Computer Science
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004e%26psl.229...15t&link_type=abstract
Earth and Planetary Science Letters, Volume 229, Issue 1-2, p. 15-29.
Computer Science
4
Palaeointensity, Microwave, Coe–Thellier–Thellier, High-Ti Titanomagnetite, Tertiary, Global Database
Scientific paper
Conventional Thellier and microwave (MW) palaeointensity experiments, accompanied by rock magnetic tests, were conducted on samples from an early Tertiary (ca. 49 Ma) basaltic intrusion [the Peats Ridge (PR) basalt] from the Sydney Basin. Thermomagnetic and low-temperature susceptibility measurements suggest that the dominant magnetic mineral is Ti-enriched titanomagnetite (˜TM65 TM50) and hysteresis results indicate that the majority of samples exhibit PSD-like behaviour. Some samples show evidence of alteration, during laboratory heating, but only at temperatures in excess of 400 °C. No alteration is observed in the dominant temperature range (~70 300 °C) used for calculation of palaeointensities. Stepwise thermal demagnetisation studies reveal single component (after removal of a small viscous), reverse polarity magnetisations in all samples, with a mean characteristic remanence (ChRM) direction of D/I=197°/+60° (α95=5°, k=62). Coe Thellier Thellier (CTT) experiments yielded a high success rate, with 68% of samples conforming to standard acceptance criteria. Microwave (MW) palaeointensity experiments, predominantly using the perpendicular applied field technique, produced a greater success rate of 82%. Mean palaeointensities of 27.1±4.4 μT (N=21) and 27.4±4.0 μT (N=28) were obtained from the CTT and MW techniques, respectively. These means could not be distinguished statistically, and the respective quality indicators were similar. These results suggest that the new microwave technique for calculating palaeointensities is, in this case, equivalent to the well-established CTT technique. This is an intuitive outcome, given that rock magnetic analyses suggest that alteration does not occur below the Curie temperature of the samples. Our results therefore provide a positive test for the equivalence of the MW and CTT techniques. The Virtual Dipole Moment (VDM) value for the intrusion is 4.7±0.7×1022 Am2, suggesting that the dipole field was approximately 59% of the present day value at ca. 49 Ma. This provides a valuable data point from the Southern Hemisphere, for a sparsely covered time period in the global palaeointensity database.
Garcia Alexander S.
Hill Mimi J.
Thomas David N.
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