numerical simulations of the extratropical transition of floyd 1999 structural evolution and responsible mechanisms for the heavy rainfall over the northeast united states abstract this paper examines the extratropical transition et of hurricane floyd along the u s east coast on 16 17 september 1999 using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 1 33 km horizontal grid spacing the 36 h mm5 simulation reproduced the basic features of the et event such as the track of floyd the development of a deep and intense baroclinic zone along the coast and its associated precipitation evolution and the tendency for the heavy 30 cm precipitation to fall in a relatively narrow 30 40 km wide band just inland of the coast however the mm5 overpredicted the moderate 10 20 cm precipitation amounts near the coast by 40 50 as the horizontal grid spacing was reduced to 1 33 km the mm5 was used to diagnose the evolution of the enhanced baroclinic zone and associated heavy precipitation to the north of floyd a deep layer of deformation frontogenesis extended from the surface to 400 mb as a result of confluence between the southeasterl

implications for intraplate volcanism and back arc deformation in northwestern new zealand from joint inversion of receiver functions and surface waves summary we employ a joint inversion of teleseismic receiver functions and surface wave phase velocities to determine the shear wave velocity structure in the crust and upper mantle beneath northwestern new zealand receiver functions primarily contain information on velocity contrasts while surface waves are sensitive to the average shear velocity with depth by performing a joint inversion we reduce the limitations of each method resulting in a more robust shear wave model inversion results reveal regions of low shear wave velocity of 2 8 km s 1 in the mid crust 10 19 km depth and 4 0 km s 1 in the upper mantle 70 90 km depth beneath quaternary intraplate basalt fields we infer that the mid crustal low velocity zones lvzs are bodies of partial melt most likely rhyolite intrusions we suggest that the upper mantle lvz is caused by the melt producing regions of the upper mantle and is a source for the basalts of the auckland volcanic field this is in agreement with models for a shallow upper mantle source rather than a deep seated mantle plume for the auckland volcanism average shear velocities for the upper crust are 3 4 3 6 km s 1 increasing to 3 6 4 0 km s 1 in the lower crust the moho is interpreted to be 29 1 km deep in the southern end of the array shallowing to 26 1 km towards the edge of the continental shelf of northern new zealand low upper mantle shear velocities of 4 2 0 1 km s 1 are observed and are thought to represent a small percentage of partial melt in the upper mantle beneath this back arc region these low velocities extend to greater depth 90 km beneath the southern stations indicating that mantle deformation associated with the mantle wedge to the south may extend as far north as the southern end of our array near surface low velocity layers extend to 6 km depth beneath a station at the northern tip of new zealand likely representing the expression of a thick sequence of sediments from the northland allochthon and the more recent northland basin

climatological analysis of manually digitized radar data for the united states east of the rocky mountains climatological analyses of manually digitized radar mdr data are presented to illustrate geographic seasonal and diurnal heterogeneities of precipitation over the united states east of the rocky mountains mdr data consist of hourly radar reflectivity data for the contiguous united states at a grid scale of approximately 40 km analyses of mdr data for the period 1978 1992 are presented mdr data are especially useful for studying the geographic contrasts in precipitation over the continental domain and the contrasts between land and ocean along the gulf of mexico and the atlantic ocean climatological analyses of fractional coverage of rainfall on a continental scale are developed using mdr data high resolution radar data from the radap ii network are used to illustrate fractional coverage of rainfall within an individual mdr grid box intercomparison studies with rain gage data point to the potential for quantitative rainfall analyses based on mdr data analyses of mdr data illustrate the potential and some of the difficulties in using radar data for hydroclimatological studies

a dual polarization radar based assessment of the 8 may 2003 oklahoma city area tornadic supercell abstract on 8 may 2003 a tornadic supercell tracked through portions of the oklahoma city oklahoma metropolitan area and produced violent damage along portions of its path this storm passed through the dense in situ radar network in central oklahoma and provided close range operational prototype polarimetric and terminal doppler weather radar observations of the storm as it made the transition into the tornadic phase the time evolving polarimetric features were scrutinized with regard to storm morphology particularly as related to the development of a rear flank downdraft pulse within the storm immediately preceding the long track tornado event two new polarimetric terms are introduced the zdr shield and kdp foot along with a discussion of the orientation of the zdr and kdp columns relative to midlevel rotation signatures storm downdraft and gust front characteristics are discussed relative to polarimetric fields and background environment characteristics highlighted for this event are a warm

rapid destruction of a stratospheric potential vorticity anomaly by convectively induced inertial instability during the southern wisconsin extreme flooding event of 20 august 2018

a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

reappraisal of the significance of volcanic fields abstract volcanic field is a term commonly used to loosely describe a group of volcanoes often it is implicitly assumed that the volcanoes on a volcanic field are small monogenetic and dominantly basaltic but none of those attributes is indispensable on some definitions of the term actually the term volcanic field can be used to describe a group of purely monogenetic edifices a group of mixed monogenetic and polygenetic edifices or even a group formed only by purely polygenetic edifices differences between each of those alternatives might be important but the extent to which those differences are truly relevant remains still to be explored furthermore there are several limitations on the current knowledge of this type of volcanic activity that explain the lack of a comprehensive effort to study volcanic fields in global contexts in this work issues concerning current definitions of a volcanic field are examined and some criteria that can be used to distinguish volcanic fields from non field volcanoes are suggested special attention is given to the role played by spatial scale on such a distinction also the tectonic implications of their spatial distribution are explored in particular it is shown that volcanic fields are an important component of volcanic activity at a global scale that is closely associated to diffuse plate boundaries and might well be considered the archetypical volcanic form of such tectonic scenarios

extreme rainfall and flooding from orographic thunderstorms in the central appalachians 1 the central appalachian region has experienced some of the largest rainfall accumulations in the world at time intervals less than 6 h including the 18 july 1942 smethport pennsylvania storm that produced 780 mm in less than 5 h the envelope curve of central appalachian flood peaks at small drainage areas less than 1000 km2 is dominated by orographic thunderstorm systems like the smethport storm orographic thunderstorm systems that have produced catastrophic flooding in the central appalachians are examined through observational and numerical model analyses using the weather research and forecasting wrf model analyses suggest that the frequency of catastrophic flooding varies over the central appalachian region and that small scale variation may be linked to the role of complex terrain in altering thunderstorm dynamics catastrophic flooding along the western margin of the central appalachians is dominated by four storms that occurred on 18 19 july 1889 1942 1977 and 1996 which were associated with warm season extratropical systems and were characterized by rapidly moving storm elements in complex terrain along the eastern margin and interior of the central appalachians catastrophic flooding is linked to four terrain locked orographic convective systems that occurred 17 18 june 1949 18 19 august 1969 27 june 1995 and 11 august 2003 wrf model simulations of the little river storm june 1949 rapidan storm june 1995 smethport storm 18 july 1942 and redbank storm 18 19 july 1996 are used to characterize ingredients of catastrophic rainstorms in the central appalachians

mantle plumes and continental tectonics abstract it is now recognised that plumes originate from a thermal boundary layer deep in the mantle a new plume consists of a large head with a diameter of approximately 800 to 1200 km and it is followed by a smaller tail which has a diameter of 100 to 200 km at the top of its ascent the head flattens to form a disk 2000 to 2500 km in diameter that may melt to produce a continental flood basalt or oceanic plateau the tail melts to produce chains of volcanic activity such as the hawaiian emperor chain the ascent of a new plume leads to surface uplift of 500 to 1000 m over a length scale of 2000 km this places the lithosphere under tension but the horizontal forces produced do not result in runaway extension unless the continental lithosphere is already anomalously hot and therefore weak if the lithosphere is cold and strong slow extension leading to a new spreading ridge may postdate plume arrival by 10 to 40 m y the time difference being the time taken to conduct heat from the plume to the overlying lithosphere plume heads may control the timing and position of new ocean ridges but are not the fundamental force that drives plate tectonics the heat from plume tails may weaken the overlying plate and pin the position of spreading the ascent of a mantle plume can also have an important influence on subduction large oceanic plateaus such as the ontong java plateau are more buoyant than normal oceanic crust because they have a thicker basaltic layer and because they are underlain by a 200 km thick layer of hot material from a mantle plume head as a consequence oceanic plateaus are more difficult to subduct than normal oceanic crust this can lead to jamming of plates at subduction zones resulting in a flip in the sense of subduction as appears to have happened in the caribbean region or to obduction of the plateau finally when a plume head is emplaced beneath continental crust heat released from the plume may lead to melting of the overlying crust the granites associated with many greenstone belts and intercontinental magmatic provinces such as the paleozoic lachlan fold belt of eastern australia and the middle proterozoic anorogenic granites of the central and southwestern united states may have formed in this way

recent developments in dating ancient crustal fluid flow several isotopic techniques have recently been developed or substantially improved allowing the accurate determination of the timing of fluid related processes these include k ar rb sr and sm nd dating of diagenetic minerals in clastic rocks u pb dating of carbonates sm nd dating of fluorite and uraninite re os and rb sr dating of sulfides 40ar 39ar and rb sr dating of fluid inclusions and u pb dating of ilmenite magnetite sphene and rutile while many of these techniques require further evaluation some have already resulted in new constraints on a variety of crustal fluid flow models

trace element and sr nd isotopic evidence for the origin of the sardinian fluorite mineralization italy abstract the fluorite bearing hydrothermal mineralization in sardinia mainly occurs within paleozoic volcanic and metasedimentary rocks only 3 occurrences are located in volcanic and siliciclastic cenozoic rocks most sardinian fluorites exhibit relatively high rare earth and y rey contents strong positive y anomalies slightly negative ce and generally positive eu anomalies these features indicate that the rey were mobilized mainly from non carbonate rocks neither sr nor nd isotopes can be used to date radiometrically the sardinian fluorites however the measured sr isotope ratios of the fluorites hosted by paleozoic rocks fit mixing lines in the 1000 sr versus 87sr 86sr plot once recalculated at 280 ma suggesting that the age inferred for the correction probably represents that of the formation of the fluorite mineralization mixing likely occurred between diluted surficial waters and brines circulating mainly through the lower paleozoic metasedimentary basement the cenozoic fluorites exhibit chemical and isotopic features similar to those of the paleozoic fluorites except the nuraghe onigu fluorite displaying a possible contribution of sr from cenozoic magmatic rocks the initial end values of the paleozoic fluorites fit the age proposed for the formation of the deposits moreover the values suggest that radiogenic nd was provided to the fluids from the ordovician siliciclastic basement except for 3 deposits where the potential source rocks of nd were mainly ordovician acidic magmatic rocks the initial end values of the cenozoic fluorites suggest a provenance of nd essentially from the leaching of variscan granitoids

a long lived supercell over mountainous terrain the life cycle of a convective storm forming over highly complex topography on the northern side of the alps is studied moist convection began ahead of a cold front in the late morning of 2 august 2007 in eastern switzerland it developed into a supercell storm that moved along the alpine main crest for more than 8 hours passed over several 2000 m high ridges and ultimately dissipated over eastern austria this study analyzes the impact of topography on the pre storm environment and on the storm development using several simulations with the weather research and forecasting wrf model at a minimum horizontal grid spacing of 833 m a hindcast simulation of the event features a convective system evolving in good agreement with observations variations in the simulated storm intensity appear to be related to the topography below the storm two idealized simulations help understand how the alpine topography affected storm initiation and development north of the alps relatively strong shear between southwesterly synoptic flow aloft and thermally induced plain to mountain flow near the ground created favorable conditions for supercell development small scale terrain features supported the upward transport of moisture via slope circulations locally reducing cin and increasing cape and ultimately enhancing the storm longevity

lidar based quantification of lava flow susceptibility in the city of auckland new zealand abstract lava flows represent one of the most significant volcanic hazards from basaltic monogenetic volcanoes such as spatter cones scoria cones maars and tuff rings they are common features emanating from parasitic vents on the flanks of polygenetic volcanoes and in dominantly flat lying intraplate volcanic fields the auckland volcanic field avf is a volcanic field that has been active for the last ca 250 ka hosting at least 50 monogenetic volcanoes morphometric parameters of lava flows such as volume length thickness and area were used to quantify the potential lava flow inundation susceptibility to new zealand s most densely populated area the city of auckland based on an airborne light detection and ranging lidar digital surface model dsm the morphometric parameters of fifteen studied flows included average length of 2 5 km range 0 7 6 5 km overall average thickness of 14 8 m range 3 4 43 8 m average of maximum thicknesses of 48 2 m range 18 3 180 5 m average area occupied of 5 1 km 2 range 0 4 25 1 km 2 and average volume of 0 12 km 3 range 0 005 1 km 3 based on these parameters and a lidar derived dsm the present topography was classified into sea topographic depressions low lying areas prone to inundation by an average lava flow buffer zones prone to inundation only by extremely thick lava flows and peaks or ridges which are unlikely to be overtopped in monogenetic fields each new vent occurs in a new location creating uncertainty around the spatial location of the volcanic hazard thus this research provides a general vent location independent approach to describe the lava flow susceptibility for a potentially active monogenetic volcanic field what this analysis reveals is that the city of auckland can be divided into two distinct areas with strongly different susceptibility to lava flow inundation the southern part of the city is predominantly flat without hindrance to lava flow whereas the hilly northern and central part has many ridges that can limit or channelise lavas these contrasting properties must be accounted for in scenario based or probabilistic hazard and risk models developed for the avf

the spatial and temporal cost of volcanic eruptions assessing economic impact business inoperability and spatial distribution of risk in the auckland region new zealand volcanic risk assessment has historically concentrated on quantifying the frequency magnitude and potential diversity of physical processes of eruptions and their consequent impacts on life and property a realistic socio economic assessment of volcanic impact must however take into account dynamic properties of businesses and extend beyond only measuring direct infrastructure property loss the inoperability input output model heralded as one of the 10 most important accomplishments in risk analysis over the last 30 years kujawaski syst eng 9 281 295 2006 has become prominent over the last decade in the economic impact assessment of business disruptions we develop a dynamic inoperability input output model to assess the economic impacts of a hypothetical volcanic event occurring at each of 7270 unique spatial locations throughout the auckland volcanic field new zealand this field of at least 53 volcanoes underlies the country s largest urban area the auckland region which is home to 1 4 million people and responsible for 35 3 nz 201481 2 billion of the nation s gdp statistics new zealand 2015 we apply volcanic event characteristics for a small medium scale volcanic eruption scenario and assess the economic impacts of an average eruption in the auckland region economic losses are quantified both with and without business mitigation and intervention responses in place we combine this information with a recent spatial hazard probability map bebbington and cronin bull volcanol 73 1 55 72 2011 to produce novel spatial economic activity at risk maps our approach demonstrates how business inoperability losses sit alongside potential life and property damage assessment in enhancing our understanding of volcanic risk mitigation

origin and granite alteration effects of hydrothermal fluid isotopic evidence from fluorite veins co galway ireland the costelloe murvey granite is a chemically evolved high heat production leucocratic component of the 400 ma old galway granite batholith and is host to hydrothermal fluorite quartz calcite veins a previously reported clinopyroxene 40ar 39ar age of 231 4 ma obtained from a pre mineralization dolerite dyke is reinterpreted as dating this mineralization the hydrothermal fluid extensively altered its granite wallrocks leading to lower sm and nd and higher rb concentrations in altered granite disturbing both its rb sr and sm nd isotopic systems the 87sr 86sr ratio of the hydrothermal fluid from which fluorite and calcite precipitated ranged from 0 7101 to 0 7139 these ratios are very much lower than in the costelloe murvey granite at the time of mineralization precluding the granite as a source for more than 2 of the hydrothermal sr the initial 143nd 144nd ratio varies between fluorite in different veins due to nd derivation from local wallrocks and between fluorite of petrographically distinct growth phases within a single hand specimen highlighting the difficulty of sm nd isochron dating of fluorite in cases where there are multiple sources of hydrothermal nd it is proposed that fluorite and calcite precipitated where hot dilute fluids rising through the granite mixed with cooler more saline fluids of basinal origin migrating through lower carboniferous limestone which then overlay the granite

intense silicification of ordovician carbonates in the tarim basin constraints from fluid inclusion rb sr isotope dating and geochemistry of quartz an unconventional porous silicified carbonate reservoir was unveiled in the middle ordovician fractured limestone within a strike slip fault zone in the tarim basin nw china the silicified carbonates are mainly composed of fine to medium crystalline fascicular quartz matrix and coarse crystalline bladed to columnar quartz cement fluid inclusion leachate residue paired rb sr isotopic dating of the quartz cement yields an isochron age of 167 15 ma attesting to a causal link to the jurassic yanshanian orogeny pervasive replacement of matrix quartz and subsequent precipitation of cement quartz through nonisothermal effervescence probably induced by episodic influxes of the hot silica and sr 87 rich basinal brines from the neighbouring deeper manjiaer depression this study thus signifies the usefulness of using rb sr isotope dating method in constraining the timing of carbonate alteration enabling to establish the deterministic relationship of basinal fluid evolution with the major tectonic activity

the initiation and growth of en echelon veins abstract numerical models are used to understand the evolution of mode i opening fractures from spatially random distributions in a brittle elastic material en echelon arrays commonly develop because mechanical fracture interaction promotes growth for this geometry this provides a new mechanism for en echelon vein formation in rock which is distinctly different than previously proposed mechanisms it is suggested that some macroscopic en echelon vein arrays may have served as zones of weakness that localized later shear zone development in a manner analogous to that observed by experimentalists examining micro cracking and subsequent shear rupture of rocks loaded under compression sigmoidally shaped veins and vein fillings are explicitly modeled showing that they can form in response to the mechanical interaction of neighboring fractures which redirects the propagation path numerical comparison of sigmoidal veins formed by brittle fracture and by ductile shear zones demonstrates some of the pitfalls of failing to correctly identify the mechanism of formation

tectonic and magmatic controls on the location of post subduction monogenetic volcanoes in baja california mexico revealed through spatial analysis of eruptive vents post subduction 12 5 ma to less than 1 ma monogenetic volcanism on the baja california peninsula mexico formed one of the densest intra continental areas of eruptive vents on earth it includes about 900 vents within an area 700 km long n s and 70 to 150 km wide w e this study shows that post subduction volcanic activity was distributed along this arc and that modes exist in the volcano distribution indicating that productivity of the magma source region was not uniform along the length of the arc vent clustering vent alignments and cone elongations were measured within eight monogenetic volcanic fields located along the peninsula results indicate that on a regional scale vent clustering varies from north to south with denser spatial clustering in the north on the order of 1 9 10 1 vents km2 to less dense clustering in the south on the order of 7 8 10 2 vents km2 san quintin san carlos jaraguay and santa clara are spatially distinct volcanic fields with higher eruptive vent densities suggesting the existence of individual melt columns that may have persisted over time in contrast the san borja vizcaino san ignacio and la purisima vent fields show lower degrees of vent clustering and no obvious spatial gaps between fields thus indicating an area of more distributed volcanism insight into the lithospheric stress field can be gained from vent alignments and vent elongation measurements within the fields located along the extinct subduction related volcanic arc elongation patterns of cinder cones and fissure fed spatter cones vent clusters and vent alignments trend nw se and n s within the santa clara field located more to the west within the forearc elongation patterns of the same volcanic features trend ne sw these patterns suggest that magmatism was more focused in the forearc and in the northern part of baja california than in its southern region within the extinct arc magma ascent created volcano alignments and elongate cones parallel to nw se to n s oriented tectonic structures in the forearc the existence of n s and ne sw oriented volcanic features indicates a rotation in the stress field orientation compared to the arc

organization and environmental properties of extreme rain producing mesoscale convective systems this study examines the radar indicated structures and other features of extreme rain events in the united states over a 3 yr period a rainfall event is defined as extreme when the 24 h precipitation total at one or more stations surpasses the 50 yr recurrence interval amount for that location this definition yields 116 such cases from 1999 to 2001 in the area east of the rocky mountains excluding florida two kilometer national composite radar reflectivity data are then used to examine the structure and evolution of each extreme rain event sixty five percent of the total number of events are associated with mesoscale convective systems mcss while a wide variety of organizational structures as indicated by radar reflectivity data are seen among the mcs cases two patterns of organization are observed most frequently the first type has a line often oriented east west with training convective elements it also has a region of adjoining stratiform rain that is displaced to the north of the line the second type has a back building or quasi stationary area of convection that produces a region of stratiform rain downstream surface observations and composite analysis of rapid update cycle version 2 ruc 2 model data reveal that training line adjoining stratiform tl as systems typically form in a very moist unstable environment on the cool side of a preexisting slow moving surface boundary on the other hand back building quasistationary bb mcss are more dependent on mesoscale and storm scale processes particularly lifting provided by storm generated cold pools than on preexisting synoptic boundaries

el estribo volcanic complex evolution from a shield volcano to a cinder cone patzcuaro lake michoacan mexico abstract el estribo volcanic complex evc is located in the northern part of the michoacan guanajuato volcanic field within the trans mexican volcanic belt tmvb el estribo is located at the southern edge of the e w patzcuaro fault that belongs to the patzcuaro jaracuaro graben a western extension of the e w morelia acambay fault system stratigraphy geochronology chemistry and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a 100 ka volcanic hiatus a emission of lava flows that constructed a shield volcano between 126 ka and b mixed phreatomagmatic to strombolian activity that formed a cinder cone 28 ka the magmas that fed these monogenetic volcanoes were able to use the same feeding system the cinder cone itself was constructed by strombolian fallouts and remobilized scoria beds followed by an erosion period and by a mixed phreatomagmatic to magmatic phase strombolian fallouts ending with lava flows soft sedimentary deformation of beds and impact sags cross bedding as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase the erupted magmas through time ejected basaltic andesitic lava flows 56 21 58 88 sio 2 that built the shield volcano and then basaltic andesitic scoria 57 65 59 05 sio 2 that constructed the cinder cone although they used the same feeding system the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart therefore the location of el estribo volcanic complex along an e w fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived questioning the classic view of the monogenetic nature of their volcanoes and yielding information about the potential volcanic risk of these settings usually considered risk free

spatial analysis of an intra plate basaltic volcanic field in a compressional tectonic setting south eastern australia abstract the newer volcanics province nvp is a pliocene to recent intra plate basaltic volcanic field bvf that has formed in a compressive tectonic setting v

a sulphur isotopic investigation of the potential sulphur sources for lower palaeozoic hosted vein mineralization in the english lake district current models for cu fe as devonian pb zn carboniferous and barite upper carhoniferous permian vein mineralization in the lake district invoke a variety of sources for fluids and metals including the skiddaw group sediments the borrowdale volcanic group the lake district batholith meteoric water and carboniferous seawater this study isotopically characterizes the sulphur reservoirs within the lower palaeozoic sedimentary and igneous sequences and late caledonian intrusives and assesses their importance as sources of sulphur for the vein mineralization the ordovician skiddaw group is a reservoir of isotopically heavy sulphur with a range of 34 s from 11 to 29 x 1 18 53 6 7 n 10 four analyses of borrowdale volcanic group rocks yielded values of 1 to 15 such positive values are thought to be the result of closed system bacteriogenic reduction of ordovician seawater sulphate in the case of the skiddaw group and mixing of mantle derived magmatic sulphur with ordovician seawater sulphate for the borrowdale volcanic rocks the sulphides in the vein systems hosted by the skiddaw group in the vale of newlands formed from fluids with 34 s h 2 s signatures ranging from 16 7 to 22 5 partially homogenized skiddaw group sulphur is considered to be the source mineralization at coniston hosted by the borrowdale volcanic group shows similar sulphur isotopic characteristics and skiddaw group at depth is considered to be the predominant source of sulphur with a possible minor input from the wallrock volcanic rocks at the site of deposition although the lake district batholith provided a heat source for the cu fe as vein mineralization the granite did not supply any sulphur to those systems however magmatic sulphur was an important constituent in mineralization associated with the shap and skiddaw granites the 34 s values for barite mineralization at force crag greenside skiddaw and shap ranges from 13 to 18 and carboniferous seawater provides the most reasonable source for sulphate

magnitudes and implications of peak discharges from glacial lake missoula new field evidence and discharge calculation procedures provide new estimates of maximum late pleistocene glacial lake missoula flood discharges for two important reaches along the flood route within the spokane valley near the point of release the peak discharge probably exceeded 17 3 million m3 sec 1 downstream at wallula gap a major point of flow convergence peak discharge was about 10 2 5 million m3sec 1 flow duration was on the order of several days these are the largest known terrestrial fresh water flows consideration of these discharge values constrains models for the failure of glacial lake missoula the maximum discharges estimated here are larger than theoretical and empirical predictions of maximum subglacial jokulhlaup style releases for lake missoula we postulate consistent with geological relations in the glacial lake missoula basin and in the channeled scabland that the largest late wisconsinan missoula flood resulted from a cataclysmic failure of the impounding ice dam of glacial lake missoula this large release may have been the result of a complete rupture of the ice dam subsequent multiple flows of lesser magnitude may have resulted from repeated subglacial releases from the lake

construction of the north head maungauika tuff cone a product of surtseyan volcanism rare in the auckland volcanic field new zealand the auckland volcanic field avf comprises at least 52 monogenetic eruption centres dispersed over 360 km2 eruptions have occurred sporadically since 250 ka predominantly when glacio eustatic sea levels were lower than today now that around 35 of the field is covered by shallow water up to 30 m depth any eruption occurring in the present or near future within this area may display surtseyan dynamics the north head tuff cone evidences eruptive dynamics caused by magma interaction with seawater the first stages of the eruption comprise a phreatomagmatic phase that built a 48 m high tuff cone north head tuff deposits contain few lithic fragments 10 vol and are characterized by deposits from collapsing tephra jets and fall from relatively wet tephra columns the conditions needed for this eruption existed between 128 and 116 ka when the sea level in the auckland area was at least 10 12 m above the pre eruptive surface the hazards associated with this type of eruption pose a risk to the densely populated coastal residential zones and the activities of one of the busiest harbours in new zealand

tracing element sources of hydrothermal mineral deposits ree and y distribution and sr nd pb isotopes in fluorite from mvt deposits in the pennine orefield england fluorite from mississippi valley type mvt deposits in the south pennine orefield england displays significantly different distributions of rare earths and yttrium rey compared to fluorite from similar mvt deposits in the north pennine orefield samples from the south pennine orefield display negative ce and positive gd and y anomalies but lack any eu anomaly indicating that the rey were mobilized from relatively pure marine sedimentary carbonates in marked contrast fluorite from the north pennine orefield lacks any ce and gd anomalies but shows a pronounced positive eu anomaly suggesting that the rey were provided by different source rock s that the mineralizing hydrothermal fluid had experienced higher temperatures prior to fluorite precipitation and that it was derived from deeper crustal levels in the north compared to the south the isotopic composition of sr in blue john fluorite from the south pennine orefield suggests that sr was mobilized from lower carboniferous tournaisian limestones whereas pb isotopes suggest that in contrast to rey and sr pb was derived from aluminosilicate rocks neither nd nor sr or pb isotopes can be used to radiometrically date the formation of blue john fluorite all isotope systems studied indicate that the limestone host rock of this fluorite mineralization did not contribute to the trace element budget of the hydrothermal fluid our results show that different solutes in a natural water hydrothermal fluid groundwater etc may be derived from different sources and that the study of a small set of elements or isotope ratios may not provide full insight into the genesis or history of a mineralization or a hydrothermal fluid our data provide evidence for the uncoupling of sr nd and pb during fluid rock interaction and fluid migration and show that the use of plots such as 87sr 86sr vs end to learn about mixing relationships as is commonly done in igneous geochemistry is unreliable when applied to natural waters and their precipitates

column on column structures as indicators of lava ice interaction ruapehu andesite volcano new zealand abstract lava flows of the mangawhero formation ca 15 60 ka on ruapehu volcano erupted during the last glaciation in a distal flow lobe at tukino on the east side of the mountain small secondary columns 10 20 cm thick have formed on the sides of large rectangular primary 0 5 3 m thick cooling columns thick 10 m zones of such small columns form a lateral and basal outer rind of the lobe as they do not mark glassy zones of quenching these secondary columns are interpreted as being formed by a second cooling event at temperatures below the boundary between the low creep and elastic regimes 600 c by rapid influx of copious amounts of water temperature drops deduced from extensional strains of the two sets of columns were used to gauge the viability of such a two stage process absence of reliable data on andesite contraction coefficients was overcome by using a sliding scale to assess a large range of values the estimates indicate that two stage chilling is feasible after flowing across relatively ice poor terrain the lava flow must have interacted with a valley glacier that provided water for further chilling the already formed primary columns and formation of the outer rind small columns given this evidence for lava ice interaction it is likely that prominent thick flows elsewhere in the mangawhero formation may have been constrained to their ridge top locations by ice conditions similar to those described by lescinsky and sisson lescinsky d t sisson t w 1998 ridge forming ice bounded lava flows at mount rainier washington geology 26 351 354

hydrothermal fluids during mesozoic reactivation of the st lawrence rift system canada c o sr and pb isotopic characterization calcite veins with accessory galena sphalerite barite and fluorite are abundant within the ottawa bonnechere and the charlevoix saguenay failed arms of the st lawrence rift system which developed during early paleozoic times within gneisses of the grenville province of canada the mineral assemblages paragenesis and precipitation temperatures of the veins resemble the mississippi valley deposits crosscutting relationships with carbonate rocks of the st lawrence lowlands and deformed carbonate rock slivers of the charlevoix astrobleme show that the ottawa graben and saguenay graben veins are younger than mid ordovician or post devonian respectively 18o and 13c values for vein calcite are positively correlated and range from 11 to 24 and 9 to 3 respectively 87sr86sr in calcite and barite range from 0 7129 to 0 7081 the fluids that precipitated calcite were part of a hydrothermal system dominated by meteoric water enriched in 18o by exchange with silicate minerals and deep seated carbon either from mantle outgassing deep seated brines of the canadian shield or from oxidation of reduced carbon in high grade metamorphic rocks veins cutting marbles of the grenville supergroup have lower 87sr86sr and higher 18o and 13c values than those hosted in quartzofeldspathic gneisses of the grenville province showing that the fluids were modified by interaction at depth with the marbles stable and sr isotope compositions are also correlated with layb ratios in calcite supporting the fact that the veins formed within similar hydrothermal systems in both the ottawa and saguenay grabens the pb isotopic compositions of vein galena are radiogenic 206pb204pb 18 0 19 7 207pb204pb 15 5 15 7 208pb204pb 37 9 41 0 and positively correlated in conventional pb pb diagrams pb isotope and ree data strongly suggest that the fluids leached selectively at the mineral scale gneisses of the grenville province the basinal fluids within the shelf sequence of the western appalachians had 208pb204pb ratios in the lower paleozoic significantly lower than those of vein galena this excludes the basin brine model of formation for the vein deposits like suggested for the mississippi valley deposits the veins rather formed in the mesozoic in response to the rifting of northeastern north america and the reactivation of the st lawrence rift

timing of the formation of the changba lijiagou pb zn ore deposit gansu province china evidence from rb sr isotopic dating of sulfides abstract the giant changba lijiagou pb zn deposit is located in the north of the xihe chengxian abbreviated as xicheng ore cluster in gansu province china the orebodies in the deposit are mainly hosted in the marble dolomitic marble and biotite calcite quartz schist of the middle devonian anjiacha formation the genesis of the deposit has previously been argued to be of sedex type sedimentary exhalative type or of epigenetic hydrothermal type this paper reports results of rb sr isotopic dating on sphalerite and pyrite taken from the main orebody which yield an isochron age of 222 3 2 2 ma for eight sphalerite samples and 222 0 3 0 ma for the eight sphalerite samples combined with four pyrite samples indicating that the deposit formed during the late triassic the 87sr 86sri value of the sphalerite is 0 71370 0 00013 and that of the sphalerite and pyrite is 0 71371 0 00014 which are identical within experimental error suggesting that the ore metals are derived mainly from the continental crust by integrating the present results with the regional geology we propose that the changba lijiagou pb zn deposit is a product of regional hydrothermal mineralization processes forced by tectono magmatic activities which took place in the xicheng ore cluster during triassic orogenic processes

fluid flow history from damage zone cements near the dent and rawthey faults nw england fault related breccias in carboniferous limestone have been well documented in the footwall damage zone to the reverse oblique dent fault this study describes breccias in the more complicated hanging wall hosted in pre deformed ordovician and silurian lithologies along the dent fault or one of its splays such as the rawthey fault brecciation style is shown to be influenced by lithology with the most extensive brecciation in mechanically strong units siliceous or calcareous mudstone cemented sandstone and fine tuff most brecciation involves dilational strain in the fault damage zones attritional breccias are rare even in fault cores dilation breccias are cemented sporadically by quartz or barite but mostly by carbonate minerals transition matrix analysis shows that the sequence of hanging wall carbonate cements matches that in the footwall first dolomite or calcite then ferroan dolomite then ferroan calcite this similarity suggests hydrological connectivity from hanging wall to footwall and through tens of cubic kilometres across the dent rawthey fault system such connectivity is predicted across upper crustal faults that cut strong mechanical stratigraphy it is proposed that fluid flow though the fault system was driven mainly by syntectonic topography above the hanging wall and possibly also by thermal convection caused by a buried granite pluton in the footwall

late cenozoic rift development and intra plate volcanism in northern new zealand inferred from geochemical discrimination diagrams abstract major and trace element discrimination diagrams are used in an attempt to discover the tectonic settings in which the late cenozoic basalts and basalt andesites of northern new zealand evolved the rocks of the northland area are shown to have rift affinities whereas those of auckland and south auckland appear to have evolved in an intraplate environment it is proposed that the common link between the two groups of volcanic rocks is the hauraki rift the northland basalts are directly associated with the rift whereas the auckland and south auckland rocks either developed on the flanks of the rift or their origin is linked to the evolution of membrane stresses during the opening of this rift the basalts and basalt andesites of the waikato district also show an affinity with the rift but the geochemistry is complicated by the influence of the developing taupo volcanic zone which adds a shoshonitic character to these rocks

rb sr dating of sphalerites from tennessee and the genesis of mississippi valley type ore deposits mississippi valley type mvt ore deposits commonly consist of some combination of lead zinc and iron sulphides accompanied by barite fluorite dolomite and calcite they are thought to form by fluid expulsion from sedimentary successions1 3 but their exact origin has remained controversial because of the scarcity of reliable geochronological data in a recent and widely quoted model the mvt deposits of the central and eastern united states formed as a result of large scale lateral fluid flow driven by the tectonic squeezing of sedimentary successions during the late palaeozoic alleghenian orogeny 330 250 myr 4 here we report the first direct rb sr dating of sphalerites from an mvt deposit and propose this as a useful geochronological technique for sulphide mineralization with poor age control rb sr data for sphalerites from coy mine east tennessee define an isochron age of 377 29 myr ruling out any genetic connection with the alleghenian orogeny instead mvt mineralization in the eastern united states was apparently generated from fluids expelled during thrusting associated with the older acadian orogeny 380 350 myr

flood peak distributions for the eastern united states 1 annual maximum peak discharge time series from 572 stations with a record of at least 75 years in the eastern united states are used to examine flood peak distributions from a regional perspective the central issues of this study are 1 mixtures of flood peak distributions 2 upper tail properties of flood peaks 3 scaling properties of flood peaks 4 spatial heterogeneities of flood peak distributions and 5 temporal nonstationarities of annual flood peaks landfalling tropical cyclones are an important element of flood peak distributions throughout the eastern united states but their relative importance in the mixture of annual flood peaks varies widely and abruptly in space over the region winter spring extratropical systems and warm season thunderstorm systems also introduce distinct flood peak populations with spatially varying control of flood frequency distributions over the eastern united states we examine abrupt changes in the mean and variance of flood peak distributions through change point analyses and temporal trends in the flood peak records through nonparametric tests abrupt changes rather than slowly varying trends are typically responsible for nonstationarities in annual flood peak records in the eastern united states and detected change points are often linked to regulation of river basins trend analyses for the 572 eastern united states gaging stations provide little evidence at this point 2009 for increasing flood peak distributions associated with human induced climate change estimates of the location scale and shape parameters of the generalized extreme value gev distribution provide a framework for examining scaling properties of flood peaks and upper tail properties of flood distributions it is shown that anomalously large values of the gev shape parameter estimates are linked to the role of tropical cyclones in controlling the upper tail of flood distributions scaling analyses of flood peaks highlight the heterogeneities in flood magnitudes over the region with maxima in scaled flood magnitudes in the high elevation appalachian mountains and minima in the low gradient coastal plain

the evolution of convective storms initiated by an isolated mountain ridge abstractthe evolution of convective storms over the black hills an isolated mountain ridge in south dakota and wyoming and a regional convection hotspot is investigated using a 10 yr observational climatology and quasi idealized numerical simulations radar observed diurnally forced mountain convection events are classified according to their maximum cell track length and duration which are quantified using an automated cell tracking algorithm environmental conditions during these events are obtained from operational radiosonde and model analysis data these data suggest that mountain forced convective cells generally struggle to survive in the convectively inhibited flow downwind of the black hills those cells that do survive downwind prefer environments with strong bulk vertical shear over the 0 6 km layer which favors organized multicellular or supercellular convection under slightly weaker shear the cells tend to dissipate rapidly as they propagate downwind relatively weak winds aloft when c

pb isotope evidence for the role of mesozoic basins in the genesis of mississippi valley type mineralization in somerset uk the mendip bristol veinfield is one of a number of british mississippi valley type deposits the genesis of which has never been fully explained the mendip bristol pb zn ba vein mineralization is hosted in carboniferous permo triassic and jurassic sediments the metal sources involved during mineralization were investigated using pb isotope analysis of vein galenas 206 pb 206 pb values range from 18 311 to 18 594 207 pb 204 pb values from 15 601 to 15 688 and 208 pb 204 pb values from 38 257 to 38 565 the data show three isotopically different mineralizing fluids which it is suggested reflect fluid expulsion from adjacent mesozoic sedimentary basins as a result of overpressuring due to rapid subsidence in the triassic jurassic

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes ii tectonic implications from venus abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type commonly have focused on volcanic features of a specific type e g large volcanoes in venus or hot spot volcanism on earth or have concentrated on relatively small regions i e vent distribution within individual volcanic fields but no comparison of extensive databases has been made by using the same tools in both planets in this work the description of the distribution of volcanic features observed over the entire surface of venus is made using the same tool used for earth and is applied to an extensive database the analysis is based on density contours obtained with the fisher kernel as a result several groupings of volcanoes are identified refining the already documented concentration of volcanoes on the bat zone in particular some doughnut like patterns are observed that might be related to the action of mantle plumes the occurrence of such features on earth as well as the existence of a uniform distribution of background volcanism on both planets suggests similarities on their geodynamic behavior that had not been identified previously

nd sr pb isotopic constraints on metal and fluid sources in w sb au mineralization at woxi and liaojiaping western hunan china this paper presents nd sr pb isotope data on scheelite inclusion fluids and residues of gangue quartz and sulfides from the w sb au ore deposits at woxi and liaojiaping ljp in the xuefeng uplift belt xub western hunan china sm and nd concentrations in scheelite from woxi are much lower than in scheelite from ljp and can be distinguished by their high 147sm 144nd ratios of 1 25 from the much lower ratios around 0 26 in scheelites from the ljp end values compared to values at 200 ma which is the average timing of granitoid emplacement during the indosinian yanshanian periods in the xub are around 10 for the ljp and compare well with the range of 5 to 11 defined by the granitoids whereas they are around 27 for scheelite from woxi this might indicate that rees in the mineralizing fluids at ljp originated from granitoids that are concentrated along the southern border of the xub whereas in the case of woxi the original fluids might have been masked by rees released during intense high temperature wall rock alteration of unexposed precambrian basement rocks at depth sr isotopes of scheelite from these two deposits show similar relations to host nearby rocks in that 87sr 86sr t 200 ma ratios of 0 721 for ljp scheelite agree with values ranging between 0 718 0 726 for granitoids whereas these ratios are much higher i e 0 745 for scheelite from woxi and correspond to the 87sr 86sr t 200 ma ratio range of 0 743 0 749 for precambrian host slates crushing experiments to release inclusion fluids from gangue quartz and sulfides deposited during later stages of ore deposition in both deposits failed to provide accurate and geologically meaningful two point fluid residue tie lines in rb sr isochron diagrams however sr released from fluid inclusions generally reveals lower initial 87sr 86sr ratios than the respective residues and shows affinities to 87sr 86sr t 200 ma values of indosinian yanshanian granitoids both at woxi and ljp pb stepwise leaching of scheelite and sulfides did not result in sufficient spreads in pb isotope diagrams and therefore no information regarding exact mineralization ages in the two deposits could be deduced overall ore pb isotopes reveal upper crustal signatures and are compatible with pb isotope signatures of the predominant precambrian slates in the woxi area steep trajectories through late stage quartz sulfide mineralization in pb isotope diagrams may hint at mixing scenarios involving pb from the host rocks and a component with lower 207pb 204pb and 208pb 204pb ratios relative to 206pb 204pb ratios which cannot be linked to any known reservoir in the xub mining district sr isotopes of four out of seven residual sulfide samples from woxi plot along a paleomixing line at an age of 199 8 ma supporting a mixing scenario for the fluids indicated by the pb isotopes and pointing to a possible genetic relationship with the emplacement of indosinian yanshanian granitoids the budgets of rees rb sr and pb in the original fluids were severely affected by contamination of these elements apparently during intense wall rock alteration but after sealing of the major pathways the mineralizing fluids tend to have better preserved their original signatures these attest a genetic relationship between the metallogeny in the xub w sb au province and the emplacement of indosinian yanshanian granitoids during mesozoic intracontinental tectonic uplift and thrusting

hydrothermal fluid origins in a fluorite rich mississippi valley type district combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the south pennine ore field united kingdom the south pennine peak district ore field united kingdom is host to several fluorite rich mississippi valley type deposits and was chosen for study as an analogue to the illinois kentucky fluorspar district united states the study was undertaken to test the idea that the large scale carbonate dissolution and fluorite rich mineralogy characteristic of both districts may require a magmatic source of hf the data also provide constraints for water rock interactions and potential fluid sources relevant to the local geology of the south pennine ore field samples were studied from two of the largest and most economically important deposits within the south pennine ore field the hucklow edge and dirtlow rakes in vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ar ar kr and the halogens cl br i this was achieved simultaneously by noble gas mass spectrometry ar ar methodology and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations in addition he isotope analyses were obtained from unirradiated fluorite the he he ratio of the pennine ore fluids 0 1 ra where ra atmospheric he he ratio of 1 4 10 is significantly lower than the maximum value recorded in the illinois kentucky fluorspar district 0 35 ra kendrick et al 2002 this volume indicating a crustal fluid source and supporting existing basinal brine models the low ar ar ratios with most 50 to 60 percent halite dissolution water br cl mol ratio 0 57 0 92 10 the salinity of fluids included in the main stage of the hucklow edge mineralization avg of 22 wt nacl equiv places an upper limit on the extent of meteoric recharge at 15 vol percent a secondary vein present at hucklow edge has a lower salinity of 40 m y a time scale compatible with models in which fluids were derived from small local basins such as the widmerpool and edale gulfs

the auckland volcanic field new zealand geophysical evidence for structural and spatio temporal relationships abstract geophysical data from the monogenetic auckland volcanic field reveal complex structural and spatio temporal relationships at different scales the volcanic field is coincident with regional magnetic and gravity anomalies that mark a major crustal suture and with a discontinuity marking a significant structural asperity here the linear regional magnetic anomaly splays into a wide band of nnw trending lineaments arising from serpentinised shear zones in the upper crust that matches the extent of the volcanic field and that may reflect a region of crustal weakness creating preferential permeability however there appears to be no simple correlation between the locations of individual vents and these lineaments that might delineate more shallow structural controls with this orientation probably as a consequence of other structural influences high resolution aeromagnetic data over the volcanic field show that the volcanoes have a wide range of magnetic signatures indicating a variability of subsurface structure scoria cone volcanoes typically have strong anomalies up to several 100 nt whilst tuff ring volcanoes typically have weak anomalies less than 50 nt though the surface geology is not always an indicator of the nature and extent of the subsurface deposits both cone and tuff ring volcanoes in the auckland field appear to be underlain by subsurface bowl shaped bodies of basalt implying that their eruption histories commonly involve lava ponding into early excavated craters the present geophysical data give no evidence for subsurface dyke like structures or for substantial near surface volumes of basaltic rocks where there are no known eruption centres or buried flows aeromagnetic and palaeomagnetic data suggest that a number of adjacent vents with an implied structural linkage may be contemporaneous though other examples occur where vents of clearly different ages exploit the same apparent structure a unique feature of the auckland field is that at least 5 widely separated and structurally unrelated volcanoes are contemporaneous these observations highlight the spatial and temporal heterogeneities that can occur in monogenetic fields and have an important bearing on recurrence rates and temporally linked eruptions which are probably more common than is generally supposed and are key factors in statistically based hazard assessments

focusing mechanisms in the texas hill country flash floods of 1978 abstract during the early morning of 2 august 1978 a stationary thunderstorm complex drenched the balcones escarpment of texas and unleashed flash floods in the hill country which killed 27 people and produced extensive damage after the storm an unofficial 24 h total of at 1east 79 cm of rain was observed near the town of bluff about 90 km northwest of san antonio five distinct mechanisms or meteorological features interacted to focus and anchor the storm complex 1 a east west oriented mesohigh outflow boundary was situated just south of the storm area 2 a rapidly moving ribbon of extremely moist boundary layer air was flowing toward the storm are from the southeast 3 an elevated warm dry layer of air extended over the area east of the hill country and capped the southeasterly low level inflow 4 a deep vertical motion field associated with a midtropospheric short wave trough was advancing toward the hill country from mexico and 5 the diurnal heating cycle with its associated production of

paleoflood evidence for a natural upper bound to flood magnitudes in the colorado river basin the existence of an upper limit to the magnitude of floods in a region is a long standing and controversial hypothesis in flood hydrology regional envelope curves encompassing maximum flood magnitudes stabilize with progressive increases in the areal coverage and period of observation wolman and costa 1984 however the short lengths of conventional gaging records limit substantial advances in testing whether this stabilization is evidence of an upper limit in the colorado river basin there are 32 120 station years of gage data but the average period at a gaging station is only 20 years with most stations having less than 70 years of observation paleoflood magnitudes derived from sediments of large prehistoric floods from 25 sites on rivers in arizona and utah provide additional data to extend the records of the largest floods the paleoflood data identify the maximum flood discharges that have occurred on individual rivers over the last several hundred to several thousand years even with this increase in the observational period the largest paleoflood discharges do not exceed the upper bound of maximum peak discharges delineated by the envelope curve derived from the available gaged and historical records this result accords with the hypothesis of an upper physical limit for flood magnitudes and suggests that for the colorado river basin the upper limit can be approximated by existing systematic and historical data for large floods similar relationships also hold when paleofloods and gaged records are presented for the subregion of southern arizona

samarium neodymium direct dating of fluorite mineralization the direct dating of many styles of hydrothermal mineralization has proved difficult limiting understanding of the geological processes that lead to crustal fluid flow and the formation of major ore deposits the hydrothermal mineral fluorite caf2 displays large variations in rare earth element ree abundance and samarium neodymium ratios within a single vein samarium neodymium dating of fluorite from the classic granite hosted tin deposits of southwest england demonstrates its use as a precise chronometer of mineralization the concentrations of light rare earth elements lrees in the fluorites are highly variable and suggest the coeval precipitation of an lree rich phase as the most likely cause of the extreme variation in samarium neodymium ratios

simultaneous inversion of local and teleseismic data for the crust and mantle structure of southern california we determined a detailed three dimensional seismic velocity structure of the crust and mantle to a depth of 800 km beneath southern california using local and teleseismic data simultaneously we used 131 372 p wave arrival times from 6437 local earthquakes and 12 134 travel time residuals from 193 teleseismic events recorded by 251 seismic stations of the caltech us geological survey southern california seismic network compared with previous local and teleseismic studies the station coverage is considerably improved and the number of data used is greatly increased in the present study this together with the local and teleseismic joint inversion approach results in a unified three dimensional 3 d p wave velocity model of the crust and mantle in southern california with a higher resolution than the previous models the result obtained shows very heterogeneous structures in the crust and upper mantle in southern california shallow crustal structures correlate well with surface geological features sedimentary basins such as the los angeles basin ventura basin and santa maria basin are imaged well as low velocities and batholiths such as the peninsular ranges and san gabriel mountains are imaged as high velocities the velocity in the crust is generally low in the mojave desert the crustal velocities change abruptly across major faults such as the san andreas san jacinto elsinore and garlock faults in the upper mantle three major anomalies are found beneath the transverse ranges salton trough and southern sierra nevada the transverse ranges feature appears as a curtain like east trending and north dipping high velocity anomaly with a thickness of approximately 50 km and extends most deeply at its eastern end to about 250 km the salton trough feature is composed of low velocities which trend southeast and extend to approximately 200 km depth the southern sierra nevada feature is a slab like high velocity anomaly which extends to about 250 km the mantle velocity is generally low in the upper 100 200 km beneath the volcanic areas in southern california the seismic velocity anomalies in the mantle beneath southern california are considered to result from small scale mantle convection

airflow within major alpine river valleys under heavy rainfall summary this study documents the aire ow within major alpine river valleys in the presence of precipitation the analysis seeks a conceptual understanding of the effect of rain on the valley e ow ground based and airborne doppler radar and surface data from the mesoscale alpine programme show that during persistent rainy periods the subsidence caused by melting and evaporation of precipitation particles contributes to the formation of a down valley e ow this down valley eow opposes moist southerly e ow aloft which is lifted over the topographic barrier and in which precipitation particles are formed

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

insights into the dynamics of planetary interiors obtained through the study of global distribution of volcanoes i empirical calibration on earth abstract the distribution of volcanic features is ultimately controlled by processes taking place beneath the surface of a planet for this reason characterization of volcano distribution at a global scale can be used to obtain insights concerning dynamic aspects of planetary interiors until present studies of this type have focused on volcanic features of a specific type or have concentrated on relatively small regions in this paper the first of a series of three papers we describe the distribution of volcanic features observed over the entire surface of the earth combining an extensive database of submarine and subaerial volcanoes the analysis is based on spatial density contours obtained with the fisher kernel based on an empirical approach that makes no a priori assumptions concerning the number of modes that should characterize the density distribution of volcanism we identified the most significant modes using those modes as a base the relevant distance for the formation of clusters of volcanoes is constrained to be on the order of 100 to 200 km in addition it is noted that the most significant modes lead to the identification of clusters that outline the most important tectonic margins on earth without the need of making any ad hoc assumptions consequently we suggest that this method has the potential of yielding insights about the probable occurrence of tectonic features within other planets

a numerical study of three catastrophic precipitating events over southern france ii mesoscale triggering and stationarity factors in the western mediterranean basin large amounts of precipitation can accumulate in less than a day when a mesoscale convective system mcs stays over the same area for several hours heavy precipitating events hpes in this region especially southern france are not only characterized by significant precipitation rates typically more than 200 mm in less than 24 or 48 hours but also by quasi stationary behaviour the aim of this present study is to use realistic simulations of past events to analyze and better understand the physical mechanisms which lead to the stationarity of hpes over southern france using a high resolution 2 5 km non hydrostatic mesoscale atmospheric model we focused on three hpes 13 14 october 1995 the cevennes case 12 13 november 1999 the aude case and 8 9 september 2002 the gard case the experimental design for simulating realistic structures and evolutions of the hpes with the meso nh model has been presented in a companion paper in that study the evolution of the synoptic patterns in which the hpes occurred were analysed in this paper the importance of mesoscale ingredients such as the moist and conditionally unstable low level jet llj is examined in terms of their ability to focus the deep convection over the same area for several hours the cevennes case is typical of a so called cevenole event in france for which orographic forcing is the primary mechanism which acts to continuously generate convective cells upwind of the massif central the unusual location of the gard event is explained by a cold pool induced by the evaporation of precipitation which acts as a relief like feature to force the conditionally unstable and moist llj to rise this constitutes a quasi stationary forcing as the cold pool is blocked in the rhone valley for the third case diabatic cooling and the massif central act to enhance the precipitation but have almost no impact on the location of the anchoring point of the precipitating system

a model for calculating eruptive volumes for monogenetic volcanoes implication for the quaternary auckland volcanic field new zealand abstract monogenetic basaltic volcanism is characterised by a complex array of behaviours in the spatial distribution of magma output and also temporal variability in magma flux and eruptive frequency investigating this in detail is hindered by the difficulty in evaluating ages of volcanic events as well as volumes erupted in each volcano eruptive volumes are an important input parameter for volcanic hazard assessment and may control eruptive scenarios especially transitions between explosive and effusive behaviour and the length of eruptions erosion superposition and lack of exposure limit the accuracy of volume determination even for very young volcanoes in this study a systematic volume estimation model is developed and applied to the auckland volcanic field in new zealand in this model a basaltic monogenetic volcano is categorised in six parts subsurface portions of volcanoes such as diatremes beneath phreatomagmatic volcanoes or crater infills are approximated by geometrical considerations based on exposed analogue volcanoes positive volcanic landforms such as scoria spatter cones tephras rings and lava flow were defined by using a light detection and ranging lidar survey based digital surface model dsm finally the distal tephra associated with explosive eruptions was approximated using published relationships that relate original crater size to ejecta volumes considering only those parts with high reliability the overall magma output converted to dense rock equivalent for the post 250 ka active auckland volcanic field in new zealand is a minimum of 1 704 km3 this is made up of 1 329 km3 in lava flows 0 067 km3 in phreatomagmatic crater lava infills 0 090 km3 within tephra tuff rings 0 112 km3 inside crater lava infills and 0 104 km3 within scoria cones using the minimum eruptive volumes the spatial and temporal magma fluxes are estimated at 0 005 km3 km2 and 0 007 km3 ka the temporal volumetric evolution of auckland is characterised by an increasing magma flux in the last 40 ky which is inferred to be triggered by plate tectonics processes e g increased asthenospheric shearing and backarc spreading of underneath the auckland region

samarium neodymium isotope systematics of hydrothermal calcites from the xikuangshan antimony deposit hunan china the potential of calcite as a geochronometer abstract the xikuangshan antimony mine located at central hunan china is the largest antimony deposit in the world hydrothermal calcites from the xikuangshan mine display relatively large variations in ree abundance and sm nd ratios and are characterized by mree and hree enriched and lree depleted patterns sm nd isotopic compositions of syn sulfide calcites fall on well defined lines in the isochron plot calcites from early and late stage mineralization form two distinct isochrons corresponding to 155 5 1 1 and 124 1 3 7 ma respectively the isochron ages suggest that sb mineralization took place during the late jurassic early cretaceous period in the xikuangshan district consistent with previous geological observations and with independent isotope data samarium neodymium dating of calcites shows potential for determining ages of hydrothermal mineralization

detecting short term evolution of etnean scoria cones a lidar based approach the 2001 and 2002 2003 flank eruptions on mount etna italy were characterized by intense explosive activity which led to the formation of two large monogenetic scoria cones one from each eruption on the upper southern flank of the volcano continuous monitoring of etna especially during flank eruptions has provided detailed information on the growth of these cones they differ in genesis shape and size a set of high resolution 1 m digital elevation models dems derived from light detection and ranging lidar data collected during four different surveys 2004 2005 2006 and 2007 has been used to map morphology and to extract the morphometric parameters of the scoria cones by comparing lidar derived dems with a pre eruption 1998 10 m dem the volume of the two scoria cones was calculated for the first time comparison of the lidar derived dems revealed in unprecedented detail morphological changes during scoria cone degradation in particular the morphologically more exposed and structurally weaker 2002 2003 cone was eroded rapidly during the first few years after its emplacement mainly due to gravitational instability of slopes and wind erosion

the transformation of tropical storm agnes into an extratropical cyclone part i the observed fields and vertical motion computations abstract this is the first of two papers dealing with the transformation of tropical storm agnes june 1972 into an extratropical cyclone synoptic analyses and vertical motion patterns are used to describe the behavior of agnes over a five day period subsequent to initial landfall during which time agnes regained tropical storm strength prior to transforming into an extratropical cyclone and dissipating input data for all calculations are obtained from optimum interpolation objective analyses with a resolution of 1 latitude longitude in the horizontal and 100 mb in the vertical a modified 9 level version of krishnamurti s 1968a diagnostic balance model is discussed and applied to the data set to determine the fields of vertical motion redevelopment of agnes subsequent to initial landfall is the result of the spread of an area of appreciable cyclonic vorticity advection aloft over the periphery of the low level circulation devoid of significant baroclinicity unlike a corresponding midlatitude sto

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

climatology of extreme rainfall and flooding from orographic thunderstorm systems in the upper arkansas river basin 1 analyses of the spatial and temporal distribution of extreme rainfall in the arkansas river basin above pueblo colorado are based on volume scan reflectivity observations from the pueblo wsr 88d radar during the period 1995 2003 a storm catalog of 66 rainfall events during the 9 year period has been developed climatological analyses of extreme rainfall are carried out both from an eulerian perspective in which distributional aspects of rainfall at fixed locations are examined and from a lagrangian perspective in which distributional aspects of rainfall are based on storm tracking algorithms of particular interest is the spatial heterogeneity of extreme rainfall in the complex terrain of the upper arkansas river basin lagrangian analyses are used to characterize the spatially varying distribution of storm initiation storm motion and storm structure climatological analyses indicate that convective rainfall in the arkansas river basin above canon city drainage area of 8070 km2 does not contribute to the extreme flood response of the arkansas river at pueblo drainage area of 12 140 km2 there is pronounced diurnal variation in warm season rainfall in the arkansas river basin and this feature of extreme rainfall is a key element of flood response in the upper arkansas river basin climatological analyses of extreme rainfall in the upper arkansas river basin are examined relative to the spatial and temporal properties of rainfall for extreme flood events that have occurred in the basin including major flood episodes in june 1921 and june 1965

the global population of mesoscale convective complexes a global set of 714 mesoscale convective complexes is compiled and some of the common properties of the convective systems are identified and examined from a global perspective the data set includes date of occurrence time of first storms initiation maximum extent termination duration cold cloud shield areas and tracks from initiation to termination it is found that the typical convective complex is nocturnal generates a cold cloud shield area of approximately 350 000 km2 and persists for about 10 h the largest systems and most persistent systems tend to occur near the summer solstices for the globe about 400 systems occur each year primarily over land areas most systems develop in favoured zones although some activity occurs over every continent except antarctica and all major oceans the concentration of activity into favoured zones indicates that there must be special dynamic and or thermodynamic conditions necessary for convection to organize into convective complexes activity is strongly tied to the solar day and shifts from 35 s in early january to about 50 n during the boreal summer and back to 35 s by december within the northern hemisphere there is a pronounced poleward migration as the jet stream shifts northward relatively little migration occurs in the ocean dominated southern hemisphere where the subtropical jet remains quasi stationary over the convective complex regions the nocturnal life cycles copious rainfall large cloud shields and great frequency of mesoscale convective complexes suggest that they may be significant contributors to the global hydrologic cycle and earth system energy budget

sm nd evidence for the age and origin of a mississippi valley type ore deposit mississippi valley type mvt ore deposits represent the relatively common product of large scale fluid transport in the continental lithosphere yet the models for their genesis have been more controversial and unconstrained than those of any other class of giant ore deposit1 2 here we show that sm nd isotope data can be used to determine the age and origin of an mvt deposit sm nd data for fluorites from the north pennine orefield are difficult to explain unless some of the mineralization is of mesozoic rather than the traditionally accepted palaeozoic age furthermore the nd and sr isotopie compositions of the fluorites do not support a variety of recent models that include derivation of the components from the mantle the lower palaeozoic basement or the underlying buried granite which served to focus the flow of hydrothermal fluids

on the stationarity of annual flood peaks in the continental united states during the 20th century 1 annual peak discharge records from 50 stations in the continental united states with at least 100 years of record are used to investigate stationarity of flood peaks during the 20th century we examine temporal trends in flood peaks and abrupt changes in the mean and or variance of flood peak distributions change point analysis for detecting abrupt changes in flood distributions is performed using the nonparametric pettitt test two nonparametric mann kendall and spearman tests and one parametric pearson test are used to detect the presence of temporal trends generalized additive models for location scale and shape gamlss are also used to parametrically model the annual peak data exploiting their flexibility to account for abrupt changes and temporal trends in the parameters of the distribution functions additionally the presence of long term persistence is investigated through estimation of the hurst exponent and an alternative interpretation of the results in terms of long term persistence is provided many of the drainage basins represented in this study have been affected by regulation through systems of reservoirs and all of the drainage basins have experienced significant land use changes during the 20th century despite the profound changes that have occurred to drainage basins throughout the continental united states and the recognition that elements of the hydrologic cycle are being altered by human induced climate change it is easier to proclaim the demise of stationarity of flood peaks than to prove it through analyses of annual flood peak data

pb isotope evidence on the origin of the west shropsh orefield england pb isotope data on ore galenas from the west shropshire orefield show a significant spread of 20 pb 204 pb values with minor variation in 207pb 204 pb and 208pb 204 pb ratios these indicate that lead was derived from multiple sources some of them uranium enriched and incompletely mixed prior to ore deposition four possible mineralizing agents are considered circulating sea water metamorphic waters basinal brines and convecting formation waters pb isotope data exclude a circulating sea water origin for the mineralization and best support a convecting formation water mineralizing agent a model involving a single fluid tapping multiple lead sources is proposed to explain the observed pb isotope variation

observations and mixed layer modeling of a terrain induced mesoscale gyre the denver cyclone abstract in northeastern colorado a frequently observed feature of the surface wind field is a stationary terrain induced mesoscale gyre which is often associated with the formation of severe weather because of the gyre s proximity to the denver metropolitan area local weather forecasters frequently refer to it as the denver cyclone the development of one such cyclone which occurred on 1 august 1985 is documented with mesonet radiosonde wind profiler radiometer and tower data mixed layer model simulations of this event closely agree with the observed gyre structure and indicate that the gyre is associated with a plume of warmer potential temperature air which originates from a ridge of higher terrain to the south of denver and advects northward into the area of gyre formation a mixed layer vorticity budget demonstrates that the formation of the gyre results from the baroclinic and slope effects on the turbulent stress divergence profile

elliptical boundary of an intraplate volcanic field auckland new zealand abstract the outer vents in the auckland volcanic field lie within 19 to 559 m mean 224 75 m of a best fit ellipse with a 28 9 km long major axis trending almost north south and a minor axis 16 5 km long the ellipse has formed the outer boundary of the field since the inception of volcanism 140 000 years ago we present the following testable hypotheses as an explanation of this pattern the boundary is the expression of a corresponding elliptical source area at depth in the lithospheric mantle possibly asthenosphere material trapped at this level the ellipse may represent a depth contour on a very small upper mantle dome or of a lens intruding into a neck of an extensional structure alternatively it could be the boundary of a flat elliptical area where tensional stresses allow decompressional melting the elliptical tensional region may either have developed in a releasing bend during strike slip faulting along a fundamental lithosphere structure inherited from mesozoic tectonics associated with the nnw trending dun mountain ophiolite belt or may represent the tip of a fracture along which the auckland volcanic province is propagating northward

shallow seated explosions in the construction of the motukorea tuff ring auckland new zealand evidence from lithic and sedimentary characteristics at least 52 eruption centres are scattered within the 360 km2 auckland volcanic field avf motukorea now an island in the waitemata harbour is one of 39 avf volcanoes that experienced a phreatomagmatic explosive phase before a magmatic phase the volcano erupted through a 200 300 m thick consolidated mudstone sandstone sequence of the miocene waitemata group which overlies the waipapa terrane greywacke basement detailed field descriptions of the sedimentary characteristics of the early phreatomagmatic deposits were carried out along with examination of lithics the ejecta ring deposit comprises 55 to 60 vol lithics of which waitemata group fragments constitute approximately 90 vol whereas 10 vol are waipapa fragments suggesting a dominance of shallow fragmentation the sedimentary characteristics of the stratigraphic sequence at motukorea suggest a dominance of wet surges at the beginning of the eruption with progression into drier sequences upwards this is reflected in increasing inter bedded juvenile pyroclast dominated fall deposits up sequence these characteristics are attributed to the changing hydrogeological conditions within the diatreme and the host rocks these findings shed light on the eruption dynamics of phreatomagmatic eruptions through consolidated rocks in the avf and enable the depiction of a scenario of future eruptions within the field in similar substrates

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

quaternary deposits and landscape evolution of the central blue ridge of virginia abstract a catastrophic storm that struck the central virginia blue ridge mountains in june 1995 delivered over 775 mm 30 5 in of rain in 16 h the deluge triggered more than 1000 slope failures and stream channels and debris fans were deeply incised exposing the stratigraphy of earlier mass movement and fluvial deposits the synthesis of data obtained from detailed pollen studies and 39 radiometrically dated surficial deposits in the rapidan basin gives new insights into quaternary climatic change and landscape evolution of the central blue ridge mountains the oldest depositional landforms in the study area are fluvial terraces their deposits have weathering characteristics similar to both early pleistocene and late tertiary terrace surfaces located near the fall zone of virginia terraces of similar ages are also present in nearby basins and suggest regional incision of streams in the area since early pleistocene late tertiary time the oldest debris flow deposits in the study area are much older than wisconsinan glaciation as indicated by 2 5yr colors thick argillic horizons and fully disintegrated granitic cobbles radiocarbon dating indicates that debris flow activity since 25 000 ybp has recurred on average at least every 2500 years the presence of stratified slope deposits emplaced from 27 410 through 15 800 ybp indicates hillslope stripping and reduced vegetation cover on upland slopes during the wisconsinan glacial maximum regolith generated from mechanical weathering during the pleistocene collected in low order stream channels and was episodically delivered to the valley floor by debris flows debris fans prograded onto flood plains during the late pleistocene but have been incised by holocene stream entrenchment the fan incision allows holocene debris flows to largely bypass many of the higher elevation debris fan surfaces and deposit onto the topographically lower surfaces these episodic high magnitude storm events are responsible for transporting approximately half of the sediment from high gradient low order drainage basins to debris fans and flood plains

geochronological isotopic and mineral geochemical constraints on the genesis of the diyanqinamu mo deposit inner mongolia china abstract the diyanqinamu mo deposit located in central inner mongolia in china is a newly discovered mo deposit due to the lack of detailed deposit scale studies the metallogenesis of the deposit has been a matter of debate in this study petrography zircon u pb geochronology sr nd and pb isotopes and apatite mineral geochemistry have been used to constrain the genesis of the diyanqinamu mo deposit petrographic evidence indicates that the granites in the diyanqinamu deposit have experienced fluid exsolution as demonstrated by the corroded quartz in the porphyritic granites skeletal quartz in the aplitic granites and the unidirectional solidification texture ust in the apex of the aplitic granites sr and nd isotopic data of the purple fluorite from the fluorite molybdenite veins showing the 87sr 86sr i 0 7046 0 7052 avg 0 7048 and end t values 2 4 3 8 avg 3 3 are similar to those of the porphyritic and aplitic granites this similarity implies that the mo ore forming fluids may have been derived from the granitic magmas the hypothesis is further supported by the fluorine content 3 79 5 48 wt avg 4 53 wt in apatite from the porphyritic granites and the widely distributed fluorite in the hydrothermal alteration mineral assemblages which indicate that the porphyritic granites contain high f content and the hydrothermal fluids are also f rich petrographic observation also shows that magnetite occurs commonly in the hydrothermal mineral assemblages indicating that the hydrothermal fluids are characterized by high oxygen fugacity fo2 it is important to note that the intruding granites are essentially barren and the mo is mainly hosted in the andesite and volcaniclastic rocks in comparison pb isotopic compositions of molybdenite are similar to those of both the andesite and k feldspar from the porphyritic granites which suggests that both the intruding granites and ore hosting andesite have contributed to the ore forming materials this hypothesis is further supported by the abnormally high mo for the andesite our new evidence suggests that the diyanqinamu mo deposit may have formed in a post collisional extensional environment ore forming materials may have been derived mainly from the granites and minimally from the host rocks the ore fluids are characterized by high fo2 and being f rich and the trigger for the mo mineralization has been attributed to the reduction of fo2 and or temperature for the ore fluids

geology geochronology and geochemistry of the dabate cu mo deposit northern chinese tien shan implications for spatial separation of copper and molybdenum mineralization abstract the dabate deposit is a porphyry cu mo deposit located in the sailimu block northern chinese tien shan the deposit shows a clear separation of cu and mo mineralization with cu mineralization occurring along the edge of the rhyolitic porphyry and mo mineralization in the inner part of the rhyolitic porphyry sm nd isotopic analyses of six fluorite samples from the cu sulfides fluorite veins yield an isochron age of 298 1 5 0 ma and re os isotopic analyses of four molybdenite samples from the molybdenite quartz veins yield an isochron age of 299 6 3 2 ma these geochronological data and accompanying geologic evidence indicate that the cu and mo mineralization belongs to the same hydrothermal system and are closely related to the rhyolitic porphyry which has a youngest zircon 206pb 238u age of 297 3 8 0 ma rare earth element ree and fluid inclusion studies were carried out for fluorite in the cu ores the fluorite related to cu mineralization have high ree 63 4 216 9 ppm and show generally similar ree patterns with the rhyolitic porphyry suggesting that the fluid of cu mineralization is closely related to the rhyolitic porphyry the slight lree depletion and ce depletion of fluorite relative to the rhyolitic porphyry may be due to preferential partitioning of hree into the fluid in neutral to weak alkaline conditions and to mixing with meteoric water which is characterized by ce depletion three types of fluid inclusions were recognized in the fluorite from the cu sulfides fluorite veins liquid vapor lv type co2 bearing c type and solid mineral bearing s type the lv type inclusions have homogenization vapor to liquid temperatures from 175 to 328 c and salinities of 0 4 14 9 wt nacl eqv mode at 0 8 wt nacl eqv and is of h2o nacl composition the c type inclusions have homogenization vapor to liquid temperatures from 206 to 279 c and salinities of 1 6 8 5 wt nacl eqv and is of h2o co2 nacl ch4 composition the s type inclusions have partial homogenization vapor to liquid temperatures of 173 233 c and salinities of 1 2 7 9 wt nacl eqv and is of h2o nacl composition the solid particle in s type inclusions did not change during heating up to 550 c indicating that the solid is not daughter mineral and the s type inclusions are actually the same as the lv type inclusions the lv type inclusions have microthermometric attributes similar to those typically found in the late stages of porphyry deposits whereas the c type inclusions have similar compositions as the inclusions in the mo ores as documented in previous studies at dabate the presence of both lv type and c type inclusions suggests that the cu mineralization may be related to mixing between meteoric water and magmatic fluids as is also indicated by the ree of fluorite comparing with data from mo ores reported in previous studies it is suggested that the mo stage fluids were more reduced and acidic and mo mineralization may be mainly related to fluid pressure decrease and immiscibility whereas the cu stage fluids were more oxidized neutral to weakly alkaline and cu mineralization may be mainly controlled by mixing and cooling the vapor phase produced by fluid immiscibility in the deep area may have carried cu as ag hf co2 and migrated to the outer part of the porphyry precipitated cu sulfides arsenopyrite and fluorite by mixing with meteoric water from the country rocks whereas the liquid phase produced by fluid immiscibility at depth may have carried mo nacl and migrated to the middle west part of the rhyolitic porphyry become immiscible and precipitated molybdenite

phreatomagmatic eruptions through unconsolidated coastal plain sequences maungataketake auckland volcanic field new zealand abstract maungataketake is a monogenetic basaltic volcano formed at 85 89 ka in the southern part of the auckland volcanic field avf new zealand it comprises a basal 1100 m diameter tuff ring with a central scoria spatter cone and lava flows the tuff ring was formed under hydrogeological and geographic conditions very similar to the present the tuff records numerous density stratified wet base surges that radiated outward up to 1 km decelerating rapidly and becoming less turbulent with distance the pyroclastic units dominantly comprise fine grained expelled grains from various sedimentary deposits beneath the volcano mixed with a minor component of juvenile pyroclasts 35 vol subtle lateral changes relate to deceleration with distance and vertical transformations are minor pointing to stable explosion depths and conditions with gradual transitions between units and no evidence for eruptive pauses this volcano formed within and on 60 m thick plio pleistocene poorly consolidated highly permeable shelly sands and silts kaawa formation capped by near impermeable water saturated muds tauranga group these sediments rest on moderately consolidated miocene aged permeable turbiditic sandstones and siltstones waitemata group magma water fuelled thermohydraulic explosions remained in the shallow sedimentary layers excavating fine grained sediments without brittle fragmentation required on the whole the resulting cool wet pyroclastic density currents were of low energy the unconsolidated shallow sediments deformed to accommodate rapidly rising magma leading to development of complex sill like bodies and a range of magma water contact conditions at any time the weak saturated sediments were also readily liquefied to provide an enduring supply of water and fine sediment to the explosion loci changes in magma flux and or subsequent stabilisation of the conduit area by a lava ring barrier led to ensuing strombolian and fire fountaining eruption phases future eruptions in littoral environments around auckland are likely to be of this type producing base surges that rapidly decrease in energy over short runout distances 1 km

initial isotopic heterogeneity and secondary disturbance of the smnd system in fluorites and fluid inclusions a study on mesothermal veins from the central and western swiss alps abstract this paper presents sm nd data on hydrothermal fluorites fluid inclusions and leach experiments on samples from the mont blanc and gotthard units swiss alps both areas have experienced alpine greenschist facies overprint 350 and 450 c respectively mont blanc samples represent late variscan fluorites from three individual veins whereas gotthard samples were taken from one hand specimen of probable late variscan age nd concentrations of fluorites range from 3 6 to 23 ppm 147 sm 144 nd ratios from 0 12 to 0 35 none of the samples sets yielded an isochron relationship imperfect correlations indicate apparent ages between late variscan and alpine reflecting neither the formation nor the age of metamorphic overprint reasons are wall rock influence during formation and post formation disturbance secondary fluorite gotthard shows the highest nd concentration and a low sm nd ratio close to that of fluid inclusion fractions a leach experiment showed the same trend even more pronounced 7 of nd and 2 of sm were removed from fluorite by 0 18 n hcl at 100 c hence secondary fluids are likely to leach and fractionate sm and nd and may easily cause dissolution and reprecipitation of fluorite consequently the system is highly suspicious if secondary fluid flow cannot totally be ruled out this is in sharp contrast to previously published conclusions however evidence for rejuvenation of the sm nd system in fluorites is also found in published data sets

aeromagnetic imaging of the dun mountain ophiolite belt in northern new zealand insight into the fine structure of a major sw pacific terrane suture a new aeromagnetic survey of the junction magnetic anomaly in northern new zealand reveals that it is associated with up to 10 subparallel lineaments the junction magnetic anomaly delineates the dun mountain ophiolite belt a remarkably linear though sigmoidally bent major boundary zone traceable through most of new zealand which separates terranes sutured onto the new zealand gondwana margin in late mesozoic time modelling of the lineaments in conjunction with a new review of structures along the dun mountain ophiolite belt throughout new zealand indicates that the dun mountain ophiolite belt in auckland consists of a number of imbricate slices most of which are likely to dip steeply to the east i e overturned away from the former trench and extend to considerable depth in the crust the source bodies for the central high amplitude magnetic lineaments are interpreted to be serpentinite shear or melange zones cutting a large lensoid body of ultramafic rocks similar to those occurring elsewhere along the length of the dun mountain ophiolite belt our data have revealed that a formerly postulated offset of the dun mountain ophiolite belt in the region instead resembles a duplex or thrust imbricate like bundling of shear zones these shear zones were probably initiated as accretion thrusts but complexities in their pattern indicate subsequent shearing including backfolding to an overturned attitude and possibly strike slip to produce the linear nature of the dun mountain ophiolite belt the outer lineaments mostly mark accretion thrusts in the adjacent terranes this study demonstrates that detailed aeromagnetic surveys can delineate the fine structure in ophiolite complexes and thereby give valuable insights into the effects of micro continental collision on an accretionary margin

hydraulics and basin morphometry of the largest flash floods in the conterminous united states abstract the maximum rainfall runoff floods measured by indirect methods in small basins 0 39 370 km2 in the conterminous united states are examined this analysis identified twelve floods that were the largest ever measured these floods all occurred in semiarid to arid areas for eleven of the twelve largest rainfall runoff floods measured in small basins by the slope area method values of hydraulic depth hydraulic radius width depth ratio n value mean velocity velocity head coefficient froude number water surface energy and channel slopes shear stress and unit stream power are tabulated estimated composite n values weighted by subsection conveyance range from 0 028 to 0 048 with a mean of 0 038 mean velocities ranged from 3 47 to 9 97 m s 1 froude numbers ranged from 0 81 to 2 49 with 9 of 12 floods having values greater than 1 00 water surface energy and channel slopes vary considerably for each flood energy slope always was less than water surface slope by values of 1 104 channel slope was greater than energy slope in eight floods shear stresses ranged between 61 and 855 n m 2 and unit stream power from 212 to 8131 w m 1 floods in these small basins produced shear stresses and unit stream powers several hundred times greater than floods in large rivers floods on other small streams with smaller unit discharges produced greater shear stresses and stream powers this indicates that the force of a flood is controlled by the depth slope product not absolute discharge in the twelve watersheds studied basin relief ranged from 165 to 1280 m elongation ratios ranged from 0 55 to 0 80 the number of first order streams basin magnitude ranged from 10 to 4297 drainage density ranged from 4 1 to 10 9 km km 2 basin slope ranged from 0 0043 to 0 2486 relief ratio ranged from 0 0097 to 0 34 ruggedness number ranged from 0 69 to 7 17 and first order channel frequency ranged from 5 1 to 38 6 km 2 elongation ratios were larger and drainage density and first order channel frequency lower than other small flash flood prone basins in the united states these twelve basins have neither the most favorable morphometric characteristics which contribute to flash flood peaks nor did the storms causing these flash floods have the greatest short duration intensities maximum flood peaks originate from an optimal combination of basin morphology and physiography and storm intensity

calcite sm nd isochron age of the shuiyindong carlin type gold deposit guizhou china abstract shuiyindong is one of the largest and highest grade stratabound carlin type gold deposits in china it is hosted in permian bioclastic limestone near the axis of an anticline hydrothermal calcite is common on the periphery of central zones of ferroan carbonate dissolution that provided the main source of iron that was sulfidized during gold deposition these calcite veins contain relatively high concentrations of rare earth elements with mree enriched patterns and yield sm nd isochron ages of 134 3 ma to 136 3 ma with significant different initial end values of 12 9 and 2 0 respectively these ages are interpreted to record age of decarbonation and gold deposition during the late stages of yanshanian orogeny the initial nd isotopic compositions of the calcites suggest that nd was primarily derived from the permian longtang formation that hosts all ore bodies at the deposit this study shows that sm nd isotopic compositions of hydrothermal calcites can be used to constrain the age and source of nd in carlin type gold deposits

spatial distribution and alignments of volcanic centers clues to the formation of monogenetic volcanic fields monogenetic basaltic volcanic fields occur worldwide in tectonic environments ranging from extensional to convergent understanding similarities and differences between these fields may help to characterize key controls on their generation such volcanic fields consist of numerous volcanic centers each of which represents a pathway of magma from its source to the surface we analyzed the spatial distribution of volcanic centers in 37 monogenetic volcanic fields and assuming that the distribution of volcanic centers relative to each other is matched by a similar source pattern within the mantle applied the following methods for each 1 the poisson nearest neighbor pnn analysis representing the degree to which the distribution of the volcanic centers departs from a predicted poisson distribution and 2 a volcanic alignment analysis to ascertain the preferential pathways if any used by the magma to reach the surface this is the first comprehensive global comparison of such analyses magma pathways within the brittle upper crust are influenced to various degrees by two end member situations 1 formation of new extension fractures perpendicular to the least compressive stress 3 and 2 re activation of pre existing fractures that are near parallel to the maximum principal stress 1 the results of the pnn analysis show that independently of the tectonic environment most volcanic fields display a clustered distribution of their volcanic centers alignment analysis shows that either the ambient tectonic environment exerts a strong influence on the preferential orientations of the volcanic alignments or that it is in competition with other factors e g pre existing structures local stress changes due to older intrusions overall these results indicate that the propagation of the magma and therefore the spatial distribution of the volcanic centers within volcanic fields is the product of an interplay between deep level influences i e nature of the magma source and shallow level influences i e stress field pre existing crustal structures of the lithosphere