Morphological ripening of fluid inclusions and coupled zone-refining in quartz crystals revealed by cathodoluminescence imaging: Implications for CL-petrography, fluid inclusion analysis and trace-element geothermometry

Cathodoluminescence (CL) studies have previously shown that some secondary fluid inclusions in luminescent quartz are surrounded by dark, non-luminescent patches, resulting from fracture-sealing by late, trace-element-poor quartz. This finding has led to the tacit generalization that all dark CL patches indicate influx of low temperature, late-stage fluids. In this study we have examined natural and synthetic hydrothermal quartz crystals using CL imaging supplemented by in-situ elemental analysis. The results lead us to propose that all natural, liquid-water-bearing inclusions in quartz, whether trapped on former crystal growth surfaces (i.e., of primary origin) or in healed fractures (i.e., of pseudosecondary or secondary origin), are surrounded by three-dimensional, non-luminescent patches. Cross-cutting relations show that the patches form after entrapment of the fluid inclusions and therefore they are not diagnostic of the timing of fluid entrapment. Instead, the dark patches reveal the mechanism by which fluid inclusions spontaneously approach morphological equilibrium and purify their host quartz over geological time. Fluid inclusions that contain solvent water perpetually dissolve and reprecipitate their walls, gradually adopting low-energy euhedral and equant shapes. Defects in the host quartz constitute solubility gradients that drive physical migration of the inclusions over distances of tens of μm (commonly) up to several mm (rarely). Inclusions thus sequester from their walls any trace elements (e.g., Li, Al, Na, Ti) present in excess of equilibrium concentrations, thereby chemically purifying their host crystals in a process analogous to industrial zone refining. Non-luminescent patches of quartz are left in their wake. Fluid inclusions that contain no liquid water as solvent (e.g., inclusions of low-density H2O vapor or other non-aqueous volatiles) do not undergo this process and therefore do not migrate, do not modify their shapes with time, and are not associated with dark-CL zone-refined patches. This new understanding has implications for the interpretation of solids within fluid inclusions (e.g., Ti- and Al-minerals) and for the elemental analysis of hydrothermal and metamorphic quartz and its fluid inclusions by microbeam methods such as LA-ICPMS and SIMS. As Ti is a common trace element in quartz, its sequestration by fluid inclusions and its depletion in zone-refined patches impacts on applications of the Ti-in-quartz geothermometer.

Proposal for the inclusion of misoprostol in the WHO model list of essential medicines

Gynuity

Perspectives on guidance and social inclusion in a global society

The world is changing rapidly. People today face numerous challenges in achieving a meaningful and fulfilling life. In many countries, there are enormous systemic barriers to address, such as: massive unemployment, HIV/AIDS, social disintegration, and inadequate infrastructure. One job for life is over. For many it never existed. Old metaphors and old models of career development no longer apply. New ways of thinking about careers are necessary, that take into account the context in which people are living, the reality of today's labour market, and the fact people's career-life journey contains many branching paths, barriers, and obstacles, but also allies and sources of assistance. Flexibility is important, as is keeping options open and making sure the journey is meaningful. Guidance professionals need to begin early, working with other professionals and those seeking assistance to develop attitudes that facilitate people taking charge of their own career-life paths. People need a vision for their life that will drive a purposeful approach to career-life planning and avoid floundering. Helping people achieve that direction can be most effectively accomplished when policy makers and practitioners work together to ensure that effective and accessible services are available for those who need them and when a large part of focus in on addressing the context in which marginalized people work and live.

Perspectives on guidance and social inclusion in a global society

The world is changing rapidly. People today face numerous challenges in achieving a meaningful and fulfilling life. In many countries, there are enormous systemic barriers to address, such as: massive unemployment, HIV/AIDS, social disintegration, and inadequate infrastructure. One job for life is over. For many it never existed. Old metaphors and old models of career development no longer apply. New ways of thinking about careers are necessary, that take into account the context in which people are living, the reality of today's labour market, and the fact people's career-life journey contains many branching paths, barriers, and obstacles, but also allies and sources of assistance. Flexibility is important, as is keeping options open and making sure the journey is meaningful. Guidance professionals need to begin early, working with other professionals and those seeking assistance to develop attitudes that facilitate people taking charge of their own career-life paths. People need a vision for their life that will drive a purposeful approach to career-life planning and avoid floundering. Helping people achieve that direction can be most effectively accomplished when policy makers and practitioners work together to ensure that effective and accessible services are available for those who need them and when a large part of focus in on addressing the context in which marginalized people work and live.

Perspectives on guidance and social inclusion in a global society

The world is changing rapidly. People today face numerous challenges in achieving a meaningful and fulfilling life. In many countries, there are enormous systemic barriers to address, such as: massive unemployment, HIV/AIDS, social disintegration, and inadequate infrastructure. One job for life is over. For many it never existed. Old metaphors and old models of career development no longer apply. New ways of thinking about careers are necessary, that take into account the context in which people are living, the reality of today's labour market, and the fact people's career-life journey contains many branching paths, barriers, and obstacles, but also allies and sources of assistance. Flexibility is important, as is keeping options open and making sure the journey is meaningful. Guidance professionals need to begin early, working with other professionals and those seeking assistance to develop attitudes that facilitate people taking charge of their own career-life paths. People need a vision for their life that will drive a purposeful approach to career-life planning and avoid floundering. Helping people achieve that direction can be most effectively accomplished when policy makers and practitioners work together to ensure that effective and accessible services are available for those who need them and when a large part of focus in on addressing the context in which marginalized people work and live.

Geochemistry, isotopes, trace elements and fluid inclusion geothermometry at DSDP Hole 83-504B

Stockwork-like metal sulfide mineralizations were found at 910-928 m below seafloor (BSF) in the pillow/dike transition zone of Hole 504B. This is the same interval where most physical properties of the 5.9-m.y.-old crust of the Costa Rica Rift change from those characteristic of Layer 2B to those of Layer 2C. The pillow lavas, breccias, and veins of the stockwork-like zone were studied by transmitted and reflected light microscopy, X-ray diffraction, and electron microprobe analysis. Bulk rock oxygen isotopic analyses as well as isolated mineral oxygen and sulfur isotopic analyses and fluid inclusion measurements were carried out. A complex alteration history was reconstructed that includes three generations of fissures, each followed by precipitation of characteristic hydrothermal mineral parageneses: (1) Minor and local deposition of quartz occurred on fissure walls; adjacent wall rocks were silicified, followed by formation of chlorite and minor pyrite I in the veins, whereas albite, sphene, chlorite and chlorite-expandable clay mixtures, actinolite, and pyrite replaced igneous phases in the host rocks. The hydrothermal fluids responsible for this first stage were probably partially reacted seawater, and their temperatures were at least 200-250° C. (2) Fissures filled during the first stage were reopened and new cracks formed. They were filled with quartz, minor chlorite and chlorite-expandable clay mixtures, traces of epidote, common pyrite, sphalerite, chalcopyrite, and minor galena. During the second stage, hydrothermal fluids were relatively evolved metal- and Si-rich solutions whose temperatures ranged from 230 to 340° C. The fluctuating chemical composition and temperature of the solutions produced a complex depositional sequence of sulfides in the veins: chalcopyrite I, ± Fe-rich sphalerite, chalcopyrite II ("disease"), Fe-poor sphalerite, chalcopyrite III, galena, and pyrite II. (3) During the last stage, zeolites and Mg-poor calcite filled up the remaining spaces and newly formed cracks and replaced the host rock plagioclase. Analcite and stilbite were first to form in veins, possibly at temperatures below 200°C; analcite and earlier quartz were replaced by laumontite at 250°C, whereas calcite formation temperature ranged from 135 to 220°C. The last stage hydrothermal fluids were depleted in Mg and enriched in Ca and 18O compared to seawater and contained a mantle carbon component. This complex alteration history paralleling a complex mineral paragenesis can be interpreted as the result of a relatively long-term evolution of a hydrothermal system with superimposed shorter term fluctuations in solution temperature and composition. Hydrothermal activity probably began close to the axis of the Costa Rica Rift with the overall cooling of the system and multiple fracturing stages due to movement of the crust away from the axis and/or cooling of a magmatic heat source.

(Table 1) Micro-inclusion counts and ion concentrations in the five GRIP ice-core sections

We provide the first direct evidence that a number of water-soluble compounds, in particular calcium sulfate (CaSO4 2H2O) and calcium carbonate (CaCO3), are present as solid, micron-sized inclusions within the Greenland GRIP ice core. The compounds are detected by two independent methods: micro-Raman spectroscopy of a solid ice sample, and energy-dispersive X-ray spectroscopy of individual inclusions remaining after sublimation. CaSO4 2H2O is found in abundance throughout the Holocene and the last glacial period, while CaCO3 exists mainly in the glacial period ice. We also present size and spatial distributions of the micro-inclusions. These results suggest that water-soluble aerosols in the GRIP ice core are dependable proxies for past atmospheric conditions.