Thermally induced chemical migration: a natural analog approach. (Technical progress report)
The objective was to understand Proterozoic granite systems in the Black Hills. Some results are outlined: (1) Source region: Nd, O, and Sr isotope characteristics indicate that the Harney Peak Granite was not derived from any sampled Proterozoic metasedimentary rock exposure in the region. The granite and the pegmatite were either derived from a single source whose average precursor became LREE-enriched during late-Archean, or they were derived from at least two sources with at least one endmember of the source having a late Archean or older mantle extraction age. (2) The Harney Peak Granite-pegmatite connection: We considered four models in our geochemical modeling: (a) crystallization from a silicate melt derived from a one-stage anatexis event; (b) crystallization from a fluid produced by exsolution from the granite or by metamorphic dehydration of metasediments; (c) a model which concerns melt scavenging of the elements enriched in pegmatites (e.g. Li, Rb, Cs) from fluids or rocks with which it comes in contact; (d) crystallization from a melt derived through some fractionation of the Harney Peak Granite. (3) Emplacement mechanism: The Calamity Peak layered complex is a satellitic composite pluton (approx.1 km/sup 2/) with many structural, textural, and chemical features mimicking the larger (approx.100 km/sup 2/) Harney Peak dome. The Calamity Peak dome (and by inference parts of the Harney Peak dome) grew by repeated conformable intrusions of granitic layers on the hanging-wall side of the initial intrusion. (4) Pegmatite internal evolution: major, minor, trace elements, and oxygen isotope compositions have been evaluated to delineate the sequence of crystallization in the zoned and highly fractionated Tin Mountain pegmatite.
- Research Organization:
- South Dakota School of Mines and Technology, Rapid City (USA). Inst. for the Study of Mineral Deposits
- DOE Contract Number:
- FG01-84ER13259
- OSTI ID:
- 5800191
- Report Number(s):
- DOE/ER/13259-T2; ON: DE86009034
- Resource Relation:
- Other Information: Portions of this document are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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