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A team of researchers in Europe has identified a new high-pressure mineral in a lunar meteorite called Oued Awlitis 001.
Fragments of Oued Awlitis 001. Image credit: Ludovic Ferrière, NHM Vienna.
Oued Awlitis 001 is a feldspar lunar meteorite that was found in 2014 in Western Sahara, Africa.
The main fragment of the space rock, originally 382 g, was found on January 15, 2014 by a group of eight travelers. It is largely covered with a green to brownish melt crust showing orientation characteristics.
Another fragment, 50.5 g, suitable for the larger one, was found a few weeks later; ~ 60% of it is covered with a cracked molten crust and shows a flipped lip on one side. Two other fragments were also found, 497 mg and 148 mg.
Oued Awlitis 001 is classified as an anorthosic lunar impact fusion rock, composed of large clasts of anorthite inserted in a poikilitic matrix of plagioclase, olivine and pyroxene.
Scientists think this meteorite was ejected from the moon about 300,000 years ago.
“This meteorite is compositionally similar to the rocks that make up the Earth’s continents,” said lead author Dr. Jörg Fritz from the Zentrum für Rieskrater und Impaktforschung in Germany and his colleagues.
“Sediments eroded from these continents are carried by wind and rivers to the oceans and subducted into the Earth’s mantle as part of the dense oceanic crust.”
“As they are dragged deeper into the Earth’s mantle, the pressure and temperature increase and the minerals transform into denser mineral phases.”
This SEM image shows donwilhelmsite crystals in Oued Awlitis 001. Image credit: Ansgar Greshake, Museum für Naturkunde Berlin.
The newly discovered extraterrestrial mineral, named donwilhelmsite, is a high-pressure silicate with a formula of CaAl4IS2OR11.
Its name honors USGS geologist Don E. Wilhelms for his groundbreaking and groundbreaking work on the geological history of the Moon.
The needle-shaped crystals of donwilhelmsite were found in 200 mm shock fusion pockets of the meteorite Oued Awlitis 001.
“Donwilhelmsite is the first high-pressure mineral found in meteorites with application for subducted terrestrial sediments,” the scientists said.
“It is mainly composed of calcium, aluminum, silicon and oxygen atoms.”
The structure of the donwilhelmsite was solved with precession-assisted 3D electron diffraction.
“The identification of donwilhelmsite in a lunar meteorite underlines that the formation of high-pressure phases in localized shock melting zones in meteorites is a common phenomenon,” the authors said.
“The natural occurrence of high-pressure phases is an important resource for understanding the geological processes that influence the magmatic evolution of terrestrial planets, such as phase transformations in the interiors of planets, crystallization of oceanic magma and plate tectonics.”
“In the Earth’s mantle, donwilhelmsite is formed during the deep recycling of aluminous crustal materials, which are also rich in volatiles and other incompatible elements in the mantle minerals.”
“In the terrestrial rock cycle, donwilhelmsite is an important agent for the transport of crustal sediments through the transition zone and the higher lower mantle (460-700 km).”
The discovery is described in an article published in the journal American mineralogist.
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Jörg Fritz et al. 2020. Donwilhelmsite, [CaAl4Si2O11], a new lunar high-pressure Ca-Al silicate with relevance to subducted terrestrial sediments. American mineralogist 105 (11): 1704-1711; doi: 10.2138 / am-2020-7393
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