Unusual carbonate-rich dikes and lamprophyres in Porcupine Dome, east-central Montana

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5807841

Doden, A G; Gold, D P ^[1]

---

1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences

Isolated carbonate dikes and lamprophyric plugs are exposed in Porcupine dome, a Laramide structure in east-central Montana. En echelon sets of carbonate dikes strike N70E, consistent with regional lineaments and local normal faults. Individual dikes are steeply dipping, only 30--70 cm in width, and up to 1 km in length. These dikes exhibit unequivocal magmatic characteristics, including chilled margins, flow-aligned micas, multiple intrusive stages, country rock xenoliths, and local small blows'' containing well-rounded carbonate autoliths. Spatially associated with the dikes are small plugs of olivine-phlogopite-garnet-carbonate-bearing silicate rocks and a diatreme of bedded tuffs with xenoliths of country rocks. The dikes consistent primarily of calcite and dolomite, phlogopite, and opaque oxides. Although the dikes are relatively homogeneous mineralogically along strike, some chemical variations are apparent in the vicinity of the plugs/diatreme. Phlogopites and carbonates, common to both dikes and plugs, may provide a genetic link between these spatially associated intrusions. These unusual associations of dikes, plugs and diatremes are not restricted to Porcupine dome, but extend at least as far as the Grassrange - Winnett area, 100 km to the NW. The regional distribution of these small carbonatite bodies suggests a different magmatic process from typical carbonatites and alkaline complexes. The closest analogy is the carbonate dikes in the Premier Diamond Mine, South Africa.

• OSTI ID: 5807841
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
CARBONATE ROCKS
CHEMISTRY
DEVELOPED COUNTRIES
DIKES
GEOCHEMISTRY
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOLOGIC STRUCTURES
LINEAMENTS
MAGMATISM
MINERALOGY
MONTANA
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
USA