Microscopic studies of hydrothermally metamorphosed shales from the Salton Sea Geothermal Field, California, USA

Thesis/Dissertation · Wed Jan 01 00:00:00 EST 1986

OSTI ID:6436331

Yau, Y C.L.

Scanning, transmission, and analytical electron microscopy have been used to study textural and chemical changes of minerals, including phyllosilicates, chain silicates and titanium oxides, in argillaceous sediments from the depth (temperature) interval of 256 m (115 C) to 1547 m (330 C) in the Salton Sea Geothermal Field, which have been subjected to low grade burial and hydrothermal metamorphism. The phyllosilicates progress from an illite zone (115-220 C), through a chlorite zone (220-310 C) and a biotite zone (310-330 C). Authigenic anatase occurred in the temperature range 115-120 C whereas titanite occurred in 300-330 C. Phyllosilicate stability relations indicate that either increase in temperature of changing ion concentrations in solution with depth are capable of explaining the observed mineral-depth zoning. The uniform crystal size of all authigenic phyllosilicate crystals, homogeneity of composition of individual crystals and the lack of replacement or dissolution textures of the pre-existing phases are all compatible with hydrothermal alteration having occurred in a single event rather than over a large time interval. Textural, chemical and microstructural relations observed in this study imply that reactions involve dissolution of detrital phases, material transport through fluid, and precipitation from solution. Such a dissolution/precipitation mechanism is compatible with an open system such as Salton Sea shales characterized by high water/rock ratio and permeability. In contrast, diffusion along edge dislocations or grain boundaries concomitant with gradual replacement of reactants by products across the reaction front dominate relatively closed systems.

• Research Organization: Michigan Univ., Ann Arbor (USA)
• OSTI ID: 6436331
• Resource Relation: Other Information: Thesis (Ph. D.)
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
SALTON SEA GEOTHERMAL FIELD
MINERALOGY
BIOTITE
CHEMICAL COMPOSITION
CHLORITE MINERALS
DISSOLUTION
GEOLOGIC HISTORY
HYDROTHERMAL ALTERATION
ILLITE
METAMORPHISM
MICROSTRUCTURE
PERMEABILITY
PRECIPITATION
SCANNING ELECTRON MICROSCOPY
SHALES
SILICATES
TEXTURE
TITANIUM OXIDES
TRANSMISSION ELECTRON MICROSCOPY
CHALCOGENIDES
CLAYS
CRYSTAL STRUCTURE
ELECTRON MICROSCOPY
GEOTHERMAL FIELDS
MICA
MICROSCOPY
MINERALS
OXIDES
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
SEPARATION PROCESSES
SILICATE MINERALS
SILICON COMPOUNDS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
150302* - Geothermal Exploration & Exploration Technology- Geochemical Techniques & Surveys