The core samples of mid-ocean-ridge basalts (including Indian and Pacific type) recovered from the Southeast Indian Ridge (SEIR) area near the Australian Antarctic Discordance during Ocean Drilling Program Leg 187 were studied using rock magnetism, mineralogy, and petrography methods. On the basis of thermomagnetic analyses and low-temperature magnetometry, the dominant magnetic carrier in most of the basalt samples (pillow basalts) is characterized as titanomaghemite, which presumably formed by low-temperature oxidation of primary titanomagnetite. Some samples from unaltered massive basalts contain nearly unoxidized titanomagnetite as the main magnetic mineral. A metadiabase sample showing greenschist facies metamorphism contains magnetic minerals dominated by magnetite. The pillow basalts contain titanomaghemite ranging from stable single-domain to pseudosingle-domain (PSD) grains, and the majority are characterized by a single stable component of remanence. The massive basalts show hysteresis features of larger PSD grains and contain a very low coercivity remanence. The values of natural remanent magnetization (NRM) of the samples in this SEIR area are on the same order as those of other oceanic ridge basalts. They show a general decreasing trend of NRM with increasing crust age. However, the values of NRM show no correlation either with the tectonic zonations (Zone A vs. Zone B) or with the mantle provinces (Pacific vs. Indian types).
1Shau, Y.-H., Torii, M., Horng, C.-S., and Liang, W.-T., 2004. Magnetic properties of mid-ocean-ridge basalts from Ocean Drilling Program Leg 187. In Pedersen, R.B., Christie, D.M., and Miller, D.J. (Eds.), Proc. ODP, Sci. Results, 187 [Online]. Available from World Wide Web: <http://www-odp.tamu.edu/publications/187_SR/204/204.htm>. [Cited YYYY-MM-DD]
2Department of Marine Resources, National Sun Yat-sen University, Kaohsiung 80424, Taiwan. yhshau@mail.nsysu.edu.tw
3Department of Biosphere-Geosphere System Science, Okayama University of Science, Okayama 700-0005, Japan.
4Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan.
Initial receipt: 1 May 2003
Acceptance: 8 September 2003
Web publication:
19 February 2004
Ms 187SR-204