HR: 1340h
AN: V53C-1585    [Abstracts]
TI: A Solute-Banding Model for the Rhythmically Banded Horizons of the Palisades Diabase Sheet of New York and New Jersey
AU: * Block, K A
EM: kblock@sci.ccny.cuny.edu
AF: Department of Earth and Environmental Sciences, The Graduate Center of the City University of New York, New York, NY 10016 United States
AU: Rice, A
EM: arice@amnh.org
AF: Department of Earth and Planetary Sciences, American Museum of Natural History 79th St. and Central Park West, New York, NY 10024 United States
AU: Steiner, J C
EM: steiner@sci.ccny.cuny.edu
AF: Department of Earth and Atmospheric Sciences, The City College of New York Convent Avenue at 138th St., New York, NY 10031 United States
AB: Oscillatory structure is present in portions of the Palisades Sill at an elevation of approximately one hundred meters above the basal contact. These oscillations are in the form of approximately horizontal bands that run parallel to strike and parallel to the dip of the basaltic sheet. The compositional variation has a wavelength of two to three centimeters and consists of alternating bands of plagioclase- (An50-An70) and clinopyroxene- (Wo42-En36-Fs22) enriched crystal fractions. Melt calculations predict a liquidus temperature of 1150-1200 deg C. The banding may be the consequence of natural convection in a multi-component melt. In metallurgical systems and in fluid dynamic studies, the appearance of rhythmic layers is termed solute banding or micro-segregation, caused by cotectic shifting. Application of solute banding theory to the Palisades rhythmically banded section yields estimates for the Rayleigh number in the range of 6x10⁴ to 3x10⁶. These estimates are within the bounds of a reasonable evolution of the cooling of a sill and denote the manifestation of mildly turbulent natural convection during this stage of cooling. The solute-banding model requires the development of a quiescent interval during the evolution of the diabase sheet. Otherwise, the vigor of input flow, and post-emplacement migration of the crystal mush would erase or convolute any vestige of banding. To date, preservation of rhythmic banding in the Palisades has been found only at Kings Bluff and at Alpine, New Jersey. The location of rhythmically banded horizons in the Palisades may be a key to establishing the location of individual magmatic pulses that, under the assumptions here, are injected rapidly, then achieve convective stability, to possibly be reactivated by later pulse activity.
DE: 8412 Reactions and phase equilibria (1012, 3612)
DE: 8434 Magma migration and fragmentation
DE: 8439 Physics and chemistry of magma bodies
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005