HR: 1340h
AN: V43A-1111    [Abstracts]
TI: Extreme differentiation in single samples from the olivine-rich zone of the Palisades Sill, NY and NJ
AU: * Chau, K X
EM: kchau001@fiu.edu
AF: Florida International University, 11200 SW 8th Street, Miami, FL 33199, United States
AU: Sen, G
EM: seng@fiu.edu
AF: Florida International University, 11200 SW 8th Street, Miami, FL 33199, United States
AU: Naslund, H R
EM: naslund@binghamton.edu
AF: SUNY Binghamton, Geological Sciences, SUNY, Binghamton, NY 13902, United States
AB: The Palisades Sill, NY and NJ, has long been the focus of much attention due to its potential contributions to the understanding of igneous differentiation. Many early authors, including N.L. Bowen, thought of the intrusion as an ideal example of crystal settling because of an olivine-rich zone that occurs close to the base of the sill. Later investigations demonstrated that at least three geochemically distinct batches of magma were emplaced at different levels within this body, one of which produced the olivine-rich zone. Here we report the results of our detailed electron probe study of 27 olivine grains, 134 plagioclase grains, and 181 pyroxene grains from four samples of the olivine-rich zone. In one of the rocks plagioclase ranges from An84 (large grain; core) to An0.5 (interstitial plagioclase), whereas olivine ranges from Fo81 - Fo69. These ranges are comparable to our other samples. The plagioclase range is far greater than what is shown by the Skaergaard (An25 - An69) and Bushveld (An30 - An80) intrusions. Though the sill has long been known to be vertically differentiated, such extreme differentiation in individual thumb-sized samples was not expected. The implication is that interstitial melt pockets were so well enclosed (i.e., zero permeability) by the surrounding crystals that they were sealed off from further communication with larger volumes of melt that may have existed at a higher levels in the sill at that time. That is, compaction and associated filter pressing was not efficient in removing the interstitial melt. It is unlikely that such a situation could occur if the olivine-rich zone formed early from a large body of magma because the load pressure of the overlying crystals and melt would be too great to avoid compaction. A better explanation is that the olivine-rich zone was emplaced as a separate magma batch (as suggested by several previous workers based on bulk rock geochemistry) in a mostly solidified magma-crystal mush. In this setting, the interstitial melt would not be able to move through the mostly solidified mush and would have been well encapsulated by the surrounding crystals.
DE: 1036 Magma chamber processes (3618)
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3640 Igneous petrology
DE: 3643 Layered magma chambers
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting