INTRODUCTION: West of the Hawaii hotspot (HHS), an age-progressing chain of seamounts extends northwestwardly ~3600 km to the Hawaii-Emperor bend, beyond which the chain continues for ~2200 km as the north-northwestwardly trending Emperor Ridge. The ridge terminates at the ~82-Myr-old Meiji Seamount, which is perched atop the outer slope of the Kuril-Kamchatka Trench. West of Meiji, at Cape Kronotsky, the ridge orthogonally disappears into the Kamchatka subduction zone. If the length of the subducted sector of the Emperor Ridge could be estimated, then the age when volcanism began above the HHS could be estimated. MEIJI DRIFT: Deposition of the Meiji drift deposits along the northern side of the far northern or Meiji-Detroit sector of the Emperor Ridge provides a way to estimate the minimum age of the HHS. The drift deposit (as thick as 1800 m) began to accumulate about 33.5 Ma (earliest Oligocene) during the Earth's climatic transition to the ice house world. South-bound abyssal currents exiting the Bering Sea Basin, possibly generated there by thermohaline circulation, deposited the drift along the ridge sector. At this time, the sector receiving drift deposits was positioned at least 2200 km SE of its present Kamchatka trench location. Also at this time, the Aleutian Ridge (arc) cordoning the Bering Sea from the north Pacific was at least 1000 km shorter than its present length, which has been greatly lengthened during the past 50 Myr by plate boundary, transform faulting. Thus, in the early Oligocene, a wide western seaway connected abyssal circulation between the Bering Sea and north Pacific Basins. MINIMUM AGE ESTIMATING: Initiation of drift deposition requires that a former continuation of the Meiji-Detroit seamount sector, referred to here as the Obruchev continuation, crossed the north Pacific and forced abyssal currents arriving from the Bering Sea to flow eastward along the continuation's northern flank. To deflect south-bound abyssal currents, the Obruchev continuation, now completely subducted beneath Kamchatka, must have been at least 1200 km in length and possibly extended across the width of the northwestern Pacific to the Kamchatka Trench. In the early Oligocene, the continuation was thus between 1200-2200 km in length, not including any part of the continuation already subducted. During the past ~82 Myr, growth of the Hawaii-Emperor chain has taken place at an average lengthening speed of ~70 km/Myr. Using this rate, the age of the seamount at the western end of the continuation can be estimated to have been 20-40 Myr older than that of Meiji Seamount. The minimum age of the Hawaiian hotspot can accordingly be estimated at 100-140 Ma.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- 8150 Plate boundary: general (3040);
- 8155 Plate motions: general;
- 8157 Plate motions: past (3040);
- 8158 Plate motions: present and recent (3040)