oxygen isotope evidence for hydrothermal alteration within a quaternary stratovolcano lassen volcanic national park california brokeoff volcano a quaternary stratocone located in the lassen volcanic center in northern california has been deeply eroded exposing a 10 km2 meteoric hydrothermal alteration zone at the core of the volcano portions of the former volcanic edifice are sufficiently well preserved that an unusual opportunity exists wherein the alteration pattern can be correlated with the position of the volcanic cone the 18o analyses of more than 100 whole rock samples consisting primarily of andesitic lavas vary from 9 8 to 0 6 per mil the highest 18o values occur in bleached solfatarically altered rocks that have interacted with low ph fumarolic hot springs associated with the present day hydrothermal system low 18o values are found in propylitically altered rocks that underwent isotopic exchange with meteoric hydrothermal fluids at elevated temperatures mostly during the stratovolcanic stage 650 400ka of the hydrothermal system but probably continuing today at depth electron microprobe analyses of secondary layer silicate minerals in strongly propylitized samples 18o 5 0 revealed the presence of discrete chlorite suggesting that temperatures up to 200 to 250 c were attained in the shallow levels of the system two zones of pervasive meteoric hydrothermal alteration defined by concentric 18o contours that are probably interconnected at depth are located within the original topographic edifice of the volcano the most intensely altered rocks within these equant zones of alteration define nnw trends that coincide with stream valleys and with regional structural patterns a comparison of the characteristics of the 18o depleted zone at brokeoff with those of more deeply eroded volcanic centers such as the comstock lode mining district criss and champion 1991 permits the construction of composite 18o cross sections through a hypothetical intact stratovolcano at both brokeoff and comstock hydrothermal fluids were strongly focused into plumelike zones of intense 18o depletion at comstock these low 18o plumes are associated with faults although major fault displacements are not observed at brokeoff the topographic and alteration patterns are consistent with the presence of a linear array of faults that acted as conduits for fluid flow up into the shallow levels of the volcano

oxygen isotope aeromagnetic and gravity anomalies associated with hydrothermally altered zones in the yankee fork mining district custer county idaho epithermal ag au vein and disseminated deposits in the yankee fork district are hosted in altered volcanic rocks having low delta 18 o values low magnetic susceptibilities low remanent magnetizations and relatively high densities these isotopic and physical quantities provide sensitive indices of rock alteration that can be contoured over areas that are much larger than zones of strong visible alteration such contour maps reveal a marked spatial association between the ore deposits the steepest delta 18 o gradients and the perimeter of zones where the rocks have extremely low total magnetizations the oxygen isotope results indicate that the ore zones coincide with steep gradients in temperature and water rock ratio in two fossil hydrothermal convective systems that involved fluids derived from tertiary meteoric waters our magnetic measurements suggest that these same high gradient zones also coincide with oxidation reduction boundaries low aeromagnetic intensities and positive bouguer anomalies are also associated with the altered zones in the yankee fork district the intensities of these geophysical features are consistent with the size of the altered zones and with the contrast in physical properties between altered and unaltered rocks contour maps of the magnetic and isotopic properties of host rocks should find application in exploration for a variety of types of hydrothermal ore deposits as well as in the study of ore controls and conditions of mineralization

epithermal alteration and mineralization in the comstock district nevada the precious and base metal deposits of the world renowned comstock district of western nevada constitute one of several superimposed miocene hydrothermal systems in the district mesozoic metasedimentary and igneous rocks are overlain by oligocene to miocene ash flow tuffs a thick sequence of middle miocene andesitic volcanic rocks and intrusions host the bulk of the hydrothermal alteration and ore deposits some of the magmatic events were directly associated with hydrothermal activity secondary biotite alteration locally affects preore dioritic intrusions preore barren quartz alunite pyrophyllite and kandite alteration high sulfidation style is zoned outward from mostly discontinuous crudely radial fractures associated with andesitic intrusions blanket like cristobalite alunite and kaolinite alteration exposed at the periphery of the district may be linked to preore alteration near the paleowater table later large volumes of subore grade massive quartz veins and quartz adularia stockworks were deposited in steeply to moderately east dipping sets of north and northeast striking faults that also localized the major precious metal bearing lodes quartz chlorite illite and very localized muscovite alteration deep low sulfidation developed coeval with vein deposition epidote bearing propylitic alteration forms halos around the higher temperature parts of the lodes adularia and rare bladed calcite indicate boiling during deep low sulfidation hydrothermal activity but little is apparently associated with ore deposition the main stage au ag cu zn pb ore was deposited late in the deep low sulfidation system in irregularly spaced lenticular dilatant zones or structural intersections massive nonbladed calcite was deposited just below and in the lower parts of orebodies in the comstock lode but it was deposited in the upper parts of orebodies or was barren elsewhere in the district pliocene to holocene reactivation of faults has disrupted the district redistributing the relative positions of many of the orebodies and alteration assemblages

large scale stable isotope alteration around the hydrothermal carbonate replacement cinco de mayo zn ag deposit mexico carbonate hosted hydrothermal deposits typically show narrow visible mineralogical and textural alteration halos which inhibit exploration targeting in contrast hydrothermal modification of the country rock s stable isotope composition usually extends far beyond the limited visible alteration hence stable isotope studies should be an effective tool to aid exploration for carbonate hosted deposits here we present new insight into the development of a large stable isotope alteration halo based on 910 o and c isotope analyses of carbonate veins and hydrothermally altered limestone hosting the cinco de mayo pb zn ag au cu carbonate replacement deposit crd in chihuahua mexico our results demonstrate that stable isotope alteration is consistent with reactive magmatic fluid flow into unaltered limestone and represents a powerful tool for the characterization of these hydrothermal ore systems synmineralization veins are texturally and isotopically distinct from those formed during pre and postmineralization diagenesis and fluid flow and show distinct gradients along the direction of mineralizing fluid flow this appears to be a promising exploration vectoring tool downhole variations in wall rock isotope values reveal aquifers and aquicludes and outline the principal hydrothermal flow paths furthermore wall rock 18ovsmow systematically decreases toward mineralization from 23 to 17 over a distance of 10 km providing another vectoring tool the extent of the stable isotope alteration halo likely reflects the overall fluid volume and areal extent of a fossil hydrothermal system which may be expected to scale with the mineral endowment this suggests that constraining the size shape and degree of isotopic alteration has direct application to mineral exploration by outlining the system and indicating the potential size of a deposit

oxygen 18 oxygen 16 and d h studies of plutonic granitic and metamorphic rocks across the cordilleran batholiths of southern british columbia hydrogen and oxygen isotope ratios of 500 samples mainly from granitic plutons were measured along a 700 km e w traverse across the accreted terranes of southern british columbia latitudes 49 52 n despite the geological complexity and range of intrusive ages late triassic to tertiary and although there are steps in the isotopic values at some geologic boundaries e g across the strait of georgia two clear patterns emerge 1 the 18 o 16 o and d h ratios of the waters involved in hydrothermal interactions with the granitic rocks show a regular eastward trend of depletion in d and 18 o enormous areas were affected by the hydrothermal processes but the most intense alteration is localized along major north trending lineaments e g okanagan lake 2 independent of the hydrothermal effects the primary 18 o values of the granitic rocks also change systematically eastward from 7 0 to 8 5 in vancouver island reaching a minimum of 5 5 to 7 0 in the western and central coast plutonic complex then increasing progressively from the eastern coast batholith to the okanagan batholith and attaining a maximum of 10 0 to 12 0 in the nelson batholith two groups of samples are unique in their high d values the first group is represented by two geographically isolated batholiths guichon and thuya that were not affected by the tertiary meteoric hydrothermal systems and that have therefore preserved their early jurassic to triassic k ar ages the second group is represented by the jurassic plutons of vancouver island there the hydrothermal fluids were both d rich and 18 o rich 18 o 0 as evidenced by the fact that feldspars in the altered granites are enriched in 18 o relative to coexisting quartz both anomalies can be explained if these terranes were located closer to the equator and or in a maritime environment at the time of intrusive and hydrothermal activity in agreement with available paleomagnetic data excluding these anomalous areas two distinct ages of meteoric hydrothermal activity can be identified cretaceous in the west and early to mid tertiary in the east the isotopic trends in the rocks are similar to the present day patterns of meteoric waters in the region with one primary difference the paleowaters are enriched in d by about 20 compatible with a northward translation of these terranes a climatic change or both the similarities of the patterns suggest a topography similar to that of the present day a mountain chain along the coast during the early tertiary the whole rock 18 o values of the granitic rocks determined by extrapolation of the trends of 18 o quartz versus 18 o feldspar to correct for hydrothermal alteration effects suggest that the main part of the coast plutonic complex formed from magmas similar to those in oceanic island arcs derived from basaltic crust or from an upper mantle source toward the east an increasingly larger component of sedimentary rocks must be present in the source regions of the granitic magmas it may be significant that right at the edge of the north american craton there is a drop in the 18 o of the plutons from 11 down to 9 5 suggesting involvement of old granitic crust instead of sedimentary rocks these new data from southern british columbia confirm and amplify previous studies that have documented 1 the existence of widespread and pervasive hydrothermal effects throughout the north american cordillera and 2 regular west to east asymmetries in the amounts of different kinds of parent rocks in the source regions from which these mesozoic and cenozoic granitic magmas were derived

hydromagnesite precipitation in the alkaline lake dujiali central qinghai tibetan plateau constraints on hydromagnesite precipitation from hydrochemistry and stable isotopes abstract the mineral hydromagnesite mg5 co3 4 oh 2 4h2o is a common form of hydrated mg carbonate in alkaline lakes yet the processes involved in its formation are not well understood this study focuses on dujiali lake in the central qinghai tibetan plateau qtp which is one of the few environments on the earth s surface with extensive holocene precipitation of hydromagnesite the hydrogeochemistry of surface waters and the mineralogical stable isotope 13c and 18o and radiogenic isotope content of hydromagnesite deposits were analyzed to investigate formation mechanisms the chemical composition of surface water around dujiali lake evolved from the rock weathering type waters of t1 ca mg hco3 water type to more concentrated sodic waters of t2 na so4 cl water type due to evaporation xrd results show that the mineralogical composition of samples is pure hydromagnesite analysis of oxygen isotopes in the hydromagnesite indicates that supergene formation with authigenic carbonate crystallization from evaporation water is the dominant precipitation process combined carbon oxygen isotope analysis suggests atmospheric co2 provided a carbon source for the precipitation of hydromagnesite these findings suggest that hydromagnesite precipitation at lake dujiali is mainly inorganic in nature and the greenhouse gas co2 is trapped and stored in the hydromagnesite directly from the atmosphere ams radiocarbon dating of samples indicates co2 was sequestered between 5845 30 to 6090 25 cal a bp in the dujiali lake hydromagnesite deposit the study contributes to improved understanding of hydromagnesite formation in modern and ancient playas

analysis of a lower tropospheric gravity wave train using direct and remote sensing measurement systems abstracton 10 august 2014 a gravity wave complex generated by convective outflow propagated across much of oklahoma the four dimensional evolution of the wave complex was analyzed using a synthesis of near surface and vertical observations from the oklahoma mesonet and atmospheric radiation measurement arm southern great plains networks two atmospheric emitted radiance interferometers aeri one located at the arm sgp central facility in lamont oklahoma and the other in norman oklahoma were used in concert with a doppler wind lidar dwl in norman to determine the vertical characteristics of the wave complex hydraulic theory was applied to the aeri derived observations to corroborate the observationally derived wave characteristics it was determined that a bore soliton wave packet initially formed when a density current interacted with a nocturnal surface based inversion and eventually propagated independently as the density current became diffuse the soliton propagated within an elevated invers

structural localization and origin of compartmentalized fluid flow comstock lode virginia city nevada bonanza grade orebodies in epithermal style mineral deposits characteristically occur as discrete zones within spatially more extensive fault and or fracture systems empirically the segregation of such systems into compartments of higher and lower permeability appears to be a key process necessary for high grade ore formation and most commonly it is such concentrations of metals that make an epithermal vein district world class in the world class silver and gold producing comstock mining district nevada several lines of evidence lead to the conclusion that the comstock lode is localized in an extensional stepover between right lateral fault zones this evidence includes fault geometries kinematic indicators of slip the hydraulic connectivity of faults as demonstrated by veins and dikes along faults and the opening of a normal fault bounded asymmetric basin between two parallel and overlapping northwest striking lateral to lateral oblique slip fault zones during basin opening thick generally subeconomic banded quartz adularia veins were deposited in the normal fault zone the comstock fault and along one of the bounding lateral fault zones the silver city fault as deformation continued the intrusion of dikes and small plugs into the hanging wall of the comstock fault zone may have impeded the ability of the stepover to accommodate displacement on the bounding strike slip faults through extension within the stepover a transient period of transpressional deformation of the comstock fault zone ensued and the early stage veins were deformed through boudinaging and hydraulic fragmentation fault motion inversion and high and low angle axial rotations of segments of the fault planes and some fault bounded wedges this deformation led to the formation of spatially restricted compartments of high vertical permeability and hydraulic connectivity and low lateral hydraulic connectivity bonanza orebodies were formed in the compartmentalized zones of high permeability and hydraulic connectivity as heat flow and related hydrothermal activity waned along the comstock fault zone extension was reactivated in the stepover along the occidental zone of normal faults east of the comstock fault zone volcanic and related intrusive activity in this part of the stepover led to a new episode of hydrothermal activity and formation of the occidental lodes

misocyclone characteristics along florida gust fronts during cape multiple doppler radar and rawinsonde data are used to examine misocyclone characteristics along gust fronts observed during the convection and precipitation electrification cape project in florida the objective of this study is to investigate the observational representativeness of previous numerical simulations of misocyclones by employing a consistent analysis strategy to 11 gust fronts observed in the same region the investigation focuses on the intensity range of misocyclones and their organization along gust fronts the relationship between misocyclone intensity and horizontal wind shear vertical wind shear and static stability and the relationship between misocyclones and convection initiation the intensity of misocyclones as indicated by the maximum values of vertical vorticity varied from 2 8 10 3 to 13 9 10 3 s 1 although all but one case exhibited values less than 6 4 10 3 s 1 organized misocyclone patterns were only found along small segments of gust fronts within those segments misocyclones were spaced between 3 and 7 km results show that the intensity of misocyclones was most closely related to the strength of horizontal wind shear across the gust front the relationship between misocyclone intensity and vertical wind shear and static stability was not as clear although convection was initiated along the gust front in 7 of the 11 cases those regions were not collocated with or in close proximity to misocyclones

geochemistry and stable isotope composition of altered rocks at the golden cross epithermal au ag deposit new zealand golden cross is a late miocene volcanic hosted epithermal au ag deposit associated with quartz calcite adularia illite assemblages located in the coromandel peninsula new zealand gold and ag bearing quartz veins occur in intensely altered flows and lesser pyroclastic volcanic rocks of andesitic and dacitic composition the primary control of whole rock geochemistry at golden cross as at other volcanic hosted epithermal deposits associated with quartz calcite adularia illite assemblages is the destruction of igneous plagioclase by hydrothermal alteration and k metasomatism from hydrothermal fluids quantitative mass change calculations indicate that irrespective of the rock type andesite versus dacite hydrothermally altered rocks are enriched in k rb as and sb around the empire vein system and stockwork in contrast na and sr are strongly depleted around the veins with fe locally depleted silicon ca mg and ba are variably enriched and depleted with si enriched immediately adjacent to the veins and ca only locally enriched the enrichment and depletion trends for these elements are directly related to the degree of alteration and the alteration mineralogy intensely altered rocks show addition of k and rb coupled with loss of na and sr which reflect the replacement of plagioclase by adularia and or illite calcium depletion also reflects the destruction of plagioclase although ca loss is locally offset by the formation of hydrothermal calcite progressively higher na and sr away from the veins reflect greater preservation of plagioclase and the transition into less altered rocks on the margins potassium rb na and sr all define anomalies that extend 200 to 350 m east of the veins and are more widespread than as and sb which are anomalous within 150 to 200 m of the veins the geochemical zonation patterns identified at golden cross are very similar to those at other epithermal deposits associated with quartz calcite adularia illite assemblages potassium na rb sr and ca enrichment and depletion patterns provide insight into the intensity and type of alteration thereby complementing traditional analyses of au ag and other pathfinder elements such as as and sb that are used to explore for epithermal au ag deposits potassium na rb sr and ca enrichment and depletion patterns at golden cross are larger than halos defined by precious metals and other trace element pathfinders thereby providing a larger target area for exploration potassium metasomatism is particularly important because the empire vein system occurs in altered rocks that are significantly enriched in k potassium metasomatism can be evaluated by raw k 2 o data or more effectively by k mass changes molar element ratios of 2ca na k al versus k al wt k 2 o 100 ppm sr rb sr ratios and k numbers k 2ca k na molar whole rock oxygen isotope patterns at golden cross are similar to those described at other epithermal deposits associated with quartz calcite adularia illite assemblages however the area defined by low 18 o values is smaller than the area that can be defined by field mapping of alteration minerals or whole rock major and trace element geochemistry

structure of an atmospheric undular bore generated from colliding boundaries during cape abstract a case study of a sea breeze front originating from the east coast of florida colliding with a gust front moving toward the southeast is presented single and multi doppler radar analyses combined with serial balloon ascents suggest that the denser sea breeze flow undercut the cold pool behind the gust front and may have generated a westward propagating undular bore in addition another undular bore was generated by the collision and propagated eastward through the cape network the latter bore propagated upstream against the southeasterly flow behind the sea breeze front and was apparent as a narrow band 5 6 km wide of near zero radial velocities embedded within an overall flow that was positive as seen by the cp 4 doppler radar as the eastern bore propagated through the dual doppler lobe defined by the ncar cp 3 and cp 4 radars a detailed and unique wind synthesis revealed its three dimensional kinematic structure significant along bore variability was shown in the convergence and verti

three dimensional oxygen isotope imaging of convective fluid flow around the big bonanza comstock lode mining district nevada oxygen isotope analyses of propylitized andesites from the con virginia and california mines allow construction of a detailed three dimensional image of the isotopic surfaces produced by the convective fluid flows that deposited the famous big bonanza orebody on a set of intersecting maps and sections the 18o isopleths clearly show the intricate and conformable relationship of the orebody to a deep 500 m gyre of meteoric hydrothermal fluid that circulated along and above the comstock fault near the contact of the davidson granodiorite the core of this gyre 18o 0 to 3 8 encompasses the bonanza and is almost totally surrounded by rocks having much lower 18o values 1 0 to 4 4 this deep gyre may represent a convective longitudinal roll superimposed on a large unicellular meteoric hydrothermal system producing a complex flow field with both radial and longitudinal components that is consistent with experimentally observed patterns of fluid convection in permeable media

an observational study of atmospheric bore formation from colliding density currents abstract observations from east central florida during the convection and precipitation electrification cape experiment are used to investigate the factors that influence atmospheric bore formation from colliding density currents ten cases involving the collision of a gust front with a sea breeze front are analyzed with doppler radar and sounding and surface mesonet data the gust fronts in these collisions were generally deeper denser and faster propagating than their sea breeze front counterparts seven of the 10 cases produced dual boundaries that moved away from each other in a relative sense after the collision post collision boundaries moving in the same direction and oriented similarly to the pre collision gust front occurred in all 10 cases they transported mass in the manner of a density current in six cases while the others behaved more like bores or bore density current hybrids as they were characterized by little or no mass transport similarity of gust front and sea breeze front prop

bores observed during ihop_2002 the relationship of bores to the nocturnal environment abstractthis study documents atmospheric bores and other convergent boundaries in the southern great plains nocturnal environment during the ihop 2002 summer campaign observational evidence demonstrates that convective outflows routinely generate bores statistically resampled flow regimes derived from an adaptation of hydraulic theory agree well with observations specifically convective outflows within the observed environments are likely to produce a partially blocked flow regime which is a favorable condition for generating a bore once a bore develops the direction of movement generally follows the orientation of the bulk shear vector between the nose of the nocturnal low level jet and a height of 1 5 or 2 5 km agl this relationship is believed to be a consequence of wave trapping through the curvature of the horizontal wind with respect to height this conclusion comes after analyzing the profile of the scorer parameter overall these findings provide an impetus for future investigations ai

symmetry of flow in the comstock lode hydrothermal system evidence for longitudinal convective rolls in geologic systems 1 hydrothermal fluid flow can be visualized by three dimensional 3 d kriging and computer contouring of oxygen isotope data on propylitized andesites in the comstock lode mining district this data set consists of 18o results for 327 samples from surface outcrops drill cores and mine workings in a 3 5 km 1 7 km 1 0 km block in the hanging wall of the comstock fault encompassing the region where the most important ore bodies were discovered the 18o contours deep in the hanging wall are not simply parallel to the comstock fault or to the boundary of the davidson granodiorite stock as would be expected for a hydrothermal convection system dominated by unicellular flow instead the subsurface 18o values exhibit a high degree of symmetry about a vertical plane directed radially toward the stock with isotopic contours being predominantly perpendicular to the comstock fault and the eastern contact of the davidson granodiorite a vertical cross section along the comstock lode shows a low 18o core with two symmetrical zones of higher 18o values to either side where the contours are steeply inclined which we infer reflects downwelling of fluids shifted by water rock exchange or steam loss this 3 d visualization of 18o values provides the first evidence that longitudinal convective rolls can be significant in geologic environments in this case within a zone of high temperature gradients and permeability near the comstock fault and the davidson granodiorite stock

evolution and vertical structure of an undular bore observed on 20 june 2015 during pecan abstractthis study documents the evolution of an impressive largely undular bore triggered by an mcs generated density current on 20 june 2015 observed as part of the plains elevated convection at night pecan experiment the university of wyoming king air with profiling nadir and zenith viewing lidars sampled the south bound bore from the time the first bore wave emerged from the nocturnal convective cold pool and where updrafts over 10 m s 1 and turbulence in the wave s wake were encountered through the early dissipative stage in which the leading wave began to lose amplitude and speed through most of the bore s life cycle its second wave had a higher or equal amplitude relative to the leading wave striking roll clouds formed in wave crests and wave energy was detected to about 5 km agl the upstream environment indicates a negative scorer parameter region due to flow reversal at midlevels providing a wave trapping mechanism the observed bore strength of 2 4 2 9 and speed of 15 16 m s 1 agree

a composite perspective on bore passages during the pecan campaign abstractatmospheric bores have been shown to have a role in the initiation and maintenance of elevated convection previous observational studies of bores have been case studies of more notable eve

whole rock δ o and δ h footprint of the canadian malartic gold deposit pontiac sub province quebec canada the canadian malartic gold deposit was produced by a hydrothermal system that altered the host metasedimentary rocks of the pontiac group metavolcanic rocks of the piche group and associated porphyritic intrusions and mafic dykes the isotopic footprint in pontiac metasedimentary rocks is marked by an increase in 2h values from 91 near mineralization to background values of ca 59 whereas 18o values remain relatively constant near 10 the isotopic footprint in mafic dykes is marked by an increase in 2h values from 84 near mineralization to background values of ca 73 and a decrease in 18o values from 9 8 near mineralization to background values of ca 8 3 kriging of oxygen and hydrogen isotopic compositions around the canadian malartic deposit delineates the isotopic footprint of the deposit in greywackes the 59 2h isopleth encircles the mineralized domain and is elongated towards the northwest and southeast in mafic dykes the 73 2h isopleth encircles the mineralized domain as well as a large area to the south and southeast whereas the 8 3 18o isopleth encircles the center of the mineralized system and extends over an area towards the southeast host rock oxygen and hydrogen isotope compositions therefore define a cryptic alteration footprint up to 2 5 km outside of the canadian malartic deposit the isotopic composition of the metamorphic fluid in equilibrium with the average least altered greywacke at upper greenschist to amphibolite conditions of ca 550 c is approximately 18o 8 6 and 2h 19 this is close to the composition of the mineralizing fluid at the canadian malartic deposit reported by previous studies fluid rock oxygen and hydrogen isotope exchange modeling indicate that the isotopic footprint formed at relatively low fluid rock ratios up to 0 5 at temperatures near 350 400 c

the spectacular undular bore in iowa on 2 october 2007 a visually impressive undular bore moved across much of iowa on 2 october 2007 and video animations were captured by numerous webcams the bore was sampled very well by doppler radar at close range and also by the high density mesoscale network of surface stations in place over iowa and 1 min automated surface observing system asos surface data at des moines iowa radar and surface observations are presented along with a brief analysis of the structure of the bore

the behavior of squall lines in horizontally heterogeneous coastal environments abstractinland squall lines respond to the stable marine atmospheric boundary layer mabl as they move toward a coastline and offshore as a storm s cold pool collides with the marine layer characteristics of both determine the resulting convective forcing mechanism over the stable layer and storm characteristics idealized numerical experiments exploring a parameter space of mabl characteristics show that the postcollision forcing mechanism is determined by the buoyancy of the cold pool relative to the mabl when the outflow is less buoyant storms are forced by a cold pool within the marine environment when the buoyancies are equivalent a hybrid cold pool internal gravity wave develops after the collision the collision between a cold pool and less buoyant mabl initiates internal waves along the stable layer regardless of mabl depth these waves are inefficient at lifting air into the storm and ascent from the trailing cold pool is needed to support deep convection storm intensity decreases with

the cold front of 15 april 1994 over the central united states part i observations abstract detailed observations of the interactions of a cold front and a dryline over the central united states that led to dramatic undulations in the boundary layer including an undular bore are investigated using high resolution water vapor mixing ratio profiles measured by raman lidars the lidar derived water vapor mixing ratio profiles revealed the complex interaction between a dryline and a cold frontal system an elevated well mixed and deep midtropospheric layer as well as a sharp transition between 5 and 6 km altitude to a drier region aloft was observed the moisture oscillations due to the undular bore and the mixing of the prefrontal air mass with the cold air at the frontal surface are all well depicted the enhanced precipitable water vapor and roll clouds the undulations associated with the bore the strong vertical circulation and mixing that led to the increase in the depth of the low level moist layer and the subsequent lifting of this moist layer by the cold frontal surface

wave disturbances and their role in the maintenance structure and evolution of a mesoscale convection system abstractthis study investigates a nocturnal mesoscale convective system mcs observed during the plains elevated convection at night pecan field campaign a series of wavelike features were obse

the potential role of atmospheric bores and gravity waves in the initiation and maintenance of nocturnal convection over the southern great plains abstractthis investigation explores the relationship among bores gravity waves and convection within the nocturnal environment through the utilization of measurements taken during the internation

tertiary meteoric hydrothermal systems and their relation to ore deposition northwestern united states and southern british columbia tertiary meteoric hydrothermal systems have altered the rocks exposed over more than 5 of the land surface of the northwestern united states and southern british columbia including at least 25 000 km 2 in idaho the systems typically involved convective circulation of fluid derived from ordinary meteoric groundwaters around crystallizing calc alkaline epizonal plutons emplaced into coeval volcanic cover rocks these individual systems had widely ranging lifetimes of 10 3 to 10 6 years and operated locally throughout the cenozoic although the most profound development of such activity occurred during eocene time individual systems varied in size from a few tens of square kilometers yankee fork idaho or less to several thousand square kilometers sawtooth and castro ring zones idaho typically regional propylitization aacompanied the fluid circulation although the higher temperature alteration assemblages were developed locally as were intense alteration effects e g silicification sericitization etc near some veins and in mining districts a significant amount probably 25 50 of the mineral production and potential in the region is closely related to tertiary meteoric hydrothermal systems oxygen and hydrogen isotopic data clearly demonstrate the close geologic association of meteoric hydrothermal systems and mineralization in 1 the paleocene cu zn pb mn main stage mineralization at butte montana 2 numerous eocene epithermal deposits principally valued for au and ag but also including significant deposits of cu pb zn f sb etc as at republic washington and in several mining districts in the idaho batholith and the challis volcanic field 3 several eocene skarn deposits valued for w ima idaho and cu mackay idaho 4 important lead silver vein and replacement deposits of tertiary bluebell british columbia and of probable cretaceous and early tertiary age wood river idaho 5 several potentially economic mo be and u bearing eocene porphyry plutons and 6 miocene epithermal deposits most prominently the au and ag bearing veins at silver city and delamar idaho the hg deposits at the mcdermitt caldera nevada and oregon and at weiser idaho and au deposits in the western cascade range and lake county oregon a close spatial association has been demonstrated between ore deposits and rocks having anomalous 18 o values and low d values the most important deposits are associated with relatively small generally 5 300 km 2 zones of low 18 o values and they are particularly closely linked with zones of very steep 18 o 16 o gradients in the altered rocks these associations hold much promise for the use of 18 o and d contour maps in future exploration efforts

fluid mineral relations in the comstock lode the comstock lode a world class precious metal vein deposit in the comstock district 15 mi 24 km southeast of reno nevada formed 13 7 ma in miocene eruptive rocks of the alta and kate peak formations and in pre tertiary metavolcanic and intrusive rocks production of 8 25 million oz 311 850 kg in gold and 192 million oz 7 26 million kg in silver came largely from bonanzas or vein segments containing hundreds of thousands to millions of tons and grading or 0 4 oz ton approximately 14 g ton gold and or 10 oz ton approximately 340 g ton silver within the 8 mi 12 9 km long comstock fault bonanza ores are distributed 3 mi 4 8 km along strike and persist from the present surface to 3 300 ft 1 007 m below the surface during the middle miocene andesitic to rhyodacitic alta and kate peak rocks formed a stratovolcano that exceeded 7 000 ft 2 134 m in elevation bonanza ores were deposited within this volcano from a 200 degrees c hydrothermal system that affected more than 37 mi 3 150 km 3 of rock at least one cretaceous and several miocene hydrothermal events were imposed on comstock district rocks the comstock lode vein assemblage which resulted from the youngest and only economically important event consists of quartz electrum silver minerals mainly acanthite pyrite base metal sulfides and minor amounts of calcite sericite chlorite k feldspar and albite andesite adjacent to veins is altered to quartz sericite and pyrite at vein contacts and quartz sericite montmorillonite chlorite and pyrite distally kaolinite is present in wall rocks adjacent to vein segments in which boiling occurred addition of the external components water co 2 and sulfur gases sufficed to produce all comstock vein alteration assemblages based on paragenetic and fluid inclusion studies multiple generations of hydrothermal fluid formed comstock district veins but the earliest and highest temperature fluid deposited ore minerals it ranged in temperature from 300 degrees c at the north end of the lode cedar hill to 6 wt percent nacl and was composed of both meteoric and magmatic water according to fluid isotopic analyses younger cospatial fluid s contained up to 2 1 wt percent co 2 the thermal center of the comstock lode hydrothermal system cedar hill is also the site of the highest measured ore fluid salinities ore fluid isotherms and to an extent salinity isopleths display reversals and convolutions that are spatially related to bonanzas these sharp temperature gradients coupled with mixing of ore fluid and at least one other high temperature fluid indicated by enthalpy salinity relationships and deuterium enrichment most likely caused precipitation of ore minerals sphalerite and electrum compositions indicate that bonanzas were deposited over a narrow range of f sub s 2 13 5 to 15 2 while sphalerites from low grade and barren vein segments indicate more widely variable f sub s 2 gold silver ratios both in electrum and bulk ore appear to be temperature controlled as higher temperatures generally correlate with high au ag ratios local boiling of 250 degrees to 285 degrees c fluid provides a paleosurface datum but vein temperatures 300 degrees c require up to 3 800 ft 1 152 m of cover over the tops of bonanzas during mineralization the distribution of both ore stage and late vein calcite partially reflects hydrothermal fluid circulation patterns in veins at district margins the abundance of late calcite marks the demise of hot water circulation and the influx of large amounts of cold miocene ground water into vein interstices kate peak intrusions between cedar hill and mount davidson share a common structural control with vein segments that comprise the comstock lode and their ages span vein ages the coeval kate peak magmas that provided heat for hydrothermal circulation formed the core of and uplifted the miocene stratovolcano which was centered over cedar hill partial symmetry of thermal compositional and kinetic gradients about cedar hill suggests that additional bonanzas await discovery along unexplored comstock fault segments within declining palcothermal gradients to the north

near surface density currents observed in the southeast pacific stratocumulus topped marine boundary layer abstractdensity currents i e cold pools or outflows beneath marine stratocumulus clouds are characterized using 30 days of ship based observations obtained during the 2008 variability of american monsoon systems vamos ocean cloud atmosphere land study regional experiment vocals rex in the southeast pacific an air density increase criterion applied to the improved meteorological imet sensor data identified 71 density current front core peak density and tail dissipating zones the similarity in speeds of the mean density current propagation speed 1 8 m s 1 and the mean cloud level advection relative to the surface layer wind 1 9 m s 1 allowed drizzle cells to deposit elongated density currents in their wakes scanning doppler lidar captured prefrontal updrafts with a mean intensity of 0 91 m s 1 and an average vertical extent of 800 m updrafts were often surmounted by low lying shelf clouds not connected to the overlying stratocumulus cloud the observed density currents were 5 10 time

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

stable isotope δ13c δ18o analysis of sulfide bearing carbonate samples using laser absorption spectrometry hydrothermally altered country rocks surrounding hydrothermal ore deposits are commonly characterized by altered 18 o and 13 c values relative to distal unaltered rocks stable isotopes have been recognized as a powerful tool to complement traditional geochemical and geophysical approaches during mineral exploration particularly in carbonate replacement and carlin type deposits however wall rock alteration and carbonate veining during ore formation is often accompanied by the precipitation of sulfide minerals complicating stable isotope analysis the classic phosphoric acid extraction technique for carbonate minerals results in the release of additional h 2 s gas interfering with isotope ratio mass spectrometry irms and laser absorption spectrometry las analysis of co 2 here we present the first results from a novel off axis integrated cavity output spectrometer oa icos instrument capable of determining the stable isotope composition 13 c 18 o of mixed co 2 h 2 s gas evolved from carbonate sulfide mixtures instrument calibration was performed by analyzing in house and commercially available caco 3 stable isotope reference materials analyses of mixed co 2 h 2 s tank gas and sulfide spiked stable isotope reference materials containing up to 40 wt chalcopyrite and sphalerite demonstrate that the method outlined here is capable of effectively analyzing previously problematic high sulfide samples the analytical capabilities together with the robust nature of the oa icos instrument may be of direct practical use for mineral exploration in carbonate hosted hydrothermal systems including ore deposits

oxygen isotope mapping of the archean sturgeon lake caldera complex and vms related hydrothermal system northwestern ontario canada the hydrothermal and magmatic evolution of the sturgeon lake caldera complex is graphically documented by a regional scale 525 km2 analysis of oxygen isotopes spatial variations in whole rock oxygen isotope compositions provide a thermal map of the cumulative effects of multiple stages of hydrothermal metasomatism before during and after volcanogenic massive sulfide vms mineralization there is a progressive upward increase in 18o from less than 2 to greater than 15 through a 5 km thick section above the biedelman bay subvolcanic intrusive complex this isotopic trend makes it clear that at least the earlier phases of this intrusive complex were coeval with the overlying vms hosting cauldron succession and provided thermal energy to drive a convective hydrothermal circulation system the sharp contrast in 18o values between late stage phases of the biedelman bay intrusion and immediate hanging wall strata indicates that the main phase of vms related hydrothermal activity took place before late stage resurgence in the cauldron related magmatic activity mineralogical and isotopic evidence indicates the presence of both syn and postmineralization hydrothermal activity defined by the presence of widespread semiconformable and more restricted discordant alteration zones that affect the pre and syncauldron strata the semiconformable alteration zones formed during early stages of hydrothermal circulation and are defined by widespread silicification and carbonatization in association with relatively high 18o values the discordant alteration assemblages containing al silicate minerals with chloritoid and or fe rich carbonate or chlorite centered on synvolcanic faults represent restricted zones of both seawater inflow and hydrothermal fluid upflow a rapid increase in 18o values 7 9 over a short distance 200 m suggests marked cooling of hydrothermal fluid from 350 c to less than 130 c either just before or during discharge onto the seafloor late emplacement of diorite sills and a dacite dome disrupted the isotopic imprint of cauldron stage hydrothermal activity the abrupt lowering of 18o values at the transition from explosive to passive volcanism andesite flows and dacite domes indicates postcauldron emergence subsequently thrust faulting disrupted the older synvolcanic hydrothermal isotopic patterns

effects of normal faulting on fluid flow in an ore producing hydrothermal system comstock lode nevada abstract normal faults in the comstock lode mining district nv usa are delineated by low 18o belts and strong isotopic gradients perpendicular to strike these faults perturb and also offset the regional pattern of 18o contours produced by pervasive hydrothermal alteration of the alta formation and have preserved the down dropped hanging wall rocks while exposing the footwall rocks to greater erosion fluid rock interaction was greatly enhanced within 200 m wide zones centered on the normal faults where permeability was increased and fluids were focused parallel to the fault plane the effects of displacement and permeability enhancement around the faults are investigated using oxygen isotope profiles through the comstock and occidental faults and across steeper secondary normal faults such as the coryell fault that may have formed after the principal faults were rotated to more shallow dips oxygen isotope profiles record both post hydrothermal displacement and syn deformational enhancement of fluid flow around the faults fluid focusing along normal faults perturbs the 18o values by increasing the water rock ratio this isotopic effect can be mathematically described for any distance x from the fault using the formula f a e bx 2 which is analogous to the fundamental solution for diffusion away from a plane source the maximum magnitude of 18o depletion a depends on the effects of permeability temperature mineralogy fluid isotopic composition and integrated fluid flux the constant b is related to the scale of exchange enhancement around the fault the characteristic width w 1 b of the fluid focusing effects is remarkably similar at 100 m for all three faults examined coupling this isotope exchange effect with a step function which accounts for fault displacement provides a good fit to the observed 18o fault profiles the 18o distribution around faults can be used to infer relationships and timing among the processes of structural deformation hydrothermal convection and ore deposition in the comstock district