How Old Is Earth?

Space.com ^ | February 7, 2019 | Nola Taylor Redd, Space.com Contributor

[ETL]

The mysterious bend in the Hawaiian-Emperor chain

June 8, 2017

-excerpt-

“...the Hawaii islands are the youngest in the chain that stretches nearly 6,000 km to Detroit seamount in the northwest Pacific, where volcanism occurred about 80 million years ago. An unprecedented 60 degrees bend characterizes the Hawaiian-Emperor Chain, dividing it into the older Emperor Chain and the younger Hawaiian Chain. The bend has been dated to 47 Ma.

“The ultimate cause for the formation of the Hawaiian-Emperor Bend (HEB) was a prominent change in the Pacific plate motion at 47 Ma,” says the lead author of the new study, Trond Torsvik from the University of Oslo and visiting researcher at GFZ at the moment. The team affirms a hypothesis by the US-geophysicist Jason Morgan who proposed that already in the early 1970s. “But it is not that simple as it was suggested forty years ago,” says Torsvik.

Jason Morgan was the first to use hotspots as a reference frame for global plate motions. In his model mantle plumes — which are manifested by hotspots at the surface — were considered fixed in the mantle, and the Hawaiian-Emperor Bend was attributed to a simple directional change of the Pacific plate motion. But his plate model with fixed hotspots became challenged from the 1980s.

“Since the late 1990s it has become clear that hotspots are not totally fixed,” says GFZ´s Bernhard Steinberger, one of the co-authors of the paper. That is now generally accepted, he adds, and mantle flow models predict that the Hawaiian hotspot has drifted slowly to the south. “But some recent studies have argued that rapid southward motion of the hotspot before 47 Ma can explain the formation of the bend without requiring Pacific plate motion change,” he says. “Such a scenario has become attractive because the geology of the plates surrounding the Pacific shows no clear evidence for a Pacific plate motion change.”

The new study shows clearly why this simply does not work. It would require an unrealistically high rate of hotspot motion of about 42 cm/year which would be much faster than the average speed of tectonic plates. Moreover, this would imply that the Emperor Chain was created in just five million years and Detroit Seamount should only be 52 million years old. This prediction is obviously falsified by the recorded Detroit Seamount island ages of about 80 Ma.

“Alternatively, a slower hotspot motion towards the WSW could explain both geometry and ages of the Emperor chain,” says Steinberger. However, such a direction of motion is inconsistent with mantle convection models.

“Our paper is a good example of how very simple simulations of plate and hotspot kinematics can be used to explore which geodynamic scenarios for the formation of the Hawaiian-Emperor Bend are possible, and which ones are not,” says Pavel Doubrovine from the University of Oslo, another co-author on the paper. “We cannot avoid the conclusion that the 60 degrees bend is predominantly caused by a directional change in the Pacific plate motion.” Yet, some southward plume motion is required, otherwise the Hawaiian-Emperor Chain would be around 800 kilometres shorter.

“Explaining the geometry, length and age progression of the Hawaiian-Emperor Chain, requires both: the change in the direction of plate motion and the movement of the hotspot,” states Torsvik. “If, after more than two decades of debating the end-member scenarios of plate motion change versus hotspot drift, geophysicists will be able to agree that neither of the two is satisfactory — then we can move forward and address a more interesting question: what actually drove the Pacific plate motion to change at about 47 million years ago?” Hopefully, it will not take further 40 years to get an answer to this, he adds.

https://www.sciencedaily.com/releases/2017/06/170608123615.htm

[ETL]

Hawaiian–Emperor seamount chain

Formation:

The oldest age for the Emperor Seamounts is 81 million years, and comes from Detroit Seamount. However, Meiji Guyot, located to the north of Detroit Seamount, is likely somewhat older.

In 1963, geologist John Tuzo Wilson hypothesized the origins of the Hawaiian–Emperor seamount chain, explaining that they were created by a hotspot of volcanic activity that was essentially stationary as the Pacific tectonic plate drifted in a northwesterly direction, leaving a trail of increasingly eroded volcanic islands and seamounts in its wake.

An otherwise inexplicable kink in the chain marks a shift in the movement of the Pacific plate some 47 million years ago, from a northward to a more northwesterly direction, and the kink has been presented in geology texts as an example of how a tectonic plate can shift direction comparatively suddenly.

A look at the USGS map on the origin of the Hawaiian Islands[11] clearly shows this “spearpoint”.

In a more recent study, Sharp and Clague (2006) interpret the bend as starting at about 50 million years ago. They also conclude that the bend formed from a “traditional” cause—a change in the direction of motion of the Pacific plate.

However, recent research shows that the hotspot itself may have moved with time.

Some evidence comes from analysis of the orientation of the ancient magnetic field preserved by magnetite in ancient lava flows sampled at four seamounts (Tarduno et al., 2003): this evidence from paleomagnetism shows a more complex history than the commonly accepted view of a stationary hotspot.

If the hotspot had remained above a fixed mantle plume during the past 80 million years, the latitude as recorded by the orientation of the ancient magnetic field preserved by magnetite (paleolatitude) should be constant for each sample; this should also signify original cooling at the same latitude as the current location of the Hawaiian hotspot.

Instead of remaining constant, the paleolatitudes of the Emperor Seamounts show a change from north to south, with decreasing age.

The paleomagnetic data from the seamounts of the Emperor chain suggest motion of the Hawaiian hotspot in Earth’s mantle.

Tarduno et al. (2009) have summarized evidence that the bend in the seamount chain may be caused by circulation patterns in the flowing solid mantle (mantle “wind”) rather than a change in plate motion.

https://en.wikipedia.org/wiki/Hawaiian%E2%80%93Emperor_seamount_chain#Formation

[Openurmind]

Great stuff. So it may have been both the plate and the hot spot that moved. But they are still not for sure. There could be other factors they are not see in this also. Like could the different magnetic alignments have come from a change in the magnetic poles rather than the crust? I have to say that this particular phenomenon has intrigued me for many years now. :)

Thanks for taking the time to share more!

[ETL]

So it may have been both the plate and the hot spot that moved. But they are still not for sure.

I was a geology major back in the 80s (unfortunately, I never completed the degree). However, I never knew about or noticed the "bend" in the Hawaiian hot spot chain until now.

[Hot Tabasco]

1.2 billion years of rock that can't be found

Find the rocks, you'll find the socks........

[Openurmind]

Kind of the same here. Studied the geology of it for years but never really paid attention to the bend much until yesterday. It was a very good question that opened up more curiosities for me. Now it’s become more complicated. lol

It raises again the theory of a possible physical polar shift that may have caused these to change direction like that.

[Openurmind]

This has been a very fun thread. Thank you! :)

[Steve Schulin]

Barry Setterfield wrote some really interesting stuff about accelerated rates of radioactive decay. The higher rates of decay were a direct result of the then-higher speed of light. But the decay rate wasn’t the only aspect of radioactivity that would have been changed by difference in speed of light. He suggested that the energy of each disintegration would have been less because of the increased speed of light. It’s wrong to fail to disclose the assumption that the billions of years of atomic time discussed in the article is equivalent to the same amount of years in orbital time.