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The Indo-Burman Ranges in western Myanmar extend along the Sunda Arc subduction zone and may be divided into a western portion of Neogene sedimentary rocks and an eastern portion of Palaeogene sedimentary rocks, separated by the Kaladan Fault. Both Himalayan and Burman sources have been proposed for these sediments. Our thermochronological analyses on detrital grains, isotopic analyses on bulk rock, and petrographic and heavy mineral data indicate that the Palaeogene Indo-Burman Ranges contain a significant component of arc-derived material, interpreted as derived from the Burmese portion of the Mesozoic--Tertiary arc to the east. And older crustal component is also identifiable, which may have been sourced from the Himalaya or the Burmese margin. By contrast, the Neogene Indo-Burman Ranges show dominant derivation from the Himalaya. A minor arc-derived component may have been sourced from the Trans-Himalaya, or recycled from the arc-derived Paleogene Indo-Burman Ranges.

Infiltration of a metabasite sill from Islay, Scotland by an [H.sub.2]O-C[O.sub.2] fluid caused (1) modification of [delta][sup.18]O and (2) carbonation at the sill margins. Maps of [delta][sup.18]O and reaction progress were constructed from a 20 x 47.7 metre sample grid across the sill. The grid consisted of 300 samples, spaced at m, dm and cm intervals, many of which were analysed for both [delta][sup.18]O and reaction progress. The [delta][sup.18]O was determined by laser fluorination of whole rock silicate powders and reaction progress was determined by rapid field-based measurement of % calcite ('fizz-o-meter', Skelton et al. 1995). Reaction and isotope fronts outlined tube-like features that emanate from the sill margin and discrete nodes that, although detached from the sill margin in two dimensions, are thought to represent sections through similar tubes in three dimensions. We envisage that these protrusions are the fossil record of metamorphic 'fluid pathways' whereby fluid permeated the sill. Isotope and reaction fronts are found to correlate spatially as predicted by a modified form of the chromatographic equation which describes this envisaged geometry, that is where isotopic and reactive transport in the fluid phase are facilitated by advection along specific fluid pathways and transverse diffusion in the surrounding rock. These fluid pathways consist of bundles of anastomosing grain boundary channels or micro-cracks, which are thought to propagate through transient cyclic infiltration, reaction, porosity enhancement and fracturing. This mechanism is self-perpetuating and accentuates random perturbations at the sill margin to form the observed tubes. We argue that this is the earliest stage of the infiltration process which has affected metabasites of the SW Scottish Highlands and that subsequent shear deformation of the reacted rims of these pathways, has caused their re-orientation and juxtaposition to form the reacted sill margins described by Skelton et al. (1995).

The tectonic setting of the Archean Ngezi Group greenstones in the Belingwe Greenstone Belt, Zimbabwe, is controversial. Both autochthonous continental and oceanic settings have been proposed. The sedimentary facies of the basal Manjeri Formation have been logged in surface sections and in drill cores. Deposition occurred under fluviatile and shallow-marine conditions followed by alluvial fans and fan-deltas. Detrital mineralogy, rare-earth-element patterns, and Sm-Nd depleted-mantle model ages between 2.9 and 3.7 Ga are consistent with derivation from very local sources. The facies and geochemical association imply sedimentation in an extensional continental setting.

Hydrothermal deposits research shows that the active Transatlantic Geotraverse (TAG) sulphide mound on the Mid-Atlantic Ridge contains anhydrite and sulphide precipitates originally found in sea water up to 37,000 years ago. The evolution of the TAG hydrothermal mound occurred in five stages. These are illustrated. Age distribution isotope measurements are given.

The oxygen isotopes (O) move to a greater distance in the silicate than in the marble rocks of the Lizzies Basin, East Humboldt Range, Nevada. The strontium isotope (Sr) moves about the same distance in both types of rocks. This is probably due to a difference in the porosity of the silicate rocks or different diffusion rates of the isotopes. Details of the isotope profiles across the marble to calc-silicate contacts are given.

The 87Sr/86Sr ratio of silicate sediments suppresses metamorphism in the Earth-atmosphere CO2 flux. Sr from oceanic and carbonate reservoirs and from juvenile crusts balance the Sr lost during erosion and weathering. This moderates the 87Sr/86Sr composition of the silicon sediment mass. The 87Sr/Sr86 is a significant tracer for several crust-mantle hydrosphere geochemical interactions.

A group of geologic experts linked the evolution of the Zimbabwe Craton to the Manjeri Formation. Through the use of sedimetological data derived from Manjeri samples, the group concluded that the Zimbabwe Carton is a product an intracontinental sequence which started in Manjeri. Such an assumption, however, drew the interest of some researchers, who claim that the Manjeri Formation has nothing to do with the Zimbabwe Craton phenomenon. No historical or geographic document has so far been produced to confirm that the Manjeri Formation is stratigraphically overlain by the Ngezi Group.

An analysis describing a textural equilibrium model is presented. The model has been criticized for its initial granite temperature setting. The objection was based on the theory that the granite formation was present before intrusion. However, analysis shows that a best-fit situation can be assumed only if the rock temperature was not greater than 150 degrees celsius and contact at intrusion temperature has not been made for more than 1,000 years.

Abstract: This paper presents the initial results of a scientific drilling project to recover core and pressurized fluid samples from a natural CO2 reservoir, near the town of Green River, Utah. The drilling targeted a stacked sequence of CO2-charged Jurassic sandstone reservoirs and caprocks, situated adjacent to a CO2-degassing normal fault. This site has actively leaked CO2 from deep supercritical CO2 reservoirs at depth >2km within the basin for over 400,000years. The project objectives were to gather samples to examine reactive fluid flow in the reservoirs, caprocks and faults, during migration of CO2 through the geological overburden from the deep supercritical CO2 reservoirs. Downhole fluid sampling and fluid element and isotope geochemistry show that the shallow reservoirs are being actively fed by inflow of CO2-saturated brines through the faults. Comparisons of shallow and deep fluid geochemistry suggest that: (i) CO2 and CO2-charged brines co-migrated from the deep reservoirs, (ii) the CO2-saturated brines migrating from depth interact with significant volumes of meteoric groundwater in aquifers in the shallower Permian and Jurassic sandstones, diluting the brine composition, and (iii) that a significant fraction of the CO2 migrating from depth is dissolved in these brine–meteoric water mixtures, with >99% of the CO2 in fluids sampled from the shallow reservoirs being derived during fluid migration, after the fluids left their source reservoir. The 87Sr/86Sr ratio of the brine flowing through the faults is significantly elevated due to the addition of Sr from silicate mineral dissolution during fluid migration. The association of bleached sandstones in the core with CO2-rich fluids supports interpretations from elsewhere that CO2-charged brines with CH4 or H2S reductants can dissolve hematite present within the sediment. Analysis of fluid geochemistry and sandstone petrology suggests that the CO2-rich fluids dissolve carbonate, hematite and gypsum in the reservoirs, as they flow away from the faults. Element and isotope geochemistry of fluid samples from the drillhole and Crystal Geyser constrain mixing models which show that, within the Navajo Sandstone, the reservoir fluids are undergoing complex mixing of: (i) CO2-saturated brine inflowing from the fault, (ii) CO2-undersaturated meteoric groundwater flowing through the reservoir and (iii) reacted CO2-charged brines flow through fracture zones in the overlying Carmel Formation caprock, into the formations above. Such multi-scale mixing processes may significantly improve the efficiency with which groundwaters dissolve the migrating CO2. [Copyright &y& Elsevier]

A model was formulated to illustrate the mineralogical consequences of fluid infiltration on rocks experiencing metamorphism. The model developed is an extension of past published work since it permits calculation of fluid fluxes for different T-Xco2 paths within a system undergoing changes in the angle of flow within time, multivariant reactions and space and lateral fluxes from adjacent more carbon dioxide or water-rich layers. The model entails computation of mineral assemblages, modes and composition.