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Silicate minerals
About: Silicate minerals is a research topic. Over the lifetime, 1794 publications have been published within this topic receiving 67064 citations.
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TL;DR: In this article, numerical simulations were conducted to model the mineralogical evolution in a hydrodynamic system and to evaluate the extent and effects of reaction retardation in contact-metamorphic aureoles.
Abstract: Mineral assemblages in contact-metamorphic aureoles are the products of the interplay between heat transfer and fluid flow induced by intrusion of magma. In wall rocks containing carbonate and silicate minerals, metamorphic reactions produce CO 2 , which then becomes part of the hydrodynamic system. Although observed assemblages are the ultimate products of T-X CO 2 fluid -t paths in aureole rocks, the complexities of the paths, and hence the evolution of a hydrodynamic system, are difficult to decipher from them. Numerical simulations were conducted to model the mineralogical evolution in a hydrodynamic system and to evaluate the extent and effects of reaction retardation. Simulations reveal that fluid composition in the inner aureole evolves rapidly toward high X CO 2 fluid as the rocks heat up before an appreciable amount of water is exsolved out of the pluton. After local fluid pressure drops when early reactions are coming to completion, infiltration of magmatic water becomes significant and can drive production of typical inner aureole minerals such as wollastonite. Fluid compositions in the outer aureole reflect largely (1) the initial CO 2 production, as fluids are driven down the pressure gradients from the inner aureole, and (2) the subsequent infiltration of magmatic H 2 O. Simulations also suggest temperature overstepping of the onset of reactions and retarded consumption of reactant minerals, which leads to coeval metastable reactions. However, the final simulated mineral assemblage in the inner aureole reflects equilibration with H 2 O-rich fluids that is usually seen in the field, although evidence for kinetic retardation may be preserved in some rocks, especially in the outer aureole.
27 citations
TL;DR: In the Bakony-Balaton Highland Volcanic Field (Western Hungary) as discussed by the authors, the authors found that the melt pockets formed at relatively high pressure through breakdown of mainly amphibole as a result of temperature increases accompanied, in most cases, by the influx of external metasomatic agents.
Abstract: Mantle xenoliths in Neogene alkali basalts of the Bakony–Balaton Highland Volcanic Field (Western Hungary) frequently have melt pockets that contain silicate minerals, glass, and often carbonate globules. Textural, geochemical and thermobarometric data indicate that the melt pockets formed at relatively high pressure through breakdown of mainly amphibole as a result of temperature increases accompanied, in most cases, by the influx of external metasomatic agents. New elemental and Sr–Nd–Pb isotope data show that in several xenoliths the external agent was either a LIL-enriched aqueous fluid or a CO2-rich fluid, whereas in other xenoliths the melt pockets were additionally enriched in LREE and sometimes HFSE, suggesting metasomatism by a silicate melt. The compositional character of the external agents might have been inherited by melting of a hydrated and probably carbonated deeper lithospheric component, which itself was metasomatized by melts with significant slab-derived components.
27 citations
TL;DR: In this article, the authors evaluated a novel approach for buffering subsurface pH that relies on the use of silicate minerals as a long-term source of alkalinity.
Abstract: Accurate control of groundwater pH is of critical importance for in situ biological treatment of chlorinated solvents This study evaluated a novel approach for buffering subsurface pH that relies on the use of silicate minerals as a long-term source of alkalinity A screening methodology based on thermodynamic considerations and numerical simulations was developed to rank silicate minerals according to their buffering efficiency A geochemical model including the main microbial processes driving groundwater acidification and silicate mineral dissolution was developed Kinetic and thermodynamic data for silicate minerals dissolution were compiled Results indicated that eight minerals (nepheline, fayalite, glaucophane, lizardite, grossular, almandine, cordierite, and andradite) could potentially be used as buffering agents for the case considered A sensitivity analysis was conducted to identify the dominant model parameters and processes This showed that accurate characterization of mineral kinetic rate constants and solubility are crucial for reliable prediction of the acid-neutralizing capacity In addition, the model can be used as a design tool to estimate the amount of mineral (total mass and specific surface area) required in field applications
27 citations
27 citations
TL;DR: Fluid compositions and bedding-scale patterns of fluid flow during contact metamorphism of the Weeks Formation in the Notch Peak aureole, Utah, were determined from mineralogy and stable isotope compositions as discussed by the authors.
Abstract: Fluid compositions and bedding-scale patterns of fluid flow during contact metamorphism of the Weeks Formation in the Notch Peak aureole, Utah, were determined from mineralogy and stable isotope compositions. The Weeks Formation contains calc-silicate and nearly pure carbonate layers that are interbedded on centimetre to decimetre scales. The prograde metamorphic sequence is characterized by theappearanceof phlogopite, diopside,and wollastonite.By accountingfor thesolution propertiesofFe, it is shown that the tremolite stability field was very narrow and perhaps absent in the prograde sequence. Unshifted oxygen and carbon isotopic ratios in calcite and silicate minerals at all grades, except above the wollastonite isograd, show that there was little to no infiltration of disequilibrium fluids. The fluid composition is poorly constrained, but X(CO2)fluid must have been>0.1, as indicated by the absence of talc, and has probably increased with progress of decarbonation reactions. The occurrence of scapolite and oxidation of graphite in calc-silicate beds of the upper diopside zone provide the first evidence for limited infiltration of external aqueous fluids. Significantly larger amounts of aqueous fluid infiltrated the wollastonite zone. The aqueous fluids are recorded by the presence of vesuvianite, large decreases in d 18 O values of silicate minerals from c. 16o in the diopside zone to c. 10o in the wollastonite zone, and extensive oxidation of graphite. The carbonate beds interacted with the fluids only along margins where graphite was destroyed, calcite coarsened, and isotopic ratios shifted. The wollastonite isograd represents a boundary between a high aqueous fluid-flux region on its higher- grade side and a low fluid-flux region on its lower-grade side. Preferential flow of aqueous fluids within the wollastonite zone was promoted by permeability created by the wollastonite-forming reaction and the natural tendency of fluids to flow upward and down-temperature near the intrusion-wall rock contact.
27 citations