HR: 1340h
AN: GP13A-0033    [Abstracts]
TI: Rock magnetic and paleointensity data from plagioclase crystals of the Stormberg (Karoo) Lavas of Lesotho
AU: * Cottrell, R D
EM: rory@earth.rochester.edu
AF: Dept. of Earth & Environmental Sciences, 227 Hutchison Hall University of Rochester, Rochester, NY 14627 United States
AU: Tarduno, J A
EM: john@earth.rochester.edu
AF: Dept. of Earth & Environmental Sciences, 227 Hutchison Hall University of Rochester, Rochester, NY 14627 United States
AU: Watkeys, M K
EM: watkeys@ukzn.ac.za
AF: School of Geological Sciences, University of KwaZulu-Natal, Durban, 4041 South Africa
AB: Rock magnetic studies are crucial for understanding how natural materials record past field strength. David Dunlop has made great strides in advancing this understanding, especially in how magnetic domain state relates to recording fidelity. Recently David and his colleagues have documented how magnetic inclusions in common mafic minerals separated from dikes have distinctly multidomain magnetic characteristics. This result emphasizes that extreme care must be taken in the interpretation of paleointensity results from whole rocks and that for some units paleointensity investigations on a mineral scale may be necessary. Here we examine the rock magnetic and paleointensity characteristics of the Jurassic Stormberg (Karoo) lavas of Lesotho. In the 1960's, van Zijl et al. (1962) reported evidence for a magnetic reversal transition from these lavas. Subsequent studies have confirmed the transition. In addition, paleointensity results based on whole rocks have been reported from some non-transitional lavas. But no results meeting modern reliability criteria have been reported to date from the transition interval. Plagioclase crystals have been isolated from some of these rocks for paleointensity analyses, following methods outlined in our prior studies on Cretaceous to Recent lavas. The plagioclase crystals separated from the Lesotho lavas are small in size (0.5 - 1.0 mm), in part due to intergrown pyroxenes. Nevertheless, they appear to be suitable for paleointensity analyses. We will discuss results from such crystals, their rock magnetic characteristics and their potential recording accuracy relative to whole rock samples.
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1535 Reversals: process, timescale, magnetostratigraphy
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005