My science/technology-related thoughts, sometimes controversial, sometimes can be based on limited knowledge base, logic can be non-perfect as well. I develop my vision in iterations. Don't take this blog as an attempt to convince anybody in anything.
Each post in this blog reflects my level of understanding of Tectonics of the Earth at the time the post was written; so, some posts may not necessarily be correct now.

28 September, 2011

Hawaii Hotspot Puzzle. Suggesting Hawaii As A Moving Convergent "Coldspot".

Two microplates - two pieces of the puzzle.
   I'm sure I am not the first to point out the next fundamental controversy about Hawaii Hotspot. Let's consider the border between the two microplates:
- first: the microplate between Mendocino and Murray Fracture Zones. Let's assume Kure Atoll, Midway Atoll belong to this microplate.
- second: the microplate between Murray and Molokai Fracture Zones. Let's assume Pearl and Hermes Atoll, Laysan Island belong to this microplate.

Rolling events back.
   Murray Fracture Zone points roughly to Pearl and Hermes Atoll that is approx 2,300 from Kilauea, current location of the hotspot. Rolling events back, we may suggest that at proposed 8-9 sm/year speed, the hotspot was at Pearl and Hermes Atoll location some 25-30 million years ago.

   To see how the microplates were positioned one relative to another back 25 MY ago, let's just cut the oceanic crust that was spread for the past 25 MY (including the crust that has been overridden by the NA continent). There is huge difference between the amount of crust that was spread by the microplates. Roughly, the second plate added approx more than 400km of it's length than the first microplate did.

Hotspot motion.
  Back 25 MY:
- the oceanic floor of Pearl and Hermes Atoll was approx 400km east relative to Midway Atoll .
- then in no time the hot spot must had jumped from Midway Atoll over that 400km east to build Pearl and Hermes Atoll. 
- then the hotspot slowly returns to its normal position; the Pearl and Hermes Atoll, that was left behind the hotspot, returns back on the faster moving microplate to get in line with Kure and Midway Atolls. This concept of "smart" oscillating hotspot looks unrealistic to me.

   Some break in the path around Pearl and Hermes Atoll seems to exist, but as the break distance is considerably less than expected 400km, we may conclude that the microplates did spread at different rates, but the spot is the feature of geometry of global tectonic forces around the region.

Suggesting another mechanism for Hawaii - moving convergent "coldspot".
   The microplates are spreading out at different rates and are bumping into the wall of oldest crust. There must be convergent/divergent zones to accommodate the different rates of the crust spreading. Why not to suggest Hawaii to be a part in the convergent process?

Comparing magma beneath the divergent boundary to the stuff beneath a convergent "coldspot".
   The material of the accommodated crust is not exactly the same as the material of the fresh magma coming from bottom into the divergent boundary. Accommodated sediments change chemical composition and melting point of the stuff beneath the convergent "spot". In fact as the melting point gets lower, the spot along the path better be called "coldspot", not "hotspot". Many other parameters should be different between the fresh magma and the stuff beneath the spot, but, I, Sergey D. Sukhotinsky, the author of this post, think that this probably should be the theme for another post.

Conditions to maintain the process of pumping magma/lava up.
- sufficient temperature gradient along the magma/lava path;
- deformations within the spot of the amplitude and speed to cause sufficient local displacements of magma/lava;

Conditions the process of pumping magma/lava stops at:- too much oceanic crust is brought up and down by the convergent coldspot:
   a)the cold layer gets too thick, the temperature gradients gets too low;
   b)the spot "diffuses"; the greater region gets the deformations, local displacements of magma/lava diminishes;
- the spot moves off the focus of global tectonic forces, the amplitude of crust deformations drops. 
The regions cools down as magma stops pumping up; the region gets resistant to deformations due to the increased thickness of crust.

The focus of global tectonic forces probably is the intersection of the two lines:
- North to South fracture line through the Pacific plate.
- West to East probable fracture line connecting south borders of Asia and North America. Thick and rigid continents prevent Pacific plate from bending between continents along West-East line when Moon's plane of orbit gets North. Thus the max bending stress of Pacific plate would be along the probable WE fracture line connecting south borders of Asia and North America.

The "coldspot" process resumes:
- the focus of global tectonic forces moves south-east on the plate as the plate itself moves north-west;
- magma under the new location is not spoiled with sediments;
- the amplitude of crust deformations is good at the location because the crust here is pre-bent by the load of the chain of volcanoes and the chain itself ceased to bend due to the increased thickness.
  New fracture segment develops south-east to the old sub-chain of volcanoes.  The fracture pumps magma up developing new segment of the volcano chain.

How to tell if the concept is correct.
   I need more time to figure it out; right now I got a couple of ideas on where to look for the evidences:
- the relief of the chain of volcanoes should show that the region is under west-east compression, that contradicts slab-pull concept but is in line with ridge-push concept; 
- there should be a gap in the age of the sediments (and crust) on the both west and east sides of the chain because some crust was consumed to build the volcanoes and to recycle the bottom of the spot into underlying magma. The time-width of the time-gap should roughly be equal to the time span a volcano was active within. That is somewhat greater time than it is now usually thought of. That's because the evidence of early activity of a segment of volcano chain is hidden deep within the volcano or even got molten and got recycled into the underlying magma. I'd like to estimate the time gap could be as great as up to 10MY.

No comments:

Post a Comment

Popular Posts

Follow by Email

Content © 2006-2014 Sergey D. Sukhotinsky