HR: 0800h
AN: GP21B-0507    [Abstracts]
TI: COOLING AFTER DOUBLE HEATING: THE LTD-THELLIER PROTOCOL FOR PALEOINTENSITY DETERMINATIONS
AU: * Celino, K R
EM: klaydson@iag.usp.br
AF: Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao, 1226 - Cidade Universitaria, Sao Paulo, SP 05508090, Brazil
AU: Trindade, R I
EM: rtrindad@iag.usp.br
AF: Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao, 1226 - Cidade Universitaria, Sao Paulo, SP 05508090, Brazil
AU: Tohver, E
EM: etohver@cyllene.uwa.edu.au
AF: School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Hwy, Perth, WA 6109, Australia
AB: We have combined low-temperature treatment to standard double-heating protocols for paleointensity studies of ancient rocks with significant presence of MD grains. The low-temperature demagnetization, involving at least five liquid nitrogen baths in a zero-field chamber, was used within Thellier double-heating measurements to estimate 1.2 Ga absolute paleointensity on basalts and gabbros from Nova Floresta Formation (Amazon Craton, Brazil), that contain single-domain to multi-domain (pure to nearly pure) magnetite carriers. They present a strong decrease in remanence after low-temperature demagnetization accompanied by an increase in median destructive fields. The incorporation of LTD improved paleointensity estimates and enabled paleofield recovery for otherwise sterile rock samples, giving twenty seven successful determinations for six sites. Site-mean paleofield values are within 4.90 μT and 15.55 μT (mean at 8.37 ± 4.07 μT). These results correspond to a mean VDM of 2.08 ± 0.94 × 10²² Am², thus increasing the number of low-field determinations that dominate the (still scarce) Precambrian database.
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting