Zircon as Earth's timekeeper: Are we reading the clock right?

October 23, 2017, Queensland University of Technology
Cathodoluminescence image from a scanning electron microscope of a typical igneous zircon crystal from samples studied by the QUT research team, revealing growth rings of the zircon. Yellow circles enclose ablation sites by a laser from which isotopic data is measured to determine the age of zircon growth. The analytical spots here show this zircon had two main growth periods approximately 20 million years apart in different magmas. Credit: QUT

Zircon crystals in igneous rocks must be carefully examined and not relied upon solely to predict future volcanic eruptions and other tectonic events, QUT researchers have shown.

  • Zircon is a robust mineral and a timekeeper of Earth history
  • Distinguishing the origins of zircon crystals, their individual chemistry and properties is not straightforward
  • Misinterpreting data from zircon crystals could skew timescales for geological events such as by millions of years
  • This has implications for understanding and the future risks they pose

The researchers' findings have been published in Earth-Science Reviews. The paper, Use and abuse of zircon-based thermometers: A critical review and a recommended approach to identify antecrystic zircons, also proposes an efficient and integrated approach to assist in identifying zircons and evaluating zircon components sourced from older rocks.

Associate Professor Scott Bryan, from QUT's Science and Engineering Faculty, said the researchers had "gone back to basic science" and reassessed large data sets of analyses of igneous rocks in Queensland and from around the world, to show that wrong assumptions can be made about zircon crystals.

Igneous rocks are formed by the cooling of magma (molten rock) which makes its way to Earth's surface, often leading to volcanic eruptions.

The QUT research team examining and sampling igneous rocks in north Queensland. Credit: QUT
"One of the assumptions being made is that the composition of the zircons and the rocks in which they have formed give an accurate record of the magmas and conditions at which the zircons and magmas formed," Associate Professor Bryan said.

"From this, we then estimate the age of the event that caused them to form.

"But some may not be related to their at all. They may have come from the source of the magma deep in the Earth's crust or they may have been picked up by the magma on its way to the surface.

"If you don't distinguish between the types of crystals then you get a big variation in the age of the event which formed the rocks, potentially millions of years, as well as developing incorrect views on the conditions needed to make magmas.

"It is critical to get the timescales of magmatism correct, so we can understand how long it might take for reservoirs of magma to build up and erupt."

The QUT research team examining and sampling igneous rocks in north Queensland. Credit: QUT

This is particularly relevant to 'supervolcanoes' which do not always have pools of sitting beneath them, Associate Professor Bryan said.

There are more than 20 supervolcanoes on Earth, including Yellowstone in the US and Taupo in New Zealand.

"Determining accurately what is telling us is fundamental to understanding Earth's history, defining major events such as mass extinctions, and how we understand global plate tectonics," he said.

"We need to understand the past, and read the geological clocks correctly, to accurately predict the future and to mitigate future hazards."

Explore further: Earth was barren, flat and almost entirely under water 4.4 billion years ago

More information: C. Siégel et al, Use and abuse of zircon-based thermometers: A critical review and a recommended approach to identify antecrystic zircons, Earth-Science Reviews (2017). DOI: 10.1016/j.earscirev.2017.08.011

Related Stories

Volcanic crystals give a new view of magma

June 15, 2017

Volcanologists are gaining a new understanding of what's going on inside the magma reservoir that lies below an active volcano and they're finding a colder, more solid place than previously thought, according to new research ...

Magma chambers have a sponge-like structure

October 5, 2017

ETH researchers show that magma chambers under supervolcanoes are more like soggy sponges than reservoirs of molten rock. Before a volcano of this kind erupts, such mush must slowly be reactivated by heat input following ...

The oldest crystals in the world

May 5, 2016

In this new article for Geology, Gavin Kenny and colleagues reveal the likely origin of Earth's oldest crystals. New research into the origin of Earth's oldest crystals suggests that they probably formed in huge impact craters ...

Zircon crystals reveal onset of plate tectonics

May 31, 2012

(Phys.org) -- We're familiar with the theory that the Earth's crust is composed of tectonic plates that move, sometimes dramatically to create earthquakes and tsunamis - but until recently, nobody knew how long this movement ...

Recommended for you

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.