HR: 16:45h
AN: V14C-04    [Abstracts]
TI: Textural Gradients in Antarctic and Canadian Sills: Evidence for Episodic Filling History
AU: * Zieg, M J
EM: michael.zieg@sru.edu
AF: Slippery Rock University, Department of Geography, Geology, and the Environment, 1 Morrow Way, Slippery Rock, PA 16057 United States
AU: Forsha, C J
EM: cjf8856@sru.edu
AF: Slippery Rock University, Department of Geography, Geology, and the Environment, 1 Morrow Way, Slippery Rock, PA 16057 United States
AB: The texture of an igneous rock preserves a record of its thermal development. Textural gradients in a magmatic intrusion can be used to reconstruct relative thermal histories of a series of rocks and to recognize irregularities in the thermal development of the intrusion. This study compares textural gradients in four igneous bodies of roughly similar composition and geometry; the Basement and Peneplain Sills in the McMurdo Dry Valleys of Antarctica, and the Sudbury Igneous Complex and Nipigon diabase, Ontario, Canada. The Sudbury Igneous Complex is the product of an impact melting event. The Basement Sill contains two discrete types of magmatic rock (an outer fine-grained diabase and an inner coarse-grained norite to orthopyroxenite). The Peneplain and Nipigon sills consist of roughly uniform medium-grained diabase. Crystal size distribution analysis has revealed that the Peneplain and Nipigon sills contain textural discontinuities similar to the break seen in the Basement Sill at the interface between the diabase and norite. These discontinuities consist of distinct reversals in the normal coarsening-inwards trend. The reversals are interpreted to be the result of a second injection event, with the textural break occurring at the interface between previously solidified rock from the initial injection and freshly injected, higher temperature magma. The Sudbury Igneous Complex, which has a simple, monotonic cooling history, lacks the textural discontinuities seen in the other bodies. A potential implication of this work is that many apparently homogeneous sills may be formed through a series of pulsed injections into the chamber rather than through an instantaneous single injection, as is frequently assumed in thermal and petrologic modeling. The use of textural gradients within igneous bodies provides a powerful, inexpensive method for placing constraints on the initial conditions for igneous cooling and differentiation models.
DE: 3618 Magma chamber processes (1036)
DE: 3625 Petrography, microstructures, and textures
DE: 3642 Intrusive structures and rocks
DE: 3690 Field relationships (1090, 8486)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005