submarine metamorphism of gabbros from the mid cayman rise an oxygen isotopic study abstract oxygen isotopic compositions of minerals in 22 samples of submarine gabbros were determined the gabbros were collected using the submersible alvin from the 700 m vertical section of the rift valley wall of the mid cayman spreading center our study indicates that in the mid cayman rise seawater barely reached the bottom of the plutonic layer abundant seawater penetration water rock mass ratio 1 was limited to the upper part of the plutonic layer from the observed oxygen isotopic compositions of coexisting minerals and from the experimental and empirical determinations of equilibrium fractionation of oxygen isotopes for mineral water and mineral mineral pairs we show the following 1 pyroxene and olivine did not exchange oxygen with seawater 2 plagioclase is in isotopic disequilibrium with pyroxene 3 the rate of oxygen exchange in plagioclase was not slowed by the absence of cation exchange 4 plagioclase and amphibole have exchanged oxygen with seawater or isotopically modified seawater 18o 3 and 5 amphibole has exchanged or acquired during formation hydrogen from seawater at 380 c t 600 c the decrease in extent of isotopic exchange of plagioclase and the decrease in amphibole abundance with depth indicate that seawater flux decreased rapidly with depth water rock mass ratio falling from 1 7 to 0 2 over a 300 m interval

rheological evolution of the ocean crust a microstructural view rheological studies of the oceanic lithosphere have used direct observations of rocks and inferences based on thermal mechanical and experimental models modeling studies help to constrain an average crust and mantle rheology and the deep seated processes that control regional scale strength and stress field variations the smoothing of fine scale variations in such models can obscure many of the geological processes that influence strain localization and deformation partitioning in the ocean crust examination of deformation mechanisms and histories in ocean crust rocks provides a complementary approach to modeling examples of structures and deformation histories in diabases from deep sea drilling project ocean drilling program site 504b the hayes and atlantis fracture zones mid atlantic ridge and the troodos ophiolite cyprus are presented in conjunction with a synthesis of microstructural studies of the ocean crust over the last 25 years a survey of brittle quasi plastic and synmagmatic viscous deformation is used to demonstrate the influence of primary compositional and textural characteristics and variable magmatic and hydrothermal histories on deformation mechanisms and strain localization in the ocean crust geological evidence indicates that hydrothermal fluids strongly influence the nature of deformation and that effective stresses may be low due to fluid overpressures melt distribution will strongly influence strain localization at the base of the crust and synkinematic hydration during crystal plastic deformation plays a key role in the relative strengths of polyphase oceanic lithologies a schematic distribution of failure mechanisms in the ocean crust is used to discuss the controls on variations in lateral and vertical strength profiles and their possible relation to spreading rates although microstructural studies of ocean crust are still in their infancy they provide valuable constraints for rheological models and further insights to explain the distribution of seismicity at spreading centers and acoustic signatures

geochemical processes and multivariate statistical analysis for the assessment of groundwater quality in the swarnamukhi river basin andhra pradesh india with rapid increase of human population swift growth of industries and intensive irrigation activities groundwater quality is being increasingly endangered by agricultural chemicals and indiscriminate disposal of urban and industrial wastes hence in water management assessment of groundwater quality is as important as quantity especially in the arid and semi arid regions evaluation of hydrogeochemical parameters and solute acquisition process controlling water chemical composition was studied by collecting 66 groundwater samples in pre monsoon and post monsoon seasons in the swarnamukhi river basin andhra pradesh india geologically the study area comprises granite and granitic gneisses quartzite and alluvium the total dissolved solids classification reveals that majority of the groundwater samples are desirable for drinking and all are useful for irrigation purposes major ion chemistry reveals the ionic dominance pattern among cations and anions is in the order na ca mg k and cl hco3 no3 so4 co3 f po4 in both the seasons 85 and 89 of samples are very hard water in pre and post monsoon respectively which needs softening for domestic uses 48 and 42 and 34 and 41 of the samples of the study area are found having sodium 200 mg l and nitrate content 50 mg l in pre and post monsoon seasons respectively more than permissible limits which is not good for human consumption natural and anthropogenic sources of the solutes have been categorized with the help of different ionic ratios plots and correlation matrix potential salinity sources include deep saline upcoming and wastewater infiltration salinity mapping shows brackish to fresh brackish water predominance in the study area the plot of major ion in the piper diagram reveals that majority of samples belongs to mixed type followed by na cl facies four principal components were extracted from chemical data to explain the major sources and processes responsible for chemical characteristics of groundwater it shows that silicate weathering agricultural runoff fertilizer input municipal wastewater infiltration play a vital role in the enrichment of ionic constituents average water quality index shows that majority of the samples are good to permissible for drinking purpose various irrigation indices show good to permissible use of groundwater in agricultural activities as per the lsi and rsi values groundwater of the area is considered very aggressive and substantial corrosion is possible

a multi isotope b sr o h and c and age dating 3h 3he and 14c study of groundwater from salinas valley california hydrochemistry dynamics and contamination processes 1 the chemical and isotope 11b 10b 87sr 86sr 18o 16o 2h h 13c 12c 14c and 3he 3h compositions of groundwater from the upper aquifer system of the salinas valley in coastal central california were investigated in order to delineate the origin and processes of groundwater contamination in this complex system the salinas valley has a relatively deep confined 400 foot aquifer overlain by a 180 foot aquifer and a shallower perched aquifer all made up of alluvial sand gravel and clay deposits groundwater from the aquifers have different 14c ages fossil 14c 21 3 percent modern carbon pmc for the 400 foot aquifer and modern 14c 72 2 98 2 pmc for the 180 foot aquifer fresh groundwater in all aquifers is recharged naturally and artificially through the salinas river the two modes of recharge can be distinguished chemically we identified several different saline components with distinguishable chemical and isotopic fingerprints 1 saltwater intrusion in the northern basin has c1 concentrations up to 1700 mg l a na cl ratio less than seawater a marine br cl ratio a ca cl ratio greater than seawater 11b between 17 and 38 and 87sr 86sr between 0 7088 and 0 7096 excess dissolved ca relative to the expected concentration for simple dilution of seawater correlates with 87sr 86sr ratios suggesting base exchange reaction with clay materials 2 agriculture return flow is high in no3 and so4 with a 87sr 86sr 0 7082 11b 19 and 13c between 23 and 17 the 3h 3he ages 5 17 years and 14c data suggest vertical infiltration rates of irrigation water of 3 10 m yr 3 nonmarine saline water in the southern part of the valley has high total dissolved solids up to 3800 mg l high so4 na cl ratio 1 11b between 24 and 30 and 87sr 86sr 0 70852 this groundwater may have acquired its geochemical signature from leaching of sedimentary rocks associated with the coast range marine deposits of mesozoic to early cenozoic age the combination of different geochemical and isotopic fingerprints enables us to delineate the impact of salt sources in different areas of the valley and to reconstruct the origin of the so4 enriched no3 depleted saline plume that is located west of the city of salinas we suggest that the latter is derived from a mixture of different natural saline waters rather than from anthropogenic contamination

intraoceanic tectonism on the gorringe bank observations by submersible the gorringe bank is a 200 km long structure oriented ne sw located at the eastern end of the azores gibraltar line at the europe africa boundary it consists of two mounts mount gettysburg at the sw 25 m and mount ormond at the ne 100 m previous works have shown that it corresponds to a section in oceanic mantle and crust a recent expedition of the submersible sp 3000 cyana may june 1981 has allowed us i to confirm that mount gettysburg essentially consists of largely serpentinized peridotites the study of two oriented samples collected in situ allows some inferences about the kinematics of emplacement for these ultramafics ii to show that mount ormond is mostly composed of various gabbros corresponding to different stages of differentiation all the samples are more or less recrystallized and display strong deformation from high temperature mylonitization to low temperature brecciation such a ubiquitous deformation is not common in ophiolite complexes and may be linked with the location of the bank at the europe africa plate boundary iii to observe two generations of undeformed dykes cutting the ormond gabbros the first one of dolerites genetically linked with the gabbros the second of alkaline rocks feeders of the more recent alkaline volcanics capping the mount

geotectonic significance of gneissic amphibolites from the vema fracture zone equatorial mid atlantic ridge a large collection of gneissic amphibolites was recovered by two close dredge hauls from the deepest part of the north facing slope of the transverse ridge forming the south wall of the vema fracture zone serpentinites and various types of gabbroic rocks ranging from undeformed slightly uralitized gabbros and norites to flaser and mylonitic gabbros were associated with the gneissic amphibolites in the shallowest of the dredge hauls petrological studies indicate that the amphibolites were derived from similar gabbroic rocks that reequilibrated under stress in the conditions of the amphibolite facies on the other hand the associated meta gabbros display sequences of secondary minerals indicating complex cooling and cataclastic histories without reaching metamorphic equilibrium we tentatively suggest that the gneissic amphibolites and associated metagabbros formed in a vertical shear zone generated in oceanic layer 3 by tectonism associated with the vema fracture zone hydrothermal circulation of seawater along the highly permeable shear zone was activated by magmatic intrusions k ar dating suggests within relatively large analytical uncertainties that the amphibolite metamorphism took place 10 m y ago i e at a time when the dredging sites were located in the vicinity of the spreading center

water geochemistry controlled by carbonate dissolution a study of the river waters draining karst dominated terrain guizhou province china concentrations of major ions and sr and sr isotopic compositions of two major river systems wujiang river and yuanjiang river in karst dominated regions and during winter were measured the rivers and their tributaries have high total dissolved solid concentrations with tz ranging from 2 1 to 6 3 meq l which are significantly higher than that of the global river average calcium and hco3 followed by mg2 and so42 dominate the chemical composition of major ions in the river waters both na k and cl si account for 5 10 of the cations and anions respectively the waters of the wujiang river have high sr2 concentrations and lower 87sr 86sr ratios 0 7077 0 7110 while those of the qingshuijiang river one of two major tributaries of the yuanjiang river system show higher sr isotopic ratios 0 7090 0 7145 and low sr concentrations the lithology and geography of the river basins largely control the chemical and isotopic compositions of these rivers analyses of the stoichiometry of the river waters show that the water chemistry is controlled by carbonate dissolution by both carbonic and sulfuric acid especially of the wujiang river and suggest an origin of sulfate mainly from atmospheric input because of coal combustion and or oxidation of sulfide minerals in the catchments we identify three main weathering sources limestone dolomite and silicates chemical and sr isotopic composition of wujiang river waters are characterized mainly by limestone weathering while those of the qingshuijiang river waters mainly by dolomite and silicate weathering chemical weathering rates of carbonate and silicate are estimated and the results indicate that the chemical weathering rates of carbonate in the catchments are remarkably high significantly higher than most large rivers it is considered that presence of sulfuric acid in the rock weathering overuse of land and deterioration of vegetation are most likely the key factors responsible for the high weathering rates of carbonate in the catchments

submarine metamorphism of gabbros from the mid cayman rise petrographic and mineralogic constraints on hydrothermal processes at slow spreading ridges the coarse grained submersible collected rocks from the mid cayman rise in our study span a vertical section of about 700 m and range from amphibolite to gabbro petrographic and mineralogic studies showed that 1 some deformation is present in all rocks 2 the distribution of deformation is not uniform within a specimen and 3 alteration has taken place preferentially in the deformed zones the abundance of amphibole decreases with sample depth and argues that seawater flux into the oceanic crust decreased with depth the compositional changes in rocks indicate that partially exchanged seawater was the metamorphic fluid that supplied na k and h2o to and removed ca from the rock in all about 15 of the original rock has been transformed to amphibolite in the 700 m vertical section our study indicates that deformation of oceanic crust is necessary for providing pathways for seawater penetration which in turn is necessary for the submarine metamorphism to occur if deformation continues to take place during the spreading of seafloor alteration may also continue to occur along newly formed fractures and cracks

re os geochronology and systematics in molybdenite from the endako porphyry molybdenum deposit british columbia canada precise re os molybdenite ages for the endako porphyry molybdenum deposit and the nithi mountain occurrence british columbia canada yield new information on the timing of molybdenite deposition three episodes of mineralization are indicated 1 154 ma 2 148 to 146 ma and 3 145 ma re os dates agree well with new u pb and 40 ar 39 ar data from granitoids of the nithi phase 155 2 1 5 ma the endako phase 148 4 1 5 ma and a preore dike 147 4 0 6 ma and the casey phase 145 1 0 2 ma plus hydrothermal biotite 144 5 0 75 ma villeneuve et al 2001 the excellent correlation between the re os dates from molybdenite and the ages of granitoids from the area indicates a direct genetic relationship between these plutons and molybdenite mineralization these re os data also provide further insight into the systematics and robustness of re os in molybdenite the endako molybdenum deposit is the product of two episodes of mineralization both associated with moderate salinity 5 15 wt nacl equiv and high temperature 440 c fluids a third low temperature 190 300 c hydrothermal event is associated with eocene faulting selby et al 2000 the clear distinction between two of the re os molybdenite dates in the deposit and the close agreement of these dates to the ages of granitoid intrusions suggest that the re os system in molybdenite is not reset by high temperature 440 c moderate salinity hydrothermal fluids in contrast magmatic biotite in a 147 ma preore dike has a 40 ar 39 ar age of 145 ma identical to the age of the hydrothermal biotite indicating that 440 c fluids reset the ar ar system in biotite hence we interpret that the re os isotope system in molybdenite is resistant to resetting by high temperature fluids 440 c in contrast to the 40 ar 39 ar system in biotite the re os system in molybdenite is also unaffected by postore hydrothermal fluids these data show that molybdenite can provide critical information in understanding sulfide mineral deposition in ore systems which is not recorded by other isotopic systems in alteration minerals

geologic section through the samail ophiolite and associated rocks along a muscat ibra transect southeastern oman mountains regional mapping at a 1 60 000 scale of a 30 km strip from the gulf of oman muscat across the oman mountains 130 km to the south provides the geologic setting for the 95 m y ibra section of the samail ophiolite where best preserved the ibra ophiolite section is an 8 km thick section of oceanic consisting of 0 5 km of pillow lavas 1 2 1 6 km of sheeted diabase dike complex 0 2 1 0 km of high level noncumulate gabbro and 3 0 5 0 km of cumulate gabbro that is underlain by tectonite peridotite 9 12 km thick the ibra section is found on the southward dipping limb of the sayah hatat antiform the tectonite peridotite represents uniformly depleted harzburgite and dunite that have been deformed by high temperature low stress asthenospheric flow discordant dunites within the tectonite peridotite appear to represent either flow crystallization products from primary picritic liquids or reaction products of these liquids with the harzburgite the structural base of the tectonite peridotite is overprinted by a high stress low temperature deformation that can be related to its oceanic detachment the layered gabbros are predominantly olivine clinopyroxene plagioclase cumulates and orthopyroxene does not occur as a cumulus phase occurrence of cumulate wehrlites and picrites at high stratigraphic levels within the layered gabbros is evidence that the gabbroic section crystallized predominantly from the bottom upward in a periodically replenished magma chamber high level gabbro represents remnants of crystallization at the roof of the magma chamber and intrudes most overlying diabase dikes both the diabase dike complex and pillow lavas are hydrothermally altered and alteration and metamorphism increase downward zeolite to epidote amphibolite facies in spite of pervasive alteration relict primary mineralogy and bulk chemistry suggest that the diabase dikes and pillow lavas are cogenetic with the underlying gabbros the present day samail thrust surface truncates ophiolite stratigraphy and puts the samail ophiolite on top of unmetamorphosed hawasina melange the last motion on this surface was probably no older than maestrichtian 70 65 m y garnet amphibolites exposed as remnants of earlier thrusting 90 m y record initial ophiolite detachment at a 14 20 km depth within the tethyan oceanic lithosphere the hawasina group which underlays the samail ophiolite is a block melange where exposed near muscat in the north and it grades into an imbricated broken formation at the southern limit of the map area the hawasina group is thrust over permian to late cretaceous shelf carbonates that represent autochthonous arabian continental shelf deposits recent post miocene collapse and dome structures such as the ibra dome have complicated ophiolite stratigraphy south of jabal dimh our geologic studies strongly indicate the samail ophiolite represents a large coherent slab of transported oceanic lithosphere formed at a late cretaceous spreading center in the tethyan sea

fluid flow patterns in fast spreading east pacific rise crust exposed at hess deep tectonic exposures of a volcanic sequence and sheeted dike complex over a 4 km wide region at hess deep equatorial pacific reveal significant spatial heterogeneity 10 103 m in the extent and nature of hydrothermal alteration in young fast spreading east pacific rise crust the volcanic sequence is fairly uniformly altered with only minor oxidation and alteration to clay minerals sheeted dikes in the eastern part of the field area are highly fractured with narrow intervals of intact dikes that dip up to 60 their alteration characteristics show a simple depth trend such that with increasing depth the dominant secondary mafic mineral changes from chlorite to amphibole clinopyroxene replacement increases 40 whole rock 18o values decreases 4 4 5 5 to 3 5 4 5 and calculated peak metamorphic temperatures increase 250 c to 450 700 c within the deepest dikes localized zones up to 400 m wide are chlorite rich and have low 18o 2 9 4 1 and low peak metamorphic temperatures 345 c these alteration patterns likely formed within broad recharge zones whereby the low 18o zones developed in the regions with the highest fluid flux in the west massive slightly rotated sheeted dikes near the volcanic sheeted dike transition are 18o and cu depleted and display higher peak temperatures 345 c than elsewhere in the shallow dikes these characteristics are consistent with formation within a high temperature hydrothermal discharge zone we propose that the spreading history of a fast spreading ridge segment can create significant spatial heterogeneity in fluid flow and alteration patterns within sheeted dike complexes similar to those preserved in many ophiolites

microstructures of the cayman trough cabbros many different deformation textures are observed in submersible collected gabbros from the mid cayman rise spreading center indicating considerable variation in conditions of deformation in this slowly spreading ridge features suggesting flow range from mechanical twins and bent crystals low strain to complete recrystallization with a well developed foliation high strain textures suggesting fracture include zones 0 1 10 mm wide of extremely reduced grain size cracked grains with undulose extinction and crosscutting fractures these textures occur separately next to and overprinting each other of the variables controlling the deformation features temperature and water pressure are most easily estimated minimum temperature during deformation is suggested by minimum temperature during deformation of mineral assemblages unaffected by this deformation this temperature is above 500 550 c for the majority of the features observed observations suggest enhanced recrystallization where primary minera

detrital transport of metals by glaciers an example from the pinchi mine central british columbia abundant cinnabar hgs mineralization is associated with the pinchi fault in central british columbia two formerly producing mercury mines have been developed on this fault pinchi and bralorne takla the mercury content of till a sediment type directly deposited by glaciers in the area of this fault is primarily controlled by the occurrence of cinnabar mineralization in bedrock and the direction of ice flow cinnabar bearing bedrock was eroded by glaciers transported in the direction of ice flow and deposited down ice from its source an example of such a dispersal train is documented for the pinchi mine area where mercury ore was transported over a distance of 12 km as measured in the clay sized fraction 3 3 of this same sediment antimony chromium and nickel dispersal trains were also detected in the region these data indicate that natural glacial processes can result in the mobilization of metals in the surficial environment a factor which has to be considered at mine sites in glaciated terrain where mine reclamation and remediation measures are now required

an integrated approach to assess the quality of groundwater in a coastal aquifer of andhra pradesh india the narava basin in visakhapatnam district situated on the east coast is a productive agricultural area and is also one of the fastest growing urban areas in india the agricultural and urban industrialization activities have a lot of impact on this coastal aquifer water quality the hydrochemistry of the groundwater was analyzed in the basin area with reference to drinking and agricultural purposes the area is underlain by precambrian rocks like khondalites charnockites and migmatites the water samples were collected from shallow wells for the year 2008 physical and chemical parameters of groundwater such as ph total alkalinity ta electrical conductivity ec total dissolved solids tds total hardness th ca2 mg2 na k hco3 cl so4 2 no3 f were determined the analytical results revealed that the most of the groundwater found to be in polluted category geographical information system gis was utilized to generate different spatial distribution maps of various chemical constituents in the study area the analytical data were used to compute certain parameters such as salinity hazard percent sodium na sodium adsorption ratio sar residual sodium carbonate rsc permeability index pi kelley s ratio kr and corrosivity ratio cr to determine the quality of water for agricultural purposes the abundance of the major ions in the basin area was found to be in the following sequence na ca2 mg2 k cl hco3 so4 2 no3 f according to gibbs diagram most of the samples fall under rock dominance as per wilcox and ussl classification most of the groundwater samples are suitable for irrigation except few samples which are unsuitable due to the presence of high salinity and high sodium hazard from the obtained data it can be concluded that the water quality profile was good and useful for normal irrigation agriculture

distribution of paleogene and cretaceous rocks around the nazko river belt of central british columbia from 3 d long offset first arrival seismic tomography across the nechako chilcotin plateau of british columbia the distribution of cretaceous sedimentary rocks which are considered prospective for hydrocarbon exploration is poorly known due to the surface cover of glacial deposits and tertiary volcanic rocks to constrain the subsurface distribution of these cretaceous rocks in 2008 geoscience bc acquired seven long up to 14 4 km offset vibroseis seismic reflection lines across a north northwest trending belt of exhumed sedimentary rocks inferred to be part of the taylor creek group p wave velocity models which are consistent with sonic logs from nearby wells have been estimated using three dimensional first arrival tomography to depths ranging from 1 to 4 km igneous basement can be identified on most lines using the 5 5 km s isovelocity contour which locates the top of the basement to an accuracy of 400 m where its depth is known in exploration wells there is no general distinction on the basis of seismic velocity between cretaceous sedimentary

oxygen isotope composition of a section of lower oceanic crust odp hole 735b 1 the oxygen and hydrogen isotope compositions of vein minerals and 18o values of 64 whole rocks from the deeper kilometer of the 1 5 km lower crustal section of odp hole 735b in the sw indian ocean were analyzed in order to investigate seawater penetration into and reaction with the lower oceanic crust vein amphiboles have d values of 35 to 65 indicating formation from seawater fluids and hydrothermal fluids containing a component of low d magmatic fluid crystal plastic shear zones reacted with 18o enriched fluids at high temperatures and have 18o values of 6 0 7 0 indistinguishable from surrounding rocks reaction with seawater dominated fluids over a range of temperatures 350 700 c led to local 18o depleted rocks but much of the section exhibits 18o enrichment 18o up to 7 6 as the result of static alteration of plagioclase over a range of temperatures 250 to 600 c and fluid compositions chloritic veins and associated alteration by 18o enriched fluids occurred at temperatures of 150 250 c and late carbonates and fe oxyhydroxides formed from cold 10 seawater associated with open fault related fractures bulk rock 18o values of the lower 1 km range from 3 7 to 10 2 but are mostly 5 6 7 6 and the section has a mean bulk 18o of 6 5 1 0 in contrast rocks from the shallower 500 m exhibit net 18o depletion 5 1 1 0 reflecting high temperature deformation and seawater hydrothermal alteration stakes 1991 the weighted average 18o for the entire gabbro section of hole 735b is 6 0 exhibiting little or no change compared to unaltered crust although tectonism at slow spreading rates may allow exposure of lower crust to greater amounts of low temperature alteration and 18o enrichment there is no evidence for a consistent difference in the bulk 18o of the plutonic sections of oceanic crust formed at fast versus slow spreading rates

lithostratigraphic and tectonic framework of jurassic and cretaceous intermontane sedimentary basins of south central british columbia1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia the south central intermontane belt of british columbia has a complex architecture comprising late paleozoic to mesozoic volcanic and plutonic arc magmatic suites marine and nonmarine clastic basins high grade metamorphic complexes and accretionary rocks jurassic and cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential the geology is complicated by cretaceous to eocene deformation dismemberment and dislocation the eocene to neogene history of the southern intermontane belt is dominated by non arc volcanism followed by pleistocene to recent glaciation the volcanic and glacial cover makes this a difficult region to explore for resources much recent work has involved re evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis this paper summarizes the lithological and stratigraphic fra

multistage hydrothermal alteration of gabbroic rocks from the failed mathematician ridge oxygen isotopic mineralogical and fluid inclusion data are presented for fresh and hydrothermally altered gabbroic rocks from the failed mathematician ridge the mathematician ridge though initially a fast spreading ridge presently has a deep central rift valley more typical of slow spreading rifts the inner rift walls expose rare plutonic rocks uncomplicated by proximity to deep large offset fracture zones undeformed mathematician ridge gabbros preserve most of the original texture and phase compositions and have been only slightly mineralogically or isotopically modified by post crystallization hydrothermal alteration metagabbros have been subjected to a pervasive ductile deformation and recrystallization to foliated rocks composed of aluminous amphibole low calcium plagioclase and ilmenite oxygen isotope and phase chemical data suggest this event began at temperatures of up to 700 c water rock ratios of less than one and produced modified seawater fluids with isotopic compositions of 3 5 6 0 the amphibolites are cross cut by multiple generation quartz epidote veins forming a network replacement of the amphibole grade mineralogies by greenschist grade mineralogies fluid oxygen isotopic compositions of 2 4 and a two phase separation in the fluid captured in conjugate vapor fluid inclusions are all associated with the formation of this network fluid inclusion data for the quartz indicate initial temperatures of over 500 c these samples may represent rocks from the 1 2 km deep plumbing system of black smoker type venting

interaction of highly saline fluid and olivine gabbro experimental simulation of deep hydrothermal processes involving amphibole at the base of the oceanic crust abstract natural occurrences of cl bearing amphibole indicate crystallization in the presence of a highly saline fluid amphibole with varying cl contents 0 1 to 5 wt cl found in lower oceanic crustal rocks demonstrates the activity of saline hydrothermal fluids at depth here we present an experimental study done in cold seal pressure vessels cspv and internally heated pressure vessels ihpv to illustrate the process by which gabbro hosted amphibole rich parageneses evolve in the presence of a hydrothermal saline fluid the starting material used was a natural gabbroic rock containing high ti magnesio hastingsite with the addition of a moderately to highly saline fluid nacl h2o with xnacl 0 02 0 07 and 0 24 6 20 and 50 wt nacl we evaluated a range of conditions from hydrothermal 500 750 c to magmatic 900 c at pressures of 200 mpa and fo2 close to nno fluid rock mass ratios used were 0 2 and 1 in subsolidus hydrothermal experiments and 0 07 in partial melting magmatic experiments new amphibole was formed on rims of the starting high ti magnesio hastingsite with product compositions corresponding to magnesio hastingsite high si magnesio hornblende tschermakite edenite hastingsite and ferro pargasite with varying cl contents up to 0 47 wt cl our results from subsolidus experiments demonstrate a decrease in olivine plagioclase and clinopyroxene in the starting rock and formation of new amphibole with decreased ival and ti with respect to starting amphibole product amphibole does not display any correlation between cl and fe2 ival and k in contrast to natural highly cl rich amphibole suggesting that these correlations hold true only at cl contents higher than those attained in our experiments in addition we found that increasing nacl in the fluid correlates with increased maximum cl contents in amphibole compositional variations found in product amphibole highlight the heterogeneities in fluid infiltration and cl activity that account for the complexity of hydrothermal fluid rock interactions in deep oceanic geological systems

metamorphism in oceanic layer 3 gorringe bank eastern atlantic gorringe bank is an anomalously high structure of the eastern part of the north atlantic which was known to be composed of mantle derived peridotites layer 4 and gabbros layer 3 during the submersible cruise cyagor ii in 1981 the contact between layer 4 and layer 3 was observed on mount gettysburg and interpreted as tectonic the overlying series of gabbro was extensively sampled on both mounts composing the bank gettysburg and ormonde coarse grained to pegmatoid clinopyroxene gabbros predominate and are associated with differentiated rocks ferrogabbros and diorites cumulate gabbros are missing the gabbroic section sampled is therefore interpreted as the upper part of the plutonic section most samples were strongly recrystallized during two distinct events metamorphism occurred close to the ridge axis from interaction of a seawater derived fluid with still hot gabbros high temperature shear zones favoured fluid circulation but the water rock ratio estimated from the sodium input was very small in undeformed rocks 1 the low w r ratio explains the strong evolution of the fluid phase and therefore some particular compositions of secondary minerals low temperature alteration occurred when the gabbros were tectonically emplaced close to the sea bottom

geologic investigations in the cayman trough evidence for thin oceanic crust along the mid cayman rise the mid cayman rise is a 110 km long accreting plate boundary 2cm yr full rate characterized by a deep rift valley eighteen transponder navigated dives were made by the submersible alvin along the rift valley walls in two areas on opposite sides of the rift valley the relief of the walls is produced by a large number of inward facing small throw fault escarpments with vertical displacements ranging from a few tens of meters to perhaps as much as 400 m from these escarpments 142 samples were collected and gabbroic rocks 116 samples characterized by a wide range of compositions and a complex metamorphic history predominate in number over other rock types basalt serpentinized ultramafic we interpret the assemblage of rocks exposed on the escarpments to indicate that a shallow level magma reservoir exists beneath the axis of accretion at the mid cayman rise and creates anomalously thin oceanic crust with a carapace of only several hundreds of meters of diabase and basalt this carapace is und

magnetic properties of the bay of islands ophiolite suite and implications for the magnetization of oceanic crust rock magnetic properties opaque mineralogy and degree of metamorphism were determined for 101 unoriented samples from the north arm and blow me down massifs of the bay of islands ophiolite complex newfoundland the weathered and metamorphosed extrusive basalt samples have a weak secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin the initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation the magnetic intensity of the gabbroic samples increases as the degree of alteration increases with the highly altered upper metagabbros having an average intensity of 3 10 3 emu c3 because magnetization of the metagabbro samples is related to nonpervasive variable alteration these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies a compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer roughly 600 m thick with no contribution from a deeper source layer recognizable from these bay of islands data

gabbroic xenoliths and host ferrobasalt from the southern juan de fuca ridge rare isotropic gabbroic xenoliths occur in sheet and lobate flow fragments of nearly aphyric ferrobasalt collected along a 12 km section of the southern juan de fuca ridge xenoliths comprise 1 of the dredge contents and range in size from 1 cm3 glomerocryst to 240 cm3 the xenoliths have ophitic to intersertal texture with 5 50 interstitial glass of ferrobasaltic composition more evolved than the host lava on the basis of texture and mineralogy the xenoliths have been subdivided into three types type i plagioclase olivine glass type ii plagioclase augite glass olivine and type iii plagioclase augite olivine glass pigeonite partially inverted fe ti oxides mineral and glass inclusion compositions suggest a sequence of evolution for the three xenolith types in which type i is the least evolved and type iii is the most evolved application of a graphical pyroxene geothermometer to augite in xenolith types ii and iii yields crystallization temperatures of 1100 1200 c and to host lamellae pairs in inverted pigeonite yields subsolidus equilibrium temperatures of 1100 1150 c coexisting titanomagnetite ilmenite pairs in type iii xenoliths yield temperature estimates of 1000 1070 c and log f02 9 7 to 10 8 we infer that the xenoliths represent the partially crystalline mush boundary zone of a magma chamber based on the abundance of interstitial glass zonation of mineral grains in the most crystalline samples and coherence of chemical trends between interstitial glass glass inclusions and mineral phases the evolved composition of the xenoliths provides evidence for the presence of melts more fractionated than the host ferrobasalt in the magma chamber the erupted ferrobasalt is a hybrid lava formed by mixing these highly evolved melts with more primitive melts

prevalence of fluorosis in the fluoride enriched groundwater in semi arid parts of eastern india geochemistry and health implications abstract fluorosis is becoming a global environmental toxicological problem and is most commonly found in water stressed regions in order to evaluate the geochemical mechanism of fluoride enrichment in groundwater and health implications in the padwakodari environs of eastern part of india a total of twenty two samples were collected and analysed for physico chemical parameters spreading across the study area geologically the area mainly comprises of phyllites granite gneiss mica schist and sandstone high fluoride concentrations found mainly in the granite gneisses which are situated central to northwestern parts of the study area the concentration of fluoride in the groundwater samples ranges from 0 3 to 11 mg l with an average of 2 mg l 64 of the groundwater samples containing fluoride concentration that exceed the who drinking water guidelines value of 1 5 mg l chronic ingestion of high doses has been linked to the development of dental fluorosis and in extreme cases skeletal fluorosis the dominant geochemical facies present in water are na ca mg hco 3 11 samples na mg ca hco 3 5 samples ca na mg hco 3 5 samples and ca mg na hco 3 1 sample sodium and bicarbonate ions being major component in majority of the water types located mostly in the granite gneiss formation has a tendency to increase fluoride concentration in groundwater by dissolving the fluoride from fluoride bearing minerals the oversaturation of half of the samples with respect to calcite and majority of samples undersaturation with respect to fluorite makes it feasible for fluoride to get released in to the groundwater decreasing ca activity downgradient recharge to discharge leads to a dominance of fluorite unsaturated conditions and consequently to mobilization of fluoride in groundwater the results indicate that the fluoride concentration in groundwater is mainly governed by high weathering of fluoride bearing minerals i e apatite and biotite in granite gneiss contains abundant fluoride alkaline hydrogeological environment high temperature low rainfall evapotranspiration and ion exchange

deep seismic reflection constraints on paleogene crustal extension in the south central intermontane belt british columbia following growth of the canadian cordillera during the mesozoic the southern cordillera was subject to extension during the paleocene and eocene that correlated with widespread volcanic activity in south central british columbia including across much of the nechako chilcotin plateau in 2008 geoscience bc acquired 330 km of deep vibroseis reflection profiles on the plateau mostly over the stikinia arc terrane but also over its eastern contact with the oceanic cache creek terrane all seven seismic reflection lines reveal a strongly reflective lower crust that extends from 7 to 9 s down to the moho which is defined by the downward termination of reflectivity at 11 12 s in the uppermost crust extension occurred by block faulting with faults soling into subhorizontal to shallowly dipping detachments above 10 km depth extension in the deeper upper and middle crust which was partly controlled by antiforms likely related to earlier shortening was accommodated on a network of anastomosing shear zones

geochemistry characterization of groundwater in an agricultural area of razan hamadan iran this study was conducted to evaluate factors regulating groundwater quality in an area with agriculture as main use thirty groundwater samples have been collected from razan area hamadan iran for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater the chemical compositions of the groundwater are dominated by na ca2 hco3 cl and so42 which have been derived largely from natural chemical weathering of carbonate gypsum and anthropogenic activities of fertilizer s source the production of so42 has multiple origins mainly from dissolution of sulphate minerals oxidation of sulphide minerals and anthropogenic sources the major anthropogenic components in the groundwater include na cl so42 and no3 with cl and no3 being the main contributors to groundwater pollution in razan area

mineralogy and stable isotope geochemistry of hydrothermally altered oceanic rocks mineralogical and isotopic variations observed in altered glassy and crystalline rocksfrom the east pacific rise and the mid atlantic ridge provide information about the temperatures of alteration and seawater rock ratios for various hydrothermal regimes within the oceanic crust a systematic increase in alteration temperature is evident for the glassy rocksin the sequence 1 nontronite and celadonite vesicle fillings 35 c 2 saponite rich pillow breccias 130 170 c 3 calcite rich greenstone breccias and epidote rich greenstone 200 350 c theseresults include the highest temperatures thus far reported for saponite formation the seawater dominated hydrothermal alteration process that formed the saponite rich pillow breccias is characterized by high water rock ratios 0 1 low to moderate temperatures a seawater origin of most of the carbon in vein calcites 13 c 0 and the predominance of fe rich saponite and calcite as secondary phases greenstones chlorite quartz epidote and greenstone breccias chlorite quartz albite calcite are altered in a rock dominated system with lower water rock ratios 50 1 to 13 c 4 the crystalline rocks diabase gabbro and metagabbro are affected to varying degrees by pervasive high temperature seawater interactions that commence soon after solidification producing varying proportions of fine grained secondary minerals including talc smectite chlorite vermiculite actinolite and sodicplagioclase hydrothermal solutions derived from alteration of the crystalline rocks are of the appropriate temperature and isotopic composition to alter the overlying glassy rocks to the observed mineralogies as well as being the source of metal rich deposits associated with the oceanic spreading centers

recharge mechanisms and geochemical processes in a semi arid sedimentary basin eastern cape south africa abstract stable isotope 18 o and 2 h and geochemical signatures are used to gain some insight into recharge processes and groundwater salinization mechanisms in a semi arid rangeland catchment the 665 km 2 catchment is underlain by fractured lower beaufort sandstones and mudstones and is intruded by several dolerite dykes chloride and isotopic relationships suggest that chloride ions in ground water are of meteoric origin the hypothesized recharge and salinization mechanism is that large storm events periodically dissolve accumulated surficial meteoric salts and after a period of evaporative enrichment at or near the soil surface leach them into the ground water geochemical variations imply that spatial differences exist in recharge volumes in evaporative enrichment or in the extent of leaching of surficial salts meteoric sodium chloride contributes greater than 90 of the dissolved sodium except at low salinities where cation exchange processes yield additional sodium inputs in exchange for dissolved calcium and magnesium at high salinities this process reverses and sodium is adsorbed releasing calcium and magnesium this process accounts for up to 40 of the dissolved calcium and magnesium contributions from geochemical weathering are relatively uniform in spite of highly variable salinities which implies that residence times are also relatively uniform

the magmatic hydrothermal transition in the lower oceanic crust clues from the ligurian ophiolites italy abstract the gabbroic bodies from the jurassic ligurian ophiolites are structurally and compositionally similar to the gabbroic sequences from the oceanic core complexes of the mid atlantic ridge initial cooling of the ligurian gabbros is associated with local development of hornblende bearing felsic dykes and hornblende vein networks the hornblende veining is correlated with the widespread development of hornblende as coronas pseudomorphs after the clinopyroxene in the host gabbros in addition the studied gabbroic body includes a mantle sliver locally containing hornblende gabbros and hornblendite veins the hornblendes from the felsic dykes and the hornblende rich rocks within the mantle sliver show a similar geochemical signature characterized by low mg cao and al2o3 negligible cl and high tio2 k2o ree y zr and nb concentrations the whole rock sm nd isotopic compositions of the felsic dykes and the hornblende rich rocks define a sm nd isochron corresponding to an age of 154 20 ma and an initial end of 9 2 0 5 the 18o of the hornblendes and coexisting zircons from these rocks about 4 5 and 5 8 respectively do not indicate the presence of a seawater component in these melts the formation of the felsic dykes and of the hornblende rich rocks within the mantle sliver involved sio2 rich silicate melts with negligible seawater component which presumably were derived from high degree fractional crystallization of mor type basalts the vein and the coronitic pseudomorphic hornblendes show high mg and cao significant cl 0 02 0 17 wt and low tio2 and k2o concentrations the coronitic pseudomorphic hornblendes have trace element compositions similar to those of the clinopyroxenes from the gabbros and 18o values 1 0 to 0 7 close to seawater suggesting an origin by reaction between migrating seawater derived fluids and the host gabbros the vein hornblendes commonly show slight lree enrichment relatively high concentrations of nb up to 2 5 ppm and 18o ranging from 3 7 to 0 8 the crystallization of these hornblendes most likely involved both seawater and magmatic components

evaluation of hydrogeochemical processes in the pleistocene aquifers of middle ganga plain uttar pradesh india evaluation of major ion chemistry and solute acquisition process controlling water chemical composition were studied by collecting a total of fifty one groundwater samples in shallow 25 m in the varanasi area hydrochemical facies mg hco3 dominated in the largest part of shallow groundwater followed by na hco3 and ca hco3 whereas ca hco3 is dominated in deep groundwater followed by mg hco3 and na hco3 high as concentration 50 g l is found in some of the villages situated in northeastern parts i e adjacent to the concave part of the meandering ganga river of the varanasi area arsenic contamination is confined mostly in tube wells hand pump within the holocene newer alluvium deposits whereas older alluvial aquifers are having arsenic free groundwater geochemical modeling using wateq4f enabled prediction of saturation state of minerals and indicated dissolution and precipitation reactions occurring in groundwater majority of shallow and deep groundwater samples of the study area are oversaturated with carbonate bearing minerals and under saturated with respect to sulfur and amorphous silica bearing minerals sluggish hydraulic conductivity in shallow aquifer results in higher mineralization of groundwater than in deep aquifer but the major processes in deep aquifer are leakage of shallow aquifer followed by dominant ion exchange and weathering of silicate minerals

protracted fluid rock interaction in the mesoarchaean and implication for gold mineralization example from the warrawoona syncline pilbara western australia abstract oxygen isotopic and geochemical analyses on whole rock and quartz veins are combined with structural observations in order to constrain the fluid circulation history within the mesoarchaean warrawoona syncline of the north pilbara craton western australia the plumbing system which is the focus of this study is localized in the so called fielding s find shear zone ffsz a km scale shear zone formed during the burial of greenstones and coeval exhumation of granitic complexes this shear zone runs parallel or close to the axial plane of the syncline it involves a prominent quartz vein network and is lined with strongly hydrothermally altered mafic felsic and sedimentary rocks towards the ffsz felsic and mafic volcanic rocks become intensely silicified with an increase in bulk rock 18 o values from 10 8 to 25 1 for altered felsic volcanics and from 7 1 to 18 3 for altered mafic volcanics geochemical modelling ascribes the silicification to a dissolution precipitation process ree and most other trace elements are strongly depleted in the silicified units with the exceptions of elements such as v cr ni and co which are enriched throughout the warrawoona syncline vein quartz 18 o data are within a small range of 13 2 2 significantly lower than their silicified host rocks these data are interpreted as the result of two main paleo fluid circulation stages intense silicification and 18 o enrichment represent alteration driven by low temperature hydrothermal convection probably involving archaean seawater in contrast the quartz veins network is related to the infiltration of metamorphic and or magmatic fluids during a later deformation episode these quartz veins represent the event responsible for the bulk of economic lode gold formation in the area the protracted fluid rock interaction history in the warrawoona syncline may have played a major role in setting the stage for the late mineralizing event the early hydrothermal circulation could have formed an efficient plumbing system characterized by high permeability low reactivity and possibly au enrichment upgrading the au endowment to the late hydrothermal fluids

oxygen isotope exchange kinetics of mineral pairs in closed and open systems applications to problems of hydrothermal alteration of igneous rocks and precambrian iron formations the systematics of stable isotope exchange between minerals and fluids are examined in the context of modal mineralogical variations and mass balance considerations both in closed and in open systems on mineral pair 18 o plots samples from terranes that have exchanged with large amounts of fluid typically map out steep positively sloped non equilibrium arrays analytical models are derived to explain these effects these models allow for different exchange rates between the various minerals and the external fluids as well as different fluid fluxes the steep arrays are adequately modelled by calculated isochron lines that involve the whole family of possible exchange trajectories these isochrons have initially steep near vertical positive slopes that rotate toward a 45 equilibrium slope as the exchange process proceeds to completion the actual data point array is thus analogous to the hand of an isotopic clock that measures the duration of the hydrothermal episode the dimensionless ratio of the volumetric fluid flux to the kinetic rate parameter u k determines the shape of each individual exchange trajectory in a fluid buffered system u k 1 the solutions to the equations 1 are independent of the mole fractions of the solid phases 2 correspond to taylor s open system water rock equation and 3 yield straight line isochrons that have slopes that approach 1 f where f is the fraction reacted of the more sluggishly exchanging mineral the isochrons for this simple exchange model are closely congruent with the isochrons calculated for all of the more complex models thereby simplifying the application of theory to actual hydrothermal systems in nature in all of the models an order of magnitude of time in units of kt separates steep non equilibrium arrays e g slope 10 from arrays approaching an equilibrium slope of unity on a diagram because we know the approximate lifetimes of many hydrothermal systems from geologic and heat balance constraints we can utilize the 18 o 16 o data on natural mineral assemblages to calculate the kinetic rate constants k s and the effective diffusion constants d s for mineral h 2o exchange these calculated values k qtz 10 14 k feld 10 13 10 12 agree with experimental determinations of such constants in nature once the driving force or energy source for the external infiltrating fluid phase is removed the disequilibrium mineral pair arrays will either 1 remain frozen in their existing state if the temperatures are low enough or 2 re equilibrate along specific closed system exchange vectors determined solely by the temperature path and the mineral modal proportions thus modal mineralogical information is a particularly important parameter in both the open and closed system scenarios and should in general always be reported in stable isotopic studies of mineral assemblages these concepts are applied to an analysis of 18 o 16 o systematics of gabbros plagioclase clinopyroxene and plagioclase amphibole pairs granitic plutons quartz feldspar pairs and precambrian siliceous iron formations quartz magnetite pairs in all these examples striking regularities are observed on and plots but we point out that plots have many advantages over their equivalent diagrams as the latter are more susceptible to misinterpretation using the equations developed in this study these regularities can be interpreted to give semiquantitative information on the exchange histories of these rocks subsequent to their formation in particular we present a new interpretation indicating that precambrian cherty iron formations have in general undergone a complex fluid exchange history in which the iron oxide magnetite precursor has exchanged much faster with low temperature 400 c fluids than has the relatively inert quartz

interpretation of structures in the southeastern nechako basin british columbia from seismic reflection well log and potential field data1this article is one of a series of papers published in this special issue on the theme of new insights in cordilleran intermontane geoscience reducing exploration risk in the mountain pine beetle affected area british columbia 2geological survey of canada contribution 20100002 the structure and stratigraphy of the southeast nechako basin which are poorly understood primarily because of substantial volcanic cover are investigated in an analysis of seismic reflection well and potential field data formation and development of the se nechako basin resulted in sub basins containing cretaceous and eocene rocks interpretation reveals that dextral transtension in the early to middle eocene created nnw trending en echelon strike slip faults linked by pull apart basins which locally contain a thickness of eocene volcaniclastic rocks of 3 km this structural pattern is consistent with regional observations that suggest the transfer of slip from the yalakom fault to the north via a series of en echelon strike slip faults in the middle to late eocene faults associated with a change in the direction of stress echoed by the north trending right lateral fraser fault reactivated and cut earlier structures a simple model agrees with local observations that northeast directed comp

hydrogeochemical parameters for assessment of groundwater quality in the upper gunjanaeru river basin cuddapah district andhra pradesh south india in the management of water resources quality of water is just as important as its quantity in order to know the quality and or suitability of groundwater for domestic and irrigation in upper gunjanaeru river basin 51 water samples in post monsoon and 46 in pre monsoon seasons were collected and analyzed for various parameters geological units are alluvium shale and quartzite based on the analytical results chemical indices like percent sodium sodium adsorption ratio residual sodium carbonate permeability index pi and chloroalkaline indices were calculated the pre monsoon waters have low sodium hazard as compared to post monsoon season residual sodium carbonate values revealed that one sample is not suitable in both the seasons for irrigation purposes due the occurrence of alkaline white patches and low permeability of the soil pi values of both seasons revealed that the ground waters are generally suitable for irrigation the positive values of chloroalkaline indices in post monsoon 80 and in pre monsoon 59 water samples indicate absence of base exchange reaction chloroalkaline disequilibrium and remaining samples of negative values of the ratios indicate base exchange reaction chloroalkaline equilibrium chadha rectangular diagram for geochemical classification and hydrochemical processes of groundwater for both seasons indicates that most of waters are ca mg hco3 type assessment of water samples from various methods indicated that majority of the water samples in both seasons are suitable for different purposes except at yanadipalle sample no 8 that requires precautionary measures the overall quality of groundwater in post monsoon season in all chemical constituents is on the higher side due to dissolution of surface pollutants during the infiltration and percolation of rainwater and at few places due to agricultural and domestic activities

eocene and neogene volcanic rocks in the southeastern nechako basin british columbia interpretation of the canadian hunter seismic reflection surveys using first arrival tomography geological investigation of the near surface in the southeastern nechako basin is difficult shallow seismic reflection imaging is poor due in part to an extensive cover of eocene and neogene volcanic rocks outcrops of these volcanic rocks and the primarily cretaceous bedrock are commonly obscured by quaternary deposits and vegetation estimates of near surface p wave velocity are derived from the tomographic inversion of seismic first arrivals an effective tool when seismic imaging is poor tomographic model velocities are in agreement with sonic logs and laboratory samples except for those from the neogene chilcotin group cretaceous sedimentary rocks have velocities of 2800 4200 ms 1 the eocene endako and ootsa lake groups which have velocities of 3000 4200 ms 1 are not distinguishable based on velocity the velocity the character density focus and penetration depth of rays and ties with well and surface geology constrain the subsurface extent of the endako group adjacent to well b 82 c

the endako batholith episodic plutonism culminating in formation of the endako porphyry molybdenite deposit north central british columbia the endako batholith is a composite batholith that consists of early foliated hornblende biotite diorites intermediate age unfoliated hornblende biotite diorites and late granodiorites to monzogranites these latter plutons host the endako molybdenite deposit a major porphyry deposit located in the central canadian cordillera extensive k ar dating on the batholith had given relatively reproducible ages centered on 140 ma indicating a short life span for magmatic activity however a combined u pb and 40ar 39ar study has resulted in a substantial reappraisal of the age and time span of intrusive activity and its association with molybdenite mineralization the new data show that the batholith had a protracted emplacement history covering 75 m y with clear evidence for periods of magmatic quiescence the oldest magmatic suite of the endako batholith the stern creek suite is dated at 220 ma and comprises foliated gabbros and diorites mafic to intermediate plutons of the stag lake suite range in age from 180 ma to 161 ma the francois lake suite is divided into two subsuites the glenannan subsuite dated at 157 ma to 155 ma and the 149 to 145 ma endako subsuite that hosts the endako molybdenite deposit 40ar 39ar dating of hydrothermal biotite indicates molybdenite mineralization is genetically associated with terminal stages of magmatic activity biotite within the mine had its 40ar 39ar systematics reset at 145 ma by hydrothermal fluids with temperatures in excess of 300 c this resetting is associated with intrusion of the 145 1 0 2 ma casey phase monzogranite the youngest phase within the endako subsuite a further partial resetting of biotite is interpreted to be coeval with eocene intrusion of the high level miarolitic sam ross creek phase and numerous mafic dikes that cut through the region hydrothermal fluids associated with this latter event were below biotite closure temperature and do not appear to have any relationship to molybdenite mineralization within the endako deposit the new geochronologic data coupled with detailed mapping show a general age progression from mafic plutonism at the margins to a central core of high level granodiorite to monzogranite the data document the existence of a long lived relatively stationary magmatic center pulsed magmatism evident even within individual magmatic suites may play a major role in concentrating and ultimately depositing molybdenite in some porphyry systems at endako molybdenite would have formed within the higher level portions of the batholith a position that would normally have rendered the deposit prone to erosional removal however subsequent eocene extensional block faulting may explain the preservation of this jurassic deposit which is the oldest economic molybdenite deposit in the cordillera of north america

suitability assessment of deep groundwater for drinking and irrigation use in the djeffara aquifers northern gabes south eastern tunisia the multilayered djeffara aquifer system south eastern tunisia has been intensively used as a primary source to meet the growing needs of the various sectors drinking agricultural and industrial purposes the analysis of groundwater chemical characteristics provides much important information useful in water resources management detailed knowledge of the geochemical evolution of groundwater and assessing the water quality status for special use are the main objective of any water monitoring study an attempt has been made for the first time in this region to characterize aquifer behavior and appreciate the quality and or the suitability of groundwater for drinking and irrigation purposes in order to attend this objective a total of 54 groundwater samples were collected and analyzed during january 2008 for the major cations sodium calcium magnesium and potassium anions chloride sulfate bicarbonate trace elements boron strontium and fluoride and physicochemical parameters temperature ph total dissolved salts and electrical conductivity the evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium chloride and sulfate contents as a result of leaching of evaporite rock in this study three distinct chemical trends in groundwater were identified the major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories 1 calcite precipitation 2 gypsum and halite dissolution and 3 ion exchange based on the physicochemical analyses irrigation quality parameters such as sodium absorption ratio sar percentage of sodium residual sodium carbonate residual sodium bicarbonate and permeability index pi were calculated in addition groundwater quality maps were elabortaed using the geographic information system to delineate spatial variation in physico chemical characteristics of the groundwater samples the integration of various dataset indicates that the groundwater of the djeffara aquifers of the northern gabes is generally very hard brackish and high to very high saline and alkaline in nature the water suitability for drinking and irrigation purposes was evaluated by comparing the values of different water quality parameters with world health organization who guideline values for drinking water piper trilinear diagram was constructed to identify groundwater groups where the relative major anionic and cationic concentrations are expressed in percentage of the milliequivalent per liter meq l and it was demonstrated that the majority of the samples belongs to so4 cl ca na cl so4 na ca and na cl hydrochemical facies as a whole all the analyzed waters from this groundwater have revealed that this water is unsuitable for drinking purposes when comparing to the drinking water standards salinity high electric conductivity sodium adsorption ratio and sodium percentages indicate that most of the groundwater samples are inappropriate for irrigation the sar vary from medium s2 to very high s4 sodicity therefore the water of the djeffara aquifers of the northern gabes is dominantly of the c4 s2 class representing 61 23 of the total wells followed by c4 s3 and c4 s4 classes at 27 27 and 11 5 of the wells respectively based on the us salinity classification most of the groundwater is unsuitable for irrigation due to its high salt content unless certain measures for salinity control are undertaken

introduction to the special issue of canadian journal of earth sciences the nechako natmap project of the central canadian cordillera the canadian cordillera in central british columbia has seen the mesozoic subduction of an oceanic terrane the amalgamation of volcanic arc terranes continued intermittent mesozoic compression and magmatism and tertiary wrenching extension and magmatism except in its northernmost mountain ranges the area is extensively cov ered in glacial drift and thin veneers of tertiary volcanic rocks in 1994 a group of scientists and technologists be lieved they could understand that cover see through it and discover the components of that collision and extensional orogen they would apply modern techniques of isotopic and paleontological geochronology lake sediment till and plant geochemistry detailed gravity magnetic radiometric paleomagnetic and electromagnetic surveys and isotopic and trace element lithochemistry as they conducted extensive bedrock and surficial mapping this special issue summa rizes a cross section of the scientific contributions derived from that mapping conducted under the auspices of the nechako natmap project it demonstrates the absolute necessity of applying modern isotopic and paleontologic geo chronology to understand the phanerozoic geology of the cordillera it emphasizes the necessity of detailed aeromag netic surveys 500 m or less line spacing in looking through covered terranes at anything more than 1 250 000 scale and it shows the immense utility of applying various geochemical techniques to solve geological problems and estab lish baselines for future research and economic development bedrock and surficial mapping in the central cordillera using these and other techniques have established the nature and timing of mesozoic crustal growth tertiary crustal thinning and the associated formation of mineral deposits

neogene chilcotin basalts in south central british columbia geology ages and geomorphic history an extensive but generally thin mantle of basalt flows the chilcotin group covers much of the interior plateau of south central british columbia it provides material for dating and for reconstructing the original form of the paleosurface on which it was deposited k ar whole rock dates demonstrate that several ages of basalt are represented from early miocene or even late oligocene to early pleistocene with particularly abundant eruptions about 14 16 9 6 and 1 3 ma ago basalts of middle miocene and later ages if not the early miocene relics as well clearly rest on land surfaces of low local relief in places the low relief surfaces had been incised to depths of 100 200 m and the valleys backfilled with mid or late cenozoic sediments prior to burial by the basalts the low relief surfaces throughout the area are believed to have been developed close to a common base level and regional differences in their present elevation are thus largely a product of post basalt deformation this is recorded

stretching of the deep crust at the slow spreading southwest indian ridge abstract the 500 metres of gabbro drilled in the southwest indian ocean during odp leg 118 allow direct observation of early high temperature extensional deformation in the deep crust of a slow spreading rift valley about 30 of the recovered gabbros have been plastically stretched at progressively decreasing temperatures granulite to lower amphibolite facies metamorphic conditions increasing water rock ratio and probably increasing deviatoric stresses the early solid state strain in granulite facies metamorphic conditions produced low dipping foliations and low strain gradients at this stage mylonitic shear zones only formed in oxide rich gabbros strain localization in the deepest and hottest part of the oceanic crust thus appears to have been influenced by the magmatic stratigraphy in upper to lower amphibolite facies metamorphic conditions the ductile strength of the gabbro was probably higher and deformation concentrated in mylonitic shear bands which may have provided access to seawater derived fluids strain localization at this stage was accompanied by brittle failure and boudinage in the mylonitic foliation of individual porphyroclasts or of thick gabbro intervals the influence of such brittle failure on hydrothermal circulations was critical it allowed for extensive crust seawater interactions at high temperatures upper amphibolite facies conditions in a spreading context where continuous magma supply provides heat and new crustal material to the axial region the mechanical behaviour of the ridge axis lithosphere should be controlled by continuous ductile deformation in granulite facies conditions this may lead to the steady state necking configuration described by tapponnier and francheteau 1978 alternatively a discontinuity of the magma supply allowing the lower crust of the axial region to cool below granulite facies temperatures should cause mylonitic shear zones characteristic of amphibolite facies deformation to extend deeper into the axial domain eventually leading to the detachment fault configuration proposed by karson in press as magma supply to slow spreading oceanic ridges is likely to be discontinuous necking and faulting periods should alternate through time

alteration of oceanic crust and geologic cycling of chlorine and water we report new estimates of transport rates for h2o and cl between the mantle and surface reservoirs our estimates take into consideration alteration of oceanic crust especially that of plutonic rocks and possible subduction of sediments the effect of hydrothermal alteration on the cl budget seems to be negligible but the effect on the h2o budget is significant altered oceanic crust excluding sediments contains about 10 times as much h2o as the unaltered crust and its subduction may result in a net transport of h2o to the upper mantle in subduction zones however the rate of expulsion of h2o from the mantle by subduction zone magmatism is comparable to the amount released by ridge magmatism and is only about 10 of the amount subducted therefore about 90 of the subducted h2o must be returned to the mantle or returned to the crust by other processes in addition subduction of oceanic sediments to mantle depths will result in 1 1 a further increase in the return rate of h2o to the mantle reservoir 2 2 possible net transfer of cl to the mantle depending on the rate of pore water expulsion

calcium rich brines and other hydrothermal fluids in fluid inclusions from plutonic rocks oceanographer transform mid atlantic ridge abstract fluid inclusions in metagabbro plagiogranite and epidosite from the oceanographer transform mid atlantic ridge were investigated using microthermometric measurements and laser raman spectroscopy inclusions in quartz reveal the presence of a high salinity average 40 wt nacl cacl 2 high temperature 340 c calcium rich na ca about 1 by weight fluid in metagabbro and plagiogranite at room temperature these fluids bear a halite daughter crystal and may also contain small crystals of calcite titanite and hematite a low density vapor rich fluid bearing a small amount of co 2 is closely associated with the briney fluids in one sample all samples contain a population of high temperature 150 to 400 c aqueous liquid dominated fluid inclusions commonly of secondary origin having seawaterlike salinity 3 to 8 wt nacl equivalent we conclude that the calcium rich brines are produced by a combination of two processes fluid phase separation and segregation of brines from vapor prior to trapping to generate the high salinities and extensive fluid mafic rock interaction at low water rock ratio to promote the calcium enrichment later introduction along microfractures of low salinity modified seawater at high water rock ratio is recorded by the secondary fluid inclusions the chemical complexity and association with co 2 may indicate that there is a magmatic component to the brines in addition to a seawater source differences between the oceanographer transform brines and those reported in previous studies of oceanic and ophiolite samples are attributed to variations in the degree of water rock interaction the host rock lithology and the influence of a magmatic fluid component

oceanic core complex development at the ultraslow spreading mid cayman spreading center roughly a third of the global mid ocean ridge system spreads at 6 km spreading centers and thought to accrete some of the thinnest 3 km crust the mcsc generates end member mid ocean ridge basalt compositions and hosts recently discovered hydrothermal vents multibeam bathymetric data reveal that axial depth varies along the mcsc with intraridge rift walls defined by kilometer scale escarpments and massifs dredging and near bottom work has imaged and sampled predominantly basaltic lavas from the greatest axial depths and 15 peridotite surrounded by gabbroic rocks from the prominent massifs the gabbroic rocks exhibit wide compositional variation troctolites to ferrogabbros and in many places contain high temperature amphibolite to granulite facies shear zones gabbroic compositions primarily reflect the accumulation of near liquidus phases that crystallized from a range of basaltic melts as well as from interactions with interstitial melts in a subaxial mush zone magnetization variations inverted from aeromagnetic data are consistent with a discontinuous distribution of basaltic lavas and structurally asymmetric spreading these observations support an oceanic core complex model for mcsc seafloor spreading potentially making it a type example of ultraslow seafloor spreading through mush zone and detachment fault crustal processes

a stable isotope study of the hydrothermal alteration of the east taiwan ophiolite abstract the east taiwan ophiolite eto occurs as allochthonous fragments in the lichi melange and has been suggested to have formed at an active ridge ridge transform fault in a marginal basin the brecciated plutonic sequence has experienced a pre brecciation ocean ridge type high temperature metamorphism as well as a post brecciation off axis type low temperature metamorphism whereas the extrusive sequence has been subjected only to an off axis low temperature hydrothermal alteration stable isotopic studies of the eto show a slightly decreasing trend in oxygen isotope compositions from basalt through plagiogranite gabbro to ultramafic rocks the isotopic compositions of the eto basalts indicate low temperature interaction with seawater under variable water rock ratios the amphiboles from the eto gabbro show low 18o i e 3 1 to 3 8 and high d i e 19 to 9 values this is interpreted as having resulted from high temperature interaction with seawater derived hydrothermal fluid the plagioclase in the gabbro is mostly albitic in composition and exhibits very high 18o values i e 12 0 which may have resulted from low temperature reaction with 18o enriched fluid such 18o enriched fluid may have been derived from a high temperature seawater plutonic rock interaction system the antigorite and lizardite chrysotile serpentinites in the eto formed in oceanic environments under pre and post brecciation metamorphic conditions respectively the isotopic compositions of the antigorite are compatible with its formation in an oceanic environment although the 18o values of the lizardites chrysotiles are comparable to those of oceanic serpentines their d values ranging from 91 to 57 are too low to be accounted for by reaction with seawater derived fluid post formation hydrogen isotope exchange between the lizardite chrysotile and local meteoric waters during after on land emplacement of the serpentinites is postulated as a probable explanation calcite veins are ubiquitous in the eto three carbon sources are identified inorganic seawater carbon juvenile carbon and organic carbon in the last case it is shown that some calcite veins may contain a substantial amount of co2 derived from the ch4 oxidation process the organic carbon was most likely derived from organics in the surrounding lichi mudstone therefore the calcite veins with an organic carbon signature are suggested to have formed after the eto emplacement within the lichi melange

evolution of oceanic gabbros from dsdp leg 82 influence of the fluid phase on metamorphic crystallizations abstract gabbro breccias were recovered from an anomalously shallow level of the ocean crust during dsdp leg 82 the rocks display evidence of metamorphic crystallization related either to localized deformation or to hydrothermal circulation of a seawater derived fluid under static conditions secondary phases consist of plagioclase amphibole and minor clinopyroxene ilmenite sphene and chlorite petrological study indicates that deformation took place at high temperature under anhydrous conditions and was followed by hydrothermal circulation the compositions of secondary minerals i e strong zonations presence of chlorine in amphiboles varying compositions of secondary plagioclase indicate that reactions of the gabbros with the fluids occurred at a low water rock ratio relations between cl na and k in amphiboles suggest penetration of at least two distinct fluids of different compositions metamorphic crystallization stopped when greenschist facies conditions were reached 350 c probably because hydrothermal circulation faded out

hydrochemical characteristics of aquifers near sutherland in the western karoo south africa the western karoo depends entirely on groundwater for domestic and agricultural use an understanding of the chemical evolution of the groundwater provides insight into the interaction of water with the environment and contributes to better resource management descriptive statistics correlation matrices and factor analysis together with stable isotope data were used to gain an understanding of the hydrochemical processes of the groundwaters in the fractured rocks around sutherland in the western karoo the main processes influencing the groundwater chemistry are salinisation mineral precipitation and dissolution cation exchange and human activity the stable isotope data indicate that the infiltration of evaporated water is partly responsible for the occurrence of saline subsurface waters the ionic oxygen and hydrogen stable isotope composition of the groundwaters suggests that the effects of localised topography are one of the overriding factors controlling the groundwater chemistry in higher lying areas ca hco3 2 type waters are prevalent while in topographical flat areas nacl type waters dominate in areas where water collects close to or at the surface saline soils are formed from these areas salts are leached to the subsurface during significant recharge periods these findings are important in that they contribute to the identification of suitable locations for developing groundwater resources that could yield a relatively better quality water q 2001 elsevier science b v all rights reserved

ridge axis deformation and coeval melt migration within layer 3 gabbros evidence from the lizard complex u k ridge parallel extensional shear zones within the layer 3 gabbros of the lizard ophiolite have recorded varied and numerous chemical and mineralogical changes under a variety of p t conditions these changes accompany tectonic exhumation of lower crustal levels by a listric fault mechanism during amagmatic extension at a slow spreading centre deformation within the mid crustal level of layer three resulted in the migration and impregnation of an evolved iron titanium rich silica poor melt along the shear zones this syntectonic infiltration occurred along the lowermost portions of listric faults which rooted in a partially molten zone beneath the ridge axis residual melt was tapped from this underlying zone and tectonically redistributed about deforming gabbros situated immediately above the partially molten zone the occurrence of sub solidus synkinematic assemblages within the shear zones which were generated at various temperatures and water rock ratios is explained in terms of their simultaneous development on listric fault planes in the presence of a hydrothermal fluid phase the sequential overprinting of pre existing assemblages arises from repeated block rotation during amagmatic episodes of extension within an oceanic slow spreading environment

pressure temperature and tectonic evolution of triassic lawsonite aragonite blueschists from pinchi lake british columbia a blueschist and eclogite terrane is associated with one of the largest faults in the canadian cordilleran orogen the pinchi fault blueschists in situ and retrogressed eclogite blocks occur along the pinchi fault zone near 54 30 n and 124 w critical blueschist facies mineral assemblages include lawsonite glaucophane jadeite lawsonite glaucophane quartz and aragonite white mica 40ar 39ar spectra on blueschist and eclogite yield ages in the range 221 8 1 9 to 223 5 1 7 ma establishing a direct link between the blueschists and eclogites preservation of aragonite sets rigid constraints on the pressure temperature fluid time conditions of unroofing k ar dates indicate that this is some of the oldest documented metamorphic aragonite comparison with computed petrogenetic grids suggests that metamorphic temperatures were in the range 200 300 c with pressures greater than 8 10 kbar 1 kbar 100 mpa unroofing likely occurred during collision of the cache creek terrane with quesnellia in the lat

oligocene climate dynamics a planktonic and benthic foraminiferal stable isotope stratigraphy of the oligocene equatorial pacific ocean drilling program site 1218 was generated at 6 kyr resolution between magnetochrons c9n and c11n 2n 26 4 30 ma on a newly developed astronomically calibrated timescale our data allow a detailed examination of oligocene paleoceanography the evolution of the early cryosphere and the influence of orbital forcing on glacioeustatic sea level variations spectral analysis reveals power and coherency for obliquity 40 kyr period and eccentricity 110 405 kyr orbital bands with an additional strong imprint of the eccentricity and 1 2 myr obliquity amplitude cycle driving ice sheet oscillations in the southern hemisphere planktonic and benthic foraminifera 18o are used to constrain the magnitude and timing of major fluctuations in ice volume and global sea level change glacial episodes related to obliquity and eccentricity variations occurred at 29 16 27 91 and 26 76 ma corresponding to glacioeustatic sea level fluctuations of 50 65 m alteration of high latitude temperatures and antarctic ice volume had a significant impact on the global carbon burial and equatorial productivity as cyclic variations are also recorded in the carbon isotope signal of planktonic and benthic foraminifera the water column carbon isotope gradient and estimated percent carbonate of bulk sediment we also investigate the implications of a close correspondence between oxygen and carbon isotope events and long term amplitude envelope extrema in astronomical calculations during the oligocene and develop a new naming scheme for stable isotope events on the basis of the 405 kyr eccentricity cycle count

ionic and isotopic ratios for identification of salinity sources and missing data in the gaza aquifer abstract groundwater is the only source of fresh water in the gaza strip however it is severely polluted and requires immediate effort to improve its quality and increase its usable quantity intensive exploitation of groundwater in the gaza strip over the past 40 years has disturbed the natural equilibrium between fresh and saline water and has resulted in increased salinity in most areas salinization in the coastal aquifer may be caused by a single process or a combination of different processes including seawater intrusion upconing of brines from the deeper parts of the aquifer flow of saline water from the adjacent eocene aquifer return flow from irrigation water and leakage of wastewater each of these sources is characterized by a distinguishable chemistry and well known isotopic ratios in this paper na cl so4 cl br cl ca hco3 so4 and mg ca ionic ratios were used to distinguish different salinization sources 11b and 87sr 86sr isotopic composition were also included in the model to study their importance in this monitoring task the task of monitoring and the associated decision making process are characterized by a high degree of uncertainty with respect to input data and accuracy of models for this reason probabilistic expert systems and more specifically bayesian belief networks bbns are used to identify salinization origins the bbn model incorporates the theoretical background of salinity sources area specific monitoring data that are characteristically incomplete in their coverage expert judgment and common sense reasoning to produce a geographic distribution for the most probable sources of salinization the model is also designed to show areas where additional data on chemical and isotopic parameters are needed

hydrothermal activity in a peculiar oceanic ridge oxygen and hydrogen isotope evidence in the xigaze ophiolite tibet china the xigaze ophiolite locally displays a 7 km thick continuous sequence which probably represents an oceanic crust formed at a slow spreading ridge it consists from top to bottom of 1 1 pillow lavas with 18o between 9 and 16 and d around 90 vs smow 2 2 rare trondjhemites 9 7 18o 13 4 and d around 75 3 3 dolerite sills and dikes with 18o between 7 0 and 9 5 and d between 77 and 40 4 4 isotropic gabbros occurring as screens of the sills and dikes and rare layered gabbros these gabbros have 18o between 4 8 and 11 0 and d around 65 and bear high 18o albitized plagioclases 18o 10 which coexist with clinopyroxenes of mantle values 18o 5 5 or having values being slightly depleted down to 3 0 5 5 ultramafic rocks are either fresh or serpentinized they have 18o mainly around mantle values and d s are between 250 and 100 for the mafic part of the ophiolite the isotopic compositions correspond to hydrothermal interaction with seawater derived fluids under zeolite to greenschist facies but the trondjhemites were additionally affected by fluids poorer in d in particular the gabbros reacted with seawater derived fluids under amphibolite facies conditions as seen from their secondary mineralogy and their 18o depleted pyroxenes and subsequently were pervasively reacted under greenschist zeolite facies conditions during which the high 18o albitized plagioclase formed this occurrence of amphibolite facies conditions followed by greenschist zeolite facies conditions can be interpreted either to be a result of slow cooling of the oceanic crust at the ridge or to result from a fundamentally lower temperature hydrothermal interaction if compared with other ophiolites in contrast the d s of the serpentine 100 from the ultramafics are attributed to fluids of meteoric origin at high elevation nevertheless the particular location of the serpentinized harzburgites just beneath the gabbros and the high d dolerite sills and dikes 60 d 40 enclosed in these serpentinized harzburgites suggests an oceanic origin and therefore the possibility of hydrogen isotope exchange between serpentine and meteoric fluids after the obduction the xigaze ophiolite sequence displays very little 18o depleted rocks relative to mantle oxygen composition they cannot balance the amount of 18o enriched rocks consequently the result of the hydrothermal interaction between the xigaze ophiolite sequence and the seawater is an 18o depletion of the seawater however the contribution of xigaze type ridges to the buffering of 18o in cretaceous seawater was probably small

geological and geophysical investigation of the mid cayman spreading centre seismic velocity measurements and implications for the constitution of layer 3 summary in this paper we present laboratory measurements of compress ional and shear wave velocities of a diverse suite of gabbroic rocks collected from the walls of the mid cayman spreading centre with dsrv alvin the degree of deformation and alteration affecting these gabbros is quite variable and we believe that they are typical of plutonic rocks emplaced at shallow levels upper portion of seismic layer 3 and shallower of the oceanic crust the compositional and textural variations are reflected in the wide range of laboratory velocities which span most of the range of seismic velocities reported for oceanic and ophiolite rock samples including basalts gabbros ultramafics and their altered derivatives based upon the laboratory velocities and the geological setting of the mid cayman gabbros it is argued that no unique lithology except anhydrous peridotite can be unequivocally identified in the oceanic lithosphere from seismic velocity data alone furthermore these data allow for the possibility of considerable lithologic heterogeneity within portions of the oceanic crust at the scale of a few centimetres to a few hundred metres such heterogeneities would go unrecog nized because seismic refraction studies mask these variations resulting in a picture of apparent uniformity