Paleomagnetism of Volcanic Rocks from Rarotonga and Rurutu, the Cook-Austral Island Chain

抄録

Rarotonga (21°15′S, 159°45′W) and Rurutu (22°30′S, 151°20′W) are volcanic islands included in the Cook-Austral island chain. Volcanic rock samples were collected at seven and ten sites in Rarotonga and Rurutu, respectively. The mean direction of magnetization for Rarotonga is 173.8° in declination and 46.2° in inclination (k=72.0 and α₉₅=7.9°) and is more reliable than that from a previous work. The mean direction for three young rock sites in Rurutu is 218.2° in declination and 39.5° in inclination (k=49.3 and α₉₅=17.7°) which for five old rock sites is 188.1° in declination and 51.4° in inclination (k=254.2 and α₉₅=4.8°).
These paleomagnetic results are in accordance with the total intensity anomaly pattern on each island, calculated using observed values of the geomagnetic field total intensity. The implication for the formation of these two islands inferred from the present results is consistent with that inferred from K-Ar ages and ⁸⁷Sr/⁸⁶Sr ratios by previous works. The formation of Rarotonga and Rurutu may be explained well by the concept of a “hot line” in a previous work rather than by the well-known “fixed hot spot” hypothesis.