HR: 14:50h
AN: GP33B-05 [Abstracts]
TI: Why is the Remanent Magnetic Intensity of Cretaceous MORB so Much Higher Than That of Mid- to Late
Cenozoic MORB?
AU: Wang, D
EM: wangdm@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1005
United States
AU: * Van der Voo, R
EM: voo@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1005
United States
AU: Peacor, D R
EM: drpeacor@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1005
United States
AB:
The fact that the natural remanent magnetization (NRM) intensity of MORB samples shows systematic variations as a function of
age has long been recognized: maximum as well as average intensities are generally high for very young samples, falling off
rather rapidly to less than half the recent values in samples between 10 and 30 Ma, whereupon they slowly rise in the early
Tertiary and Cretaceous to values that approach those for the very young samples. NRM intensities measured in this study
follow the same trends as those observed in previous publications. In this study we take a statistical approach and examine
whether this pattern can be explained by variations in one or more of all previously proposed mechanisms: chemical
composition of the magnetic minerals, abundance of these magnetization carriers, vectorial superposition of parallel or
antiparallel components of magnetization, magnetic grain or domain size patterns, low-temperature oxidation to
titanomaghemite, or geomagnetic field behavior. We find that the samples do not show any compositional, petrological,
rock-magnetic or paleomagnetic patterns that can explain the trends. Geomagnetic field intensity is the only effect which can
not be directly tested on the same samples, but shows a similar pattern as our measured NRM intensities. We therefore
conclude that the geomagnetic field strength was, on-average, significantly greater during the Cretaceous than during the
Oligocene and Miocene, although it was perhaps rather variable on a short time scale.
DE: 1517 Magnetic anomalies: modeling and interpretation
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005