Development and application of laser microprobe techniques for oxygen isotope analysis of silicates, and, fluid/rock interaction during and after granulite-facies metamorphism, highland southwestern complex, Sri Lanka
The extent of fluid/rock interaction within the crust is a function of crustal depth, with large hydrothermal systems common in the brittle, hydrostatically pressured upper crust, but restricted fluid flow in the lithostatically pressured lower crust. To quantify this fluid/rock interaction, a Nd-YAG/CO[sub 2] laser microprobe system was constructed to analyze oxygen isotope ratios in silicates. Developed protocols produce high precision in [sigma][sup 18]O ([+-]0.2, 1[sigma]) and accuracy comparable to conventional extraction techniques on samples of feldspar and quartz as small as 0.3mg. Analysis of sub-millimeter domains in quartz and feldspar in granite from the Isle of Skye, Scotland, reveals complex intragranular zonation. Contrasting heterogeneous and homogeneous [sigma][sup 18]O zonation patterns are revealed in samples <10m apart. These differences suggest fluid flow and isotopic exchange was highly heterogeneous. It has been proposed that granulite-facies metamorphism in the Highland Southwestern Complex (HSWC), Sri Lanka, resulted from the pervasive influx of CO[sub 2], with the marbles and calc-silicates within the HSWC a proposed fluid source. The petrologic and stable isotopic characteristic of HSWC marbles are inconsistent with extensive decarbonation. Wollastonite calc-silicates occur as deformed bands and as post-metamorphis veins with isotopic compositions that suggest vein fluids that are at least in part magmatic. Post-metamorphic magmatic activity is responsible for the formation of secondary disseminated graphite growth in the HSWC. This graphite has magmatic isotopic compositions and is associated with vein graphite and amphibolite-granulite facies transitions zones. Similar features in Kerela Khondalite Belt, South India, may suggest a common metamorphic history for the two terranes.
- Research Organization:
- Wisconsin Univ., Madison, WI (United States)
- OSTI ID:
- 5630770
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
HYDROTHERMAL SYSTEMS
ROCK-FLUID INTERACTIONS
SILICATES
ION MICROPROBE ANALYSIS
ISOTOPE RATIO
SRI LANKA
GEOCHEMISTRY
FELDSPARS
FLUID FLOW
GRANULITES
ISOTOPIC EXCHANGE
OXYGEN ISOTOPES
PETROLOGY
QUARTZ
ASIA
CHEMICAL ANALYSIS
CHEMISTRY
DEVELOPING COUNTRIES
ENERGY SYSTEMS
GEOLOGY
GEOTHERMAL SYSTEMS
ISLANDS
ISOTOPES
METAMORPHIC ROCKS
MICROANALYSIS
MINERALS
NONDESTRUCTIVE ANALYSIS
OXIDE MINERALS
OXYGEN COMPOUNDS
ROCKS
SILICATE MINERALS
SILICON COMPOUNDS
150200* - Geology & Hydrology of Geothermal Systems
152003 - Geothermal Data & Theory- Rock-Water-Gas Interactions
580000 - Geosciences