2.4 Seamount chains associated with Wegener Crater
We have seen that an impact generates a hotspot and as the tectonic plate drifts away from the impact site carrying the crater with it.
The drift of the Wegener Crater with (and from) the Nazca Plate – at the that time located at the south pole – is fully evidenced by the seamount volcanic chains stretching along the Pacific Ocean.
To understand the mechanics of seamount chains, it is important to consider:
· The volcanoes closest to the crater are the oldest in the mountain chain.
· The closer to the crater, the more active were the extinct volcanoes that constitute the seamounts.
· The farther in time, the greater the distance the plate travels, the greater the range of the mountain chain.
· Knowing the tectonic plate's travel speed allows you to calculate the age of the various volcanic mounts along the mountain chain based on the distance it has traveled.
Analysis of the seamount volcanic chains from Mariana Trench shows that the activity of the various Antarctic hotspot volcanoes (the site of impact) was increasingly intense and massive the closer they were to the crater – and on the timescale, closer to the moment of the impact.
There are two continuous main seamount chains, both of which originate from the Nazca Plate and go through advancing across the Pacific Plate until they reach Wegener Crater.
This shows that although the plates move themselves in almost opposite directions, their displacement is interlocked according to the northbound vector — so, Nazca Plate was located far south away from its present position.
This shows that although the plates move themselves in almost opposite directions, their displacement is interlocked according to the northbound vector — so, Nazca Plate was located far south away from its present position.
In the case of the Pacific Plate, we see the seamount chains as if they were changing direction chaotically, but it is a misleading interpretation.
The change from northwest to northward direction was the result of the crater colliding with the Eurasian Plate, and the return to the direction northwest resulted from the fracture that originated the Mariana Trench.
The relatively recent Hawaii-Emperor seamount chain shows evidence that the Pacific Plate changed its direction from north to northwestward sometime between 48 and 50 million years ago.
1) The twisting seamount chains
Something that hinders the understanding of the volcanic seamount chains rising process is their seemingly chaotic path and lack of rectilinear arrangement between the Nazca Plate hotspots up to the present position of the crater, although the Nazca and Pacific tectonic plates drifting occurred mostly in constant direction.
Why the Hawaii-Emperor seamount ridge is so straight (except for the shift at the encounter of both halves), while the chains associated to Wegener are so chaotically tortuous?
Current theory attempts to explain the phenomenon in terms of spontaneous and mobile mantle plumes originating hotspots that migrate randomly below the Earth's crust, as if the behavior of mantle plumes within the Earth were spontaneous and chaotic in away similar to the plasma filaments of a decorative light bulb.
But, if we shift our point of view and do consider the hotspots at a fixed location as result of a major impact event – in those cases not linked to volcanic activities arising from subduction processes – the actual generation evolution of these seamount chains is easy to understand:
Each Pacific Ocean seamount chain related to the Wegener impact is not generated by a single volcano – such as the Hawaii or Reunion islands hotspots, with their unique and continuous seamount chains.
In Wegener's case, there are several active volcanoes scattered along an igneous province of sub-continental dimensions — and like bubbles in a pan filled up with boiling water, the hot fluid emerges randomly, each time from a different place.
As the Pacific Plate moves over this set of volcanoes, and the seamount chains were formed by the activity of various volcanoes erupting at various moments, a seemingly chaotic picture was formed.
Our brains tend to interpret points in proximity as forming a continuous line, but it is not the case.
We can compare the process of generating volcanic chains to that old perforated roll of paper that runs a player piano – the paper represents the tectonic plate, and the holes of the musical programming represent the volcanoes.
They are active only in the moment that the paper/plate passes through the scanning head/hotspot array of volcanoes, and they stop reproduction/are extinct as they drift away from it.
While the paper/plate drifts continuously and invariably in the same direction, the holes/volcanoes appear to be displaced chaotically.
Image: PLAYER PIANO, in Wikipedia
If we look only at the sequence of holes/volcanoes, we will see only a chaotic and curvilinear path.
Our natural tendency is to focus only on the sequence of volcanoes without seeing the big picture behind the phenomenon – after all, volcanoes are clearly visible, and the tectonic plate drift is imperceptible on a human time scale.
Based on this perception, some geologists claim that hotspots are random phenomena that drift in relation to their plates,[1] when in fact what happens is that the Pacific Plate has drifted over nearby active volcanoes spread over the area of the hotspot.
These volcanoes were only discovered recently in Antarctica – without this discovery, the overall picture still would be very difficult to understand.
[1] The mysterious bend in the Hawaiian-Emperor chain, Helmholtz Association of German Research Centers
ATTENTION: Blog in reverse order. To continue reading, go to the post below ("Postagem mais antiga").
ATTENTION: Blog in reverse order. To continue reading, go to the post below ("Postagem mais antiga").
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