This new information presents further evidence for the creation
of less-dense areas beneath the Earth's crust, which could later
cool, contract,and perhaps leave or create huge cavernous
regions.
Note this excerpt:
"This superposition of a denser layer over a lighter one is called
a density inversion, since it goes counter to the general trend
observed on Earth of density increasing with depth.
"Nevertheless, these density inversions have occurred
repeatedly on Earth as a consequence of collisions of different
terrains due to the ever-moving tectonic plates.
"In other areas, the fact that density decreases with increasing
temperature may create such a density inversion in the crust
even without collisions and thrusting of heavy layers over lighter
ones."
--Mike
TERRADAILY
U.Hawai'i Researchers Propose New Geological Formation
Theory
Thermal measurements were taken between Papua New
Guinea and the D'Entrecasteaux Islands because these islands
are metamorphic core complexes that are rising at the same
time that the floors of the surrounding basins are deepening.
Company MapHonolulu - July 7, 2001
Throughout geologic history, continents have been pulled apart
by tectonic forces forming rifts that eventually become new ocean
basins.
Sometimes during this process rock layers near the earth's
surface are pulled apart and rocks from depths of 35 kilometers
or more are exposed at the Earth's surface.
These deep "crustal" rocks are usually metamorphic rocks that
have been re-crystallized by heat and pressure. Surface
exposure often forms domes called metamorphic core
complexes, which are higher than surrounding terrain.
How these formations develop has been a much-debated
question in geology. University of Hawai'i researchers Fernando
Martinez, Andrew M. Goodliffe, and Brian Taylor have proposed a
new explanation for these formations by studying the offshore
areas of Papua New Guinea. Their findings were published in
the June 21 issue of Nature Journal.
Eastern Papua New Guinea is a present-day example of a
continental land-mass in the early stages of rifting and forming a
new ocean basin. Here the processes that rift continents and
form ocean basins can be studied directly in their active stages.
The heat flowing from the Earth's interior can be used as a
measure of the degree of stretching of the upper strong layer of
the Earth. Where there has been a great deal of stretching, this
upper layer is thin and the hotter deeper layers are closer to the
surface of the Earth producing a high flow of heat.
Using sensitive thermal probes, the researchers measured the
flow of heat from the Earth's interior in the deep sea sediment.
Thermal measurements were taken between Papua New
Guinea and the D'Entrecasteaux Islands because these islands
are metamorphic core complexes that are rising at the same
time that the floors of the surrounding basins are deepening.
The thermal measurements revealed that the basins do not
have elevated heat, but the islands do.
Examining what is known about the geology of the islands and
surroundings, the Hawaii researchers formulated their new
model for the formation of the islands.
They discovered that the basin and islands are in a region that
was once a continuous layer of dense oceanic crust and mantle
(the layer of the Earth between the crust and the core), the type of
material that is generally present for the formation of the floors of
major ocean basins.
This dense oceanic layer was thrust over part of Australia 50 to
60 million years ago. The result was a heavy oceanic layer
pressed tightly over a lighter continental layer.
When the current extension began, the upper layer was split and
the lower layer was squeezed up and out through the crack like
toothpaste, which was the formation of the islands.
The flow and thinning of the lower continental layer caused the
upper oceanic layer of the surrounding basins to sink but not
stretch. The heat from the thinning lower layer did not have
sufficient time to cross over the upper layer, except where the hot
lower layer was squeezed out at the islands.
This superposition of a denser layer over a lighter one is called a
density inversion, since it goes counter to the general trend
observed on Earth of density increasing with depth.
Nevertheless, these density inversions have occurred repeatedly
on Earth as a consequence of collisions of different terrains due
to the ever-moving tectonic plates.
In other areas, the fact that density decreases with increasing
temperature may create such a density inversion in the crust
even without collisions and thrusting of heavy layers over lighter
ones.
The processes at work in raising the islands of eastern Papua
New Guinea may provide a general explanation for the formation
of many similar core complexes throughout the world.