Cl Enrichment Research Articles

Carbon dioxide reaction processes in a model brine aquifer at 200 °C and 200 bars: implications for geologic sequestration of carbon

The reactive behavior of supercritical CO 2 under conditions relevant to geologic storage and sequestration of C is largely unknown. Experiments were conducted in a flexible cell hydrothermal apparatus to determine the extent of fluid–rock reactions, in addition to carbonate mineral precipitation, that may occur in a brine aquifer–aquitard system that simulates a saline aquifer storage scenario. The system was held at 200 °C and 200 bars for 59 days (1413 h) to approach steady state, then injected with CO 2 and allowed to react for another 80 days (1924 h). In addition to magnesite precipitation, silicate minerals (quartz, plagioclase, microcline and biotite) in the aquifer and the aquitard display textures (etch pits, mineralization) indicating significant reaction. Changes in elemental abundances in the brine following addition of CO 2 include pH decrease and enrichment in Cl −, partly due to supercritical CO 2 desiccation of the brine. Geologic sequestration systems have potential for geochemical reactions that extend beyond simple aqueous dissolution of CO 2 and precipitation of carbonate. These reactions may produce geochemical and geotechnical consequences for sequestration and provide important characteristics for monitoring and evaluation of stored CO 2. An understanding of multi-phase equilibrium relationships between supercritical CO 2 and aquifer–brine systems also raises new questions for a variety of geologic systems. Multi-phase fluid equilibria may, for example, account for the large amounts and heterogeneous distributions of calcite cement in a wide variety of geologic systems, particularly in sedimentary basin sandstones.

Widespread assimilation of a seawater-derived component at Loihi Seamount, Hawaii

Many tholeiitic and transitional pillow-rim and fragmental glasses from Loihi seamount, Hawaii, have high Cl contents and Cl/K 2O ratios (and ratios of Cl to other incompatible components, such as P 2O 5, H 2O, etc.) relative to other Hawaiian subaerial volcanoes (e.g., Mauna Loa, Mauna Kea, and Kilauea). We suggest that this results from widespread contamination of Loihi magmas by a Cl-rich, seawater-derived component. Assimilation of high-Cl phases such as saline brine or Cl-rich minerals (halite or iron–hydroxychlorides) with high Cl/H 2O ratios can explain the range and magnitude of Cl contents in Loihi glasses, as well as the variations in the ratios of Cl to other incompatible elements. Brines and Cl-rich minerals are thought to form from seawater within the hydrothermal systems associated with submarine volcanoes, and Loihi magmas could plausibly have assimilated such materials from the hydrothermal envelope adjacent to the magma chamber. Our model can also explain semiquantitatively the observed contamination of Loihi glasses with atmospheric-derived noble gases, provided the assimilant has concentrations of Ne and Ar comparable to or slightly less than seawater. This is more likely for brines than for Cl-rich minerals, leading us to favor brines as the major assimilant. Cl/Br ratios for a limited number of Loihi samples are also seawater-like, and show no indication of the higher values expected to be associated with the assimilation of Cl-rich hydrothermal minerals. Although Cl enrichment is a common feature of lavas from Loihi, submarine glasses from other Hawaiian volcanoes show little (Kilauea) or no (Mauna Loa, Mauna Kea) evidence of this process, suggesting that assimilation of seawater-derived components is more likely to occur in the early stages of growth of oceanic volcanoes. Summit collapse events such as the one observed at Loihi in October 1996 provide a ready mechanism for depositing brine-bearing rocks from the volcanic edifice into the top of a submarine summit magma chamber.

Radionuclide concentrations in underground waters of Mururoa and Fangataufa Atolls

In 1997 an expedition to Mururoa and Fangataufa Atolls was carried out to sample underground waters from cavity-chimneys and carbonate monitoring wells. The aim of this study was to determine the prevailing concentration and distribution status of radionuclides. Elemental analysis of interstitial waters was carried out in the water fraction as well as in particles collected at 11 underground monitoring wells. 238Pu, 239,240Pu, 241Am, 137Cs, 90Sr, 3H, 125Sb, 155Eu and 60Co were analyzed in both fractions by alpha-, beta- and gamma-spectrometry. Measurements showed that at 60% of the sites, pH and Eh seemed to be related to tidal cycles; in contrast HTO was constant during the sampling time. Interstitial waters from carbonates and transition zones shared similar chemical composition that were not different from that of the surrounding seawater. Waters collected from basalt cavities left after nuclear tests, (Aristee and Ceto) have a different chemical signature characterized by a deficiency in Mg, K and SO 4 as well as enrichment in Sr, Si, Al and Cl compared to the rest of the stations. Radionuclide concentrations present in both, water and particulate fractions, were significantly higher at Ceto and Aristee than at any other monitoring wells, except for Fuseau and Mitre monitoring wells (Fangataufa) where values similar to Ceto were found (e.g. 239,240Pu: >20 mBq g −1). Considering that Pu isotopes showed high K d values compared to non-sorbing radionuclides such as 3H, 90Sr and 137Cs it is very unlikely that migration from cavities to monitoring wells accounts for the concentration of Pu isotopes and Am at Fuseau 30 and Mitre 27. Perhaps the contact of lagoon waters with the well before sealing could be a possible source of the transuranics found at these sites. The 238Pu/ 239,240Pu ratios measured in the particles were similar to that of the lagoon (0.38), thus supporting this hypothesis. The fact that transuranics were found only in the particle fraction, in the water (colloids included) these radionuclides were below detection limits, may be accounted for the conspicuous quantity of iron oxy-hydroxides present in the particulate fraction that under the appropriate redox conditions may be interacting selectively with elements in solution (scavenging) resulting in the enhanced transuranic signal. While transuranics have been found in places of their origin, radionuclides with low K d values ( 3H, 90Sr, 137Cs) have already been transported to monitoring wells, as well as to the atolls' lagoons and the open ocean.

Geochemical exploration using acid insoluble residues of rocks for volcanic-hosted massive sulphide deposits, Rosebery area, western Tasmania

The Rosebery deposit is one of the major massive sulphide deposits in the Mount Read Volcanic belt of the western Tasmania. The 200×20 km belt of the Mount Read Volcanics, which is one of the world's richest provinces of volcanic-hosted massive sulphide (VHMS) deposits, hosts more than 40 mineral occurrences including major massive sulphide deposits at Mount Lyell, Hercules, Rosebery, Que River and Hellyer. In this study, hot HNO 3 insoluble residues of rocks were used to define the geochemical halos associated with VHMS deposits, and to identify alteration related to VHMS mineralisation. The residues after the acid treatment are composed mainly of quartz, mica and feldspar (plagioclase and K-feldspar) with traces of chlorite and kaolinite in some samples. Quartz, sericite, chlorite, carbonate, etc., are the principal alteration products and relate to both VHMS mineralisation and to metamorphism and deformation in the region. There are no significant differences between the VHMS related and unrelated mineralogical alteration. There are two types of geochemical halos in the Rosebery area. The type-1 halo trends NE–SW, is related to wall-rock alteration, and is defined by enrichment in Cl, and possibly K and Rb, and depletion in Al, Ca, Na, Ti and Sr. It passes discordantly from the west to east across the White Spur Formation, the altered footwall, the host rock of the Rosebery deposit, the hanging wall and the Mount Black Volcanics. The type-2 halo, trending N–S (largely stratabound), is related to massive sulphide mineralisation and is characterised by enrichment in Fe, Mn, Ba, Zn, Pb and possibly K, Rb and F. It outlines the mineralised host rock and footwall alteration zone, and also extends toward the south into the unaltered footwall and hanging wall rocks. Both halos intersect at Rosebery in zones of mineralisation and associated footwall alteration. Recognition of geochemical halos has led to formulation of geochemical indices for identification of alteration related to VHMS mineralisation. Binary relations between (Mn × Ba × F) and (Ca × Na × Sr), and (Mn × Ba) and (Na × Sr), and their ratios (Mn × Ba × F)/(Ca × Na × Sr) and (Mn × Ba)/(Na × Sr) identify the alteration related to massive sulphide mineralisation and distinguish it from alteration unrelated to the mineralisation in the Rosebery area. These geochemical indices are also used for the other deposits which all display similar geochemical alteration signatures. The alteration related to VHMS mineralisation can be distinguished from alteration unrelated to mineralisation by higher values of the geochemical indices of (K × Mn × Ba × Rb), (Mn × Ba × F) and (Mn × Ba).

Assimilation of seawater-derived components in an oceanic volcano: evidence from matrix glasses and glass inclusions from Loihi seamount, Hawaii

We report major element, H 2O, Cl, B, and Be analyses of matrix glass and olivine-hosted glass inclusions from two pillow lava samples dredged from 4200 m on the southern rift zone of Loihi seamount, Hawaii. Matrix glasses (MgO∼9 wt.%) have H 2O, Cl, and B contents considerably in excess of the values expected from mantle melting or fractional crystallization of parental Loihi magmas. Glass inclusions have H 2O, Cl, and B contents ranging from the high values of the matrix glasses to lower concentrations that are more typical of Hawaiian magmas. Concentrations of other incompatible elements (e.g., K 2O, P 2O 5, and Be) in matrix glasses and glass inclusions are uncorrelated with their H 2O, Cl, and B contents. Glass inclusions show considerable scatter in major element compositions compared to matrix glasses, but except for H 2O, Cl, and B, the average glass inclusion composition corresponds well to the matrix glass compositions. We propose that the glass inclusions represent compositionally diverse liquids present within the magmatic plumbing system at Loihi that were mixed and homogenized to produce the liquid that quenched to the matrix glass on eruption. This range of liquid compositions present at depth was trapped by crystallizing olivine prior to blending and homogenizing and therefore preserves a compositional diversity not present in erupted whole rocks. The high H 2O, Cl, and B contents of matrix glasses and some glass inclusions, and the range of H 2O, Cl, and B concentrations in glass inclusions, are best explained by variable extents of assimilation by Loihi magmas of H 2O–Cl–B-rich, seawater-derived components prior to eruption. The required assimilants range from material similar in composition to seawater to materials with Cl/H 2O and B/H 2O ratios much higher than seawater. Our preferred explanation (similar to that suggested for MORB by Michael and Schilling, 1989) [Michael, P.J., Schilling, J.-G., 1989. Chlorine in mid-ocean ridge magmas: Evidence for assimilation of seawater-influenced components. Geochim. Cosmochim. Acta, 53, pp. 3131–3143.] is that most of the assimilated materials were brines (or rocks containing brines in inclusions or along grain boundaries) enriched in Cl by high temperature phase separation of seawater in sub-sea-floor hydrothermal circulation systems. Addition of ∼1.0 wt.% of a 15 wt.% NaCl brine can explain the H 2O and Cl contents of the matrix glasses. Addition of altered basalt cannot readily account for the Cl and H 2O contents of matrix glasses and glass inclusions, but may be required to account for their elevated B contents. The enrichment in Cl and contamination with atmospheric noble gases observed in other samples from Loihi could also result from assimilation of Cl-enriched, seawater-derived components.

Chlorine stable isotope composition of granulites from Lofoten, Norway: Implications for the Cl isotopic composition and for the source of Cl enrichment in the lower crust

The Cl isotopic composition of lower crustal rocks, as revealed from granulites from the Lofoten Islands, Northern Norway, centres around the value of Standard Mean Ocean Chloride (SMOC). The investigated rocks and mineral separates of Cl-amphibole and Cl-biotite have δ 37Cl values ( 37Cl/ 35Cl normalized to SMOC) of −1.12‰ to +0.79‰ with most values concentrated in the range of −0.3‰ to +0.11‰ and an average of −0.15‰ Samples from gabbroic and from dry granitic rocks (magmatic mangerites and charnockites) with highly Cl-enriched hydrosilicates and from a later amphibolite with low-Cl amphiboles show no distinct differences in their δ 37Cl values. The results indicate that there was only minor involvement of mantle-derived Cl in fluid-involving processes in the middle and lower crust. Assuming a δ 37Cl of 4.7‰ for the undegassed mantle [1], Cl isotopic values of the granulites do not support the influx of significant amounts of mantle derived Cl. The maximum possible mantle contribution to the sample with the highest δ 37Cl is about 33%. Thus the common occurrence of Cl-enriched minerals in granulite facies terrains is regarded as a product of remobilized crustal Cl, either during magmatism or during later fluid activity. The results support the hypothesis that the crust can be regarded as a reservoir with Cl isotopic values very similar to SMOC.

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

We have studied the distribution of light and volatile elements (Li, Be, B, H2O, F, Cl) in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the Cerro Toledo Rhyolite, which were erupted from the Bandelier magma chamber between two caldera‐forming eruptions at 1.608 Ma and 1.225 Ma. Since the small‐volume tephras of the Cerro Toledo Rhyolite record chemical evolution of the upper parts of the magma chamber during this 383‐kyr period, we can track volatile evolution in the magma during its differentiation, specifically, the development of a separate fluid phase from the magma, the partitioning of volatile and light elements between this fluid and the magma, and the timing of the second caldera eruption at 1.225 Ma. The melt inclusion data reveal that Li, Be, and B were progressively enriched with time at the top of the magma chamber, showing a similar three fold enrichment. By contrast, F, Cl, and F2O show more variable behavior. F was enriched 3.6 times in the magma and Cl increased 2.5 times, while water concentrations remained constant. Evidence for a separate fluid phase includes (1) comparatively small magmatic enrichment factors for Cl and H2O, elements which are known to partition into fluid, (2) decline of the Cl/Be and Cl/B ratios in melt inclusions with time, indicating preferential loss of Cl, and (3) maximum Cl contents of 2900–3000 ppm in melt inclusions, which are concentrations at or close to the saturation limit for Cl in a two‐phase gas‐saturated magma. The lack of temporal H2O enrichment in the magma suggests that it became gas saturated at an early stage. The Cl fluid‐magma partition coefficient was initially low, due to the presence of a low‐salinity single‐phase vapor. The fluid is calculated to have increased its salinity from 0.76 wt % equivalent NaCl to 3.1 wt % NaCl by crystallization and Cl enrichment in the magma. Consequently, the fluid was transformed to two immiscible phases. As a result, the Cl partition coefficient increased, and the Cl content in the magma was buffered at 2900–3000 ppm. Overpressures in the magma chamber have been modeled as a function of crystallization, total pressure and depth, H2O solubility in rhyolite, resurgence, crystallization contraction, and initial fluid mass. For the large amounts of crystallization (40–70%) required by the geochemical relations, unrealistically large overpressures (>75 MPa) are indicated, unless (1) the magma existed as a foam or (2) the chamber was able to degas passively, and thus buffer the buildup of pressure. To maintain realistic overpressures in the magma chamber (<50 MPa), an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing. The change from a one‐phase vapor to a two‐phase immiscible fluid before the Upper Bandelier Tuff eruption may have promoted partial or complete sealing of the magmatic‐hydrothermal system, permitting significant overpressures to develop. The result could have been a cataclysmic caldera‐forming eruption.

Metallogenesis in back-arc environments; the Lau Basin example

Geologic investigations with the submersible Nautile in the Lau basin represent one of the first detailed studies of hydrothermal activity on a modern back-arc volcanic ridge, the Valu Fa Ridge. Three major hydrothermal fields (Hine Hina, Vai Lili, and White Church) were discovered in the areas of the greatest differention of volcanic rocks. The type of hydrothermal deposit is controlled by the type of volcanism and by tectonic activity which increases from south to north. Three stages of sulfide formation are proposed and described. Vent fluids at Valu Fa have much higher metal contents than those at midocean ridges. Cl enrichment is best explained by mixing with deep brine rather than by subcritical phase separation and there is no evidence for a magmatic fluid contribution. Some characteristics of the fluids, such as low pH (2) and low concentration of H[sub 2]S, can be explained by subsea-floor sulfide formation. Vertical mineralogical zonation within the mound differs from midocean ridge deposits but is similar to that of a kuroko deposit. At the surface of the deposit, the virtual absence of pyrite and the high amount of sphalerite, barite, tennantite, galena, and locally, native gold are remarkable. Compared to midocean ridges, Lau basinmore » deposits are enriched in Ba, Zn, As, Pb, Ag, Au, and Hg and depleted in Mo, Se, and Co. Their mineralogy, chemical composition, and geologic setting show that the southern Lau basin deposits are intermediate between oceanic and continental back-arc deposits.« less

Chemical mobility during low-grade metamorphism of a Jurassic lava flow: Río Grande Formation, Peru

Chemical and mineralogical changes produced by very low-grade metamorphism in a 40 meter thick, K-rich, calc-alkaline andesite flow of the marine Jurassic Río Grande Formation of southern coastal Peru are discussed. This metamorphism (=spilitization) was non-deformational and generated spilitic domains at (and near) both vesicular margins of the flow, whereas the massive central zone remained relatively unaltered. The metadomains are characterized by mineral associations of the zeolite facies. Primary minerals are Ca-plagioclase, augitic pyroxene, iron-titanium oxides, and (pseudomorphs after) olivine. Metamorphic minerals are: albite (three generations), K-feldspar, pumpellyite, chlorite, interlayered chlorite-celadonite, celadonite, various mixed-layer Si- and Fe-rich phyllosilicates, “iddingsite,” calcite, analcime, titanite, and white mica. The effect of the metamorphism on the rock chemistry is reflected in changes especially observed at the marginal zones of the flow which affect major, trace, and RE elements: 1) strong increase of the iron oxidation ratio (Fe 2O 3/FeO); 2) enrichment in Na 2O accompanied by a concomitant depletion of CaO in non-amygdaloidal domains; 3) depletion of SiO 2; 4) strong enrichment in H 2O and CO 2; 5) marked depletion of Sr and Rb; 6) enrichment in Cl and S; and 7) slight depletion in RE elements, notably in the top zone of the flow. Conversely, elements such as Ti, P, Nb, and Y were fairly immobile, whereas Zr and K were only slightly mobilized. The effect of the metamorphism on the mineral chemistry is expressed by the predominance of metastable equilibrium evidenced by the existence of wide compositional ranges in the phyllosilicates, the incomplete albitization of the Ca-plagioclase, and the Al-rich character of the pumpellyites. The metamorphism is considered to be of hydrothermal-burial type, which takes place at low temperature and pressure — probably about 125–230°C and less than 3 kb, and is produced mainly through permeability-controlled seawater/rock interaction.

Chloride depletions and enrichments in seafloor hydrothermal fluids: Constraints from experimental basalt alteration studies

Na-K-Ca-Cl fluid was reacted with diabase at 400° and 425°C, 400 bars and fluidrock mass ratio of 0.5 to assess the relative mobility of dissolved Cl. Fluids from the present experiments reveal relatively large time and temperature dependent decreases in Cl; temperature increase enhances Cl removal, whereas reaction progress has the opposite effect. These changes are not due to boiling and/or phase separation. At 400° and 425°C, 400 bars, Cl removal from solution is accompanied by Ca and Na fixation, respectively. Both experiments produced mixed-layer chlorite/smectite, clinozoisite and albite(?). Olivine was not detected by X-ray diffraction or petrographic analysis of run products from either experiment, however, we propose that the time dependent changes in dissolved Cl result from olivine replacement by an Fe-hydroxy chloride phase followed by hydration effects. Quenched and washed alteration products, however, did not reveal anomalous Cl, which suggests that the Cl-bearing phase is characterized by retrograde solubility. This is consistent with the relative magnitude of Cl fixation observed for experiments at both temperatures and from results of an isobaric cooling experiment. The experiments provide evidence for the non-conservative behavior of Cl during hydrothermal alteration of basalt. The data are particularly important in light of the Cl-depleted nature of some ridge crest hot spring fluids, and suggest temperatures of formation for these fluids of approximately 410°C, assuming sub-seafloor pressure of 400 bars. In addition, the retrograde solubility of the Cl-bearing phase responsible for Cl fixation during high temperature basalt alteration, may help to explain Cl enrichment in hot spring fluids which have conductively cooled below 350°C

A chemical and isotopic study of the Tokaanu-Waihi geothermal area, New Zealand

The Tokaanu-Waihi geothermal area lies on the northeast flanks of the Tongariro Volcanic Centre, an andesitic massif which forms part of the Taupo Volcanic Zone arc-subduction system. Geothermal activity consists of hot springs, pools, a geyser and an area of steaming ground, fumaroles and acidic springs. At Tokaanu, the near-neutral-pH, boiling waters are notable for a high mineral content (3000 mg/kg Cl) relative to other Taupo Volcanic Zone geothermal systems, a high B/Cl ratio and high Li/Σ alkali ratio. The Waihi waters and bore waters are lower in mineral content but higher in HCO 3 , SO 4 , Mg and Ca and represent mixing of deep hot waters with steam-heated groundwaters and dilution with cold surface water. The sulphate-water geothermometer indicates that the deep hot water is at 250°C. Higher temperatures (350–400°C) are indicated for greater depths by the H 2 S-SO 4 S-isotope ratios and the CH 4 -CO 2 carbon-isotope measurements. A minimum residence time of 0.25 Ma for CO 2 and CH 4 below the reservoir is proposed, but H 2 S and SO 4 in the reservoir cannot have coexisted for more than 200 a. Isotopic analyses of the Tokaanu hot spring waters show a significant δ 18 0 shift (up to 4 ‰) from the local meteoric waters. Some samples show further δ 18 0, D and Cl enrichment as a result of steam loss at depth and surface evaporation.

Genetic implications of halide enrichment near a mississippi valley-type ore deposit

Host dolomite, Buick lead-zinc-copper deposit, Viburnum Trend, Missouri. Halide enrichment extends up to 250 ft from the deposit and is in close association with trace element enrichments. The Br and Cl enrichment zone is strong additional evidence that the ore-forming solutions of the Viburnum Trend were metal-rich Na-Cl brines. Br/Cl ratios also display an asymptotic decrease with distance from the deposit. The Br/Cl ratios of the whole-rock samples from within and near the deposit and from the water soluble leachate reveal that the ore-forming solutions were enriched in Br relative to seawater. The elevated Br/Cl ratios indicate that the ore-forming solutions were initially formed from the evaporation of seawater past the point of halite precipitation. This implies that the ore-forming solutions evolved from bitterns which formed contemporaneously with evaporite sequence. These bitterns subsequently underwent mixing with less saline waters prior to or during ore mineralization.--Modified journal abstract.

Effects of canopy removal and nitrogen enrichment on a Distichlis spicata-edaphic diatom complex

Edaphic diatoms were collected seasonally from a monotypic stand of Distichlis spicata (L.) Greene on Graveline Bay Marsh, Mississippi, in which the marsh surface had been enriched with NH 4 Cl and exposed to high light intensity by clipping the grass shoots. Clipping greatly reduced species diversity ( H′ ) and the number of taxa in a sample ( S ) in all seasons except winter, but did not stimulate the growth of filamentous algae. Nitrogen enrichment increased H′ and S in spring. Of the 111 taxa encountered, clipping eliminated nine pre-existing texa and introduced three new taxa into the community. No such effect was induced by nitrogen enrichment. A 3-way ANOVA (light×nitrogen×date) of the relative abundances of the 16 most abundant taxa revealed that 11 taxa were characterized by a significant 3-way interaction term. As with community diversity, effects due to clipping were more prevalent than those due to nitrogen enrichment. When all responses were considered, the specific combination of clipping and NH 4 Cl enrichment had for all practical purposes the same effects on community structure as did clipping alone. Nitrogen enrichment greatly stimulated the aerial yield of intact D. spicata stands and the regrowth of those clipped 3 months earlier.

Effect of Chloride Ion on the Localized Breakdown of Nickel Oxide Films

The effect of chloride ion on the passivation of nickel is studied and a mechanism for pit initiation on electrodes anodized in Cl−‐containing solutions is proposed. Although Cl− does not directly influence the nickel dissolution reaction, , it does interfere with formation and thereby retards passivation. This is manifested by an increase in the anodic passivation charge upon stepping the potential into the passive region. At a constant anodic potential, both the extent of retardation of oxide formation and the probability for pitting increase with increasing [Cl−]. Under conditions where pitting will occur, the anodic current falls substantially during the first 30–60 sec (after the potential step) but then begins to increase as pitting occurs. The original low bulk concentration of Cl− (≤0.1M) was not considered sufficient to cause pitting and this suggests a localized enrichment in Cl− during the 30–60 sec current decay. The oxide film is viewed as undergoing continuous breakdown and repair at localized areas and when sufficient Cl− has accumulated in some areas, repair of the oxide is not possible. For a constant bulk [Cl−], the pitting probability increases sharply with increasing potential of anodization; however, the corresponding extent of oxide retardation actually decreases. This increased pitting probability is explained in terms of the higher rate of nickel dissolution (from oxide‐free areas where the film has broken down) at the higher anodic potential being able to effectively concentrate Cl− in localized areas of the surface. The presence of Cl− ion in the anodizing solution does not result in any change in average oxide film thickness or substantial Cl−incorporation within the film.

Port Chalmers Breccia and adjacent early flows of the Dunedin volcanic complex at Port Chalmers

Abstract At least 230 m of basalt flows underlie trachytes of the Initial Eruptive Phase of Benson at Port Chalmers in the eroded core of the Dunedin volcano. The basalts may be equivalent to the lowest basaltic tuffs in the nearby Blanket Bay and Waipuna Bay sedimentary inliers, and thus are probably the oldest of the Dunedin volcanics. The flows abut the Port Chalmers Breccia which consists largely of fragments of pre existing volcanics filling a former vent. Explosive gas eruptions in the vent produced a thorough intermingling of schist and subvolcanic material derived from shallow crustal depths, with fragments of disintegrated vent intrusions and material eroded from the vent walls. Subvolcanic fragments found in the upper levels of the breccia range from gabbroic to syenitic rocks of varying undersaturation. Nepheline syenites with sodalite, katophorite, and eucolite indicate an agpaitic differentiation trend with enrichment in Na, Cl, F, and H2O. These, and the adjacent quartz-bearing trachyte flow...

Port Chalmers Breccia and adjacent early flows of the Dunedin volcanic complex at Port Chalmers

Abstract At least 230 m of basalt flows underlie trachytes of the Initial Eruptive Phase of Benson at Port Chalmers in the eroded core of the Dunedin volcano. The basalts may be equivalent to the lowest basaltic tuffs in the nearby Blanket Bay and Waipuna Bay sedimentary inliers, and thus are probably the oldest of the Dunedin volcanics. The flows abut the Port Chalmers Breccia which consists largely of fragments of preexisting volcanics filling a former vent. Explosive gas eruptions in the vent produced a thorough intermingling of schist and subvolcanic material derived from shallow crustal depths, with fragments of disintegrated vent intrusions and material eroded from the vent walls. Subvolcanic fragments found in the upper levels of the breccia range from gabbroic to syenitic rocks of varying undersaturation. Nepheline syenites with sodalite, katophorite, and eucolite indicate an agpaitic differentiation trend with enrichment in Na, Cl, F, and H2O. These, and the adjacent quartz-bearing trachyte flows, are the most highly evolved of the Dunedin igneous rocks, and represent trends to extreme undersaturation and slight oversaturation in silica respectively within a single alkaline volcanic province.

Role of Gravity, Temperature Gradients, and Ion-Exchange Media in Formation of Fossil Brines

Calculations show that gravitational settling of ions in an isothermal sediment column could produce increases of equilibrium concentrations in pore waters ranging from 1 percent per 100 m depth for chloride to 4 percent per 100 m depth for strontium. The migration of ions in a thermal gradient (Soret effect) would cause minor salt enrichment upward toward the colder pole, but the presence of cation-exchanging particles such as clays would reverse this tendency and cause pumping of salt downward. A model calculation using literature data for the thermal potentials suggests that about 5-percent enrichment in Cl per 100 m depth may occur under steady-state conditions. These mechanisms do not explain the greater enrichments commonly found in subsurface brines, but may modify salt distributions due to other phenomena.