Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. Title from title screen (viewed Mar. 22, 2007). Includes bibliographical references (leaves 189-206). Online version of the print original.

Thesis (M.A.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 189-206).

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / 1 map on folded leaf in pocket. Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 174-180).

Twelve ultramafic nodules from Neogene alkaline lavas of British Columbia are Cr-diopside series peridotite. Nodules are depleted or undepleted with respect to Cr, Al, Ti and Na abundance per diopside or enstatite formula unit, and either Ti-metasomatised or unmetasomatised. Four samples from the Josephine Peridotite are even more depleted than the depleted nodules and lack Ti-metasomatism. Pyroxene geothermobarometry (Mercier, 1980) was modified and used for clino- and ortho-pyroxene equilibrium temperature, pressure and depth calculations. Nodules came from a mantle depth of 30-50 km (936-l008°C, 9-15.5 kb). Josephine Peridotite came from a mantle depth of 30-65 km (1003-1042°C, 10-20 kb) After establishing an average total Rb blank of 0.26 ng and Sr blank of 3.3 ng, Rb and Sr contents and Sr isotopic compositions of whole rock, acid-leached mineral separates (ol, cpx and opx) and acid leachate from the nodules, eleven host and associated whole rock "basalts, and acid leached mineral separates (ol, cpx and opx) from the Josephine Peridotite have been analysed. The host basalts have ⁸⁷Sr/⁸⁶Sr (0.70238-0.70289) similar to MORB, but very much higher Rb, Sr and ⁸⁷Rb/⁸⁷Sr ratios (12.7-62.1 ppm, 702-1514 ppm and 0.028-0.138, respectively). This is attributed to a low ⁸⁷Sr/⁸⁶Sr mantle with small degree of melting or melting after recent metasomatism by a low ⁸⁷Sr/⁸⁶Sr fluid. Nodules occur only in ne normative alkali basalts and basanites. Diopside is the main carrier of Rb and Sr (Rb = 0.125-3.47 ppm in nodules and 0.023-0.076 ppm in Josephine Peridotite, Sr = 9.3-239 ppm in nodules and 0.256-0.582 ppm in Josephine Peridotite), with low ⁸⁷Sr/⁸⁶Sr ratio (0.7022-0.7041 in nodules and 0.7054-0.7063 in Josephine Peridotite) and ⁸⁷Rb/⁸⁶Sr ratio (0.004-0.1 in nodules and 0.23-0.38 in Josephine Peridotite). Olivines contain the least Rb and Sr (Rb = 0.055-0.27 ppm in nodules and 0.084-0.102 ppm in Josephine Peridotite, Sr = 0.11-3.5 ppm in nodules and 0.153-0.305 ppm in Josephine Peridotite) and give the highest ⁸⁷Sr/⁸⁶Sr ratios (0.7036-0.7 197 in nodules and 0.7089-0.7133 in Josephine Peridotite) and ⁸⁷Rb/⁸⁶Sr ratios (0.19-2.06 in nodules and 0.8-1.73 in Josephine Peridotite). Nodules from Jacques Lake, depleted in Sr and undepleted in major elements, could be a MORB-source-type mantle. Other nodules represent somewhat less Sr-depleted mantle. Whole rock nodule data fall on or off the corresponding mineral isochrons. The latter phenomenon is due to relatively recent contamination with interstitial material having a high Rb/Sr ratio. "Synthetic" whole rocks, calculated from leached-mineral data, have higher ⁸⁷Sr/⁸⁶Sr ratios than host basalts. Together with the well defined mineral isochrons, this supports the conclusion that the nodules and host basalts are not cognate. Equigranular nodules give a mid-Proterozoic mineral isochron date (1518-1537 Ma and (⁸⁷Sr/⁸⁶Sr)₀ = 0.70185). Protogranular nodules give late Precambrian (645 Ma and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7037. early-mid Paleozoic (276-576 Ma and (⁸⁷Sr/⁸⁶Sr) ₀ = 0.7024-0.7032) and Mesozoic (104 Ma and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7029) isochron dates. Porphyroclastic nodules do not define reliable mineral isochrons, but also show evidence of old age (at least 560-790 Ma and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7028-0.7030). Depleted Josephine Peridotite gives middle Paleozoic mineral isochron dates (366-441 Ma and (⁸⁷Sr/⁸⁶Sr)₀ = 0.7038-0.7041), in conflict with the general view that the Josephine Peridotite was generated in Late Jurassic time. This implies that the ophiolite base does not necessarily have the same age as overlying volcanic rocks and dykes. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Insets of large anhedral minerals in kimberlites are proposed to mainly have their origin from the disaggregation of mantle-derived xenoliths through mechanical abrasion by the ascending kimberlite magma. Garnet, despite being an important constituent of both mantle-derived peridotite and eclogite, forms only a minor constituent of kimberlites. This suggests that a large proportion of garnet liberated into the kimberlite through the disaggregation of such xenoliths, is consumed before the emplacement of kimberlite. This study records the breakdown mechanism of garnet by the ascending kimberlite magma by conducting experiments between pressures of 2 and 4 GPa and temperatures between 1100 and 1300°C. The starting material used in the experiments was prepared from a natural hypabyssal kimberlite that closely resembles the composition of a proposed primary Group I kimberlite magma. To the kimberlite material 5 wt % garnet, sourced from a natural peridotite, was added. It was found that garnet is not a stable equilibrium phase within the kimberlite magma under the investigated temperature and pressure conditions. Based on large volumes of phlogopite in the experiments it is concluded that garnet melts incongruently in the kimberlite magma to form phlogopite as a peritectic product and melts transitional in composition between silicate and carbonate melts. This is in contrast to more SiO2 -rich melt compositions produced as a consequence of the incongruent breakdown of both orthopyroxene and omphacite within kimberlite magmas. The consequence of the melt compositions produced in the experiments is increased solubility of CO2 in the form of carbonate (CO32-). This finding has implications for both kimberlite ascent mechanisms and the solubility of diamond transported within kimberlite magmas. / AFRIKAANSE OPSOMMING: Dit word voorgestel dat groot oneenvormige mineraalinsluitsels in kimberliet hoofsaaklik afkomstig is van xenolitiese mantelmateriaal wat verbrokkel weens die meganiese werking van die stygende kimberliet magma. Ten spyte daarvan dat granaat ‘n belangrike komponent is van peridotiet en eklogiet xenoliete afkomstig uit die mantel, vorm granaat slegs ‘n geringe deel van die kimberliet mineraalsamestelling. Dit dui daarop dat ‘n beduidende gedeelte van die granaat wat vrygstel word in die kimberliet magma deur die verbrokkeling van xenolitiese materiaal, afgebreek word deur die stygende kimberliet magma voordat dit stol. Hierdie studie ondersoek die afbreekmeganisme van granaat afkomstig van die mantel in die stygende kimberliet magma deur eksperimente uit te voer by drukke tussen 2 en 4GPa en temperature tussen 1100 en 1300°C. Die materiaal met die aanvang van die eksperimente was voorberei uit ‘n natuurlike hipabissale kimberliet wat soortgelyk is in samestelling as ‘n voorgestelde primêre Groep I kimberliet magma se samesteling. Vyf gewigspresent (5 wt %) granaat, verkry van n natuurlike peridotiet, is bygevoeg tot die kimberlietmateriaal. Daar is gevind dat granaat nie ‘n stabiele ewewigsfase is in die kimberliet magma binne die temperatuur-en drukstoestande ondersoek nie. Groot volumes flogopiet teenwoordig in die eksperimente dui daarop dat granaat inkongruent smelt in die kimberliet magma om flogopiet as ‘n peritektiese produk te vorm te same met ‘n smelt wat neig na ‘n karbonatitese smeltsamestelling. Die bevinding is in teenstelling met meer SiO2-ryke smeltsamestellings as gevolg van die inkongruente afbreek van beide ortopirokseen en omfasiet in die kimberliet magma. Die gevolg van die meer karbonatitese smeltsamestellings, is ‘n toename in die oplosbaarheid van CO2 in die smelt in die vorm van karbonaat (CO32-). Die bevinding het nagevolge vir beide kimberliet stygingsmeganismes asook die oplosbaarheid van diamant tydens die vervoer van diamant deur kimberliet magmas.

Carbon dioxide capture and storage will be necessary to mitigate the effects of global climate change. Mineral carbonation - converting carbon dioxide gas to carbonate minerals - is a permanent and environmentally benign mechanism for storing carbon dioxide. The peridotite section of the Samail Ophiolite is host to exceptionally well-developed, naturally occurring mineral carbonation and serves as a natural analog for an engineered carbon dioxide storage project. This work characterizes the geochemistry and hydrogeology of peridotite aquifers in the Samail Ophiolite. Water samples were collected from hyperalkaline springs, surface waters, and boreholes in peridotite, and recent mineral precipitates were collected near hyperalkaline springs. Samples were analyzed for chemical composition. Geochemical data were used to delineate water-rock-CO₂ reactions in the subsurface and constrain a reaction path model for the system. This model indicates that mineral carbonation in the natural system is limited by the amount of dissolved carbon dioxide in water that infiltrates deep into the aquifer. The amount of carbon dioxide stored in the system could potentially be enhanced by carbon dioxide injection into the aquifer. Reaction path modeling suggests that injection of water at saturation with carbon dioxide at 100 bars pCO₂ and 90⁰C could increase the carbonation rate by a factor of up to 16,000 and bring carbonation efficiency to almost 100%. Dissolved gas samples from boreholes were collected at in situ conditions and analyzed for chemical composition. Boreholes with pH > 10 contain millimolar levels of dissolved hydrogen and/or methane, indicating these boreholes are located near areas of active low temperature serpentinization. Serpentinization rates were calculated using groundwater flow estimates and dissolved gas concentrations, and range from 3x10⁻⁸ to 2x10⁻⁶ volume fraction peridotite serpentinized per year. Additionally, laboratory incubation experiments show dissolved hydrogen can be stored in sealed copper tubes for at least three months with neither diffusive loss nor production of hydrogen from oxidation of the copper. These experiments demonstrate that copper tubes can be practical containers for collecting and storing dissolved hydrogen in freshwater. Groundwater ages in the peridotite section of the Samail Ophiolite are investigated through analysis of tritium, dissolved noble gases, and stable isotopes. Tritium-³Helium dating was used to estimate the age of modern groundwaters (< 60 years old), and helium accumulation was used as relative age indicator for pre-bomb groundwaters (> 60 years old). Waters with pH < 9.3 have ages from 0-40 years, while waters with pH > 9.3 are all more than 60 years in age. Helium accumulation indicates pH < 10 waters contain only atmospheric and tritiogenic helium, while pH > 10 waters have accumulated 30-65% of their helium from radiogenic production or mantle helium. pH > 10 waters are thus significantly older than pH < 10 waters. Noble gas temperatures are generally around 32⁰C, close to the current mean annual ground temperature. One hyperalkaline borehole has noble gas temperatures 7⁰C cooler than the modern ground temperature, indicating the water at that site may have recharged during a glacial period. Stable isotope data (Δ¹⁸O and Δ²H) for waters with pH < 11 plot between the northern and southern local meteoric water lines, in the typical range for modern groundwater. Hyperalkaline boreholes and springs are enriched in Δ¹⁸O, which suggests they recharged when the southern vapor source dominated, perhaps during glacial periods. Lastly, the potential for in situ mineral carbonation in peridotite is investigated through reactive transport modeling of dissolved CO₂ injection into a peridotite aquifer. Injection was simulated at two depths, 1.25 km and 2.5 km, with reservoir conditions loosely based on the peridotite section of the Samail Ophiolite. The dependence of carbonation extent (mass of carbon dioxide sequestered as carbonate minerals per unit volume) on different factors - such as permeability, reactive surface area, and temperature - was explored. Carbonation extent is strongly controlled by reactive surface area (RSA), with geometric RSA models producing 10 to 770 times more carbonation than conservative RSA models with the same initial permeabilities and temperatures. The ratio of carbon dioxide supply to RSA is also a key factor. The ideal relationship between CO₂ supply and RSA appears to be from 5x10⁻⁴ to 0.2 kg CO₂ /day per m²/m³ RSA. Temperature has also has an impact on carbonation rate: for the same initial permeability, carbonation is 7-35% faster at 90⁰C than at 60⁰C. Simulations of a 50-year carbon dioxide injection show that fracture porosity and permeability do not become overly clogged and carbonation continues at a more or less constant rate. We estimate that one dissolved CO₂ injection well in peridotite could store 1.4 Mtons CO₂ in 30 years with a storage cost of $6/ton. This suggests that an engineered carbon dioxide storage project in peridotite could be both feasible and economical. In situ mineral carbonation in peridotite should continue to be investigated as a safe and permanent mechanism for carbon dioxide storage.

Alteration of ultramafic rocks is ubiquitous to their occurrence near the surface. Primary mantle minerals like olivine and pyroxenes are unstable at low pressure and temperatures and undergo hydration (serpentinization), carbonation and weathering reactions forming hydrated and carbonated minerals. Employing a variety of analytical techniques including: electron microprobe, X-Ray diffraction, major and trace element geochemistry, Mg isotopes geochemistry and geochemical modelling this work seeks to contrain conditions ofa lteration and trace changes in composition of peridotite during alteration. In Wadi Fins in the southeast of Oman peridotites outcrop at the bottom of a canyon overlaid by a thick sequence 1.5 km of Cretaceous to Eocene shallow oceanic limestones and dolostones. The peridotites exhibit different types of alteration. While the common view is that serpentinization and carbonation of peridotites is isochemical this is not the case for alteration in Wadi Fins. Peridotites tens of meters below the unconformity are characterized by a striking grid of carbonate and serpentine veins. The calcite veins and relatively low MgO/SiO2 suggest that the peridotites reacted with a hydrous fluid derived from interaction of seawater with the overlying sediments composed of limestones with minor amounts of chert. This is further affirmed by average δ13C, δ18O and 87Sr/86Sr from carbonate veins in the peridotites that are similar to values of the sediments. Clumped isotope thermometry on calcite veins in peridotite establish that they formed at 25–60 ℃. Reaction path modeling of carbonate- quartz derived fluids with peridotite reproduces the observed mineral assemblage composed of carbonate and serpentine with similar Mg and MgO/SiO2 at high water to rock ratios, with carbon, H2O and silica added to the rock by the reacting fluid. Close to the unconformity the altered peridotites are characterized by concentric alteration halos recording variable fO2 and fS2. The partially serpentinized cores preserved primary minerals and record extremely low oxygen fugacities (fO2~10^(-75) bars). Two alteration zones are present evident from the alteration color. These zones exhibit nonisochemical alteration characterized by intergrowths of stevensite/lizardite. The alteration zones record progressively higher (fO2) recorded by Ni-rich sulfides and iron oxides/hydroxides. The alteration zones lost 20-30% of their initial magnesium content, together with mobilization of iron over short distances from inner green zones into outer red zones, where iron was reprecipitated in goethite intermixed with silicates due to higher fO2. The loss of magnesium in this peridotites motivated the final section of work. Mg isotopic compositions of partially serpentinized harzburgites and dunites in Oman are identical to average mantle and bulk silicate Earth (δ26Mg=-0.25‰) while altered periodites from Wadi Fins get heavier with increasing alteration. Analyses of peridotite alteration products including samples from Wadi Fins and carbonates from Wadi Tayin were used to show that isochemical serpentinization at low W/R does not fractionate Mg isotopes. I propose a mechanism that with increasing W/R and co-precipitation of Mg-carbonates and serpentine leads to carbonates with light isotopic compositions (Magnesite δ26Mg =-3.3 and dolomite δ26Mg=-1.91) and serpentine with heavy compositions (up to δ26Mg =-0.96 in serpentine veins). This complementary enrichment-depletion and the finite 14C ages of the carbonates suggest that serpentinization is ongoing along carbonation in Oman at ambient temperatures. Rates of calcite precipitation in travertines inferred from Δ26Mgcal-fl suggest that travertine formation in Oman sequesters a total of 10^6-10^7 kg CO2/yr.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 22, 2010). Appendices are available as supplemental PDF files. Includes bibliographical references (p. 249-263).