numerical simulations of radiative cooling beneath the anvils of supercell thunderstorms abstract numerical simulations of supercell thunderstorms that include parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps to investigate the effects of anvil shadows on the near storm environment if the simulated storm is nearly stationary the maximum low level air temperature deficits within the shadows are about 2 k which is roughly half the cooling found in some previous observations it is shown that the extinction of downwelling shortwave radiation by the anvil cloud creates a differential in the flux of downwelling shortwave radiation between the sun and the shade that is at least an order of magnitude greater than the differential of any other term in either the surface radiation or the surface energy budgets the loss of strong solar heating of the model surface within the shaded regions leads to a reduction of surface temperatures and stabilization of the model surface layer beneath the anvil the reduction in vertical mixing

polarimetric and dual doppler radar observations of the lipscomb county texas supercell thunderstorm on 23 may 2002 abstract polarimetric and dual doppler observations of a supercell observed by the national center for atmospheric research ncar s band polarimetric spol radar two doppler on wheels dow radars and the greek xpol radar on 23 may 2002 during the international h2o project ihop are presented the polarimetric radar observations began as the storm organized into a supercell and continued for over an hour while the storm was in its mature phase the hydrometeor distribution within the mature storm was retrieved using a fuzzy logic hydrometeor classification algorithm the dual doppler radar observations began around the time that the polarimetric radar observations concluded and they covered the end of the mature phase and much of the dissipation phase of the storm the dual doppler wind syntheses are used to evaluate the importance of the forward flank outflow in augmenting the horizontal vorticity field near the storm above 400 m in this case having a relatively weak low level mesocyclone the pa

observations of a colorado tornado part ii combined photogrammetric and doppler radar analysis abstract an integrated analysis of photographic and doppler radar observations of a tornadic storm during the convection initiation and downburst experiment cinde is presented high resolution single doppler radar measurements are combined with cloud photogrammetry to reveal the detailed structural relationship of the hook echo and the misocyclone with visual features of the tornado vertical cross sections of dual doppler winds in the plane of the photographs were also examined to determine the complex motions within and surrounding the vortex the tornado was found to be within a weak echo hole of the hook echo the hole progressed upward above cloud base as the tornado matured an annulus of higher reflectivity that formed a book echo is hypothesized to have been composed of sparse but large raindrops the airflow fields suggest that vortex breakdown and axial downdrafts were present near the ground at early stages shortly after the tornado became visible later axial upward flow dominated at all le

identification of deep groundwater discharge areas in the boggy creek catchment southeastern manitoba using excess aqueous helium the hydrogeology of the lac du bonnet batholith at the whiteshell research area wra in southeastern manitoba has been studied extensively although the general structure of the batholith is well known its near surface structure is less well known because of the overburden consequently the precise locations of groundwater discharge from deep fractures into local surface water remain uncertain deep groundwater in the wra is highly enriched with radiogenic he from the decay of natural u and th he is up to 50 ml l 1 surface waters normally equilibrate with atmospheric he and contain a standard he of 47 nl l 1 we hypothesized that areas of deep groundwater discharge from the lac du bonnet batholith should be characterized by elevated aqueous he concentrations we surveyed boggy creek and boggy lake at the wra in the late winter of 1989 for such he anomalies in boggy creek three significant anomalies were identified whereas in boggy lake several were found the largest occupying the southeast q

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part ii intensification of low level rotation abstractthe dynamical processes responsible for the intensification of low level rotation prior to tornadogenesis are investigated in the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the circulation of material circuits that converge upon the low level mesocyclone is principally acquired along the southern periphery of the forward flank precipitation region which is a corridor characterized by a horizontal buoyancy gradient thus much of the circulation appears to have been baroclinically generated the descending reflectivity core drc documented in part i of this paper has an important modulating influence on the circulation of the material circuits a circuit that converges upon the low level mesocyclone center prior to the drc s arrival at low levels approximately the arrival of the 55 dbz reflectivity isosurface in this case loses some of its previously acquired circulation during the final f

distribution of uranium and thorium in core samples from the underground research laboratory lease area southeastern manitoba canada abstract petrographic examination of core samples from seven boreholes in the underground research laboratory lease area of the lac du bonnet batholith revealed that the granitic core can be divided into four sample groups 1 grey granite 2 pink granite 3 deep red granite and 4 cream coloured clay rich granite the order of these four groups represents an evolutionary sequence that can be related to the alteration of the grey granite u and th concentrations were determined for the four groups of granitic core samples the u concentration in the four groups of core samples showed a distinct variation whereas the th concentration showed little variation the distribution pattern of u in the four sample groups can be related to its mobility and concentration under various stages of rock alteration while the uniform distribution of th is interpreted to be due to its limited mobility

evolution of low level angular momentum in the 2 june 1995 dimmitt texas tornado cyclone abstract the life cycle of the 2 june 1995 dimmitt texas tornado cyclone observed during the verification of the origins of rotation in tornadoes experiment vortex is described the tornado cyclone here is defined as a significantly axisymmetric flow larger than the visible tornado and characterized by increasing angular momentum with increasing radius its life cycle included three phases with somewhat differing evolution of angular momentum herein called intensifying transition and weakening during the intensifying stage the funnel and debris cloud gradually increased in size the azimuthally averaged secondary circulation of the larger scale tornado cyclone as determined using high resolution single doppler data obtained by a mobile radar was primarily inward and upward consistent with the presence of a wall cloud outside the tornado the azimuthally averaged angular momentum increased monotonically away from the tornado so inward advection allowed the angular momentum to increase slowly

a severe frontal rainband part ii tornado parent vortex circulation abstract by means of multiple doppler radar analysis part i established the stormwide hydrodynamic structure as an intense gravity current which advances on a prefrontal low level jet part ii examines the initiation and evolution of a tornado parent vortex circulation in the context of stormwide vorticity production tilting of the prefrontal inflow below the low level jet axis accounts for production of observed vorticity 10 2 s 1 at the surface front the two dimensional flow pattern is modified by the development of an inflectional instability with a wavelength of 13 km breaking or roll up of this instability occurs on a time scale of roughly 500 s and results in small scale vortices along the surface front one such vortex is examined in detail this vortex is the parent circulation of a small tornado the parent vortex structure is determined to be quite similar to those observed in summertime deep convection this suggests a generality to the findings concerning parent vortex initiation and

the lagrange tornado during vortex2 part i photogrammetric analysis of the tornado combined with single doppler radar data abstractthis study presents a single doppler radar analysis combined with cloud photography of the lagrange wyoming tornado on 5 june 2009 in an attempt to relate the radar observed hook echo weak echo hole weh and rotational couplet to the visual characteristics of the tornado the tornado was rated ef2 the circulation at low levels went through two intensification periods based on azimuthal shear measurements the first intensification was followed by the appearance of a brief funnel cloud the second intensification was coincident with the appearance of a second funnel cloud that remained in contact with the ground until the tornado dissipated a deep weh rapidly formed within the hook echo after damaging wind was identified at the ground and before the appearance of a funnel cloud the echo pattern through the hook echo on 5 june undergoes a dramatic evolution initially the minimum radar reflectivities are near the surface 15 dbz and the weh does not suggest a tapered structure near the gro

simulated supercells in nontornadic and tornadic vortex2 environments abstractthe composite near storm environments of nontornadic and tornadic supercells sampled during the second verification of the origins of rotation in tornadoes experiment vortex2 both appear to be generally favorable for supercells and tornadoes it has not been clear whether small differences between the two environments e g more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite are actually determinative of storms tornadic potential from the vortex2 composite environments simulations of a nontornadic and a tornadic supercell are used to investigate storm scale differences that ultimately favor tornadogenesis or tornadogenesis failure both environments produce strong supercells with robust midlevel mesocyclones and hook echoes though the tornadic supercell has a more intense low level updraft and develops a tornado like vortex exceeding the ef3 wind speed threshold in contrast the nontornadic supercell only produces shallow vortic

actualistic models of mantle metasomatism documented in a composite xenolith from dish hill california major and trace element whole rock and mineral variations in composite hornblendite peridotite xenolith ba 2 1 from dish hill ca are due to a single event of metasomatism in the mantle the hornblendite is the crystallized selvage of a dike conduit charged with incompatible element enriched hydrous mafic magma the magma infiltrated the refractory peridotite wallrock reacted with its constituent minerals and simultaneously deposited amphibole the systematic data from this study show considerable variation in isotopic values and trace elements these data provide insight into a mantle process that was defined previously from samples without context lacking evidence about the number or source of metasomatic events in the contact zone of ba 2 1 peridotite is enriched in fe ti co2 and h2o clinopyroxene and amphibole also are enriched in fe and ti but clinopyroxene appears slightly depleted in cao compared to chondrites peridotite clinopyroxene and probably amphibole are enriched in light rare earth lreecn and other incompatible trace elements values of 87sr86sr and 143nd144nd in the contact zone are close to isotopic equilibrium with the dike whole rock and constituent clinopyroxene compositions change to those of refractory peridotite with distance from the contact these compositional variations were modelled using gresens equation for whole rock major and minor elements and calculations for isotopic ratios and rees which emulate the effects of chromatographic fractionation the choice of endmembers was restricted to compositions actually present in mantle samples from dish hill model results indicate that 1 1 the variations can be explained as the result of a single metasomatic event probably a single pulse of previously fractionated liquid 2 2 the ratio of total interacting liquid to peridotite was at least 1 3 by weight in the contact zone and 3 3 the composition of the metasomatic liquid changed progressively as it infiltrated beyond that zone the small distance over which variations occur is due to the small amount of liquid that infiltrated only in the contact zone was peridotite wallrock saturated by a liquid composition similar to the dike comparison of the ba 2 1 data with those of another xenolith from dish hill suggests that the compositional variations of mantle metasomatism result from both the compositional contrast between the metasomatizing liquid and wallrock and the relative abundances of each compositional and volumetric variations of mantle partial melts and their fractionates and repeated events of melting and reaction in contiguous mantle can create broad ranges of metasomatic signatures from the same process

helium in soil gas a method of mapping groundwater circulation systems in fractured plutonic rock abstract the carnmenellis granite is one of seven variscan plutons exposed in sw england which intrude a folded and thrusted succession of metasedimentary and metavolcanic rocks of devonian and carboniferous age the granite contains higher than average radionuclide concentrations which give rise to enhanced heat flow and fracture controlled low enthalpy hydrothermal circulation measurements of4he in soil gas have been made at 91 sites over the pluton and the surrounding host rocks in order to assess variation of4he emanation in relation to the distribution of radionuclides and the groundwater circulation system the pattern of variation obtained shows little correlation with the results of an airborne total gamma ray activity survey but agrees well with the distribution of4he in spring waters because the occurrence of zones of high4he concentration in these spring waters shows a significant correlation with local variations of heat flow within the pluton it is believed that the distribution of upwelling limbs of groundwater circulation cells controls the groundwater4he flux the spatial association of high values of4he in soil gas with high values in spring waters thus suggests that fracture controlled groundwater circulation systems can be mapped using the soil gas method even in the absence of springs however the variation of4he concentrations in soil gas is more complex than that given by spring waters this is due to variation in soil moisture content affecting the pore space concentration of4he nevertheless resolution of this effect is possible by statistical analysis of the4he distribution

metamorphic evolution of kyanite staurolite bearing epidote amphibolite from the early palaeozoic oeyama belt sw japan early palaeozoic kyanite staurolite bearing epidote amphibolites including foliated epidote amphi bolite fea and nonfoliated leucocratic or melanocratic metagabbros lmg mmg occur in the fuko pass metacumulate unit fpm of the oeyama belt sw japan microtextural relationships and mineral chemistry define three metamorphic stages relict granulite facies metamorphism m1 high p hp epidote amphibolite facies metamorphism m2 and retrogression m3 m1 is preserved as relict al rich diopside up to 8 5 wt al2o3 and pseudomorphs after spinel and plagioclase in the mmg suggesting a medium p granulite facies condition 0 8 1 3 gpa at 850 c an unusually low variance m2 assemblage hbl czo ky st pg rt ab crn occurs in the matrix of all rock types the presence of relict plagioclase inclusions in m2 kyanite associated with clinozoisite indicates a hydration reaction to form the kyanite bearing m2 assemblage during cooling the corundum bearing phase equilibria constrain a qualitative metamorphic p t condition of 1 1 1 9 gpa at 550 800 c for m2 the m2 minerals were locally replaced by m3 margarite paragonite plagioclase and or chlorite the breakdown of m2 kyanite to produce the m3 assemblage at 0 5 gpa and 450 500 c suggests a greenschist facies overprint during decompression the p t evolution of the fpmmay represent subduction of an oceanic plateau with a granulite facies lower crust and subsequent exhumation in a pacific type orogen

a study of the tornadic region within a supercell thunderstorm abstract the transition of a supercell thunderstorm into its tornadic phase is investigated through high resolution numerical cloud model simulations initiated within the interior portion of a previously simulated mature supercell storm with the enhanced grid resolution the low level cyclonic vorticity increases dramatically and the gust front rapidly occludes as small scale downdrafts develop in the vicinity of the low level center of circulation as the occlusion progresses a ring of high vorticity air surrounds the circulation center and could be conducive to multiple vortex tornado formation numerous features of the simulated transition bear resemblance to those observed in tornadic storms in the model simulation the large low level vorticity is generated through the tilting and intense stretching of air from the inflow side of the storm this vertical vorticity is derived from the horizontal vorticity of the environmental shear and also from horizontal vorticity generated solenoidally as low l

impacts of lapse rates on low level rotation in idealized storms abstractadiabatic lapse rates appear to be a common feature in the lower troposphere on tornado days this article reviews physical reasons why lapse rates may influence surface vortex intensification and reports on numerical simulations designed to study the key processes in the idealized numerical model an initial mesocyclone like vortex and nonvarying convection like heat source are used in different environmental stability profiles the scales of interest in these simulations typify those of a parent supercell and the developing circulations constitute direct responses to the imposed heating downward parcel displacements are needed for surface vortex development in environments with no preexisting surface vorticity in the simulations under neutral stratification there is strong heating induced subsidence anchored near the storm edge whereas under stable stratification there are instead gravity waves that propagate away to the far field in addition under weak or neutral low level stratification

seismic anisotropy under extended crust evidence from upper mantle xenoliths cima volcanic field california abstract a model of p wave velocity anisotropy and shear wave splitting for upper mantle under extended crust is derived from comparisons of seismic field measurements and observed xenolith anisotropies seismic velocity measurements and anisotropies calculated from petrofabric measurements of 15 upper mantle xenoliths from the cima volcanic field eastern mojave desert california show average maximum anisotropies of 6 9 for v p and 4 5 for v s xenolith compressional wave velocities corrected for upper mantle temperature and pressure agree well with field observations in the vicinity of the cima volcanic field the velocities calculated from the olivine fabrics suggest that upper mantle foliations beneath the region are horizontal and lineations trend ene the fabrics are believed to originate from early cenozoic extension in the area which had the same trend as the lineations the unusually high upper mantle temperatures in this region apparently have not significantly affected upper mantle fabrics

near surface vortex structure in a tornado and in a sub tornado strength convective storm vortex observed by a mobile w band radar during vortex2 abstractas part of the second verification of the origins of rotation in tornadoes experiment vortex2 field campaign a very high resolution mobile w band doppler radar collected near surface 200 m agl observations in an ef 0 tornado near tribune kansas on 25 may 2010 and in sub tornado strength vortices near prospect valley colorado on 26 may 2010 in the tribune case the tornado s condensation funnel dissipated and then reformed after a 3 min gap in the prospect valley case no condensation funnel was observed but evidence from the highest resolution radars in the vortex2 fleet indicates multiple sub tornado strength vortices near the surface some with weak echo holes accompanying doppler velocity couplets using high resolution doppler radar data the authors document the full life cycle of sub tornado strength vortex beneath a convective storm that previously produced tornadoes the kinematic evolution of these vortices from genesis to decay is investigated via ground based velocity

linear and nonlinear propagation of supercell storms abstract a nonlinear formula for updraft motion in supercell storms is derived from petterssen s formula for the motion of systems and the vertical equation of motion and tested on form preserving disturbances at each level continuous propagation of an updraft maximum is determined largely by the horizontal gradient of the nonhydrostatic vertical pressure gradient force nhvpgf at the updraft center the nhvpgf is deduced from the formal solution of the poisson equation for nonhydrostatic pressure in anelastic flow subject to homogeneous neumann boundary conditions at the ground and top boundary recourse also is made to published fields of partitioned vertical pressure gradient force updraft motion is partitioned into parts forced by horizontal gradients of hydrostatic pressure linear interaction between the environmental shear and updraft and nonlinear dynamical effects the dynamics of supercell storms for nearly straight and highly curved hodographs are found to be different nonlinear rotation

single and dual doppler analysis of a tornadic vortex and surrounding storm scale flow in the crowell texas supercell of 30 april 2000 abstract fine resolution single and dual doppler data were collected in the tornadic region of a supercell storm intercepted by two doppler on wheels radars on 30 april 2000 near crowell texas eleven dual doppler analyses characterize the 2d and 3d near surface wind fields associated with a tornado during a 13 min period an interesting evolution of the low level rotation is observed initially concentric tornado 500 m wide and tornado cyclone 2 km wide radar velocity couplets make a transition into a solitary intermediate sized 750 m wide circulation that widens and makes a further transition into a two celled multiple vortex structure with an asymmetric distribution of vertical vorticity the asymmetry and eventual disruption of the multiple vortex structure may have been partially controlled by locally strong outflow winds that affect the convergence fields in its vicinity a smaller 500 m wide tornado embedded in a broad area of rotation is subsequently observed the dual doppler wi

lithology and evolution of the crust mantle boundary region in the southwestern basin and range province mantle and crustal xenoliths from volcanic rocks in the southwestern basin and range province and colorado plateau transition zone reveal histories of episodic magmatism and deformation that have profoundly influenced the crustal structure of this region seismic transects in this area show a strongly reflective moho of generally low relief which in the area of modern transects consists of a thin zone 2 km thick of short reflectors the upper mantle is transparent and has a pn of 7 8 8 0 km s similar to much of the western united states a lower crustal zone 2 13 km thick has variable internal reflectivity and a relatively low velocity of 6 6 6 8 km s upper mantle peridotite xenoliths show both ductile and brittle deformational features and have structures and compositions affected by magmatic intrusion intrusions form complex dike systems and extensive zones of grain boundary infiltration in peridotite xenoliths whereas melt infiltration preceded and followed ductile deformation brittle deformation represented by closely spaced joint systems and faults followed ductile deformation and is related to the youngest magmatic episodes these structural characteristics and high uppermost mantle temperature 1000 c may combine to explain the relatively low pn alternating layers of ductily deformed and undeformed peridotites with or without igneous intrusions may contribute to the reflectivity of the moho lower crustal xenoliths are dominantly igneous textured pyroxenites and mafic to intermediate gabbros identical to the dikes in peridotite xenoliths the crustal xenoliths also commonly are jointed and in addition many show partial melting and have abundant cavities that probably were filled with co2 rich fluids these rocks are interpreted as products of underplated magmas that were fed through the mantle dike systems and may represent the lowest crustal unit identified in the seismic records the mafic compositions and high densities of the crustal xenoliths indicate that the low velocity of the lower crust may be caused in part by fracture systems partial melts and high temperatures garnet granulite xenoliths from a locality with no mantle peridotite xenoliths probably represent crust of the region before late miocene extension felsic granulite xenoliths from two localities have velocities like those of the two lower crustal units identified seismically and could be present in the modern crust as unequilibrated remnants of old crust the preferred model for the evolution of the lower lithosphere is one in which extension affects the upper mantle as well as the crust and is overlapped in time by multiple magmatic episodes the earliest magmatic events preceded extension and later events accompanied and followed extension

the 8 june 1995 mclean texas storm part ii cyclic tornado formation maintenance and dissipation abstract on 8 june 1995 scientists participating in the verification of the origins of rotation in tornadoes experiment vortex collected a unique dataset with the electra doppler radar eldora the eldora observations document the sequential life cycles of storm scale circulations associated with three large tornadoes in a supercell thunderstorm near mclean texas a qualitative description of the evolution of the storm was provided in part i of this paper during the first stage of development of each storm scale circulation interaction of the updraft with the environmental low level horizontal vorticity produced a vorticity column that increased in intensity with height as the vortex matured vorticity increased greatly at low levels i e below 2 km agl and exceeded that aloft each tornadic vortex was located near the rear side of the updraft where the surrounding low level horizontal vorticity was modified locally most likely by weak baroclinity within the storm tilting of low level horizo

platinum group element geochemistry of peridotite xenoliths from the sierra nevada and the basin and range california abstract the nature of pge re pge pt pd os ir ru behavior in subcontinental lithospheric mantle was investigated using new high precision pge re abundance measurements and previously published re os isotopic analyses of peridotite xenoliths from the sierra nevada and mojave province california ru ir ratios and ir concentrations are constant over a wide range in s content and major element fertility indices e g mg mg fe indicating that ru and ir are not only compatible during partial melting but also that their partitioning behaviors may not be controlled entirely by sulfide pt ir pd ir os ir and re ir ratios range from slightly superchondritic to distinctly subchondritic for all xenoliths except for one anomalous sample 1026v which is characterized by radiogenic 187os 188os low re os ratio and large enrichments in cu os pt pd and s relative to ir copps metasomatism assuming chondritic initial relative abundances the magnitudes of some of the depletions in pt pd os and re relative to ir and ru require incompatible behavior or substantial secondary loss in detail some samples which are otherwise characterized by fertile major element indices exhibit low s contents and subchondritic os ir and pd ir ratios indicating that depletions in pd and os relative to ir are not simple functions of the degree of melting as inferred from major elements possible mechanisms for depleting pt pd os and re relative to ir and ru include partitioning into chromian spinels and alloys partitioning between sulfide and sulfide liquids mobilization by aqueous fluids or secondary loss associated with late stage sulfide breakdown however it is not possible to explain all of the depletions in pt pd os and re by any single mechanism the preferential enrichment in os over re and ir in sample 1026v is somewhat paradoxical because this sample s radiogenic 187os 188os requires a metasomatic agent originating from a source with a high time integrated re os ratio the abundant garnet websterite xenoliths may be a suitable source because they have high re os ratios radiogenic os and abundant garnet which may sequester re over os during partial melting however their extremely low os contents require the processing of large amounts of garnet websterite to concentrate enough os into the metasomatic sulfides needed to enrich sample 1026v in os the homogeneity in 187os 188os ratio in the remaining xenoliths suggest that their os isotopic compositions were not significantly affected by pge metasomatism the singular nature of 1026v s composition emphasizes the rarity of copps metasomatism

post eruptive sediment transport and surface processes on unvegetated volcanic hillslopes a case study of black tank scoria cone cima volcanic field california abstract conical volcanic edifices that are made up from lapilli to block bomb pyroclastic successions such as scoria cones are widespread in terrestrial and extraterrestrial settings eruptive processes responsible for establishing the final facies architecture of a scoria cone are not well linked to numerical simulations of their post eruptive sediment transport using sedimentological geomorphic and 2d fragment morphology data from a 15 ky old scoria cone from the cima volcanic field california this study provides field evidence of the various post eruptive sediment transport and degradation processes of scoria cones located in arid to semi arid environments this study has revealed that pyroclast morphologies vary downslope due to syn eruptive granular flows along with post eruptive modification by rolling bouncing and sliding of individual particles down a slope and overland flow processes the variability of sediment transport rates on hillslopes are not directly controlled by local slope angle variability and the flank length but rather by grain size and morphological characteristics of particles such as shape irregularity of pyroclast fragments and block lapilli ratio due to the abundance of hillslopes degrading in unvegetated regions such as those found in the southwestern usa granulometric influences should be accounted for in the formulation of sediment transport laws for geomorphic modification of volcanic terrains over long geologic time

numerical simulation of tornadogenesis in a high precipitation supercell part i storm evolution and transition into a bow echo abstract a nested grid primitive equation model rams version 3b was used to simulate a high precipitation hp supercell which produced two weak tornadoes six telescoping nested grids allowed atmospheric flows ranging from the synoptic scale down to the tornadic scale to be represented in the simulation all convection in the simulation was initiated with resolved vertical motion and subsequent condensation latent heating from the model microphysics no warm bubbles or cumulus parameterizations were used part i of this study focuses on the simulated storm evolution and its transition into a bow echo the simulation initially produced a classic supercell that developed at the intersection between a stationary front and an outflow boundary as the simulation progressed additional storms developed and interacted with the main storm to produce a single supercell this storm had many characteristics of an hp supercell and eventually evolved into a bow echo with a rotating comma head structure an analysi

colorado plateau magmatism and uplift by warming of heterogeneous lithosphere the forces that drove rock uplift of the low relief high elevation tectonically stable colorado plateau are the subject of long standing debate while the adjacent basin and range province and rio grande rift province underwent cenozoic shortening followed by extension the plateau experienced approximately 2 km of rock uplift without significant internal deformation here we propose that warming of the thicker more iron depleted colorado plateau lithosphere over 35 40 myr following mid cenozoic removal of the farallon plate from beneath north america is the primary mechanism driving rock uplift in our model conductive re equilibration not only explains the rock uplift of the plateau but also provides a robust geodynamic interpretation of observed contrasts between the colorado plateau margins and the plateau interior in particular the model matches the encroachment of cenozoic magmatism from the margins towards the plateau interior at rates of 3 6 km myr 1 and is consistent with lower seismic velocities and more negative bouguer gravity at the margins than in the plateau interior we suggest that warming of heterogeneous lithosphere is a powerful mechanism for driving epeirogenic rock uplift of the colorado plateau and may be of general importance in plate interior settings

high temporal resolution observations of the 27 may 2015 canadian texas tornado using the atmospheric imaging radar abstracton 27 may 2015 the atmospheric imaging radar air collected high temporal resolution radar observations of an ef 2 tornado near canadian texas the air is a mobile x band imaging radar

finescale radar observations of the dimmitt texas 2 june 1995 tornado abstract the mature and dissipating stages of a strong tornado were observed from close range by the prototype doppler on wheels mobile radar volumetric observations repeated eight times over an 840 s period with resolution volumes at the center of the tornado as low as 61 m 61 m 75 m 2 8 105 m3 revealed new details about three dimensional tornado vortex structure and evolution observed structures included a conical debris envelope a low reflectivity eye multiple windfield maxima and multiple semiconcentric bands of reflectivity surrounding the eye the three dimensional structure of the debris and single doppler wind field were well characterized as well as more rapid dissipation of the tornado aloft compared to near the ground volumetric measures of tornado strength are introduced a downdraft exhibiting w 30 m s 1 indicative of a partial two cell vortex was observed only during the earliest radar scans when the tornado was near maximum intensity comparisons with simple conceptual m

miniature supercells in an offshore outer rainband of hurricane ivan 2004 abstract airborne doppler radar observations are used to document the structure of three miniature supercells embedded in an outer rainband of hurricane ivan on 15 september 2004 the cells were located more than 100 km offshore beyond the doppler range of coastal radars the combination of large cape large vertical wind shear and moderate cell relative helicity with an apparent midlevel dry air intrusion provided an offshore environment supporting rotating storms each shallow cell contained a 5 7 km diameter mesocyclonic updraft with midlevel updraft and vorticity maxima that exceeded 6 m s 1 and 0 008 s 1 respectively such offshore structures are consistent with miniature supercells observed onshore in association with tropical cyclone tornado outbreaks the strong updrafts resulted from a combination of kinematic convergence thermal instability and shear induced vertical perturbation pressure gradients mesocyclone production largely resulted from the tilting and subsequent stretching of low l

doppler radar observations of anticyclonic tornadoes in cyclonically rotating right moving supercells abstractsupercells dominated by mesocyclones which tend to propagate to the right of the tropospheric pressure weighted mean wind on rare occasions produce anticyclonic tornadoes at the trailing end of the rear flank gust front more frequently mesoanticyclones are found at this location most of which do not spawn any tornadoes in this paper four cases are discussed in which the formation of anticyclonic tornadoes was documented in the plains by mobile or fixed site doppler radars these brief case studies include the analysis of doppler radar data for tornadoes at the following dates and locations 1 24 april 2006 near el reno oklahoma 2 23 may 2008 near ellis kansas 3 18 march 2012 near willow oklahoma and 4 31 may 2013 near el reno oklahoma three of these tornadoes were also documented photographically in all of these cases a strong mesocyclone i e vortex signature characterized by azimuthal shear in excess of 5 10 3 s 1 or a 20 m s 1 change in doppler velocity over 5 km

measurement of advective water velocity in lake sediment using natural helium gradients abstract natural helium he concentration profiles in the sediments of lakes at the experimental lakes area in northwestern ontario are modelled using the advection diffusion equation to calculate groundwater velocities two headwater lakes with little excess he in bottom water have sediment he concentration profiles indicating slow 2 7 cm a 1 recharge of lake water to groundwater data from three lakes showing he enrichment in bottom water indicate groundwater seepage at some sites sediment he gradients in headwater lake 239 were usually weak although a strong gradient was found at one site probes located within suspected seepage areas in lake 239 indicated groundwater discharge velocities of 3 22 cm a 1 fifth order lake 240 had a he gradient suggesting groundwater seepage at 11 17 cm a 1 eighth order lake 625 a lineament basin with high he concentrations in bottom water had very strong he gradients in sediment one probe indicated diffusive he transport through sediment whereas another indicated seepage at 3 6 cm a 1 direct he fluxes to the lakes estimated from its accumulation in bottom water during summer stratification are in reasonable agreement with fluxes calculated independently from the he gradients in sediment measurements of natural he gradients in lake sediment give a sensitive and reliable indication of the direction and rate of groundwater transport at velocities of 1 100 cm a 1

mobile doppler radar observations of a tornado in a supercell near bassett nebraska on 5 june 1999 part ii tornado vortex structure abstract this is part ii of a paper detailing an analysis of high resolution wind and reflectivity data collected by a mobile w band doppler radar the analysis depicts the near surface life history of a tornado in a supercell in north central nebraska on 5 june 1999 the structure of the tornado vortex near the ground is described from a sequence of sector scans at 10 15 s intervals during much of the lifetime of the tornado the formation of the tornado vortex near the ground is described in part i the wind and reflectivity features in the tornado evolved on timescales of 10 s or less a time history of the azimuthally averaged azimuthal and radial wind profiles and the asymmetric components of the azimuthal and radial wind fields in the tornado were estimated by applying the ground based velocity track display gbvtd technique to the doppler wind data if the magnitude of the asymmetric part of the radial wind component were indeed much less than that of the azimuthal wind component a necessary req

hydrogeochemistry groundwater ages and sources of salts in a granitic batholith on the canadian shield southeastern manitoba abstract the hydrogeochemistry of the lac du bonnet granitic batholith has been determined for the region of the whiteshell research area wra in southeastern manitoba canada this work forms part of the geosciences studies performed for the canadian nuclear fuel waste management program over the period 1980 1995 by atomic energy of canada limited aecl knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the canadian shield groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay rich overburden from packer isolated borehole zones intersecting fractures or fault zones in the bedrock and from boreholes in unfractured rock in aecl s underground research laboratory url eighty six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the lac du bonnet batholith in addition 28 groundwaters from piezometers in a large wetland area near the url have been sampled and analysed to determine the influence of clay rich overburden on the bedrock hydrogeochemistry analyses have been made for major and minor ions ph eh trace metals and stable and radioactive isotopes to characterise these groundwaters and relate them to their hydrogeologic regimes shallow groundwaters in the fractured bedrock are generally dilute tds 500 m na ca cl so4 waters of increasing salinity up to 50 g l with depth are found and in some fractures the waters have evolved to a ca na cl composition isotopic data indicate that these waters are warm climate and pre glacial in origin with residence times of over 1 ma pore fluids observed to drain from the unfractured rock matrix in the url facility are almost pure ca cl in composition 90 g l salinity and have a 2h 18o composition displaced well to the left of the global meteoric water line about which all other wra groundwaters lie this information indicates that these pore fluids have undergone prolonged water rock interaction and have residence times of 101 103 ma most of the deeper fracture groundwaters and pore fluids have low br cl ratios and moderate to high 34s values of dissolved so4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith these fluids may have entered the batholith during early paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western canada the hydrogeochemical data and interpretations show that below 500 m in the wra fracture hosted groundwaters are very saline reducing and old and are therefore indicative of stagnant conditions over the period of concern for nuclear waste disposal 1 ma the intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics the pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 103 ma

the structure and evolution of a numerically simulated high precipitation supercell thunderstorm the structure and evolution of a high precipitation hp supercell thunderstorm is investigated using a threedimensional nonhydrostatic cloud scale numerical model tass the model is initialized with a sounding taken from a mesoscale modeling study of the environment that produced the 28 november 1988 raleigh tornadic thunderstorm tass produces a long lived convective system that compares favorably with the observed raleigh tornadic thunderstorm the simulated storm evolves from a multicell type storm to a multiple updraft supercell storm the storm complex resembles a hybrid multicell supercell thunderstorm and is consistent with the conceptual model of cool season strong dynamic hp supercells that are characterized by shallow mesocyclones the origin of rotation in this type of storm is often in the lowest levels interactions between various cells in the simulated convective system are responsible for the transition to a supercellular structure an intense low level updraft core forms on the southwest flank of the simulated storm and moves over a region that is rich in vertical vorticity the stretching of this preexisting vertical vorticity in the storm s lowest levels is the most important vertical vorticity production mechanism during the initial stages of the main updraft s development interactions with an extensive cold pool created by the storm complex are also important in producing vertical vorticity as the main updraft grows overall the development of vorticity associated with the main updraft appears similar to nonsupercellular tornadic storms however classic supercell signatures are seen early in the simulation associated with other updrafts e g formation of vortex couplet due to tilting of ambient horizontal vorticity storm splitting etc and are deemed important in the storm s supercell stage rotation is sustained in the lowest levels of the storm despite large amounts of precipitation located near and within the main mesocyclone pulsating downdrafts periodically invigorate the storm and the gust front never occludes thus allowing the main updraft to persist for a prolonged period of time the storm s intensity is also maintained by frequent updraft mergers

impact of blasting on groundwater composition in a fracture in canada s underground research laboratory groundwater composition in a discrete water bearing fracture in granitic rock at the underground research laboratory manitoba was monitored during a period of underground excavation of adjacent rock to determine the impact of conventional blasting techniques and rock fracturing on the concentration of dissolved constituents this work has relevance to the study of hydrogeochemical anomalies associated with seismic activity short lived anomalies such as decreases in dissolved anion cl f br so4 and gas he rn concentrations and concurrent increases in no3 and o2 concentrations were seen shortly after two blasts located opposite the groundwater sampling site a third blast downstream of the site resulted in variability in dissolved gases concentrations but showed no impact on dissolved anion concentrations the results are compared with various models used to account for hydrogeochemical fluctuations associated with earthquakes the data best fit a general form of the aquifer breaching fluid mixing model in which hydrochemical responses are caused by localized changes in hydraulic conductivity along the plane of a fracture which in turn cause changes in mixing ratio of groundwater at the monitoring site

photogrammetric analysis of the 2013 el reno tornado combined with mobile x band polarimetric radar data abstractthis study presents rapid scanning x band polarimetric radar data combined with photogrammetry of the el reno tornado of 31 may 2013 the relationship between the hook echo weak echo hole weh weak echo column wec and the rotational couplet with the visual characteristics of the tornado are shown for the first time cross correlation coefficient hv and differential reflectivity zdr data are included in the photogrammetric analyses the tornado was accompanied by a large tornadic debris signature tds with a diameter 2 km wide during the analysis time the center of the tds was not collocated with the weh and the rotational couplet instead the tds was displaced 1 km to the north and within the weak echo notch of the hook echo a debris overhang was identified in vertical cross sections of the hv fields the overhang was located in a weak echo trench and a notch of high hv consistent with the position of the tornado updraft the updraft was hypothesized to be carrying small deb

dynamical influences of anvil shading on simulated supercell thunderstorms abstractnumerical simulations of supercell thunderstorms including parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps model to investigate how low level air temperature deficits within anvil shadows affect the simulated storms the maximum temperature deficits within the modeled cloud shadows are 1 5 2 0 k which is only about half that previously observed within the shadows the loss of strong solar heating cools and stabilizes the near surface layer which suppresses vertical mixing and modifies the near surface vertical wind shear in a case of a stationary storm the enhanced easterly shear present beneath the anvil leads to a thinning of the outflow layer and corresponding acceleration of the rear flank gust front far ahead of the overlying updraft weakening the low level mesocyclone it is further shown that the direct absorption and emission of radiation by clouds does not significantly affect the simulated supercells varying th

observations of wall cloud formation in supercell thunderstorms during vortex2 abstractthis study presents an integrated analysis of dual doppler cloud photogrammetry surface mobile mesonet and sounding data to examine wall cloud formation in two supercells observed during the verification of the origins of rotation in tornadoes experiment ii vortex2 one of the wall clouds contained significant rotation and spawned an enhanced fujita ef2 tornado while the other was clearly displaced horizontally from the mesocyclone and exhibited little rotation at the time of data collection backward parcel trajectories show that the majority of the air entering the wall cloud base originates in the forward flank region a small fraction of the parcels enter the wall cloud base from the inflow some rear flank downdraft parcels descend into the strongly rotating wall cloud for both wall clouds much of the observed wall cloud lowering is attributed to evaporatively cooled parcels in the forward flank region being ingested into the low level updraft additional wall cloud base lowering is

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

tornado maintenance investigated with high resolution dual doppler and enkf analysis abstractdual doppler wind synthesis and ensemble kalman filter analyses produced by assimilating doppler on wheels velocity data collected in four tornadic supercells are examined in order to further understand the maintenance of tornadoes although tornado scale features are not resolved in these analyses larger scale processes involved with tornado maintenance are well represented the longest lived tornado is maintained underneath the midlevel updraft within a zone of low level horizontal convergence along a rear flank gust front for a considerable time and dissipates when horizontally displaced from the midlevel updraft the shortest lived tornado resides in a similar zone of low level convergence briefly but dissipates underneath the location of the midlevel updraft when the updraft becomes tilted and low level convergence is displaced several kilometers from the tornado this suggests that a location beneath the midlevel updraft is not always a sufficient condition for tornado maintenance particu

the garden city kansas storm during vortex 95 part i overview of the storm s life cycle and mesocyclogenesis abstract analysis of a supercell storm that produced an f1 tornado near garden city kansas is presented this event provided one of the first opportunities to synthesize data collected by a new airborne radar platform called eldora electra doppler radar developed by the national center for atmospheric research the early stages of development of the midlevel mesocyclone and the entire evolution of the low level mesocyclone are captured over a 70 min period the low level mesocyclone began as an incipient shallow circulation along a synoptic scale trough the circulation intensified and grew in depth via vortex stretching under the influence of a strong updraft as this rotation built up from the boundary layer it initially remained separate and distinct from the midlevel mesocyclone subsequently the two mesocyclones merge to produce a single column of rotation 4 5 km in diameter an occlusion downdraft develops within the mesocyclone circulation during the last passes by the storm signaling the beg

an investigation of the goshen county wyoming tornadic supercell of 5 june 2009 using enkf assimilation of mobile mesonet and radar observations collected during vortex2 part ii mesocyclone scale processes affecting tornado formation maintenance and decay abstractstorm scale and mesocyclone scale processes occurring contemporaneously with a tornado in the goshen county wyoming supercell observed on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 are examined using ensemble analyses produced by assimilating mobile radar and in situ observations into a high resolution convection resolving model this paper focuses on understanding the evolution of the vertical structure of the storm the outflow buoyancy and processes affecting the vertical vorticity and circulation within the mesocyclone that correspond to changes in observed tornado intensity tornadogenesis occurs when the low level mesocyclone is least negatively buoyant relative to the environment possesses its largest circulation and is collocated with the largest azimuthally averaged convergence during the analysis period the average buoyancy circulation and convergence within the near surface mesocyclone on spatial scales resolved by the

finescale structure of the lagrange wyoming tornado during vortex2 gbvtd and photogrammetric analyses abstracta ground based velocity track display gbvtd analysis of the lagrange wyoming tornado on 5 june 2009 during the second verification of the origins of rotation in tornadoes experiment vortex2 is photogrammetrically combined with a series of pictures of the funnel cloud this analysis reveals the relationship between the vertical velocity radial and tangential velocities perturbation pressure vertical vorticity and angular momentum with the visual features of the tornado an intense axial downdraft was evident and was supported by a downward directed perturbation pressure gradient the radial inflow at low levels was weak and difficult to retrieve owing to a combination of centrifuging of hydrometeors debris in the intense circulation and the inability of the radar beam to fully resolve the flow the tornado was weakening during the analysis period which was supported by angular momentum being advected out of the tornado the availability of a dual doppler wind synthesis for this tornadic e

dual doppler and single doppler analysis of a tornadic storm undergoing mergers and repeated tornadogenesis abstract dual doppler observations with unprecedented finescale spatial and temporal resolution are used to characterize the vector wind field in and near a tornado occurring near kiefer oklahoma on 26 may 1997 analyses of the dual doppler vector wind fields document in detail for the first time several structures associated with the tornado a proximate updraft region a rear flank downdraft wrapping around the tornado a double gust front structure occluding near the tornado and a region of enhanced vorticity separated from the tornado that may have been associated with cyclic tornadogenesis the analyses are compared to conceptual and computer models of tornadic storms a subsequent tornadogenesis was observed with radar every 18 s providing a finescale temporal view of the genesis process the genesis process was complex and the evolution of tornado intensity parameters was not monotonic in time low level rotation contracted and intensified then broadened then contracted and intensified a se

variations in supercell morphology part i observations of the role of upper level storm relative flow abstract it is hypothesized that the precipitation intensity beneath a supercell updraft is strongly influenced by the amount of hydrometeors that are reingested into the updraft after being transported away in the divergent upper level flow of the anvil this paper presents the results of a climatological analysis of soundings associated with three types of isolated supercells having distinctive precipitation distributions the so called classic low precipitation lp and high precipitation hp storms it is shown that storm relative flow at 9 10 km above the ground is strongest in the environments of lp storms and relatively weak in the environments of hp storms with classic storms occurring in environments with intermediate magnitudes of upper storm relative flow it is plausible that comparatively strong flow in the anvil bearing levels of lp storms transports hydrometeors far enough from the updraft that they are relatively unlikely to be reingested into the updraft leading to greatly diminishe

high resolution mobile doppler radar observations of cyclic mesocyclogenesis in a supercell abstract on 15 may 2003 two ground based mobile doppler radars scanned a supercell that moved through the texas panhandle and cyclically produced mesocyclones the two radars collected data from the storm during a rapid cyclic mesocyclogenesis stage and a more slowly evolving tornadic period a 3 cm wavelength radar scanned the supercell continuously for a short time after it was cyclic but close to the time of tornadogenesis a 5 cm wavelength radar scanned the supercell the entire time it exhibited cyclic behavior and for an additional 30 min after that the volumetric data obtained with the 5 cm wavelength radar allowed for the individual circulations to be analyzed at multiple levels in the supercell most of the circulations that eventually dissipated moved rearward with respect to storm motion and were located at distances progressively farther away from the region of rear flank outflow the circulations associated with a tornado did not move nearly as far rearward relative to the storm the mean

constraining groundwater discharge in a large watershed integrated isotopic hydraulic and thermal data from the canadian shield or a thin veneer of coarse grained sediments natural conservative d 2 h d 18 o cl and specific conductance radioactive 222 rn and thermal tracers are integrated with streamflow measurements and a steady state advective model to delimit the discharge locations and quantify the discharge fluxes to lakes wetlands creeks and the tay river the groundwater discharge rates to most surface water body types are low indicating that the groundwater and surface water system may be largely decoupled in this watershed compared to watersheds underlain by porous media groundwater discharge is distributed across the watershed rather than localized around lineaments or high density zones of exposed brittle fractures the results improve our understanding of the rate localization and conceptualization of discharge in a large fractured rock watershed applying hydraulic isotopic or chemical hydrograph separation techniques would be difficult because the groundwater discharge signal is small compared to the background surface water inflows or volumes of the surface water bodies although this study focuses on a large watershed underlain by fractured bedrock the methodology developed is transferable to any large regulated or unregulated watershed the low groundwater discharge rates have significant implications for the ecology sustainability and management of large crystalline watersheds

a comparison of fracture styles in two granite bodies of the superior province a quantitative comparison is made between fracture styles in two late archean granite intrusions of the superior province the lac du bonnet batholith ldbb and eye dashwa pluton edp these intrusions have a similar geological setting similar mineral and chemical composition and similar physical properties but vary markedly in volume ldbb 9060 km3 edp 122 km3 the fracture style of the ldbb consists of mainly low angle thrust faults within otherwise poorly fractured granite subvertical fractures are restricted to within 200 m of surface or zones encompassing the thrust faults the mineral assemblage chlorite iron oxide carbonate is widespread in fractures in contrast fractures of the edp are closely spaced variably oriented pervasive to depth and dominated by subvertical transcurrent faults epidote is an abundant fracture filling material most fractures formed in response to early proterozoic compression under low greenschist conditions in the ldbb and upper greenschist conditions in

velocities of southern basin and range xenoliths insights on the nature of lower crustal reflectivity and composition to reconcile differences between the assessments of crustal compositioninthesouthernbasinandrangeprovinceonthebasis of seismic refraction and reflection data and lower crustal xenoliths we measured velocities of xenoliths from the cima volcanic field in southern california lower crustal samples studied includedgabbro microgabbro andpyroxenite wefindthatthemafic xenolith velocities are compatible with regional in situ measurements from seismic refraction studies provided that a mixture of gabbro and pyroxenite is present in the lower crust supporting thismodelareobservationsthatmanyofthelower crustalxenoliths from the cima volcanic field are composites of these rock types with igneous contacts vertical incidence synthetic seismograms show that a gabbroic lower crust with occasional pyroxenite layering can produce a reflective lower crust that is similar in texture to that shown by seismic reflection data recorded nearby

seismic evidence for lithospheric modification beneath the mojave neovolcanic province southern california 1 the mojave neovolcanic province mnvp located in the mojave block of southern california comprises late miocene to quaternary small volume basaltic centers geochemistry indicates an asthenospheric source for the mnvp beginning in the late miocene but no physical evidence of missing mantle lithosphere has been presented we utilize receiver functions and ambient noise tomography to image the lithosphere beneath the mojave block regionally we find thin crust that thickens distal to sites of mnvp volcanism shear wave velocities between 40 and 75 km depth are consistent with the presence of mantle lithosphere in the southern mojave block and very thin or missing mantle lithosphere to the north with one exception mnvp volcanoes lie along this sharp boundary our observations together with the established geologic history and geochemistry of the mnvp can be explained by small scale edge driven convection producing ongoing lithospheric removal within the mojave block our results provide another example of lithospheric instability that occurs in response to rapid changes in mantle dynamics induced by major changes in tectonic plate geometry

noble gases their carrier phases and argon chronology of upper mantle rocks from zabargad island red sea abstract three ultramafic bodies on zabargad island contain fresh peridotites with mostly unfractionated primitive bulk major and trace element abundances and mostly monomineralic vein rocks pyroxenites olivinites homblendites etc we analyzed a set of coarse grained vein rocks with the 40ar 39ar technique applying high resolution stepheating neutron induced argon isotopes derived from ca k and cl and the specific degassing behaviour of major and accessory minerals enabled us to separate and identify different trapped and radiogenic argon components and their hosts within two clinopyroxenites trapped argon is present in 1 low temperature low 40 ar 36 ar phases serpentine and or fluid inclusions 2 pyroxene related cl rich carriers pyroxene and or associated microinclusions and 3 amphiboles which are intimately and nonseparably intergrown with pyroxene the amphiboles which can texturally chemically and isotopically be divided into different generations formed by interaction of spinels and pyroxenes with mantle fluids during different stages of diapiric uplift agrinier et al 1993 formation of these amphiboles and microinclusions in pyroxenes along with incorporation of isotopically distinct ar with 40 ar 36 ar ratios up to 8000 can be related to recent mantle metasomatism also evident in arabian xenoliths henjes kunst et al 1990 and must have been induced by a variety of mantle fluids for a homblendite in situ radiogenic and excess argon components could be separated the plateau age of 18 7 1 3 ma is in perfect agreement with a zircon pb pb age of 18 4 1 0 ma oberli et al 1987 interpreted as the age of crustal intrusion obviously the formation of the hornblendite occurred during the final stage of uplift most probably by interaction with seawater as suggested by strontium oxygen and hydrogen isotopic data agrinier et al 1993 and the low 40 ar 36 ar ratio 305 of the trapped argon 4he 20ne 40ar and 36ar were measured in the orthopyroxenite vein rock z31 by stepwise crushing and subsequent total fusion isotopic ratios show a well defined correlation with crushing step that indicates the presence of two different types or generations of inclusions which were subjected to different degrees of contamination by atmosphere type noble gases as inclusions were trapped before tje main deformation of the peridotite complex kurat et al 1993 argon with relatively low 40 ar 36 ar ratios 1500 was trapped in the mantle which requires an admixture of argon of atmospheric composition to the source region of the peridotites radiogenic isotopes 4he 40ar are dominated by the mantle source however the 4 he 40 ar ratio 0 16 is much lower than expected from long term decay of radioactive parent nuclides u th and k such low ratios which have previously been observed also in mantle xenoliths obviously reflect the indigenous peridotitic source and are most probably due to fractionation processes in the mantle