Figure 61. Seismic Tomographic section from Pacific Ocean to Arabia showing continuity of brittle lithosphere, Pacific subduction, Mid Atlantic Ridge and Europe/Africa collision geological features.

General description.

View the AusIMM webinar on North America at https://www.ausimm.com/videos/community-event/south-west-wageoscience-society—digital-tech-talk-new-discoveries-in-the-structural-geology-mineralization–exploration-targeting-of-north-america/

This figure shows the seismic tomography section from the west coast of North America to Saudi Arabia and eastern Africa and which extends from the outer core to the surface.

It shows that the lithosphere is continuous over this whole section of Earth with no real break for the Mid-Atlantic Ridge. The section shows a dramatic change at about 500 km depth (yellow arc) from fairly finally laminated Upper Lithosphere to Lower Lithosphere of brittle nature with much coarser structure.

 

Description of the upper and lower lithosphere from Africa to western North America – refer to figure 61 above.

Africa

The collision zone between Africa and Europe is well defined (2.30 o’clock yellow).  The Upper Lithosphere under Africa is up to 1,000 kilometres thick and shows the fine detail of the up, and down thrusting collision.

This collision zone appears to extend to the core as a wide, subvertical snaking structure?

The Lower Lithosphere under Africa looks quite rigid with strong defined structures.

Europe

There is a continuous slab of Upper Lithosphere under Europe only about 200 kilometres thick. This extends to about level with the British Isles (1 o’clock).

Then there is a thinning, but with no complete break, of the Upper Lithosphere for about 300 km west and then there is another 200 kilometre thick slab  which extends to under the centre of Greenland (12 o’clock).

This slab does not appear to be affected by the Mid Atlantic Ridge?? This slab is in the position of the Norway to Greenland Caledonides Orogen in the crust but extends a lot further to the west in the lithosphere. This means that Greenland should be live for mineralisation using the parameters of the Caledonides Orogen (the answer to a geologist’s question on my last LinkedIn post).

It is interesting that the Caledonides Orogen is reported as multiple collision zones between various  proto-continents while drifting all over the Earth from 500 – 250 million years ago.

However, these proto-continents are underlain by a single brittle  lithosphere with continuous structures right across it. These structures would not be continuous if the above collisions of continents was a reality.

The Lower Lithosphere under Europe, through to the Mid Atlantic Ridge, looks more ‘fuzzy’ which may mean that it is hotter and more ‘melded or fused together’. However, there are many large structures transecting this area suggesting that it has been brittle and relatively immobile for a very long time.

Mid Atlantic Ridge.

The mid-Atlantic Ridge can hardly be seen except as an orange coloured zone or hotter (or wetter) rock.

There is a bulge of lineated? lithosphere (12.30 o’clock position on section, subvertical orange line) centered under Iceland which could represent the Mid Atlantic Ridge. This bulge is only in the top 1,000 kilometres depth and extends mainly to the west of Iceland for about 500 kilometres.

There is a neck (following the orange line) of more clearly defined structure that extends nearly down to the outer core with the expected slight east dip imparted by the differential movement of the lithosphere from the core to the crust. This may represent the feeder zone for the Mid Atlantic Ridge which appears to be only an upper lithosphere structure.

This steep dip suggests that this movement is only about 1,000 kilometres westward from the outer core to the crust. This suggests that the Earth has had limited outer core to surface translational movement in this area, perhaps even from its formation??

Greenland to the west coast of North America.

From Greenland right through to the west coast of North America there is a 200 – 400 kilometre thick, finely laminated Upper Lithosphere.

The Glenville Line pushing structure (11.50 o’clock yellow) off the east coast of North America is seen. This is further East than its surface expression in Eastern North America and this may be the reason that its exact location or even its existence is a hot topic of discussion. However it can be quite clearly seen as a pushing structure in this cross section.

The Lower Lithosphere west of the Glenville Line (10 o’clock) is more solid, like that under Africa.

The original, solid looking, Lower Lithosphere under continental North America (9.30 to 10 o’clock) has been almost completely replaced by the jumbled Pacific Plate subduction material (west of white arc).

Near Core Lithosphere

There is observed a very solid lithosphere for 500 km above the Outer Core for all except the Pacific Subduction Zone (see figure 61 and 57a above). I suggest that this is the remnants of the down-thrust material from under the continental areas that is melted and scraped off by the 5,000 C Outer Core.

This material would be resorbed into the liquid outer core and then as it cooled and differentiated be precipitated out on the base of the Lower Lithosphere.  It would then be spread around the earth above the outer core. The reason I suggest this is that this solid looking lithosphere is absent from under the Pacific Plate subduction area where it would be melting, not precipitating (see 57a above).

The problem of the lack of an identifiable mantle.

One thing that cannot be seen at all is a relatively structure-less, amorphous zone that would relate to the ductile Mobile Mantle. Through-going, brittle structures transect the whole  of the section.

Either side of the mid-Atlantic Ridge there are areas that look like more fused lithology but strong structures still continue through this area. These limited areas are the only places that could be possibly construed as Mobile mantle.

These hotter areas could be feeding the mid-Atlantic Ridge vulcanism. The mechanism would be more like a crack seal magma hotspot than a large crack opening up and separating.

One roughly interpreted version of this section that I have used suggests that there is a circular movement of the whole mantle in this area with the Mid Atlantic Ridge area going up and the outside towards America and Europe going down.

This absolutely cannot happen and still retain brittle structures throughout the whole area. The whole mechanism of ridges and hotspots needs revision.

The following section shows a 3D rotating Earth with earthquake epicentres. These epicentres occur right down to the outer core which validates my concept of a brittle lithosphere.

Earthquakes to the outer core!! Right through the ductile Mantle??

7 November 2021 by Robert Watchorn

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