Unbelievably, the one place that I needed to find continental rocks
in support of the conjecture regarding the crustal shift of the
Pleistocene Nonconformity happens to be the Indian Ocean about were
this item focused. The land masses were there and what was missing
was knowledge regarding just what they were deep down.
Had they been merely oceanic rocks then cultural records and the
crustal shift theory would have had a problem.
The crustal shift generated two natural regions of subsidence. One
is the Caribbean and the other is on the other side of the Globe
generated by balancing compression and stretching over the equator.
A last echo of that subsidence caught the Atlantean world in 1159 BC.
Ages as usual reflect ages of rocks and not of movements.
Ancient
'Micro-Continent' Found Under Indian Ocean
By Charles Q. Choi,
The remains of a
micro-continent scientist call Mauritia might be preserved under huge
amounts of ancient lava beneath the Indian Ocean, a new analysis of
island sands in the area suggests.
These findings hint
that such micro-continents may have occurred more
frequently than previously thought, the scientists who conducted the
study, detailed online Feb. 24 in the journal Nature Geoscience, say.
Researchers analyzed
sands from the isle of Mauritius in the western Indian Ocean.
Mauritius is part of a volcanic chain that, strangely, exists far
from the edges of its tectonic plate. In contrast, most volcanoes are
found at the borders of the tectonic plates that make up the surface
of the Earth.
Investigators suggest
that volcanic chains in the middle of tectonic plates, such as the
Hawaiian Islands, are caused by giant pillars of hot molten rock
known as mantle plumes. These rise up from near the Earth's core,
penetrating overlying material like a blowtorch. [What Is Earth Made
Of?]
Mantle plumes can
apparently trigger continental breakups, softening the tectonic
plates from below until they fragment — this is how the lost
continent of Eastern Gondwana ended about 170 million years ago,
prior research suggests A plume currently sits near Mauritius and
other islands, and the researchers wanted to see if they could find
ancient fragments of continents from just such a breakup there.
Digging in the sand
The beach sands of
Mauritius are the eroded remnants of volcanic rocks created by
eruptions 9 million years ago. Collecting them"was actually
quite pleasant," said researcher Ebbe Hartz, a geologistat the
University of Oslo in Norway. He described walking out from a
tropical beach, "maybe with a Coke and an icebox, and you dig
down underwater into sand dunes at low tide."
Within these sands,
investigators discovered about 20 ancient zircon grains (a
type of mineral) between 660 million and 1,970 million years old. To
learn more about the source of this ancient zircon, the scientists
investigated satellite maps of Earth's gravity field. The
strength of the field depends on Earth's mass, and since the planet's
mass is not spread evenly, its gravity field is stronger in some
places on the planet's surface and weaker in others.
The researchers
discovered Mauritius is part of a contiguous block of abnormally
thick crust that extends in an arc northward to the Seychelles
islands. The finding suggests Mauritius and the adjacent region
overlie an ancient micro-continent they call Mauritia. The ancient
zircons they unearthed are shards of lost Mauritia.
The researchers
meticulously sought to rule out any chance these ancient grains were
contaminants from elsewhere.
"Zircons are
heavy minerals, and the uranium and lead elements used to date the
ages of these zircons are extraordinarily heavy, so these grains do
not easily fly around — they did not blow into Mauritius from a
sandstorm in Africa," Hartz told OurAmazingPlanet.
"We also chose a
beach where there was no construction whatsoever — that these
grains did not come from cement somewhere else," Hartz added.
"We were also careful that all the equipment we used to collect
the minerals was new, that this was the first time it was used, that
there was no previous rock sticking to it from elsewhere."
Peeling continent
pieces
After analyzing marine
fracture zones and ocean magnetic anomalies, the investigators
suggest Mauritia separated from Madagascar, fragmented and dispersed
as the Indian Ocean basin grew between 61 million and 83.5 million
years ago. Since then, volcanic activity has buried Mauritia under
lava, and may have done the same to other continental fragments.
"There are all
these little slivers of continent that may peel off continents when
the hotspot of a mantle plume passes under them,"
Hartz said. "Why that happens is still mind-boggling. Why, after
something gets ripped apart, would it rip apart again?"
Finding past evidence
of lost continents normally involves tediously crushing and sorting
volcanic rocks, Hartz explained. The researchers essentially let
nature do the work of pulverization for them by looking at sand.
"We suggest lots
of scientists try this technique on their favorite volcanoes,"
Hartz said.
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