Longevity on the continents of the Earth in the face of destructive tectonic activity is an essential geological background for the emergence of life on our planet. This stability depends on the basic mantle attached to the mainland. New research by a group of Carnegie geologists, the Geological Institute of America and the University of Alberta show that diamonds can be used to reveal how the floating part of the mantle on some continents has become thick enough to provide long-term stability.
"We found a way to use the traces of sulfur from ancient volcanoes that penetrated the mantle and eventually are in diamonds to provide evidence of a particular process of building the continent," explained Karen Smith of the Geological Institute of America, chief author of paper the group that appears this week Science. "Our technique shows that the geological activity that forms the West African continent is due to the fertile tectonic movement of oceanic sinks that sink into the mantle."
Diamonds may be loved by jewelry collectors, but they are really the best friend of the geologist. Since they originate deep inside the Earth, fine mineral grains trapped inside the diamond are often considered undesirable in diamond trade, can reveal details of the conditions under which it was formed.
"In this way, diamonds act as mineralogical emissaries from the depths of the Earth," explained Carnegie co-author Steve Shiri.
About 150 to 200 kilometers, 93 to 124 miles below the surface, geological formations called mantle keels act as stabilizers for the continental crust. The material it constitutes must be thickened, stabilized and cooled under the continent to form a strong, flame, keel that is fundamental to the preservation of surface land surfaces against the relentless destructive forces of tectonic activity on Earth. But how this is accomplished, it is a debate in the scientific community.
"Resolving this mystery is the key to understanding how continents have come to exist in their current incarnations and how they survive on an active planet," explained Shiri. "Because this is the only tectonic active, rocky planet we know, understanding geology of the formation of our continents is a key part of an insightful way that makes the Earth fit for living."
Some scientists believe that small cells are formed by a process called subduction, by which oceanic plates sink from the surface of the earth to its depths, when a tectonic plate slides below another. Others believe that the stones are created by a vertical process in which warm hot magma rises from much deeper on Earth.
A geochemical tool that can detect whether the source of makeup on the rug rug is derived from surface plates or from upgrading the deeper material for the cloak is needed to help resolve this debate. Fortunately, small cells have ideal conditions for forming diamonds. This means that scientists can discover the origin of the mantilla kale by studying the subsets of diamonds formed in it.
An analysis of the research group of sulfur-rich minerals, called sulphides, in diamonds mined in Sierra Leone suggest that the region experienced two subduction events during its history.
They succeeded in making this decision because the chemistry of sulphide mineral grains is only seen in Earth's surface samples more than 2.5 billion years ago – before oxygen is so abundant in the atmosphere of our planet. This means that the sulfur in these mineral substrates must have existed ever on the surface of the Earth and was then pulled into a mantle with subduction.
A comparison of the diamond team from Botswana showed similar evidence of cell creation through subduction. But comparison with diamonds mined from northern Canada does not show the same sulfur chemistry, which means that small cavers in this region originated in a way that did not include surface material.
The group's findings suggest that the thickening and stabilization of the mantil core under the West African continent occurred when this part of the mantle was clamped with collision with the sinking material on the ocean floor. This method for thickening the cores and stabilizing the continent is not responsible for the formation of a carpet under a section of northern Canada. Sulfid minerals in Canadian diamonds do not tell the researchers how this nucleus was formed, just as not.
"Our work shows that sulphide inclusions in diamonds are a powerful tool for exploring the continent's processes of building," concluded Smith.
This work was supported by GIA, University of Alberta, NSF and Carnegie. It is a contribution to the Deep Observatory.