Northwest Africa (NWA) 11119, a stone meteorite found in December 2016 in Mauritania, is the world’s oldest igneous meteorite, according to new research.
An artist’s rendition of NWA 11119 (far right bottom corner of illustration), the oldest-ever igneous meteorite. Image credit: University of New Mexico.
“The age of NWA 11119 is the oldest, igneous meteorite ever recorded,” said University of New Mexico’s Professor Carl Agee, co-author of the study.
“Not only is this just an extremely unusual rock type, it’s telling us that not all asteroids look the same. Some of them look almost like the crust of the Earth because they’re so light colored and full of SiO2. These not only exist, but it occurred during one of the very first volcanic events to take place in the Solar System.”
Using an electron microprobe and a computed tomography scan, Professor Agee and colleagues examined the composition and mineralogy of NWA 11119.
“The mineralogy of this rock is a very, very different from anything that we’ve worked on before,” said study lead author Poorna Srinivasan, also from the University of New Mexico.
“We examined the mineralogy to understand all of the phases that comprise the meteorite.”
“One of the main things we saw first were the large silica crystals of tridymite which is a similar to the mineral quartz.”
“When we conducted further image analyses to quantify the tridymite, we found that the amount present was a staggering 30% of the total meteorite — this amount is unheard of in meteorites and is only found at these levels in certain volcanic rocks from the Earth.”
NWA 11119 is a single stone of 453 g, and resides at the Maine Mineral & Gem Museum. A 23 g subsample deposited at the Institute of Meteoritics at the University of New Mexico was used for this study. Image credit: B. Barrett / Maine Mineral & Gem Museum.
“Based on oxygen isotopes, we know NWA 11119 is from an extraterrestrial source somewhere in the Solar System, but we can’t actually pinpoint it to a known body that has been viewed with a telescope.”
“However, through the measured isotopic values, we were able to possibly link it to two other unusual meteorites (NWA 7235 and Almahata Sitta) suggesting that they all are from the same parent body — perhaps a large, geologically complex body that formed in the early Solar System.”
One possibility is that this parent body was disrupted through a collision with another asteroid or planetesimal and some of its ejected fragments eventually reached the Earth’s orbit, falling through the atmosphere and ending up as meteorites on the ground.
“The oxygen isotopes of NWA11119, NWA 7235, and Almahata Sitta are all identical, but this rock stands out as something completely different from any of the over 40,000 meteorites that have been found on Earth,” Srinivasan said.
Most meteorites are formed through the collision of asteroids orbiting the Sun in a region called the asteroid belt.
Asteroids are the remains from the formation of the Solar System formation some 4.6 billion years ago.
The chemical composition ranges of ancient igneous meteorites, or achondrites, are key to understanding the diversity and geochemical evolution of planetary building blocks.
Achondrite meteorites record the first episodes of volcanism and crust formation, the majority of which are basaltic.
“The meteorite we studied is unlike any other known meteorite. It has the highest abundance of silica and the most ancient age (4.565 billion years old) of any known igneous meteorite,” said study co-author Daniel Dunlap, a graduate student at Arizona State University.
“Meteorites like this were the precursors to planet formation and represent a critical step in the evolution of rocky bodies in our Solar System.”
The research is published in the journal Nature Communications.
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Poorna Srinivasan et al. 2018. Silica-rich volcanism in the early solar system dated at 4.565 Ga. Nature Communications 9, article number: 3036; doi: 10.1038/s41467-018-05501-0
