Title of article :
Comparison of the Coe–Thellier–Thellier and microwave palaeointensity techniques using high-titanium titanomagnetites: results from a Tertiary basaltic intrusion from the Sydney Basin, New South Wales
Author/Authors :
Thomas، نويسنده , , D. Neil and Hill، نويسنده , , Mimi J. and Garcia، نويسنده , , Alexander S.، نويسنده ,
Issue Information :
روزنامه با شماره پیاپی سال 2004
Pages :
15
From page :
15
To page :
29
Abstract :
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). ellier–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. rtual 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.
Keywords :
microwave , global database , tertiary , Palaeointensity , Coe–Thellier–Thellier , high-Ti titanomagnetite
Journal title :
Earth and Planetary Science Letters
Serial Year :
2004
Journal title :
Earth and Planetary Science Letters
Record number :
2324207
Link To Document :
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