Abstract:
According to Wilson's (1963a, b) hypothesis, the volcanoes of the Hawaiian-Emperor Chain are formed as the Pacific lithospheric plate moves over a source of magma in the mantle. Morgan (1971, 1972) proposed that these "hot spots" resulted from "mantle plumes" that rise vertically from the core/mantle boundary and that are fixed about the deep mantle and rotating globe poles. The age of volcanoes increases with distance away from the recent "hot spot" beneath Kilauea volcano. The Hawaiian-Emperor bend indicates that the direction of motion of the Pacific plate changed about 40 m.y. ago. Recent data on the ages of the Hawaiian volcanoes agree with this hypothesis, although the increase in age with distance away from Kilauea volcano along the chain appears to be not exactly linear (Dalrymple et al., 1974; Jackson, 1976; Jarrard and Clague, 1977). The Hawaiian-Emperor bend is about 42 m.y. old (Dalrymple and Clague, 1976). The DSDP Leg 55 data and data on fossil ages of sediments from the holes of DSDP Legs 19 and 32 (Creager, Scholl, et al., 1973; Larson, Moberly, et al, 1975) and the radiometric age of mugearite from Suiko Seamount (Saito and Ozima, 1975) give evidence that a tendency of increasing age with distance from the Hawaiian Ridge is valid also for the Emperor Seamount chain. On the basis of the age of sediments, the minimum age of volcanic rocks from the Meiji Guyot, located on the Obrutchev Rise, is 72 + or - 3 m.y. (Creager, Scholl, et al., 1973). The Obrutchev Rise, probably representing a continuation of the Emperor Ridge, extends northwestward parallel to the Aleutian deep-sea trench up to its junction with the Kurile-Kamchatka trench, and then on to the Kronotsky Peninsula in Kamchatka (Figure 1). It seems likely that Kronotsky Peninsula is a direct continuation of the Obrutchev Rise, broken by a deep-sea trench. It is probably supported by tectono-magmatic structures of northwestern trend extending in East Kamchatka from Kronotsky Peninsula to the Tumrok Ridge, against the background of structures of northeastern trend general for Kamchatka. If this assumption is valid, a chain of volcanoes similar to the volcanoes of the Hawaiian-Emperor chain would be expected on a continuation of the Obrutchev Rise in East Kamchatka, and these volcanoes should be older than the Meiji Guyot, i.e., more than 72 m.y. old. Judging from Morgan's reconstructions (this volume), a former rift zone (Pacific-Kula lithospheric plate boundary) should be roughly at the latitude of Kronotsky Peninsula. A precise position of this boundary, subducted now beneath Kamchatka and the Aleutian Islands, is unknown. This is followed by the fact that the age of volcanoes may not increase but rather may decrease northwestward.