Magmatic and hydrothermal processes in layered intrusions

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:7024600

Schiffries, C M

The Bushveld Complex is of special interest because it is the largest known layered intrusion and it contains a major fraction of the world's reserves of chromium, vanadium, and the platinum-group elements. The fractionation of oxygen isotopes between coexisting plagioclase and pyroxene from the Bushveld Complex indicates that most samples have retained their magmatic isotopic signature and were not strongly affected by subsolidus exchange. The Bushveld magmas were enriched in {sup 18}O and {sup 87}Sr relative to the contemporaneous bulk mantle. The systematics of the isotopic data indicate that the Bushveld magmas assimilated a significant amount of material during their ascent through the continental crust. In addition to its isotopic effects, crustal contamination may have had a large effect on the chemical composition and crystallization sequence of the Bushveld magmas. A systematic search for evidence of fluid-rock interactions in the Bushveld Complex resulted in the recognition of a major hydrothermal system that was active while the intrusion crystallized and cooled. The Bushveld hydrothermal system provides insights into the nature of large-scale fluid flow at crustal depths ranging to at least 15 km and temperatures ranging to at least 700 C. Stable isotopic data indicate that the Bushveld hydrothermal system was a rock-dominated system on a regional scale, but fluid-dominated conditions were achieved on a local scale as a consequence of structurally controlled fluid flow. Many of the hydrothermal fluids were chloride-rich brines, and such fluids have the capacity to transport appreciable quantities of dissolved metals. Hydrothermal processes may have played a more significant role in determining the distribution of sulfide minerals and precious metals than has been previously recognized.

• Research Organization: Harvard Univ., Boston, MA (USA)
• OSTI ID: 7024600
• Country of Publication: United States
• Language: English

Related Subjects

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AFRICA
ALKALINE EARTH ISOTOPES
ANORTHOSITES
BETA DECAY RADIOISOTOPES
CHEMICAL COMPOSITION
CHEMISTRY
CHROMIUM ORES
CRYSTALLIZATION
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
ENERGY SYSTEMS
ENRICHMENT
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FLUID FLOW
FLUIDS
GABBROS
GEOCHEMISTRY
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOTHERMAL FLUIDS
GEOTHERMAL SYSTEMS
HOURS LIVING RADIOISOTOPES
HYDROTHERMAL SYSTEMS
IGNEOUS ROCKS
INTERMEDIATE MASS NUCLEI
INTRUSION
ISOMERIC TRANSITION ISOTOPES
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MAGMA
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METALS
MINERALS
NUCLEI
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OXYGEN 18
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PHASE TRANSFORMATIONS
PLATINUM
PLATINUM METALS
PLUTONIC ROCKS
PYROXENES
RADIOISOTOPES
RESERVOIR FLUIDS
ROCK-FLUID INTERACTIONS
ROCKS
SILICATES
SILICON COMPOUNDS
STABLE ISOTOPES
STRONTIUM 87
STRONTIUM ISOTOPES
TRANSITION ELEMENTS
VANADIUM ORES