Unearthing history

October 28, 2019

Chestnut Hill, Mass. (10/28/2019) - A new analysis has revealed the source of oxidation found in rock samples from the coast of Greece, where geological activity spawned explosive arc volcanoes about 45 million years ago, a team of researchers reports in the journal Nature Geoscience.

Arc volcanic rocks are highly oxidized, which has led scientists to speculate that the fluids coming from subducted oceanic rocks might be the oxidizing agent, said Boston College Professor of Earth and Environmental Sciences Ethan Baxter, a co-author of the report.

To test that hypothesis, Baxter's team at Boston College along with colleagues from the Sorbonne, the University of South Carolina, and Durham University (UK) sought to identify a fingerprint of the fluid source in the remnants of ancient subducted oceanic crust found on the Greek island of Sifnos.

The team of researchers studied samples of large garnet crystals, which contain concentric rings of growth, much like the rings of a tree. Within these rings are chemically unique zones that change from the core of the crystal to the rim, said Baxter. These zones reflect the evolution of the rock system within which the garnet grows over millions of years.  In these rocks, the iron isotope composition varies from core to rim in a way that supports the release of an oxidizing fluid.

The team used electron microprobe analysis and iron isotopic analysis to document progressive changes in the rock system recorded in these strongly zoned garnets, said Baxter, whose research is funded by the National Science Foundation.

"Garnet chemical and iron isotope zonation supports the idea that these rocks released oxidizing fluids during subduction," said Baxter. "We have chemically 'fingerprinted' a source of these oxidizing fluids in subduction zones."

These novel measurements reveal for the first time that garnet crystals preserve zonation of iron isotopic composition from early formed core to later forming rims, the team reports.

"When we found significant zonation in iron isotope composition within these garnets, we knew we had found an untapped archive of fluid-related chemical change," said Baxter, who co-authored the report with Boston College researchers Anna R. Gerrits and Paul G. Starr, Edward C. Inglis of the Sorbonne, Besim Dragovic of the University of South Carolina, and Kevin W. Burton of Durham University (U.K.).

Baxter said the next steps in this research involve further testing the hypothesis by exploring what caused the fluids to be oxidizing.

"These oxidizing fluids carry certain agents capable of oxidizing rocks they enter," Baxter said. "The most familiar example would be the way that oxidizing fluids can cause iron-bearing materials to rust as they weather. Based on the garnet chemical zonation, we know the fluids liberated from our samples are oxidizing, but we don't know why they are oxidizing or what the oxidizing agents are."
-end-
The team is looking at other samples to study and exploring how to reconstruct the timescale over which these fluids were produced using zoned garnet geochronology in Baxter's lab at Boston College.

Boston College

Related Iron Articles from Brightsurf:

How stony-iron meteorites form
Meteorites give us insight into the early development of the solar system.

Bouillon fortified with a new iron compound could help reduce iron deficiency
Iron fortification of food is a cost-effective method of preventing iron deficiency.

Iron nanorobots go undercover
Customizable magnetic iron nanowires pinpoint and track the movements of target cells.

Iron deficiency in corals?
When iron is limited, the microalgae that live within coral cells change how they take in other trace metals, which could have cascading effects on vital biological functions and perhaps exacerbate the effects of climate change on corals.

Blocking the iron transport could stop tuberculosis
The bacteria that cause tuberculosis need iron to survive. Researchers at the University of Zurich have now solved the first detailed structure of the transport protein responsible for the iron supply.

Observed: An exoplanet where it rains iron
Nature magazine is publishing today a surprising study about the giant, ultra-hot planet WASP-76b in which researchers from the Instituto de Astrofísica de Canarias (IAC) have taken part.

An iron-clad asteroid
Mineralogists from Jena and Japan discover a previously unknown phenomenon in soil samples from the asteroid 'Itokawa': the surface of the celestial body is covered with tiny hair-shaped iron crystals.

It's Iron, Man: ITMO scientists found a way to treat cancer with iron oxide nanoparticles
Particles previously loaded with the antitumor drug are injected in vivo and further accumulate at the tumor areas.

The brain may need iron for healthy cognitive development
Iron levels in brain tissue rise during development and are correlated with cognitive abilities, according to research in children and young adults recently published in JNeurosci.

The regulators active during iron deficiency
Iron deficiency is a critical situation for plants, which respond using specific genetic programmes.

Read More: Iron News and Iron Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.