estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

geologic and geochemical relationships between the contact sublayer inclusions and the main mass of the sudbury igneous complex a case study of the whistle mine embayment more than half of the giant ni cu platinum group element pge sulfide ores of the sudbury igneous complex are associated with a discontinuous unit at the base of the main mass known as the sublayer the sublayer is comprised of two fragment rich members 1 a metamorphic textured footwall breccia and 2 an igneous textured contact sublayer the contact sublayer occurs as a thick unit in depressions at the base of the sudbury igneous complex termed embayments it is associated with disseminated to massive sulfides and contains a range of inclusion types such as diabase melanorite olivine melanorite metamorphosed melanorite wehrlite and dunite we present data for a case study of the whistle mine embayment and show that the igneous textured sublayer matrix is geochemically unlike the main mass norites quartz gabbros and granophyres for example the igneous textured sublayer matrix in the whistle mine has la sm 4 0 la nb 5 1 and th zr 0 02 and the main mass norites quartz gabbros and granophyres have ratios of 5 5 to 7 2 8 to 4 2 and 0 04 to 0 05 respectively this matrix contains partially digested hornfels diabase fragments and ghost textures of magnetite remaining from the melting of diabase the igneous textured sublayer matrix at the whistle mine can be modeled with small amounts of assimilation of local country rock granitoids approximately 10 large degrees of assimilation of diabase that are not derived from the immediate country rocks approximately 70 and small contributions from the main mass magma type approximately 20 mafic norite the amount of diabase assimilation would be too large for traditional assimilation models controlled by the available heat of the mafic magma even with a superheated magma 70 percent assimilation is too large a model is proposed where the melting of the target rocks initially produces a felsic melt sheet which is laden with mafic fragments these fragments sink to the base of the melt sheet in the crater and are concentrated and further melted to produce the mafic sublayer there are significant differences in the composition of the igneous textured sublayer matrix between different embayments which may reflect differing degrees of digestion of compositionally different protolith fragments the melanorite inclusions in the sublayer at the whistle mine have ratios of the incompatible trace elements essentially similar to those of the inclusions in the igneous textured sublayer matrix but they have similar high incompatible element concentrations e g olivine melanorites have 20 65 ppm ce in rocks with 15 21 wt mgo 1 to 10 percent interstitial sulfide up to 0 5 percent apatite 1 to 15 percent biotite and 1 85 ga age zircon and baddeleyite the mafic ultramafic inclusions are interpreted to be the broken up remnants of an earlier cumulate formed at depth from a main mass magma this parental magma has compositional traits which suggest that crystal accumulation took place from a magma which contains a large contribution from the diabase olivine compositional data for the mafic inclusions fo sub 71 79 500 3 800 ppm ni in the absence of reequilibration indicate that olivine crystallization both predated and postdated sulfur saturation of the magma cr rich spinels from these rocks confirm that the parental magma was especially cr rich and based on the olivine compositional data had a tholeiitic mg fe ratio

origin and formation of metabreccia in the parkin offset dike sudbury impact structure canada the 1 85 ga sudbury impact structure is considered a remnant of a peak ring or multi ring basin with an estimated original diameter of 150 to 200 km the offset dikes are radial and concentric dike

distribution of groundwater seepage to large surface water bodies the effect of hydraulic heterogeneities abstract at 26 sites on the upper great lakes and their connecting channels where groundwater seepage measurements have been made seepages decrease continually offshore at only seven 26 instead 17 63 of the sites have offshore seepages which substantially exceed those at some locations closer to shore the distributions fall into two consistent patterns one where a nearshore decrease in seepage with increasing distance is succeeded offshore by an increase and a second where nearshore seepages are relatively constant and then increase farther offshore the patterns have been observed in two independent studies using two totally different seepage meter designs and emplacement methods and are attributed to hydrogeologic heterogeneities beneath the surface water body detailed marine geophysical measurements at seven sites on green bay show that the anomalously high offshore seepages there are associated with local thinning of the relatively low hydraulic conductivity glacial sediments separating the bay from the underlying aquifer a fractured dolomite at these locations heterogeneity in sediment thickness is a stronger factor in causing seepage anomalies than is heterogeneity of either sediment or bedrock hydraulic conductivity insufficient information exists to confirm a parallel cause effect relation at the other sites but evidence points in that direction similar seepage anomalies have been observed at other smaller lakes by other researchers but never with this frequency it is argued that the cause of the difference is the size of the great lakes seepage occurs and measurements have been made over much greater offshore distances than in smaller lakes and the likelihood that heterogeneities will occur within the zone of measurement is thus also much greater

pore pressures and permeabilities measured in marine sediments with a tethered probe a new probe for measuring pore fluid pressures in marine sediments has been constructed and tested in two hydrologic environments on the juan de fuca ridge the instrument utilizes a highly incompliant high sensitivity differential pressure transducer and a small 4mm diameter sensing probe that telescopes within a larger diameter 1 5 m long currently 2 5 m strength member the small probe diameter and the low compliancy serve to minimize the time required for pressures to approach equilibrium after penetration observed decay times are short enough to permit the instrument to be used in a tethered mode the mechanical configuration enables the small diameter probe to penetrate the sediments without buckling and to be pulled out without bending this allows multiple penetrations to be completed during a single instrument lowering ten measurements were made during the development and testing of the instrument in fine grained turbidite sediments on the juan de fuca ridge four penetrations were uninterrupted by mechanical disturbances or instrumentational problems and although equilibrium conditions were approached during only one penetration 2 7 hours maximum undisturbed decay period all provided useful constraints on equilibrium pore pressures values at two sites where sediment cover is thick and heat flow relatively low were unresolvably different from hydrostatic values estimated from two penetrations located within a few hundred meters of a hydrothermal vent field within the sedimented axial valley of the northern juan de fuca ridge middle valley exceeded hydrostatic and yielded pressure gradients of roughly 0 5 kpa m 1 permeabilities were estimated from the rates of decay of the penetration transients values ranged from 5 10 16 to 1 10 14 m2 and agreed well with values measured on core samples collected near the probe penetrations which ranged from 8 10 16 to 1 10 14 m2 using the values determined from the probe measurements from middle valley the implied rate of fluid flow upward through the sediments in the vicinity of the vent field is roughly 5 10 10 m s 1 or 15 mm yr 1 with the current practical limit of resolution of roughly 10 10 m s 1 3 mm yr 1 this direct measurement technique provides a means of determining pore fluid flow rates that is roughly 1 order of magnitude more sensitive than the method of estimating the rate of flow from the perturbation of the conductive thermal regime measured by typical marine heat flow instruments

effect of anisotropy and groundwater system geometry on seepage through lakebeds 1 analog and dimensional analysis abstract distribution of seepage through lakebeds is controlled partly by geometric configuration of the lake and of the groundwater system interacting with the lake to evaluate the effect of these factors conductive paper electric analog models were used to analyze a number of lake and groundwater settings having different geometric configurations most settings analyzed are of lakes that do not penetrate the groundwater system the width ratio the ratio of half the lake width to thickness of the groundwater system is the principal geometric characteristic used in this study because the distribution of groundwater seepage into a lake is not uniform across the lakebed the concept of a streamlinecrowding factor is developed and is used to determine seepage patterns from geometric characteristics of the lake and its contiguous groundwater system analysis of fourteen different width ratios of lake and groundwater systems indicates that lakes can be defined by three general groups of seepage patterns which include flow patterns volumes and rates 1 lakes having width ratios less than 0 6 show relatively uniform distribution of seepage across the lakebed 2 lakes having width ratios of 0 6 to 2 0 change in absolute and relative streamline crowding in the near shore region and 3 lakes having width ratios greater than 2 0 show stable flow patterns near shore however with increasing lake width the relative streamline crowding increases relative to that width for deep lakes and those in anisotropic media the crowding effect is decreased resulting in more uniform seepage across the lakebed

the isotopic and hydrologic response of small closed basin lakes to climate forcing from predictive models application to paleoclimate studies in the upper columbia river basin simulations conducted using a coupled lake catchment hydrologic and isotope mass balance model indicate that small closed basin lakes in north central washington are isotopically sensitive to changes in precipitation relative humidity and temperature most notably model simulations predicted inconsistent lake responses to precipitation changes due to differences in lake outseepage rates and surface area to volume sa v ratios greater outseepage within model experiments resulted in increased sensitivity to changes in mean precipitation moreover simulations suggest that in lakes with appreciable outseepage sa v ratio changes resulting from lake level variations control the direction of changes in lake water oxygen isotope composition 18o specifically in lakes with a sa v ratio that increases at higher lake levels steady state 18o values will increase in response to greater long term average precipitation these results suggest that closed basin lakes with low outseepage rates will exhibit a transient isotopic response to stochastic variability in hydrologic forcing but will not strongly respond at steady state to variation in mean hydrologic conditions conversely closed basin lakes with appreciable outseepage will exhibit strong isotopic responses to both stochastic variability and variation in mean hydrologic conditions i e mean precipitation relative humidity and temperature control of catchment hydrologic inputs to the lake these relationships provide a mechanism for explaining inconsistencies in the isotopic responses of lakes within a given region to hydrologic forcing and demonstrate that semiquantitative models for describing the relationship between lake hydrologic and isotopic responses to climate variability are not appropriate for all closed basin lakes

the nature age and petrogenesis of the cartier batholith northern flank of the sudbury structure ontario canada abstract the cartier batholith exposed about 50 km northwest of sudbury ontario canada is a late archean k rich granitic batholith along with the levack gneiss complex it forms the footwall of the north range of the sudbury igneous complex the cartier batholith dominantly monzogranitic to granodioritic is relatively homogeneous unfoliated and contains k feldspar megacrysts it shows several distinctive chemical features including high concentrations of zr th u and lree and low concentrations of nb ti and hree several discriminants suggest a post orogenic tectonic environment for the batholith this inference is consistent with a u pb age of 2642 1 ma obtained on zircon only slightly younger than the inferred timing of high grade metamorphism of the levack gneiss complex the cartier batholith could have formed as a result of approximately 33 partial melting of the levack gneiss complex

heat flow variations correlated with buried basement topography on the juan de fuca ridge flank systematic heat flow variations are commonly observed on sedimented flanks of mid ocean ridges these variations have been attributed to the convective circulation of pore fluids within the oceanic crust and have been used to estimate the scale and pattern of this circulation here we report similar systematic variations observed in a detailed heat flow and seismic reflection survey over sediment covered 3 myr old sea floor on the eastern flank of the juan de fuca ridge we find that heat flow peaks are located above buried basement ridges and adjacent to two minor basement outcrops heat flow lows are found where thick sediments fill basement valleys the simple inverse relationship between heat flow and sediment thickness defined by the data indicates that hydrothermal circulation sealed within the permeable portion of the oceanic crust is vigorous enough to maintain approximately isothermal 10 k conditions at the sediment crust interface as no systematic variations in estimated basement temperatures are observed it seems that at this location the heat flow variations result only from sediment thickness variations and do not reflect a particular convective pattern

geochemical relationships in the sudbury igneous complex origin of the main mass and offset dikes petrological models relating the different rock types constituting the 1 85 ga sudbury igneous complex are constrained with extensive new geochemical data we show that the main mass felsic norite transition zone quartz gabbro and granophyre have similar ratios of the highly incompatible trace elements e g la sm 4 5 7 la nb 2 8 4 2 th zr 0 04 0 05 and that these variations are consistent with the crystallization and differentiation of magma types largely 80 derived from the upper crust with a smaller contribution from a mantle source although there is presently no conclusive proof that magma was generated in situ as a melt sheet produced by meteorite impact we find no principal reason why this model should be rejected however we propose that a small contribution of mantle derived picritic magma is required to explain the abundant ni cu and platinum group elements pge in the sudbury deposits as well as the compositions of the ultramafic inclusions mgo 12 36 wt fo sub 68 87 olivines with 450 3 700 ppm ni and abundant chrome rich spinel and the magnesian composition of the mafic norite 8 14 wt mgo and the sublayer 6 12 wt mgo we believe that the main mass of the sudbury complex achieved its present composition through incorporation of up to 20 percent mantle derived picritic magma emplaced along crustal fractures produced by the impact event these picritic magmas entered the melt sheet as a dense plume vigorously mixing with it and due to the marked compositional shift the mixed magma formed magmatic sulfides which sank through the magma column depleting the melt in ni cu and pge since both the felsic norite and granophyre have indistinguishable ratios of the incompatible trace elements we see no requirement to derive these units of rock by the crystallization of magmas derived from different sources rather the compositional difference between the felsic norite and granophyre is attributed to the in situ differentiation of the magma we show that the main mass has many compositional traits similar to those of most of the offset dike quartz diorites e g the parkin offset dike la sm 6 3 la nb 4 5 th zr 0 05 and of embayment related leucocratic norites from the whistle mine la sm 6 2 la nb 5 0 th zr 0 02 these rocks have compositions intermediate between the felsic norite and the granophyre and therefore crystallized from the same magma type arguably the unmineralized quartz diorites provide the best possible estimate of the original magma from which the sudbury complex crystallized in detail there are subtle variations in composition within and between offset dikes with the largest difference being between the north and south range offsets the north range offset dikes cut archean granitoids and gneisses and have elevated sr la yb la sm and gd yb and low tio 2 whereas the south range dikes cut early proterozoic sediments mafic volcanics and intrusions and have low sr la yb gd yb la sm and high tio 2 these differences may be caused by the assimilation of different country rocks during emplacement of the dike a strongly mineralized offset dike at the creighton mine has geochemical variations that are different when compared to the main mass and in the case of creighton are more similar to the local mineralized sublayer these data suggest that mineralized and barren quartz diorites have different geochemical compositions and that these traits may be of value in mineral exploration

emplacement of metabreccia along the whistle offset dike sudbury implications for post impact modification of the sudbury impact structure the whistle offset dike is a radial dike linked to the ca 1850 ma sudbury igneous complex sic in sudbury ontario it is linked through the funnel shaped whistle embayment which formed as a depression along the floor of a superheated impact melt sheet represented by the present day sic the dike consists of metabreccia quartz diorite and inclusion bearing quartz diorite emplaced in older archean gneisses and intrusions metabreccia has a fine grained igneous textured matrix surrounding archean basement clasts it overlaps in major element compositions mgo cao sio 2 with the two quartz diorites the three have similar chondrite normalized rare earth element patterns characterized by pronounced negative slopes i e la yb n 17 29 and a weak negative eu anomaly this suggests that they originated from the same source melts metabreccia has higher high field strength element hfse ratios i e gd yb ce yb zr y and lower model initial 207 pb 204 pb isotopic ratios than the two quartz diorites suggesting that it assimilated more archean rocks with higher hfse ratios and lower 207 pb 204 pb ratios it formed as sic melts mixed with melted basement rocks at the sic basement contact this produced a strongly contaminated inclusion bearing melt which drained downward into an offset structure or fault entrained more fragments plucked from the walls of the fault and crystallized as metabreccia less contaminated quartz diorite was then emplaced in the still viscous metabreccia during reactivation of the fault caused by isostatic readjustment of the gravitationally unstable crater more melting assimilation of clasts and mixing of sic melts at the sic basement contact produced inclusion bearing quartz dioritic melts that were emplaced last along the whistle offset fault

factors influencing groundwater seepage in a large mesotrophic lake in new york abstract groundwater seepage is gaining recognition as a critical feature of lake shoreline environments yet our understanding of this process is complicated by the considerable spatial heterogeneity observed in flow rates within and among lakes this research investigated spatial patterns in groundwater seepage around the shoreline of oneida lake a 207 km2 lake located in central new york usa replicated shielded seepage meters with associated controls were used to quantify rates and directions of groundwater flow along a 120 m stretch of shoreline throughout the summers of 1997 1999 these reference meters exhibited an average flow rate of 72 ml m 2 h 1 n 840 se 5 with individual flow rates as high as 1200 ml m 2 h 1 additional meters monitored in 1998 indicated that seepage patterns were highly synchronous but increased in magnitude of flow rate with increasing distances offshore up to 100 m from shore in 1999 private landowners assisted in weekly monitoring of seepage meters at 28 additional sites distributed around the 88 km perimeter of oneida lake the highest groundwater flow rates averaging 100 ml m 2 h 1 consistently occurred along the northern and eastern shorelines lowest flow rates including areas of groundwater recharge occurred along the western and southwestern shorelines proximal to the lake s outlet spatial patterns in groundwater flow were surprisingly unrelated to substrate texture despite wide variability observed around the lake edge from silty clays to sands gravels and boulders broad scale factors of underlying bedrock geology and regional precipitation patterns appear to be driving the observed spatial patterns in oneida lake s groundwater contributions

using hydrogeophysical methods to assess the feasibility of lake bank filtration abstract lake tisso is the fourth largest lake in denmark with sufficient continuous surface water input making lake bank filtration an optimal surface water extraction method provided that there are suitable shallow aquifers with a good hydraulic connection to the lake the shallow subsurface under the lake was mapped by five waterborne electrical resistivity tomography ert and eight ground penetrating radar gpr surveys to locate potentially suitable aquifers distributed temperature sensing dts was used for the general characterisation of the hydraulic connection between the lake and aquifer the waterborne ert surveys showed several zones of coarser material along the shore extending up to five meters depth below the lake surface while on land ert surveys confirmed that these zones extend to the lakeshore with similar thickness both waterborne ert and gpr profiles agreed that at a selected field site the highest possibility of coarse sediments is 60 140 m from the lakeshore lakebed temperatures measured in december 2016 may and june 2017 all indicated potential groundwater discharge to the lake at approximately 135 m from the shoreline supporting the results of geophysical surveys showing coarser sediments in that area a 2d numerical flow model of the area with a geological setup based on geophysical information and slugtest data also showed upward groundwater discharge peaks at 60 and 140 m from the shoreline confirming the findings of the field surveys thus this study shows that the combination of waterborne ert and gpr surveys with dts measurements is a fast and efficient way to assess the feasibility of lake bank filtration in these settings this approach of combined hydrogeophysical methods is robust and has a potential to site lake bank filtration areas not only next to large rivers where coarse sediments are found in abundance but even in different sedimentary environments where suitable layers for lake bank filtration are more difficult to identify

spring sapping on the lower continental slope offshore new jersey undersea discharge of ground water during periods of lower sea level may have eroded valleys on part of the lower continental slope offshore new jersey steep headed basins cliffed and terraced walls and irregular courses of these valleys may have been produced by sapping of exposed near horizontal tertiary strata joints in eocene calcareous rocks would have localized ground water movement some karstlike features of the submarine topography and the outcrops suggest that solution of the calcareous rocks also took place

seepage measurements from long lake indiana dunes national lakeshore long lake located near lake michigan within the dune complexes of indiana dunes national lakeshore usa was formed some time during the pleistocene and holocene epochs a surficial aquifer underlies long lake which is either a source or sink for the later the hydrologic processes in the lakeshore and surrounding environs have been significantly altered during the agricultural municipal and industrial development of the region limited data suggest that the organisms of long lake have elevated levels of several contaminants this study attempts to quantify seepage within the lake to assess the potential threat to groundwater quality seepage measurements and minipiezometric tests were used to determine seepage within the lake seepage measurements and minipiezometric tests suggest that water seeps out of long lake thus recharging the groundwater that flows southwest away from the lake there is a great deal of variability in the seepage rate with a mean of 11 5 10 4 11 2 10 4 m d 1 the mean seepage rate of 0 3 m yr 1 for long lake is greater than the 0 2 m yr 1 recharge rate estimated for the drainage basin area the long lake recharge volume of 2 5 105 m3 yr 1 is approximately 22 of the volume of the lake and is significant when compared to the total surface recharge volume of 4 8 105 m3 yr 1 to the upper aquifer of the drainage area there is a potential for contamination of the groundwater system through seepage from the lake from contaminants derived from aerial depositions

estimates of velocity dispersion between seismic and ultrasonic frequencies it is generally accepted that acoustic velocities in fluid saturated rocks vary with frequency evidence comes from experimental measurements and from theoretical causality arguments we have developed a simple analysis technique that gives estimates of total velocity dispersion between zero frequency and any measurement frequency the technique requires compressional p and shear s wave velocity measurements on dry and fully saturated rock assuming that the dry velocities are independent of frequency the biot gassmann equations are used to calculate the zero frequency velocities in the fully saturated rock any difference between the measured velocities and the calculated zero frequency velocities is interpreted as evidence of dispersion application of this analysis technique to a variety c ultrasonic data sets gives consistent results in many rocks dispersion between zero frequency and ultrasonic frequencies is on the order of 10 percent at low effective stress and it decreases to only a few pe

rare earth element characteristics and origin of the sudbury igneous complex ontario canada abstract systematic geochemical studies have been carried out on the sudbury igneous complex sic and its country rocks the two main rock types of the sic norite and granophyre show contrasting chemical features the norite contains 54 58 wt sio2 whereas the granophyre has a sio2 content of 65 71 wt all rocks are characterized by high absolute rare earth element contents ree 63 314 ppm the granophyre having more than twice the ree contents of the norite and by lree enriched chondrite normalized distribution patterns huronian volcanic rocks and huronian plutonic granites have the highest ree contents and hree enrichment among the country rocks archean rocks are characterized by very steep ree patterns and positive eu anomalies nipissing diabase contains the lowest ree contents and has a flat ree pattern within the sic the ree values are more or less constant through the norite but the abundances of some elements such as ce and yb decrease slightly upward with stratigraphy ree contents increase sharply in passing from norite to granophyre and the eu eu ratio decreases from around unity to 0 66 the contrasting ree contents of the norite and granophyre combined with their distinctive major and trace element contents are considered to indicate that they resulted from two separate batches of magma probably emplaced at about the same time the previous models in which the sic was considered to originate from a single magma either contaminated mantle magma or crustal melt are not adequate a new hypothesis is developed based on the chemical features observed in this study the sic is considered to have comprised two independent intrusions the norite was derived from a heavily contaminated mantle magma 30 60 the main contaminant being archean granulite facies rocks of the lower crust the granophyre represents a crustal melt 75 archean rocks and 25 huronian granite induced by meteorite impact the new hypothesis better accounts for the large proportion of granophyre in relation to norite and for the ni cu sulfide mineralization associated with the sic it is also favored by the rb sr isotopic data

groundwater lake interactions ii nearshore seepage patterns and the contribution of ground water to lakes in central alberta abstract seepage flux was measured with seepage meters placed along transects from the lake shore to 30 110m offshore in 10 lakes in central alberta during may august 1986 in the study area the predominant surficial deposit is glacial till which is underlain by sedimentary bedrock seepage flux into the lakes ranged from 3 10 10 to 2 10 7 ms 1 seepage out of the lakes was recorded at only one of 92 seepage meter sites at one lake seepage was measured fortnightly along transects at two locations from may to august 1986 seepage patterns were consistent throughout that period in the nearshore region of six of 10 lakes seepage flux to the lakes decreased with distance from shore deviations from that pattern were probably a result of 1 spatial variability of seepage flux within a small area of lakebed 2 intertill sand and gravel lenses near the lake 3 preglacial bedrock channels of sand and gravel underlying some of the lakes ground water was the major source of water 49 of total inflow to one lake at the other lakes ground water was a relatively small component 10 of total inflow

geology mineralization and emplacement of the whistle parkin offset dike sudbury the whistle parkin dike is a 12 km long radial offset dike located in the northeast sector of the 1 85 ga sudbury impact structure the dike is connected to the sudbury igneous complex via a 0 5 km long 250 m wide embayment the whistle segment of the dike narrows to a width of approximately 30 m and extends for about 1 5 km from the complex where it is cut by the post creek fault zone this fault displaces the dike 2 km to the northwest beyond which it continues as the parkin portion of the dike the parkin segment extends a further 10 km north northeast the dike and genetically associated embayment are comprised of numerous rock types these include the sublayer radial breccia mafic sulfide bearing breccia inclusion rich quartz diorite and inclusion poor quartz diorite economic ni cu pge mineralization is found in association with the sublayer mafic sulfide bearing breccia and inclusion bearing quartz diorite phases rare earth element ree data reveal that the dike lithologies are representative of bulk sudbury igneous complex melt we propose a multistage emplacement mechanism for the dike the breccia units including the inclusion bearing quartz diorite phase were forcefully injected laterally into an impact generated radial crack during the excavation stage of crater formation subsequent early modification processes facilitated the intrusion of inclusion poor quartz diorite particularly along the dike margins inclusion poor quartz diorite emplacement may have been gravitationally driven from the overlying impact melt sheet later stage modification i e final transient cavity collapse caused decoupling of the whistle and parkin dike segments via faulting this occurred concurrently with the settling of the sublayer unit and associated economic sulfides into the embayment and main dike segments

osmium isotope evidence for a crustal origin of platinum group elements in the sudbury nickel ore ontario canada abstract sulphide ores from the international nickel company s inco creighton mine sudbury were analysed for osmium isotope ratios by icp ms rhenium and osmium abundances were determined by isotope dilution using a mixed spike in solid solution in a nickel sulphide matrix calculated initial 187 os 188 os ratios at 1 85 ga the emplacement age of the sudbury complex cluster around 0 60 the occurrence of less radiogenic compositions is attributed to post emplacement open system behaviour of the re os system the creighton results strongly overlap the initial ratios of published osmium data from two other sudbury mines suggesting a narrow range of isotope ratio in the original ore within the range of estimated osmium isotope compositions in the country rock at 1 85 ga using published and new data therefore the sulphide ores of the sudbury complex can have an entirely crustal source without a mantle derived contribution this conclusion is consistent with published neodymium isotope data for the complex and supports the meteorite impact hypothesis since this is the most effective means of fusing the large quantity of crustal rocks necessary to generate the complex the extraction of platinum group elements pge from this silicate melt by a nickel sulphide liquid was probably analogous to the laboratory fire assay procedure

measurement of hydraulic properties in deep lake sediments using a tethered pore pressure probe applications in the hamilton harbour western lake ontario estimates of groundwater seepage flux in lake bottom sediments require knowledge of the hydraulic gradient at the sediment surface water interface and the hydraulic conductivity of the lake bottom materials in deep waters in situ measurement of these parameters can be accomplished through the use of piezometer probes lowered and monitored remotely from a surface vessel in this research work a new tethered piezometer probe was developed and tested for use in collecting hydraulic property data in deep lake bottom sediments the probe uses a variable reluctance transducer to measure the differential sediment pore pressure between two ports spaced 100 cm apart the dissipation of pore pressure transients that develop during rapid emplacement of the probe were extrapolated in time to estimate equilibrium hydraulic gradients in addition various data analysis techniques were evaluated for determining sediment hydraulic conductivity and specific storage through interpretation of the pore pressure dissipation data the probe was used to estimate groundwater seepage in the bottom sediments of the hamilton harbour at the western end of lake ontario upward gradients were measured at nine locations within the harbor ranging from 0 010 to 0 425 and a downward gradient of 0 015 was recorded at one site along the harbor s eastern boundary hydraulic conductivities determined from pore pressure dissipation over time ranged from 6 9 10 9to 4 8 10 7 m s specific storage values ranged from 0 08 to 0 19 m 1 calculated average linear seepage velocities ranged from 4 3 10 8 to 8 5 10 9 m s the groundwater contribution to the harbor through the deeper fine grained sediments was estimated to be 9 1 10 2 m3 s or 2 9 106 m3 yr this represents approximately 1 0 of the harbor basin s total volume 15 of precipitation s contribution 1 2 of the contribution of surface inflows excluding the burlington ship canal and 0 22 of the total surface outflow passing through the burlington shipping canal which connects the harbor to lake ontario

chemical variations and genetic relationships between the hess and foy offset dikes at the sudbury impact structure offset dikes are found concentrically around and extending radially outward from the sudbury igneous complex sic which represents an 3 km thick differentiated impact melt sheet the dikes are typically composed of an inclusion rich so called quartz diorite iqd in the center of the dike and an inclusion poor quartz diorite qd along the margins of the dike new exposures of the intersection between the concentric hess and radial foy offset dikes provide an excellent opportunity to understand the relationship between the radial and concentric offset dikes and their internal phases the goal was to constrain the timing of the dike emplacements relative to the impact and formation of the sic results herein suggest that 1 the timing between the emplacement of the qd and iqd melts was geologically short 2 the hess and foy dikes coexisted as melts at the same time and the intersection between them represents a mixture of the two 3 the foy dike has a slightly more evolved chemical composition than the hess dike and 4 the iqd melt from the foy dike underwent some degree of chemical fractionation after its initial emplacement

numerical investigation of lake bed seepage patterns effects of porous medium and lake properties abstract three dimensional steady state numerical models were used to investigate the relative significance of several factors controlling lake bed seepage patterns lake depth lake bed slope orientation of an asymmetric lake with respect to a regional hydraulic gradient lake bed sediments and heterogeneity and anisotropy of the porous medium we considered both inflow and flow through lakes and our focus was on the details of seepage flux at the lake bed not on the surrounding porous medium while porous medium factors anisotropy and heterogeneity are important we found several conditions where lake bed factors were nearly as important in controlling the distribution of seepage varying lake bed slope from 0 013 to 0 04 in different simulations had a significant effect on shoreline seepage rates were 10 40 higher for lakes of low slope than lakes of steep slope also significantly elevated seepage in some cases a local maximum was observed offshore at the break in bed slope between the sloping side and flat central portions of the lake bed whenever the surrounding porous medium had a high anisotropy 1000 or 100 for flow through lakes in media of high anisotropy the annual volume of groundwater inseepage was significantly higher about 20 in lakes with steep bed slope compared to those with low slope this effect of slope was smaller at lower anisotropy for an asymmetric flow through lake a lake with a steep bed slope on one side moderate slope on the other the percentage of lake bed experiencing inseepage was greatest when the steep side was downgradient and the effect was larger at higher anisotropy these effects illustrate the complex interaction between lake bed slope and the anisotropy of the surrounding porous medium in controlling lake groundwater exchange adding low conductivity lake sediments and decreasing their conductivity shifted groundwater seepage further offshore in inflow lakes increasing the anisotropy of the surrounding porous medium had the same effect adding sediments and increasing anisotropy also decreased nearshore seepage in flow through lakes but without increasing offshore seepage in this case the net effect was a smaller annual volume of lake groundwater exchange at the same time the percentage of the lake bed experiencing inseepage increased in flow through lakes even as the annual volume of inseepage was decreasing thus for flow through lakes a larger area of inseepage may not be a good indicator of a greater volume of inseepage lake depth did not have a significant effect on the quantity or distribution of seepage to inflow or flow through lakes many of the physical factors investigated here influence the amount of lake groundwater exchange and the proportions of nearshore and offshore seepage therefore they are potentially significant to lake water quality and ecology in addition to hydrology

the sudbury structure controversial or misunderstood the origins of the sudbury structure and associated igneous complex have been controversial most models call for a major impact event followed by impact induced igneous activity although totally igneous models are still being proposed much of the controversy is due in our opinion to a misunderstanding of the size of the original sudbury structure by analogy with other terrestrial impact structures the spatial distribution of shock features and huronian cover rocks at the sudbury structure suggest that the transient cavity was 100 km in diameter which places the original final structural rim diameter in the range of 150 200 km theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in 104 km3 of impact melt more than sufficient to produce a melt body the size of the igneous complex present volume 4 8 103 km3 for the igneous complex to be an impact melt sheet it must have a composition similar to that of the target rocks evidence for this has been presented previously for sr and nd isotopic data which suggest a crustal origin here we also present new evidence from least squares mixing models that the average composition of the igneous complex corresponds to a mix of archean granite greenstone terrain with possibly a small component of huronian cover rocks this is a geologically reasonable mix based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size the igneous complex is differentiated which is not a characteristic of previously studied terrestrial impact melt sheets this can be ascribed however to its great thickness and slower cooling that large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted if this working hypothesis is accepted namely that both the sudbury structure and the igneous complex are impact in origin then previous hybrid impact igneous hypotheses can be discarded and the sudbury structure can be studied specifically for the constraints it provides to large scale cratering and the formation of basin sized multiring impact structures

the basal onaping intrusion in the north range roof rocks of the sudbury igneous complex the 1 85 ga sudbury impact structure is one of the largest impact structures on earth igneous bodies the so called basal onaping intrusion occur at the contact between the sudbury igneous complex sic and the overlying onaping formation and occupy 50 of this contact zone the basal onaping intrusion is presently considered part of the onaping formation which is a complex series of breccias here we present petrological and geochemical data from two drill cores and field data from the north range of the sudbury structure which suggests that the basal onaping intrusion is not part of the onaping formation our observations indicate that the basal onaping intrusion crystallized from a melt and has a groundmass comprising a skeletal intergrowth of feldspar and quartz that points to simultaneous cooling of both components increasing grain size and decreasing amounts of clasts with increasing depth are general features of roof rocks of coherent impact melt rocks at other impact structures and the basal onaping intrusion planar deformation features within quartz clasts of the basal onaping intrusion are indicators for shock metamorphism and together with the melt matrix point to the basal onaping intrusion as being an impact melt rock by definition importantly the contact between granophyre of the sic and basal onaping intrusion is transitional and we suggest that the basal onaping intrusion is what remains of the roof rocks of the sic and thus is a unit of the sic and not the onaping formation we suggest henceforth that this unit be referred to as the upper contact unit of the sic

a textural mineralogical and statistical study of the footwall breccia within the strathcona embayment of the sudbury structure the footwall breccia is one of the main ni cu pge ore hosting units of the sudbury camp this polymict matrix supported contact metamorphosed breccia occurs between the sudbury igneous complex and the footwall rocks along the west north and east margins of the sudbury structure in areas where there are depressions or embayments in the footwall the footwall breccia and basal units of the sudbury igneous complex are thickened and the footwall breccia is variably mineralized mineralogical and textural variations of footwall breccia samples from the strathcona embayment in proximity to the fraser mine suggest that the mineralogy and texture of this unit vary as a function of proximity to the sudbury igneous complex proximity to ore and location within the embayment the most mafic footwall breccia mineralogy is present proximal to the base of the sudbury igneous complex within a transition zone the presence of relatively mafic hydrous and cl rich silicate minerals e g biotite and amphibole characterize the footwall breccia matrix around ore zones and form an alteration halo of up to 5 m thick textural variations include a coarsening of quartz and feldspar grains with increasing proximity to the sudbury igneous complex contact textural coarsening also occurs from the margins of the strathcona embayment to the center together these mineralogical and textural variations influence the color of the footwall breccia matrix and can explain some of the gray colors that are typical of mineralized footwall breccia these variations also constrain the timing of formation of this unit and suggest that at least three phases of footwall breccia exist

the sudbury structure constraints on its genesis from lithoprobe results results of the lithoprobe transect provide additional corroboration of the impact model for the origin of the sudbury structure high resolution seismic reflection data indicate that the sudbury igneous complex sic is indeed continuous under the sudbury basin there is no indication of a feeder dike system or a previously assumed hidden mafic mass all these observations strongly support the interpretation of the sic as a coherent impact melt sheet in addition the seismic and to a lesser extent magnetic and gravity results point to a highly assymmetric structure to the sic at depth with significant tectonic disruption in the south range the present non circularity of the sic is caused by post impact ductile deformation and thrusting due to northwest directed compression decompressing this strain pattern leads to an original diameter of the sic between 60 and 80 km which in consequence would extend the original diameter of the final crater up to a maximum of 280 km

the galapagos spreading center at 86 w a detailed geothermal field study appendix is available with entire article on microfiche orderfrom american geophysical union 2000 florida avenue n w washington d c 20009 document j80 013 01 00 payment mustaccompany order we report here measurements of the heat flow field of the galapagos spreading center on crust of age less than 1 0 m y the 443 measurements in an area of about 570 km2 reveal the general planform of the geothermal flux and permit the first truly areal estimate of the near axis conductive heat flux the intrusion process and associated hydrothermal circulation dominate the surface heat flow pattern with circulation apparently continuing beyond the limits of our survey the areal average of the conductive heat flux is 7 1 0 8 hfu 295 33 mw m2 about one third the heat flux predicted by plate models the remaining heat is apparently removed by venting of hydrothermal waters at the spreading axis and through basalt outcrops and hydrothermal mounds off axis the pattern of surface heat flux is lineated parallel to the axis and the strongly lineated topography sharp lateral gradients in the heat flow greater than 10 hfu km near escarpments and commonly expressed as high heat flow at the tops of the scarps and lower heat flow in the valleys may indicate a local concentration of the circulation by surface fault systems and or variable sediment thickness

the sudbury structure ontario canada a tectonically deformed multi ring impact basin the occurrence of shock metamorphic features substantiates an impact origin for the 1 85 ga old sudbury structure but this has not been universally accepted recent improvements in knowledge of large scale impact processes combined with new petrographic geochemical geophysical lithoprobe and structural data allow the sudbury structure to be interpreted as a multi ring impact structure the structure consists of the following lithologies sudbury breccia dike breccias occurring up to 80 km from the sudbury igneous complex sic footwall rocks and footwall breccia brecciated shocked crater floor materials in part thermally metamorphosed by the overlying sic sublayer and offset dikes main mass of the sic and basal member of the onaping formation of geochemically heterogeneous coherent impact melt complex ranging from inclusion rich basal unit through a dominantly inclusion free to a capping inclusion rich impact melt rock grey member of of melt rich impact breccia suevite green member of of thin layer of fall back ejecta black member of of reworked and redeposited breccia material onwatin and chelmsford formations post impact sediments observational and analytical data support an integrated step by step impact model for the genesis of these units analysis of the present spatial distribution of various impact related lithologies and shock metamorphic effects result in an estimated original rim to rim diameter of the final crater of 200 or even 280 km for the sudbury structure prior to tectonic thrusting and deformation during the penokean orogeny

dynamic recrystallization of quartz under greenschist conditions abstract the sem electron channelling technique has been used to investigate the dynamic recrystallization of three quartz grains representative of optical textures observed in quartzite deformed under greenschist facies conditions the degree of recrystallization has been determined at 10 20 50 and 100 respectively we demonstrate that dynamic recrystallization is a sequential process involving subgrain grain rotation and grainboundary migration it initiates via subgrain polygonization on a single crystal slip system and continues via subgrain and neoblast rotation on several slip systems in the early stages of recrystallization

the pele offset dykes sudbury impact structure canada the offset dykes are impact melt bearing dykes related to the 1 85 ga sudbury impact structure currently the dykes extend radially outward from or occur concentrically around the sudbury igneous complex which is the remnant of a differentiated impact melt sheet and the source of the dykes the recently identified three pele offset dykes intrude into the archean rocks north of the sudbury igneous complex in this study the pele dykes are characterized for the first time by a combination of fieldwork optical microscopy electron microprobe analyses and bulk geochemical analyses the pele offset dykes stand out from the other offset dykes at sudbury in two significant ways i all other known offset dykes consist of an inclusion rich lithology in the center of the dyke and an inclusion poor lithology along the margins the pele dykes however are only composed of the inclusion poor phase ii the pele dykes particularly the central and eastern dykes have a more evolved chemical composition relative

effect of anisotropy and groundwater system geometry on seepage through lakebeds 2 numerical simulation analysis abstract the interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system and anisotropy of the porous media within the system numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations these analyses indicate that for a given geometric setting as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry because of the different slopes of the water table and lakebed resulting from the scale transformations a series of numerical experiments were made for various geometric configurations for a given anisotropy these analyses indicate that as thickness of the groundwater system decreases relative depth of the local flow system increases and seepage from the lake decreases

polyorogenic reworking of ore controlling shear zones at the south range of the sudbury impact structure a telltale story from in situ u pb titanite geochronology

formation of large scale impact melt dikes a case study of the foy offset dike at the sudbury impact structure canada abstract hypervelocity impacts frequently result in the formation of dikes in the crater floor and central uplift impact melt bearing dikes in large terrestrial impact basins such as the offset dikes at the sudbury impact structure occur at a large scale often tens of meters wide and several kilometers in length the offset dikes host significant ni cu pge deposits which include several well known mines such as totten and copper cliff that have been mined for nearly 100 years the offset dikes typically consist of a clast and sulfide rich core and clast poor margins their formation has been a subject of debate for decades the most widely proposed model is the early emplacement of clast poor impact melt shortly after the impact event followed by the later emplacement of clast and sulfide rich impact melt in the center of the dike an alternative hypothesis is that a single pulse of clast rich impact melt flowed into the fractured target rocks and flow differentiation resulted in a clast rich core and a clast poor margin in this study we examine field and petrographic relationships of the foy offset dike to better understand its emplacement our results show that the characteristics of the foy offset dike namely the gradational nature of the contact between the clast rich and clast poor phases the alignment of clasts sub parallel to this contact the geochemical similarities and the presence of sulfides within both phases of the dike are more consistent with the single injection and flow differentiation hypothesis

hydrate dissolution as a potential mechanism for pockmark formation in the niger delta received 17 february 2010 accepted 9 march 2010 published 11 august 2010 1 based on acquired geophysical geological and geotechnical data and modeling we suggest hydrate dissolution to cause sediment collapse and pockmark formation in the niger delta very high resolution bathymetry data acquired from the niger delta reveal the morphology of pockmarks with different shapes and sizes going from a small ring depression surrounding an irregular floor to more typical pockmarks with uniform depression geophysical data in situ piezocone measurements piezometer measurements and sediment cores demonstrate the presence of a common internal architecture of the studied pockmarks inner sediments rich in gas hydrates surrounded by overpressured sediments the temperature pressure and salinity conditions of the studied area have allowed us to exclude the process of gas hydrate dissociation gas hydrate turns into free gas water mixture as a trigger of the observed pockmarks based on numerical modeling we demonstrate that gas hydrate dissolution gas hydrate becomes mixture of water and dissolved gas under a local decrease of the gas concentration at the base of the gas hydrate occurrence zone ghoz can explain the excess pore pressure and fluid flow surrounding the central hydrated area and the sediment collapse at the border of the ghoz the different deformation or development stages of the detected pockmarks confirm that a local process such as the amount of gas flow through faults rather than a regional one is at the origin of those depressions

simulating the influence of lake position on groundwater fluxes groundwater flow around three hypothetical flow through lakes located in the upper middle and lower portions of a watershed was numerically simulated in cross section under steady state and transient conditions results showed that 1 groundwater fluxes into and out of the lake located in the lowest position were higher and more stable than for lakes farther upgradient and 2 periods of intense groundwater recharge caused flow reversals and the formation of a stagnation point downgradient of the uppermost lake thereby causing a net increase in groundwater inflow these simulation results provide guidance on monitoring network design including the frequency of monitoring and or sampling

groundwater interaction with a kettle hole lake relation of observations to digital simulations abstract observations made on a small fully penetrating kettle hole lake are used to test predictions made using digital stimulation about the exchange of water between lakes and groundwater systems on the upgradient side of lower nashotah lake groundwater inseepage decreases exponentially away from the shore water exchange on the downgradient side is controlled by the presence and strength of a groundwater mound but that mound and its effects are ephemeral when the mound increases in strength it generates a local groundwater flow cell beneath it which contains water of chemical composition distinct from deeper regional groundwater the growing mound also causes local inseepage of groundwater to the lake in an expanding zone along the downgradient shore all of these phenomena occur as they have been predicted in published studies where digital simulation of relatively simple groundwater lake systems has been carried out the field observations thus confirm the validity of the simulation studies and their usefulness as a tool for understanding water exchanges in unmonitored systems

tectonic influences on the morphometry of the sudbury impact structure implications for terrestrial cratering and modeling impact structures developed on active terrestrial planets earth and venus are susceptible to pre impact tectonic influences on their formation this means that we cannot expect them to conform to ideal cratering models which are commonly based on the response of a homogeneous target devoid of pre existing flaws in the case of the 1 85 ga sudbury impact structure of ontario canada considerable influence has been exerted on modification stage processes by late archean to early proterozoic basement faults two trends are dominant 1 the nnw striking onaping fault system which is parallel to the 2 47 ga matachewan dyke swarm and 2 the ene striking murray fault system which acted as a major paleoproterozoic suture zone that contributed to the development of the huronian sedimentary basin between 2 45 2 2 ga sudbury has also been affected by syn to post impact regional deformation and metamorphism the 1 9 1 8 ga penokean orogeny which involved nnw directed reverse faulting uplift and transpression at mainly greenschist facies grade and the 1 16 0 99 ga grenville orogeny which overprinted the se sector of the impact structure to yield a polydeformed upper amphibolite facies terrain the pre syn and post impact tectonics of the region have rendered the sudbury structure a complicated feature careful reconstruction is required before its original morphometry can be established this is likely to be true for many impact structures developed on active terrestrial planets based on extensive field work combined with remote sensing and geophysical data four ring systems have been identified at sudbury the inner three rings broadly correlate with pseudotachylyte friction melt rich fault systems the first ring has a diameter of 90 km and defines what is interpreted to be the remains of the central uplift the second ring delimits the collapsed transient cavity diameter at 130 km and broadly corresponds to the original melt sheet diameter the third ring has a diameter of 180 km the fourth ring defines the suggested apparent crater diameter at 260 km this approximates the final rim diameter given that erosion in the north range is 6 km and the ring faults are steeply dipping impact damage beyond ring 4 may occur but has not yet been identified in the field one or more rings within the central uplift ring 1 may also exist this form and concentric structure indicates that sudbury is a peak ring or more probably a multi ring basin these parameters provide the foundation for modeling the formation of thisrelatively large terrestrial impact structure

aquifer characteristics derived from the interaction between water levels of a terminal lake dead sea and an adjacent aquifer the water level of the dead sea a terminal hypersaline lake total dissolved solids approximately 340 g l has decreased at an average rate of 0 5 m yr since 1960 and by 0 8 m yr between 1981 and 1989 the dramatic long term water level variation of the dead sea and the seasonal short term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer a general methodology based on a simplified yet reliable one dimensional flow model together with continuous measurements of groundwater levels in observation wells enables analysis of aquifer structural and hydraulic properties furthermore this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels

chemical evolution of groundwater near a sinkhole lake northern florida 1 flow patterns age of groundwater and influence of lake water leakage leakage from sinkhole lakes significantly influences recharge to the upper floridan aquifer in poorly confined sediments in northern florida environmental isotopes oxygen 18 deuterium and tritium chlorofluorocarbons cfcs cfc 11 ccl3f cfc 12 ccl2f2 and cfc 113 c2cl3f3 and solute tracers were used to investigate groundwater flow patterns near lake barco a seepage lake in a mantled karst setting in northern florida stable isotope data indicated that the groundwater downgradient from the lake contained 11 67 lake water leakage with a limit of detection of lake water in groundwater of 4 3 the mixing fractions of lake water leakage which passed through organic rich sediments in the lake bottom were directly proportional to the observed methane concentrations and increased with depth in the groundwater flow system in aerobic groundwater upgradient from lake barco cfc modeled recharge dates ranged from 1987 near the water table to the mid 1970s for water collected at a depth of 30 m below the water table cfc modeled recharge dates based on cfc 12 for anaerobic groundwater downgradient from the lake ranged from the late 1950s to the mid 1970s and were consistent with tritium data cfc modeled recharge dates based on cfc 11 indicated preferential microbial degradation in anoxic waters vertical hydraulic conductivities calculated using cfc 12 modeled recharge dates and darcy s law were 0 17 0 033 and 0 019 m d for the surficial aquifer intermediate confining unit and lake sediments respectively these conductivities agreed closely with those used in the calibration of a three dimensional groundwater flow model for transient and steady state flow conditions

re os isotope systematics of ni cu sulfide ores sudbury igneous complex ontario evidence for a major crustal component sudbury igneous complex sublayer ores from the levack west falconbridge and strathcona mines were analyzed for their re and os concentrations and os isotopic compositions the re os isotope systematics of three ores from the different mines give isochron ages of1 840 60 ma 1770 60 ma and 1780 110 ma suggesting that the re os system became closed at the time of or soon after the 1850 1 ma crystallization age of the complex the os isotopic compositions of different portions of the complex at the time of crystallization varied considerably with initial187os 186os1850 ranging from 4 64 at levack west to 7 55 at strathcona these heterogeneities require that the os and probably also the other platinum group elements contained in the ores were derived from at least two sources in addition the high initial187os 186os ratios indicate that the os was derived predominantly from ancient crust previous studies have suggested that the complex either crystallized from a mixture of mantle derived basaltic melt and ancient continental crust or was derived exclusively from the fusion of ancient continental crust resulting from a meteorite impact results of modelling suggest that if a contemporaneous mantle derived basaltic melt was involved in the origin of the sic it likely contributed 50 of the os to all three ores the large percentage of ancient crust involved in the production of the ores is most consistent with an interpretation of substantial crustal fusion resulting from meteorite impact

igneous rocks formed by hypervelocity impact abstract igneous rocks are the primary building blocks of planetary crusts most igneous rocks originate via decompression melting and or wet melting of protolith lithologies within planetary interiors and their classification and compositional petrographic and textural characteristics are well studied as our exploration of the solar system continues so too does the inventory of intrusive and extrusive igneous rocks settings and processes the results of planetary exploration have also clearly demonstrated that impact cratering is a ubiquitous geological process that has affected and will continue to affect all planetary objects with a solid surface whether that be rock or ice it is now recognized that the production of igneous rocks is a fundamental outcome of hypervelocity impact the goal of this review is to provide an up to date synthesis of our knowledge and understanding of igneous rocks formed by hypervelocity impact following a brief overview of the basics of the impact process we describe how and why melts are generated during impact events and how impact melting differs from endogenic igneous processes while the process may differ we show that the products of hypervelocity impact can share close similarities with volcanic and shallow intrusive igneous rocks of endogenic origin such impact melt rocks as they are termed can display lobate margins and cooling cracks columnar joints and at the hand specimen and microscopic scale such rocks can display mineral textures that are typical of volcanic rocks such as quench crystallites ophitic porphyritic as well as features such as vesicles flow textures and so on historically these similarities led to the misidentification of some igneous rocks now known to be impact melt rocks as being of endogenic origin this raises the question as to how to distinguish between an impact versus an endogenic origin for igneous like rocks on other planetary bodies where fieldwork and sample analysis may not be possible and all that may be available is remote sensing data while the interpretation of some impact melt rocks may be relatively straightforward e g for clast rich varieties and those with clear projectile contamination we conclude that distinguishing between impact and endogenic igneous rocks is a non trivial task that ultimately may require sample investigation and analysis to be conducted caution is therefore urged in the interpretation of igneous rocks on planetary surfaces

fluid circulation and seepage in lake sediment due to propagating and trapped internal waves 1 it has long been known that surface gravity waves induce significant seepage through the porous layer found at the lake bottom away from coastal regions however the pressure signature of surface waves at the lake bottom is weak we consider fully nonlinear internal gravity waves whose long wavelength and slow motion implies a sustained and strong pressure perturbation even in the deep regions of the lake we argue that internal waves can induce significant seepage through the sediment layer in regions where surface gravity waves have negligible impact the pressure profile at the fluid porous layer interface is computed from the exact dubreil jacotin long theory giving a reliable profile even for large waves this profile is used in conjunction with darcy s law to compute the seepage within the porous region we find that the geometric distribution of seepage is strongly controlled by both the ratio of porous media thickness to the horizontal length of the pressure perturbation and the bottom topography when it is present based on work on the interaction of internal solitary waves with the bottom boundary layer we develop a model to account for the changes in permeability due to wave induced instabilities in the bottom boundary layer and enhanced benthic turbulence this turbulence acts to unplug the pores near the surface by lifting the detritus that clogs them the resulting changes in permeability significantly enhance exchange between the free fluid and the porous medium on the downstream side of the wave

strontium and neodymium isotopic characteristics of a heterolithic breccia in the basement of the sudbury impact structure canada abstract rb sr and sm nd measurements were undertaken on footwall breccia samples originating from levack township in the north range of the sudbury structure the granitic to quartzdioritic matrix of this heterolithic breccia which contains shocked rock and mineral fragments yields a rb sr isochron age of 1 825 0 021 ga isr 0 70356 0 00005 2 errors based on the analysis of 3 6 mm thick adjacent whole rock slabs from a large hand specimen this age is interpreted as a cooling age after the thermal metamorphism of the footwall breccia by the 1 85 ga old sudbury igneous complex which had caused temperatures in excess of 1000 c in the matrix near the contact mafic rock fragments in this breccia were excluded from the sr isotope exchange at that time the sm nd system of the identical small whole rock samples was only partly disturbed by the sudbury igneous complex the data points scatter around a 2 05 0 49 ga regression line without age significance plagioclase k feldspar and mafic mineral phases of the breccia matrix combined with the corresponding whole rocks display a range in rb sr ages from 1 67 0 08 ga to 1 430 0 015 ga obviously associated with metasomatic processes in the footwall breccia during the declining penokean metamorphism strontium and neodymium model parameters of the footwall breccia matrix near levack show little variation esrt 16 33 to 18 07 endt 10 69 to 11 79 t 1 86 ga and mean tnddm 2 74 0 04 ga based on these results bedrocks exposed in the south range and rocks now forming the sedimentary filling of the sudbury basin can be excluded as major components in the matrix of the analyzed footwall breccia the convergence of neodymium model ages with u pb ages on zircons from the levack gneiss which forms the crystalline basement adjacent to the footwall breccia in the levack area support an exclusively local origin for matrix and fragments of this breccia it is proposed that the footwall breccia is part of the uplifted floor of the sudbury crater

analysis and application of in situ pore pressure measurements in marine sediments recent measurements of in situ subseafloor pore pressure in sediment ponds on the flank of the mid atlantic ridge using a pop up pore pressure instrument have provided important information regarding fluid exchange processes at the seafloor as well as in situ estimates of physical properties of marine sediments the in situ pore pressure recordings of 4 5 days duration contain three distinct components the early part of the record is dominated by the decay of a pressure pulse associated with probe penetration the rate of decay of this pulse is used to estimate in situ permeabilities which range from 3 1 10 16 m2 to 6 5 10 15 m2 the recording also exhibits a low amplitude oscillation that is associated with tidal pressure variation on the seafloor a study based on biot s theory shows that amplitudes and phases of tidally induced pore pressure oscillations are determined by both the frame compressibility and the permeability of the sediments and thus the oscillation components are used to estimate these parameters the frame compressibilities and the permeabilities estimated from tidal oscillations range from 1 2 10 8 pa 1 to 4 1 10 8 pa 1 and from 1 1 10 15 m2 to 4 8 10 15 m2 respectively laboratory measured permeabilities range from 7 6 10 16 m1 to 1 2 10 15 m2 permeabilities determined by these three methods are comparable the third component is the ambient equilibrium pore pressure negative pore pressure gradients were identified on all deployments when combined with the permeabilities of the sediments the estimated average rates of drawdown of water through the sedimentary layers in the ponds are 2 7 mm yr the pore pressure gradient near the seafloor can be used to construct a pore pressure profile through the sediment extrapolated pore pressure at the top of the basement is about 80 kpa 0 8 bar below the hydrostatic pressure

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

role of a groundwater lake interface in controlling seepage of water and nitrate summary the effects of the hydraulic characteristics of a groundwater lake interface on discharge and nitrate loading to a lake were investigated the interface is defined as the zone separating the adjacent aquifer 10 s of m and the lake bed 10 s of cm itself the study combines field data using several tracers water oxygen isotopes and nitrate and numerical modeling the hydraulic head distribution a nitrate plume and seepage rates were observed over a two year period along a 100 m long transect reaching from an agricultural field into the lake the groundwater lake interface system was simulated with a 2d steady state flow and nitrate transport model feflow the observations showed that discharge to the lake was doubled peaked with a peak discharge near the shore line followed by an almost classical exponential decrease and a second peak further off shore the nitrate plume also extended 60 80 m off shore by calibrating the model to measured discharge and the outline of the nitrate plume it was demonstrated that 1 the ratio of horizontal to vertical hydraulic conductivity anisotropy was very important and on the order of 50 and 2 the lake bed acted as a hydraulic barrier by having a much lower hydraulic conductivity than that of the relatively homogeneous aquifer we suggest that the barrier is formed by an extensive plant cover that can trap finer materials and produce a surface colmation layer the simulation results show that when a barrier is present the total groundwater discharge to the lake can be up to a factor of two lower and that approximately 50 of the nitrate bypasses the barrier this proportion of the nitrate loading will therefore also bypass the plant cover and discharge directly to the lake off shore potentially leading to algal blooms under n limited conditions in the lake water column

vertical leakage and vertically averaged vertical conductance for karst lakes in florida in the karst lake district in peninsular florida in the southeastern united states as many as 70 of the lakes lack surface outlets and groundwater outflow is an important part of the water budgets of these lakes for 11 karst lakes in the central lake district vertical leakage from the lakes to the upper floridan aquifer averages 0 12 to 4 27 m yr 1 the vertically averaged vertical conductance kv b a coefficient that represents the average of the vertical conductances of the hydrogeologic units between the bottom of a lake and the top of the upper floridan aquifer was determined to range from 0 0394 to 1 00 yr 1 for these lakes for six of the lakes various hydraulic parameters previously calculated by other investigators are shown to be equivalent to the kv b values calculated in this study if kv b is determined for a lake then vertical leakage can be estimated for other conditions of lake stage and hydraulic head in the upper floridan aquifer using kv b for the lake and darcy s equation written for vertical flow the methodology described in this paper for quantifying kv b which requires only limited data i e vertical leakage lake stage and hydraulic head in the upper floridan aquifer could be used to investigate the apparent association between relatively large kv b values and lake level instabilities at some lakes in the central lake district and similar hydrogeologic settings this methodology for calculating vertical leakage is applicable to the central lake district in florida and to other similar lake and groundwater systems

hydrothermal venting and geothermal heating in cascadia basin observations in cascadia basin on the eastern flank of the northern juan de fuca ridge reveal significant bottom water modification as a result of regional conductive heating and local hydrothermal venting seafloor conductive heating occurs throughout the sedimented basin while hydrothermal fluid discharge is confined to small 1 km2 isolated igneous basement outcrops in the northern sector of the plateaulike basin the vertical fluxes of heat and mass associated with these seafloor processes lead to the formation of a 250 to 350 m thick geothermal boundary layer characterized by anomalously high temperature reduced vertical stability and high dissolved silicate concentration using a basinwide average lithospheric heat flux of 0 3 w m 2 and the observed thermal anomaly structure of the water column we obtain a mean residence time of 1 to 2 years for the deep water over cascadia basin detailed water property data collected in 1992 and 1993 within the immediate vicinity of three isolated igneous basement outcrops in the north central sector of the basin indicate that local bottom water heating arises from low temperature venting through the summit and flanks of the outcrops near the smallest edifice especially well defined layers of anomalously warm particle laden water were found within 20 m of the outcrop summit depth of 2610 m maximum anomalies of temperature light attenuation coefficient and dissolved silicate concentration in the layers were 0 040 c 0 015 m 1 and 5 mol l 1 respectively we estimate the local heat flux fo from the smallest outcrop to be 2 4 0 8 u 109 w where u m s 1 is the mean horizontal current at the venting depth for reasonable mean currents in the range 10 3 to 10 2 m s 1 we find fo 0 2 to 2 4 107 w assuming that the depressed conductive heat flow of 0 05 w m 2 observed through the sedimented seafloor surrounding the smallest outcrop reflects the advective loss of heat through the outcrop the radial distance over which crustal fluids must collect heat and converge on the outcrop is about 10 km

installing piezometers in deepwater sediments a new method has been developed for installing piezometers in the sediments of deep harbors and lakes where it has been difficult to measure hydrogeological parameters and collect pore waters for geochemical analyses using an underwater hammer operated from the surface piezometers have been installed as much as 12 m below the water sediment interface the piezometer screen is held in place by barbs on the drive head and is connected to the water surface via flexible tubing these piezometers have been installed from boats and from ice cover in water up to 30 m deep however installation in water more than 100 m deep should be possible

geology mineralization and emplacement of the foy offset dike sudbury impact structure the foy offset dike is the longest of the known radial dikes associated with the 1 85 ga sudbury igneous complex the foy dike extends for at least 30 km from the complex into the north range archean and proterozoic footwall rocks of the sudbury impact structure the dike ranges in width from 400 m where it connects to the sudbury igneous complex to 50 m at its most distal known exposure we divide the dike into a proximal segment and a distal segment based on where it intersects the concentric hess offset dike three main dike lithologies are distinguished all referred to as varieties of quartz diorite inclusion rich pyroxene quartz diorite occurs in the embayment adjacent to the base of the main mass of the sudbury igneous complex this constitutes the sublayer northward the sublayer gives way to amphibole biotite inclusion bearing quartz diorite and amphibole biotite inclusion poor quartz diorite the dike is mineralized and deposits in the proximal segment have been mined mineralization is associated with the inclusion rich dike phase at the nickel offset mine the dike contains inclusion bearing massive ni cu sulfides that also host platinum group minerals the orebodies occurred as strike parallel sheets within the central parts of the dike in association with inclusion bearing quartz diorite the geochemistry of the dike lithologies indicates that both the inclusion poor and inclusion bearing quartz diorite varieties are close in composition to the postulated bulk composition of the sudbury igneous complex this implies that the dike was emplaced prior to any significant fractionation of the main melt body and hence very early in the evolution of the sudbury complex we envisage dike emplacement rapidly following rebound and central uplift formation as part of the impact process early dike emplacement implies that the ore was also introduced early in the evolution of the melt sheet when the inclusion poor quartz diorite phases were still unconsolidated uplift would have caused extension in the target rocks and so dilated the footwall fractures and faults that then became hosts primarily via gravitationally driven intrusion to the primitive polymict impact melt breccias and sulfide ores the chilled margin compositions of the foy inclusion poor quartz diorite are considered good indicators of the original bulk composition of the sudbury igneous complex this idea is supported by comparison with calculated estimations of the bulk composition a shift in geochemical trends a grain size increase and a decrease in inclusion content occurs 22 km along the length of the dike which we believe corresponds to a fault system that downfaults to the north given that the dense ore would have preferentially settled toward the base of the foy dike fracture system postimpact downfaulting of the distal segment of the dike may have displaced any mineralized zones present to deeper levels relative to the proximal segment

groundwater lake interactions i accuracy of seepage meter estimates of lake seepage abstract the use of seepage meters to identify nearshore seepage patterns and to quantify seepage in lakes was evaluated with a monte carlo simulation model the model simulated seepage flux as would be derived from seepage meter measurements along a transect extending from the shore of a hypothetical lake to 40 or 100m offshore along the transect simulated seepage velocities decreased exponentially with distance from shore according to patterns measured at narrow lake alta and lake sallie mn to determine statistical parameters needed in the model seepage flux was measured in situ with closely spaced seepage meters at four different sites in narrow lake seepage velocities within a small area of lakebed were log normally distributed and the variance was positively correlated with mean seepage flux the modeling indicated that the most sensitive parameter affecting the accuracy of seepage meter estimates of seepage patterns and average seepage flux along the transect was the variability in the spatial distribution of seepage flux within a small area of lakebed there was little improvement in the accuracy of estimates of seepage patterns or transect flux when more than ten seepage meters were simulated along the transect when the transect was sampled more than twice or when seepage meters along the transect were simulated to follow a stratified rather than a systematic design

a comparison of theoretical rock models with laboratory data abstract a number of rock modelling theories based on single crystal data were tested in order to assess their effectiveness in modelling actual laboratory rock data these theories included the voigt reuss and hashin shtrikman bounds for isotropic single phase pore free aggregates and composites and the self consistent inclusion theories of hashin shtrikman wu and walsh and thomsen s biot consistent approach for porous materials the results for very low porosity rocks effectively pore free indicate that models based on hashin shtrikman theory yield narrow bounds which accurately predict mean laboratory p and s wave velocities however meaningful comparisons require careful and accurate rock characterization in terms of mineral composition and texture the theories for porous rock models yielded s wave velocities which were not as consistent as their counterpart p wave velocities in matching the laboratory data moreover the discrepancies increase markedly as rock porosity increases this result reflects primarily differences in internal microcrack structure and composition between that assumed in the theoretical modelling procedures and that present in the actual rock samples saturated and dry rocks containing cracks were most successfully modelled by the biot consistent theory proposed recently by thomsen 1985

grenville age deformation of the sudbury impact structure evidence from magnetic modelling of the sudbury diabase dyke swarm terra nova 24 213 220 2012 abstract the sudbury structure is located 10 km from the grenville front the northern boundary of the grenville metamorphic terrane previous geological studies have suggested that late grenvillian deformation 1000 1070 ma of the sudbury structure was limited to minor brittle deformation olivine diabase dykes which were intruded at 1238 ma before the last pulse of grenville deformation cross much of the sudbury structure any grenville age deformation of the sudbury structure therefore should produce systematic displacements in the geometry of the dykes this study uses information derived from an aeromagnetic survey of the sudbury structure to map and measure fault displacements lateral displacements of dyke segments define a progressive increase in fault rotation from ne to sw across the basin a two dimensional inversion modelling of magnetic anomaly profiles across segments of the dykes outlines a series of fault blocks with common dip the dyke dip detected by the inversion models suggests that displacement on the faults included rotation about an axis perpendicular to the trend of the fault the resulting model of scissor or splay faults is compatible with previously published palaeomagnetic studies of the olivine dykes in the sudbury region

origin of the sudbury complex by meteoritic impact neodymium isotopic evidence samarium neodymium isotopic data on whole rocks and minerals of the sudbury complex in canada gave an igneous crystallization age of 1840 21 x 10 6 years the initial epsilon neodymium values for 15 whole rocks are similar to those for average upper continental crust falling on the crustal trend of neodymium isotopic evolution as defined by shales the rare earth element concentration patterns of sudbury rocks are also similar to upper crustal averages these data suggest that the sudbury complex formed from melts generated in the upper crust and are consistent with a meteoritic impact

differentiation and emplacement of the worthington offset dike of the sudbury impact structure ontario the offset dikes of the 1 85 ga sudbury igneous complex sic constitute a key topic in understanding the chemical evolution of the impact melt its mineralization and the interplay between melt migration and impact induced deformation the origin of the melt rocks in offset dikes as well as mode and timing of their emplacement are still a matter of debate like many other offset dikes the worthington is composed of an early emplaced texturally rather homogeneous quartz diorite qd phase at the dike margin and an inclusion and sulfide rich quartz diorite iqd phase emplaced later and mostly in the centre of the dike the chemical heterogeneity within and between qd and iqd is mainly attributed to variable assimilation of host rocks at the base of the sic prior to emplacement of the melt into the dike petrological data suggest that the parental magma of the worthington dike mainly developed during the pre liquidus temperature interval of the thermal evolution of the impact melt sheet 1200 c based on thermal models of the cooling history of the sic the two stage emplacement of the worthington dike occurred likely thousands to about ten thousand years after impact structural analysis indicates that an alignment of minerals and host rock fragments within the worthington dike was caused by ductile deformation under greenschist facies metamorphic conditions rather than flow during melt emplacement it is concluded that the worthington offset dike resulted from crater floor fracturing possibly driven by late stage isostatic readjustment of crust underlying the impact structure

impact of seafloor sediment permability and thickness on off axis hydrothermal circulation juan de fuca ridge eastern flank sediment permeability plays a key role in controlling both the flux of solute and heat through marine sediments and patterns of hydrothermal circulation within the underlying oceanic crust interlayered silt rich and clay rich sediments almost completely bury basement on the eastern flank of the juan de fuca ridge laboratory measurements indicate that silt rich sediment permeability is 1 to 2 orders of magnitude greater than clay rich sediment permeability at similar depths numerical simulations of coupled fluid flow and heat transfer using a simplified model of a sedimented ridge flank with smooth basement topography illustrate how differences in permeability between the two sediment types can influence patterns of hydrothermal circulation and the flux of heat and solute across the seafloor the layered structure of the model domain is inferred from reflection seismic and seafloor heat flow data two distinct patterns of hydrothermal circulation are obtained depending on whether silt rich or clay rich sediments compose the sediment layer above a permeable upper basement aquifer a clay rich sediment column nearly isolates circulation within the basement aquifer resulting in closed convection computed seafloor heat flow profiles resemble heat flow measurements made on the eastern flank of the juan de fuca ridge computed vertical fluid fluxes across the sediment column are small in agreement with fluid fluxes estimated from sediment geochemical profiles when the sediments are silt rich 17 of the flow within a convection cell crosses the sediment column open convection where basement topography is smooth is probably rare because sediment columns overlying oceanic crust are unlikely to be entirely silt each pattern of convection persists over a wide range of sediment thicknesses for a given sediment permeability and basal heat flow a transition from open to closed convection occurs when the effective permeability of the sediment column is only slightly less than that of an entirely silt rich column thus the addition of only a small amount of clay to an otherwise silt rich sediment column may effectively isolate the crustal aquifer from the ocean

preliminary analysis of the hydrologic and geochemical controls on acid neutralizing capacity in two acidic seepage lakes in florida in late 1988 parallel studies of lake five o ph 5 14 in the florida panhandle and lake barco ph 4 50 in north central florida were initiated to develop hydrologic and major ion budgets of these lakes as part of an overall effort to improve understanding of the hydrologic depositional and biogeochemical factors that control acid neutralizing capacity anc in seepage lakes preliminary findings from these studies indicate that earlier perceptions of lake hydrology and mechanisms of anc regulation in florida seepage lakes may have to be revised the traditional perspective of seepage lakes in the florida panhandle views these systems as dominated by precipitation inputs and that anc regulation is due largely to in lake processes our results for lake five o show modest to steep hydraulic gradients almost entirely around the lake in addition the horizontal hydraulic conductivity of the surficial aquifer is high 8 74 m day 1 indicating that large quantities of groundwater flow into lake five o calculations of net groundwater flow from hydrologic budgets also indicate that groundwater may comprise at least 38 to 46 of the total inflow for lake barco net flow estimates of the minimum groundwater inflow range from 5 to 14 of total inflow enrichment factor and ion flux calculations for lake five o and lake barco indicate that terrestrial as well as in lake processes contribute significantly to anc regulation the extent that terrestrial processes contribute to anc generation is directly related to the magnitude of groundwater inflow as well as the degree of ion enrichment or depletion that occurs in the surficial aquifer net anc generation in both study lakes was dominated by anion retention no3 and so42 where previous studies concluded that in lake reduction was the primary sink for so42 our preliminary calculations show that adsorption of so42 within the watershed is perhaps twice as important as in lake reduction as a source of anc net base cation enrichment in both lakes was negligible

isotopic evidence for distinct crustal sources of north and south range ores sudbury igneous complex lead isotope ratios were measured on fe cu ni sulphide ores and associated silicate phases from nine mines on the north and south ranges of the sudbury igneous complex sic these data are compared with the lead isotope signatures of country rocks and shock melted sudbury breccias around the complex both ore and feldspar data from the south range fall along a 1 85 ga reference line the age of the igneous complex and indicate a magmatic origin for lead in the ore data from the north range are also consistent with a magmatic origin but are displaced to lower 206pb 204pb and 207pb 204pb ratios these two suites fall close to the lead isotope composition of country rocks adjacent to the south and north ranges respectively furthermore there is a close correspondence between lead signatures of the sic and sudbury breccia on each side of the complex the evidence suggests an origin for the sic by shock melting of different crustal units on the two sides of the complex this is consistent with the impact of a meteorite on the southward thickening apron of huronian strata which overlay the margin of the superior craton at 1 85 ga

indirect detection of subsurface outflow from a rift valley lake abstract naivasha highest of the kenya gregory rift valley lakes has no surface outlet however unlike other rift lakes it has not become saline despite high potential evaporation rates which indicates that there must be some subsurface drainage the fate of this outflow has been the subject of speculation for many years especially during the general decline in lake water level during the 1980 s particularly to the south of the lake there are few opportunities to obtain information from direct groundwater sampling however the stable isotopic composition of fumarole steam from late quaternary volcanic centres in the area has been used to infer groundwater composition using a simple mixing model between rift flank groundwater and highly evaporated lakewater this has enabled subsurface water flow to be contoured by its lakewater content by this method outflow can still be detected some 30 km to the south of the lake stable isotope data also confirm that much of the steam used by the local olkaria geothermal power station is derived from lakewater though simple balance considerations show that steam use cannot alone be responsible for the fall in lake level observed during the 1980 s

groundwater seepage into northern san francisco bay implications for dissolved metals budgets 1 nonconservative excesses of dissolved metals in northern san francisco bay indicate that there are internal sources of metals within the bay we quantified groundwater seepage and bioirrigation rates in this area to determine their roles in transporting dissolved metals from benthic sediments to surface waters we deployed seepage meters and collected sediment pore water and bottom water samples at three sites we determined seepage rates from seepage meters and modeled the transport of water through the sediment using pore water data to constrain rates of diffusion advection and bioirrigation a groundwater flow model incorporating sediment physical properties and local topography constrains more regional seepage estimates the seepage meters indicate upflow rates from 7 to 56 cm yr 1 in march and april 1999 with some large 50 cm yr 1 daily fluctuations that greatly exceed predictions based on sediment physical properties and tidally induced pore pressure variations during this period results from modeling pore water chemical data are consistent with a small bioirrigation rate 1 5 10 7 s 1 relative to values determined for southern san francisco bay and an average groundwater upwelling speed of 15 cm yr 1 the speed and direction of flow changed throughout the year with best fits to the data ranging from 20 cm yr 1 upflow to 34 cm yr 1 downflow and averaging 4 cm yr 1 upflow confidence intervals 95 are about 10 cm yr 1 for this method yet the range of acceptable seepage rates for temporally successive periods only overlap in one of four cases suggesting that temporal variability can be discerned from potential artifacts groundwater flow modeling suggests that the seepage rates determined at our sites represent 45 of the average seepage rate for the area applying one consolidation and permeability relationship to all sediments if we apply these approximations to all of northern san francisco bay benthic fluxes of dissolved metals to the surface waters could account for a relatively large amount 60 of the unknown sources of dissolved cobalt and a relatively small amount 4 of the unknown sources of dissolved silver cadmium copper nickel and zinc more focused groundwater discharge or elevated metals concentrations are required to have a larger impact on trace element budgets in this setting

the sudbury igneous complex a differentiated impact melt sheet the sudbury structure ontario is the remnant of a 1 85 ga old impact crater which originally had a diameter of 200 to 250 km the sudbury igneous complex occurs within the sudbury structure the sudbury igneous complex is a 2 5 to 3 0 km thick 60 27 km elliptical igneous rock body which consists of four major lithologies from top to bottom traditionally termed granophyre quartz gabbro norite and contact sublayer sulfide and inclusion bearing noritic rock with the exception of the latter all these lithologies are continuous across the structure modal analyses reveal that following the iugs system of nomenclature quartz gabbro samples are in fact quartz monzogabbros a few of the norite samples are quartz gabbros and most norite samples are quartz monzogabbros in view of these observations and in order to clarify the nomenclature an updated terminology is proposed from top to bottom upper unit middle unit lower unit and contact sublayer the bulk composition of the sudbury igneous complex from north range data is granodioritic continuous and gradational mineralogical and geochemical variations between the lithological units are evidence that the complex behaved as a single melt system all the sudbury igneous complex lithologies have the same light to heavy rare earth element ree ratio and an overall pattern of increased light ree and depleted heavy ree the occurrence of primary hydrous minerals hornblende and biotite deuteric alteration and abundant micrographic and granophyric intergrowths demonstrate that the melt was rich in h2o moreover the granophyric and other far from equilibrium textures are most likely due to rapid crystallization triggered by exsolution of a volatile phase the sudbury igneous complex differs from traditional layered mafic complexes in the following aspects it has an overall intermediate composition a hydrous nature a crustal isotopic signature normative corundum and an unusually large volume of granophyre the sudbury complex differs from known terrestrial impact melt sheets only by its great thickness and the presence of chemical and therefore mineralogical layering reported here for the first time and similar to those found in impact melt rocks elsewhere are the occurrences of plagioclase xenocrysts with complex twinning and zoning patterns and planar deformation features in quartz xenocrysts the well known ore deposits of the sudbury region are directly related to the genesis of the sudbury igneous complex some ores precipitated from the sudbury melt whereas others were concentrated by hydrothermal fluids that percolated through the crystallized complex it is concluded that the sudbury igneous complex is the best exposed and only well documented to date terrestrial impact melt sheet to have differentiated

impact of crustal evolution on changes of the seismic properties of the uppermost ocean crust one of the most important observations of oceanic crustal evolution is that the uppermost part of the igneous crust layer 2a appears to thin and eventually disappear as its seismic velocity doubles from approximately 2 2 to 4 5 km s 1 in the first 40 m y the most likely cause is decreasing porosity in extruded basalts that compose the uppermost igneous crust by filling cracks with hydrothermally generated minerals a by product of off axis hydrothermal circulation and alteration of basalts new insights from two recent papers on crustal hydrothermal circulation patterns and modeling of the effects of crack geometry distributions upon seismic velocities provide guidance to relate filling of cracks within the basement to seismic velocity increases a qualitative model of layer 2a crustal evolution is outlined that satisfies many geophysical and geochemical observations some seemingly unrelated somewhat surprisingly the crustal age at which layer 2a seismic velocities reach their maximum value is primarily controlled by the integrated permeability of the overlying sediment which in turn controls the hydrologic regime necessary for secondary mineral precipitation speculative predictions can be used to verify refine or invalidate this dynamic model of crustal evolution major scientific and technical obstacles must be overcome before a definitive model can be quantified with such a rigorous model of crustal upper crustal evolution in hand remote geophysical sensing tools can begin to fulfill the promise of interpreting the physical state composition and past history of oceanic crust

3 d kinematic restoration of the eastern sudbury igneous complex canada and its importance for cu ni pge sulphide exploration abstract kinematic restorations of deformed igneous terranes have rarely been attempted due to the general absence of 1 planar primary lithological contacts 2 tightly constrained deformation kinematics and 3 geometric constraints on lithologies and structures at depth because of the vast number of exploration drill holes the deformed and layered 1 85 ga sudbury igneous complex sic in ontario canada is reasonably well understood with respect to 1 and 3 we therefore explored the kinematics of folding and faulting in the eastern sic and use the subsurface geometry of faults extracted from a model integrating surface mapping and drill core logs in an attempt to restore the geometry of part of the sic specifically we identified rotation magnitudes and the tilt axis of a kilometer scale plunging fold the west bay anticline which appears to have folded the eastern part of the sic we combined a 3 d model of the faults and lithological contacts of the sic fault kinematics calculated from the inversion of brittle shear faults at surface and limb rotations of the west bay anticline to kinematically restore the eastern part of the sic results of restorations using simple shear and flexural slip algorithms highlight the importance of slip on prominent curved faults that displaced the sic and facilitated its folding flexural slip appears to be the more plausible mechanism of the two as it removed the curvature of and displacement on prominent faults flexural slip restoration helps to estimate primary thickness variations of the sic and the results show that thickened parts of the main mass of the sic correspond spatially with known cu ni pge sulfide deposits this result demonstrates that 3 d restoration can be an important tool for mineral exploration in igneous terranes

delineating a road salt plume in lakebed sediments using electrical resistivity piezometers and seepage meters at mirror lake new hampshire u s a electrical resistivity surveys seepage meter measurements and drive point piezometers have been used to characterize chloride enriched groundwater in lakebed sediments of mirror lake new hampshire u s a a combination of bottom cable and floating cable electrical resistivity surveys identified a conductive zone 100 ohm m overlying resistive bedrock 1000 ohm mbeneaththelake shallowpore watersamples frompiezometersinlakebedsedimentshavechlorideconcentrations of 200 1800 eq liter and lake water has a chloride concentrationof104 eq liter theextentoftheplumewasestimated and mapped using resistivity and water sample data the plume2035 mwideandatleast3 mthickextendsnearlythe full length and width of a small inlet overlying the top of a basin formed by the bedrock it would not have been possible to map

transient hydrogeological controls on the chemistry of a seepage lake a solute mass balance method was used to estimate groundwater inflow and outflow rates for nevins lake michigan a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes a 4 year study 1989 1992 of the hydrology and geochemistry of nevins lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals a pronounced acidification of nevins lake from 1986 to 1988 was likely caused by drought induced diminished groundwater inflow rates in this study dissolved calcium the major cation in water of nevins lake groundwater and precipitation was used for estimating mass flow rates during the 1989 1992 period nevins lake showed a reproducible annual cycle in calcium mass immediately following spring snowmelt and the resulting hydraulic gradient reversal the mass of dissolved calcium in the lake increases rapidly and then it decreases steadily throughout the summer and early fall at which time the lake becomes hydraulically mounded and receives no groundwater inflow groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore but spatial and temporal variability in pore water chemistry must be considered stable isotope analyses 18o and 2h of lake water groundwater and pore water samples show that water discharging to nevins lake in the spring is entirely recycled lake water and no groundwater derived from terrestrial recharge reaches the lake the conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

flow path composition relationships for groundwater entering an acidic lake the relationship of groundwater flow paths to the acid base status and composition of groundwater was examined by directly monitoring groundwater inputs to an acidic adirondack new york lake dart s lake groundwater inputs near the shoreline of the lake were acidic throughout the year ph 40 mu eq l sup minus 1 elevated concentrations of basic cations and alkalinity as well as lower concentrations of organic anions and sulfate were characteristic of deep ground water entering the lake at the study site spatial variability of groundwater chemistry was found to be substantial over a relatively short distance 6 m from the lake shoreline and indicates that input to the lake of components dissolved in groundwater are highly flow path dependent

grain boundary migration microstructures in a naturally deformed quartzite abstract in this study several grain scale microstructures are presented that are thought to demonstrate the migration direction of once mobile grain boundaries in a naturally deformed quartzite an analysis is presented of the sense of migration of the boundaries and the characteristics of the patterns of relative grain growth and shrinkage grain boundary migration seems to be correlated with the relative crystallographic orientations of neighbouring grains for the quartz quartz grain boundaries and the pattern of preferred grain growth is roughly symmetrical about the mica foliation plane

hydrogeology and its effect on slope stability along the coastal aquifer of nice france abstract along the ligurian continental margin off nice western mediterranean a considerable portion of the sediments is affected by pore pressure transients resulting from groundwater charging by the nearby river var and also from leaching clay mineral bearing deposits which results in sensitive weak clays in 1979 the area suffered a tsunamigenic landslide that generated several casualties and material damage to the coastal zone the seafloor presently shows evidence for soft sediment deformation and pore water freshening in this paper we present the first comprehensive in situ pore pressure data set collected over space and time between 2006 and 2009 in a landslide prone area using piezometers ifremer brest france and dynamic cone penetrometers ff cptu marum bremen germany as well as a simple modelling approach we illuminate what governing factors control strength and pore pressure in marine slope sediments affected by the var aquifer our results attest i a strong link between pore pressure transients and local precipitation over a period of 11 months ii overpressure at levels where groundwater flow occurs coarse intervals containing sand and gravel and iii fluidised fractures and channels that indicate high pore pressures at least temporarily in essence seepage and repeated pore pressure fluctuations weaken the sediment effectively so that it cannot be ruled out that the currently stable portion adjacent to nice airport may fail in the near future

massive sulfides in a sedimented rift valley northern juan de fuca ridge a number of mounds each several hundred meters across and up to sixty meters high have been observed with seamarc ii acoustic imagery and seabeam bathymetry in the sediment filled axial valley at the northern end of the juan de fuca ridge the mounds are located a few kilometers west of the eastern valley bounding normal fault scarp where the local sediment fill is approximately 300 m thick all of the mounds are believed to be of hydrothermal origin and one is associated with anomalously high heat flow in excess of 1 w m 2 a piston core collected from that mound comprises coarse clastic sulfide units interbedded with sulfidic muds hydrothermal minerals present in the 2 3 m section include pyrrhotite pyrite marcasite sphalerite chalcopyrite iss intermediate solid solution in the cufezns system chalcopyrrhotite galena talc barite and amorphous silica mineral fabrics of the clasts indicate that the material was precipitated at or near the sea floor by mixing of hot hydrothermal fluids with cold seawater low concentrations of zn cu cd and ag relative to those found in unsedimented ridge hydrothermal deposits and the presence of pyrrhotite as an early phase mineral indicates that the vent fluids have been modified by reaction with sediments beneath the mound rapid sedimentation in a rift valley is clearly conducive to the formation of large hydrothermal mineral deposits like those believed to be present within and beneath these mounds the relatively impermeable sediment cover insulates the crust inhibits groundwater recharge promotes long lived discharge at a restricted number of sites provides a substrate for the efficient subsurface precipitation of minerals and through continued sedimentation protects surficial deposits from the corrosive effects of seawater no reliable estimate of the bulk composition of the mounds can be made with existing data but their size is comparable to major hydrothermal mineral deposits found on land ancient settings in which many land deposits formed are in many ways similar to the one in which the features described here are currently forming

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

groundwater s dynamic role in regulating acidity and chemistry in a precipitation dominated lake abstract the role of groundwater in regulating the hydrologic and chemical regime ofan acid susceptible lake situated in a sandy silicate aquifer in northern wisconsin was determined by direct groundwater measurements using a network of 68 piezometers groundwater inputs were compared with precipitation and dryfall components of the hydrologic and chemical budgets for the lake groundwater contributed only 10 of the water to crystal lake in 1982 but was the major source of alkalinity calcium magnesium sodium potassium silicon and chloride precipitation contributed 90 of the water and was the major source of hydrogen and sulfate ions continuing analyses suggest that groundwater consistently supplies the bulk of the inoorganic constituents to the lake on annual basis the flux of groundwater and dissolved solids to the lake is highly seasonal with large pulses of groundwater inflow occuring after spring snowmelt and in the fall for certain nonconservative elements such as silicon the periodic influx of chemically concentrated groundwater can trigger significant changes in the chemical and biological balance in the lake despite the fact that the aquifer contains no carbonate minerals and the area experiences acid precipitation ph 4 6 the alkalinity of the small amount of groundwater entering crystal lake is more than enough to neutralize all of the acidity contributed by precipitation in lake sulfate reduction may generate an equal amount of alkalinity this buffering of ph helps to regulate aluminum concentrations at low levels thus minimizing potential aluminum toxicity in the lake most lakes in the region probably receive even larger amounts of alkalinity rich groundwater than crystal lake because most lie further downgradient in the regional flow system this may help to explain why most lakes in this acid susceptible area are no more acidic today than they were 50 years ago

the effect of target lithology on the products of impact melting impact cratering is an important geological process on the terrestrial planets and rocky and icy moons of the outer solar system impact events generate pressures and temperatures that can melt a substantial volume of the target however there remains considerable discussion as to the effect of target lithology on the generation of impact melts early studies showed that for impacts into crystalline targets coherent impact melt rocks or sheets are formed with these rocks often displaying classic igneous structures e g columnar jointing and textures for impact structures containing some amount of sedimentary rocks in the target sequence a wide range of impactgenerated lithologies have been described although it has generally been suggested that impact melt is either lacking or is volumetrically minor this is surprising given theoretical constraints which show that as much melt should be produced during impacts into sedimentary targets the question then arises where has all the melt gone the goal of this synthesis is to explore the effect of target lithology on the products of impact melting a comparative study of the similarly sized haughton mistastin and ries impact structures suggests that the fundamental processes of impact melting are basically the same in sedimentary and crystalline targets regardless of target properties furthermore using advanced microbeam analytical techniques it is apparent that for the structures under consideration here a large proportion of the melt is retained within the crater as crater fill impactites for impacts into sedimentary bearing target rocks thus it is suggested that the basic products are genetically equivalent but they just appear different that is it is the textural chemical and physical properties of the products that vary

190pt 186os and 187re 187os systematics of the sudbury igneous complex ontario abstract we measured by negative thermal ionization mass spectrometry ntims re os and 186 os 188 os and 187 os 188 os in 26 samples of 18 ni cu sulfide ores from the falconbridge mccreedy west and strathcona mines at sudbury ontario at mccreedy west and falconbridge the isochron re os ages are 1835 70 ma and 1827 340 ma and the initial 187 os 188 os ratios 0 514 0 019 and 0 550 0 024 respectively the ages agree with the canonical value of 1850 1 ma for the sudbury igneous complex sic for hangingwall and deep zone ores at strathcona the age of 1780 7 ma may reflect resetting by dyke activity the high initial 187 os 188 os of 0 934 0 005 in these ores is distinct from those at mccreedy west and falconbridge strathcona deep copper zone ores have highly radiogenic os giving a mean model age of 1883 54 ma that is similar to ages at mccreedy west and falconbridge but distinct from other strathcona sulfides initial 186 os 188 os in two strathcona ores with low 190 pt 188 os average 0 119 826 0 000 009 n 3 and 0 119 827 0 000 004 n 3 respectively with a grand mean of 0 119 827 0 000 003 this ratio may be slightly lower than the chondritic value at that time similar ores at falconbridge and mccreedy west show more scatter averaging 0 119 855 0 000 008 n 6 and 0 119 867 0 000 020 n 3 respectively these values are substantially suprachondritic the re os isotope systematics of sudbury ores are clearly of crustal origin and may be derived from a binary mixture of superior province and huronian metasedimentary rocks with strathcona falconbridge and mccreedy west ores containing respectively 55 16 and 12 of os from superior sediments the suprachondritic 186 os 188 os at mccreedy west and falconbridge may be due to admixture of archean or paleozoic mafic rocks with 190 pt 188 os 0 1 no trace of the asteroid that produced the sudbury structure has been reported at the whistle mine s poor olivine melanorite inclusions with high ni and os and low 187 os 188 os may contain the signature of a magmatically fractionated asteroidal core contributing 1 to 2 5 metal the s poor melanorite ni and os data are equally well explained by admixture of 40 mantle peridotite however