The majority of diamonds are created deep inside the Earth and are
transported to the surface by little but mighty volcanic eruptions of a kind
of rock known as "kimberlite."
Our
supercomputer simulation, which was published in the journal Nature Geoscience, demonstrates that
these eruptions are driven by enormous "pillars of heat" that are buried
2,900 kilometers (1,802 miles) below the surface, right above our planet's
core.
Targeting mineral deposits, including those for important minerals like
nickel and rare earth elements as well as diamonds, may be done by
understanding Earth's interior history.
Warm blobs and kimberlite
An iconic deep, carrot-shaped "pipe" of kimberlite rock, which frequently
has diamonds, is left behind by kimberlite eruptions. Around the planet,
hundreds of these eruptions from the last 200 million years have been found.
The majority of them were discovered in Brazil (70), South Africa (158),
Angola (71) and Canada (178 eruptions).
The mantle, a substantial layer of heated, somewhat gooey rock, sits
between the solid crust of Earth and its molten core. Geophysicists have
studied the sluggish, long-term movement of the mantle using computers for
many years.
One research from the 1980s
suggested
that tiny thermal plumes in the mantle, which rise upward beneath slowly
moving continents and resemble feathers, may be related to kimberlite
eruptions.
At a depth of 2,900 kilometers, the mantle-core barrier had previously been
suggested as the possible source of these plumes in the 1970s.
Then, in 2010,
geologists suggested that kimberlite eruptions may be explained by thermal plumes that were
produced by the margins of two hot, deep blobs that were anchored beneath
Africa and the Pacific Ocean.
Additionally,
we noted that
these anchored blobs are more mobile than we initially believed last
year.
However, we were still unsure of the precise mechanism guiding kimberlite
eruptions, which was caused by deep mantle activity.
Heat pillars
Geologists believed that mantle plumes could be what sparks kimberlite
eruptions. A significant puzzler remained, though: how was heat getting from
the deep Earth to the kimberlites?
We developed three-dimensional geodynamic models of the Earth's mantle
using supercomputers in
Canberra, Australia, in order to answer this question. Our models take into
consideration how continents have moved over the last billion years, both on
the surface and beneath the mantle.
We computed the heat flow from the core and found that the extremely deep
Earth is connected to the surface via wide mantle upwellings, or "pillars of
heat". Our simulation demonstrates that these pillars provide heat beneath
kimberlites and that they account for the majority of kimberlite eruptions
during the previous 200 million years.
The kimberlite eruptions in Africa, Brazil, Russia, and to a lesser extent
in the United States and Canada were successfully represented by the model.
Our simulations also indicate that kimberlite eruptions in East Antarctica
and the Yilgarn Craton of Western Australia, which were previously unknown,
may have taken place.
Mantle plumes rise more quickly and transport dense material over the
mantle into the heart of the pillars, which might account for the varying
chemical composition of kimberlites on
various continents.
Some of the Canadian kimberlites, which may be connected to a separate
geological phenomenon known as "plate subduction," are not explained by our
models. The oldest kimberlites can be dated to one billion years ago, which
is the limit of our ability to recreate tectonic plate motions
at this time.
This article is republished from
The Conversation under a
Creative Commons license. Read the
original article.
