HR: 1340h
AN: V43A-1121    [Abstracts]
TI: Mineralogy and Texture of the Peneplain Sill, McMurdo Dry Valleys, Antarctica
AU: * Forsha, C J
EM: cjf8856@sru.edu
AF: Department of Geography, Geology, and the Environment, Slippery Rock University, 1 Morrow Way, Slippery Rock, PA 16057, United States
AU: Zieg, M J
EM: michael.zieg@sru.edu
AF: Department of Geography, Geology, and the Environment, Slippery Rock University, 1 Morrow Way, Slippery Rock, PA 16057, United States
AB: The Peneplain sill, part of the Jurassic Ferrar Large Igneous Province, is a 335 m thick diabase sill in the Dry Valleys, Antarctica. Mineralogical and textural data were collected for a 335 meter transect through the sill at Pandora's Spire, Solitary Rocks. Variations in the modal abundance of plagioclase, pyroxene, opaque minerals, and granophyric intergrowth through the Peneplain sill were determined by point counting. The mineralogical composition of the rocks varies from ~54% plagioclase, ~34% pyroxene, and ~10% granophyre near the lower contact to ~51% plagioclase, ~40% pyroxene, and ~7% granophyre at 145 m (approximately the center of the sill). In the upper half of the sill, the composition returns to values close to those at the lower contact, ~56% plagioclase, ~30% pyroxene, and ~12% granophyre. In summary the modal mineralogy is very homogeneous through the sill. There is a slight (<5%) increase in pyroxene abundance with a more significant decrease in granophyre abundance near the center of the sill. Textural variations in the Peneplain sill were quantified using plagioclase crystal size distributions (CSDs). CSDs for the Peneplain sill reveal a high population density of small (~0.1 mm) crystals, and a low population density of large (~1.0 mm) crystals near the contacts. Towards the center of the sill, the population density of small crystals decreases slightly while the population density of large crystals remains nearly constant. There is a slight irregularity in the population density trend in the small size classes at a height of ~50 m, but the significance of this is unclear. Texturally, mineralogically, and geochemically, the Peneplain sill is remarkably homogeneous. Many other apparently homogeneous intrusions are seen to be heterogeneous upon closer inspection. This sill therefore provides a unique opportunity to study an important end-member of intrusion petrogenesis.
DE: 3618 Magma chamber processes (1036)
DE: 3625 Petrography, microstructures, and textures
DE: 3642 Intrusive structures and rocks
DE: 9310 Antarctica (4207)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting