and spessartine and have low mn cores and high mn rims their y hree contents are high and generally decrease from core 1 2 wt to rim average 4955 ppm all of these granites are characterized by variable whole rock initial 87 sr 86 sr 0 7053 0 8000 e nd t 12 6 to 9 4 and e hf t 12 3 to 8 5 as well as variable zircon e hf t and 18 o with values of 16 3 to 7 4 and 7 6 to 10 0 respectively they contain abundant zircon xenocrysts and xenoliths of micaceous schist all of these features are consistent with a process of crystal fractionation of crustally derived magmas coupled with strong assimilation of sedimentary rocks the assimilation of meta sedimentary materials increased the concentrations of tungsten alumina and manganese in the magmas whereas high degrees of crystal fractionation further enriched them in the evolved granitic rocks the w enriched magmatic fluids formed the tungsten bearing quartz veins revealing the genetic relationship between tungsten mineralization and emplacement of garnet bearing two mica or muscovite granites in the nlr

finescale vertical structure and evolution of a preconvective dryline on 19 june 2002 abstract high resolution airborne cloud radar data and other international h2o project datasets are used to describe the vertical structure of an unusual prefrontal dryline this dryline observed in northwestern kansas on 19 june 2002 first progressed eastward and tilted toward the west and later became more stationary and reversed its tilt toward the moist side the convective boundary layer cbl depth difference also reversed only in the later phase did the dry side cbl become deeper than on the moist side echo and single dual doppler velocity data in a vertical transect across the dryline suggest a solenoidal circulation dynamically consistent with the observed horizontal buoyancy gradient both this gradient and the solenoidal circulation reversed in the later phase simultaneously confluence toward the dryline increased resulting in an increasing moisture gradient as well as a deepening cbl in the dryline convergence zone it is speculated that the baroclinically generated horizontal vortici

what is the mechanism for the modification of convective cloud distributions by land surface induced flows abstract the aim of this study is to determine the mechanism that modulates the initiation of convection within convergence zones caused by land surface induced mesoscale flows an idealized modeling approach linked quantitatively to observations of vegetation breezes over tropical benin was used a large eddy model was used with a prescribed land surface describing heterogeneities between crop and forest over which vegetation breezes have been observed the total surface fluxes were constant but the bowen ratio varied with vegetation type the heterogeneous land surface created temperature differences consistent with observations which in turn forced mesoscale winds and convection at the convergence zones over the crop boundaries at these convergence zones optimum conditions for the initiation of convection were found in the afternoon the equivalent potential temperature was higher in the convergence zones than over anywhere else in the domain due to reduced entrainment and the mesoscale convergence

textural and chemical constraints on the formation of disseminated granite hosted w ta nb mineralization at the dajishan deposit nanling range southeastern china the dajishan deposit located in the nanling range of southeastern china is the largest wolframite deposit in the world approximately two thirds of the tungsten resource is contained in large quartz wolframite k feldspar muscovite scheelite sulfide beryl veins but the remainder occurs as wolframite and lesser scheelite disseminated through the nb ta mineralized no 69 granite which is characterized by abundant snowball quartz crystals disseminated granite hosted wolframite mostly occurs as a replacement after lath shaped muscovite although an interstitial variety is present in some samples the major element chemistry of the disseminated and vein hosted wolframite is similar however the former has one to two orders of magnitude higher concentrations of high field strength elements hfse including nb and ta disseminated muscovite in the no 69 granite is fe and mg rich replacement rims on these muscovite crystals are enriched in ta sn and cs but more depleted in nb related to the original phase vein hosted muscovite is characterized by lower nb ta rb and cs contents than the granite hosted muscovite although sn and w concentrations are comparable columbite mn is the principal nb ta ore mineral and occurs disseminated through the no 69 granite where it is hosted by snowball quartz crystals some of the columbite has been altered and overgrown by wodginite the restriction of these altered columbite crystals to within snowball quartz along with the ta and sn enrichment of the alteration rims on muscovite tie the formation of snowball quartz to a ta sn metasomatic event high ge ti and al ti ratios in the snowball quartz relative to interstitial quartz are also consistent with a late stage of formation for the former variety the disseminated granite hosted w mineralization formed through fluid rock interaction the fluids that precipitated the disseminated wolframite were most likely those that formed the veins but were modified through reaction with the hfse enriched no 69 granite nb ta mineralization however is represented by magmatic columbite and by a later metasomatic stage of wodginite the low solubility of ta in aqueous fluids combined with the evidence for ta sn metasomatism suggests that the ta sn metasomatic event was caused by hydrosilicate liquids a transitional fluid that lies compositionally between silicate magmas and hydrothermal fluids whole rock and mineral chemistry both suggest that deep level fractional crystallization of the no 69 granite was required to elevate ta and nb concentrations to allow saturation of columbite

convective initiation on 19 june 2002 during ihop high resolution simulations and analysis of the mesoscale structures and convection initiation 1 the 19 june 2002 convective initiation ci case from the international h2o project ihop is simulated using the arps at 1 km grid spacing it involves three distinct ci groups ci a ci b and ci c associated with a cold front dryline system initial condition at 1800 utc 19 june 2002 was created using the arps 3dvar including standard as well as special observations the simulation captured the three groups of cis rather well with small timing and spatial errors ci a is most typical of dryline initiation vertical cross sections through the initiation locations show typical dryline structures with an upward moisture bulge forced by lifting along the dryline convergence for ci b the model predicted mesoscale structures agree with special ihop aircraft dropsonde observations closely strong low level convergence from opposing cold front and dryline circulations produces deep symmetric upwelling of moist air and the convection is initiated at the crest of the moisture bulge ci c is more typical of frontal convection where deep convection is first initiated at the front edge of the cold air for ci b and ci c north south moisture bands that have dryline characteristics and can be considered multiple drylines and contain enhanced vertical motion and upward moisture bulges intercept the dryline and cold front respectively providing the most favored locations on the dryline or cold front for initiation furthermore the air parcels feeding the initial cells at ci b and ci c have trajectories along the moisture bands and have already experienced uplifting when they reach the dryline and cold front locations

impact of a front dryline merger on convection initiation near a mountain ridge in beijing abstracta case study is presented of convection initiation ci resulting from the merger of a cold front with a dryline in southwestern beijing china on the afternoon of 11 june 2011 this process is analyzed with s band doppler radar data surface automatic weather station data and mesoscale numerical simulation results the formation of this dryline is analogous to that on the great plains of the united states and it is conducive to ci with mesoscale updrafts generated from the baroclinic frontogenesis and with favorable instability immediately on the moist side prior to the front dryline merger as the cold front approached the observed boundary layer convergence line or the simulated meso scale secondary dryline ci occurred ahead of the cold front with little contribution from frontogenetic baroclinity of the dryline the cold front then merged with the dryline and the baroclinity of the dryline was enhanced by the associated convergence to a degree comparable to that caused by frontogene