A Mineral Is Stealing Iron From Earth’s Crust

Posted: May 20 2018, 4:26am CDT | by , Updated: May 20 2018, 5:03am CDT, in News | Latest Science News

A Mineral is Stealing Iron from Earth’s Crust
Garnet pyroxenite xenolith from Sierra Nevada, California. Credit: C. Lee/Rice University

New study says that iron is removed from continental crust by a mineral called garnet

Scientists have found a subtle chemical signature in the rocks of Arizona and they say it could explain why Earth’s continents lack iron.

Earth is made up of three distinct layers: the crust, the mantle and the core which can be further divided into the outer core and inner core. Earth’s crust is a rocky surface containing iron, silicon, magnesium and other minerals. If the iron content of surface rocks was just a fraction higher as it is in the rocks beneath Earth's oceans, our planet might look more like Mars. Mars seems red because of the abundance of iron oxide.

Scientists have long assumed that a mineral called magnetite is causing a decline in Earth’s iron content. But a new study says that another mineral garnet is the reason behind the depletion of Earth’s iron.

"The standard view, which even we agreed with and wrote papers agreeing with, is that iron is removed from continental crust by another mineral called magnetite," said Rice University petrologists Cin-Ty Lee. "I think people haven't thought much about garnet, possibly because it doesn't show up very much and magnetite shows up in a lot of samples."

Tracking the main culprit is not easy because this certain iron disappears many miles below active volcanoes. Scientists have no instruments to directly observe continental volcanic arcs. So, the missing iron mystery must be solved with deductive reasoning about Earth's inner workings and rare rocks that hold clues for these processes.

The interior of Earth is extremely hot. When we go towards the center of the planet, the heat and pressure get increasingly intense. Researchers say that Almandine, a type of garnet, is more easily made under high pressure and high-temperature volcano-like conditions.

Some of the rocks inside volcanoes are spewed out by past volcanic eruptions. These rocks exist 60 to 80 kilometers deep and are called xenoliths. Researchers made a trip to southern Arizona for collecting xenoliths. Analysis of the xenoliths showed that these rocks formed below a continental arc and were rich in garnet. Further analysis suggested that Arizona xenoliths formed in less-oxidized conditions and contained an unusual ratio of element Europium.

"There is a relationship between iron depletion and the garnet fractionation signatures, which means magmas that fractionate more garnet are more depleted in iron," said researcher Ming Tang. "This is born out in the global record, but the evidence is something that wouldn't be obvious from looking at just one or two cases. It's the kind of thing that requires a global database, and those have only recently become available."

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<a href="/latest_stories/all/all/47" rel="author">Hira Bashir</a>
The latest discoveries in science are the passion of Hira Bashir (). With years of experience, she is able to spot the most interesting new achievements of scientists around the world and cover them in easy to understand reporting.




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