You need to think of the Earth as a fractional distillation column where

lighter materials migrate toward the surface, and the denser materials migrate toward the core, and the Earth is continually evolving. This means it is producing more gas, and water, and it gradually grows larger, and it occasionally expands,

which adds more surface area, which keeps the atmosphere from becoming

too thick and too dense, and too hot, and it keeps the increase in the volume of the water from burying the continents under an ever increasing depth of water.

Long term climate change can then be associated with sudden growths and expansions of the planet, which lead to glaciation, and the lowering of ocean levels.

This is a temporary condition that reverses as the ocean floor rises, and the continent sinks, and the atmosphere move upward, which warms the planet,

and melts the glaciers.

I think you can see that this is a cyclical process that oscillates between

ice on land, to water in oceans, and then another expansion, and the process repeats

itself over and over.

One of the by-products is the Illusion of subduction where the rising ocean floors,

and the settling continents bend the rock at the interface between thin and thick

crust. This is the natural process of on-going isostacy of a growing planet.

We are currently in a warming trend that melted the continental ice sheets,

then it melted the mountain glaciers, and it will eventually melt Greenland,

and Antarctica The rise in water will be 216 feet. Then it will really start getting

hot..

If you mean the underplated mafic refractory material beneath the continental lithosphere, it may have sunk into the lower mantle by crustal delamination and waiting to be digested!!

The Earth becomes progressively more and more stratified, that is the

materials separate into layers of similar composition and density.

The lighter materials migrate toward the surface of the planet, and the

densest materials migrate toward the core.

This process is how planets mature eventually becoming gas giants

when the mass is great enough to increase the rate of segregation of

the materials.

As long as there is a continuing supply of materials for accretion, the planets

will continue to accrete. In our solar system, the supply is running low,

but it is not exhausted, so planets continue to accrete additional materials.

Fortunately for life on Earth, this process is now fairly slow, and the

thickness of the atmosphere limits surface destruction by slowing down,

and burning up most of the incoming materials. The result is dust

in the atmosphere which settles out, and is rained out, or is collected by

snow, and ends up on the surface of the planet, or at the bottom of the oceans.

The stratification process comes with some both desirable, and undesirable

side effects. The segregation of materials under great self compressive

forces of gravity aids the separation of the materials, and it also

leads to 80% of the planet being lighter weight materials, and 20 %

being very dense materials. The 80% undergo expansion as the stratification

process proceeds and the 20 % undergoes further compression, and

densification. The combined result is an overall expansion of the planet

which is accelerating. The expansion is now up to a net increase in

radius of about 4.15 mm to 4.17 mm per year based on the 2003

re calibration of the reference point for the Global Positioning System.

This number is probably biased on the low side because the GPS

re calibration is based mostly on points on the surface of continents,

and very few points are on islands in oceans.

Originally in 2003 there were over 1200 reference points used,

but if you look at the same data now, they use only 157 points

that cluster within plus or minus 4 mm of a zero average.

Since GPS is now primarily used for Surveying it made since for them

to skew the data to only include points that do not allow the planet

to grow larger, or show expansion. I plotted on a graph 927 of the

1200 plus points or roughly 80% of them for Delta Z with a range of

minus 8 mm on the left to plus 16 mm on the right. The 157 cluster

in a small group that crosses the Delta Z = zero line. The 927 were

chosen for my graph because the form a fairly straight line with a fairly

constant slope. The 10 % highs, and the 10 % lows were way off the

line formed by the other 927 points.

The changes in the radius of the Earth are not really smooth as they

progress. The indicators or growth and expansion come in groups

when earthquakes come in groups scattered around the world.

Well as usual I have gone off on a tangent.

Consumption of crust via Subduction is an illusion created by humans wanting

there to be convection cells inside the planet.

The illusion of subduction is created at the margins by ocean floors rising

faster than continental crust. The result being that the thinner oceanic

crust bends down where it touches the thicker continental crust.

The supply of materials for the oceanic spreading ridges comes from

beneath the continents, thus the continental crust is thinning and thus

rising more slowly than the oceanic crust. This is the active process

of " dynamic " iso- static equilibrium. That would make it

Iso-dynamic equilibrium of a growing and expanding planet.

The material supplied is basalt which is denser than Granite which was

some of the earlier materials of lower density that segregated and moved

upward to form continental crust.

71 % of our planets crust is thin ( 5 to 7 km ) and mostly basalt.

29% of our planets crust is thicker ( 38.8 km ) and mostly underlain by

granite. Originally all this material was under the 29% continental

crust area, which implies the crust was much thicker.

It may have been as much as 133 km thick if all the materials came

from under th continents, but probably less if the rest of the Earth's

layers supplied some of the materials for the oceanic crust.

Now if this theory is correct, the density of the basalt near the margins

should be different from the density of the basalt nearer the spreading ridges,

unless there is some thorough mixing process that occurs , and

has continued to occur over the last 180 plus million years.

That would make a good question for this Research Gate.

Is there a variation in the density of the basalt between the margins

and the spreading ridges?

Dear Bulusu,

You might be interested in the following paper which shows evidence for structures beneath the Sierra Nevada Mountains that may be the very delamination process that you suggest.

Zandt, G., Gilbert H., Owens, T.J., Saleeby, J., and Jones, C.H., 2004, Active foundering of a continental arc root beneath the southern Sierra Nevada in California: Nature, v. 431, p. 41-46.

Regards,