Hawaiian geology gets update
By Jan TenBruggencate
Advertiser Science Writer
By Jan TenBruggencate
Geologists have established a new date for a sharp "bend" in the line of seamounts at the western end of the Hawaiian archipelago to 50 million years ago, which links it with the start of extended volcanic activity near the Marianas Islands, and possibly with the collision of India into Eurasia.
The work of David Clague and Warren Sharp brings a key feature of Hawaiian geology into global focus. In a paper published in Thursday's issue of Science magazine, the scientists say that a series of massive geological events all appeared about the same time, and may all have been connected:
NEW DATING TECHNIQUES
Geologist Clague, a former staffer at the Hawaiian Volcano observatory, works with the Monterey Bay Aquarium Research Institute and geochemist Sharp at the Berkeley Geochronology Center. They used modern radio-isotope dating techniques to establish the ages of volcanic rocks collected on seamounts on both sides of the Hawaiian-Emperor Bend.
They dated the Suiko Seamount at 60.9 million years ago, the north side of Koko Seamount at 52.6 and the south side of Koko at 50.4 million years ago. Koko is just north of the bend. To the southeast of the bend is Kimmei Seamount at 47.9 million years ago and southeast of it, Daikakuji at 46.7.
HAWAIIAN HOT SPOT
All these seamounts and the Hawaiian Islands were formed — according to geological theory — by the same feature. The Hawaiian Hot Spot is believed to be a generally stationary hot plume that delivers molten rock from deep in the earth to the surface. As the Pacific Plate moves over it, older islands are carried away from the hot spot — the farther away an island or seamount is, the older it is.
The rocks in the region of the Hawaiian-Emperor Bend had been estimated at 43 million years old. That created a mystery because there wasn't much else happening geologically at that time that would have explained the change in direction. One suggestion floated by wondering geologists was that perhaps the plate didn't change direction so much as the Hawaiian Hot Spot itself was moving.
The new dating data seems to create a package that makes geological sense — and attributes the bend to the movement of the Pacific Plate rather than the hot spot.
And it suggests that the whole thing took its time.
"India's collision into Asia went on for millions of years," Sharp said.
And the rock dates suggest the Pacific Plate changed direction just as slowly — less like a sports car and more like a city bus.
"The bend was not a quick event," Clague said.
"Our new ages show that the (Hawaiian-Emperor) bend formed over about 8 million years, much longer than previously believed," Sharp said.
Does any of this matter? In an age in which tsunamis and earthquakes are regular features in the public perception, it does, he said.
"Overall, our understanding of how plates move, broadly, is going to help us understand what the earthquake hazards are," he said.
Reach Jan TenBruggencate at firstname.lastname@example.org.