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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.

Abstract: Coupled analysis of the pressure–temperature (PT) evolution and accessory phase geochronology of a single sample reveals the burial-uplift history of part of the Lesser Himalaya during the Middle Miocene. Phase-equilibria calculations indicate that a peak temperature of 600–640 °C followed burial to approximately 25 km depth. Laser-ablation monazite geochronology yields a weighted mean 206Pb⁎/238U age of 11.1±2.0 Ma and a Tera-Wasserburg Concordia intercept age of 10.6±0.9 Ma, with no distinguishable age difference between matrix and inclusion grains. Considerations of the likelihood of excess 206Pb further suggest that the crystallization age lies in the range 9–10 Ma. Textural analysis suggests that monazite grew during prograde metamorphism. Peak metamorphic conditions were followed by exhumation and cooling, forming a distinctively tight PT path closure. Both the shape of this path and its relatively young prograde phase distinguish Lesser Himalayan evolution from that typically inferred for the High Himalaya, and allow exploration of the thermal mechanisms that operated in the western Himalaya during the interval ca. 23–6 Ma. The PTt history is characteristic of footwall heating due to rapid overthrusting of hot rock (the Higher Himalaya), followed by incorporation into a thrust sheet that exhumed the sequence rapidly enough to preserve an inverted metamorphic gradient. [Copyright &y& Elsevier]

The episodic variation of the seawater [sup 87]Sr/[sup 86]Sr ratio has been attributed to either variations in the Sr flux or the Sr-isotopic composition of the riverine-dissolved load derived from weathering of the continental crust. The discovery that Himalayan rivers are characterized by high concentrations of dissolved Sr concentrations with high [sup 87]Sr/[sup 86]Sr ratios has raised the possibility that collisional orogens play a critical role in moderating the variations in seawater [sup 87]Sr/[sup 86]Sr ratios. Here we describe Himalayan carbonates and calc-silicates from Garhwal, the headwaters of the Ganges, with extreme [sup 87]Sr/[sup 86]Sr ratios (> 1.0). Elevated Sr-isotope ratios result from exchange with Rb-rich silicate material during both Himalayan and pre-Himalayan metamorphic episodes, and the carbonates contribute a significant fraction to the Ganges [sup 87]Sr flux. Particularly elevated [sup 87]Sr/[sup 86]Sr ratios are found in calc-silicates from the Deoban Formation of the Lesser Himalaya. A detailed traverse of shales and calc-silicates from this unit confirms that carbonate horizons have increased [sup 87]Sr/[sup 86]Sr ratios as a result of isotopic exchange over length scales of 10-30 cm. We conclude that metamorphism of carbonates may cause elevation of their [sup 87]Sr/[sup 86]Sr ratios and that uplift of metamorphosed carbonates may be a consequence of collisional orogens, which contributes to the elevation of seawater [sup 87]Sr/[sup 86]Sr ratios. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of river water, rock, travertine and soil from the high altitude, negligible vegetation setting of the Southern Tibetan Plateau demonstrates that Ca and Mg isotope ratios are fractionated during weathering. Dissolved Ca in the two rivers studied is derived primarily by limestone dissolution. δ44/ 42Ca in the rivers averages 0.43‰ and is statistically distinct from limestone at 0.31‰. The range in δ44/ 42Ca in these small rivers is 0.43‰, equivalent to the entire range in δ44/ 42Ca recorded in marine carbonate over the last 80Ma. Precipitation of isotopically light travertine with a δ44/ 42Ca of 0.21‰ enriches solute Ca in heavy isotopes. The Mg isotope composition of the rivers is intermediate between limestone and silicate rock averaging −1.5‰. Silicate soil has a δ26Mg of −0.03‰, heavier than silicate rock by 0.5‰. These fractionations in the soil create a companion groundwater reservoir of heavy Ca and light Mg. Seasonal variations in Ca and Mg isotope ratios in the dissolved load are small, but define an array which can be modelled as a mixture between a fractionated groundwater reservoir and surface runoff (reflecting the isotopic composition of the lithology). Fractionation of Ca during the weathering of the continents is of importance to the global cycle of Ca. The riverine input of Ca to the oceans (dominated by carbonate weathering) is controlled not only by the composition of the primary continental crust but also by the size and composition of a fractionated reservoir on the continents. The impact on the oceanic cycle of Ca depends on the relative residence times of dissolved Ca in the ocean and the storage time of fractionated Ca. [Copyright &y& Elsevier]

Numerical modeling plays an essential role in both identifying and assessing sub-surface reservoirs that might be suitable for future carbon capture and storage projects. Accuracy of flow simulations is tested by benchmarking against historic observations from on-going CO 2 injection sites. At the Sleipner project located in the North Sea, a suite of time-lapse seismic reflection surveys enables the three-dimensional distribution of CO 2 at the top of the reservoir to be determined as a function of time. Previous attempts have used Darcy flow simulators to model CO 2 migration throughout this layer, given the volume of injection with time and the location of the injection point. Due primarily to computational limitations preventing adequate exploration of model parameter space, these simulations usually fail to match the observed distribution of CO 2 as a function of space and time. To circumvent these limitations, we develop a vertically-integrated fluid flow simulator that is based upon the theory of topographically controlled, porous gravity currents. This computationally efficient scheme can be used to invert for the spatial distribution of reservoir permeability required to minimize differences between the observed and calculated CO 2 distributions. When a uniform reservoir permeability is assumed, inverse modeling is unable to adequately match the migration of CO 2 at the top of the reservoir. If, however, the width and permeability of a mapped channel deposit are allowed to independently vary, a satisfactory match between the observed and calculated CO 2 distributions is obtained. Finally, the ability of this algorithm to forecast the flow of CO 2 at the top of the reservoir is assessed. By dividing the complete set of seismic reflection surveys into training and validation subsets, we find that the spatial pattern of permeability required to match the training subset can successfully predict CO 2 migration for the validation subset. This ability suggests that it might be feasible to forecast migration patterns into the future with a degree of confidence. Nevertheless, our analysis highlights the difficulty in estimating reservoir parameters away from the region swept by CO 2 without additional observational constraints. [ABSTRACT FROM AUTHOR]

Abstract: We have measured the magnesium (Mg) isotope ratios in 45 rivers including 16 of the largest rivers in the world, covering a range of geologic, tectonic and climatic drainage basin environments. The range in riverine δ26Mg is 2.5‰, half the variation in terrestrial rock. Although the Mg isotopic composition of the source rock is important for small rivers, at a global scale lithology is of limited significance for Mg isotope ratios in rivers. Part of the variability at a global scale may be attributed to fractionation in the weathering environment. The rivers analysed constitute 30% of the global Mg riverine flux to the oceans and a flux weighted Mg isotope composition of global runoff has been estimated at −1.09‰. Even taking into account uncertainty, this is distinct from seawater at −0.82‰. This difference arises either from the fractionation of Mg isotope ratios in the ocean and/or a Mg budget which is not at steady state. The difference is consistent with fractionation by carbonate precipitation. In the simplest steady state scenario, where the oceanic mass balance is maintained by riverine input and hydrothermal and dolomite output, Mg isotope ratios imply a minimum dolomite Mg flux of 9% of the total output Mg flux. The implications of the distinct isotopic composition of the riverine flux from modern seawater, is that the Mg isotope ratio of seawater has probably varied outside of current analytical uncertainty. Mg isotope ratios may therefore provide a valuable new tracer in palaeo-oceanography. [Copyright &y& Elsevier]