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月球陨石中发现的新矿物

编译者:zhoubz发布时间:2020-12-1点击量:512 来源栏目:研究进展

一组欧洲研究人员在月球陨石Oued Awlitis 001中发现了一种新的高压矿物,命名为donwilhelmsite[CaAl4Si2O11]。来自德国Zentrum für Rieskrater und Impaktforschung Nördlingen的团队和位于波茨坦的德国地球科学研究中心GFZ、柏林自然历史博物馆、维也纳自然历史博物馆、捷克科学院物理研究所、奥斯陆自然历史博物馆、曼彻斯特大学奥斯陆自然历史博物馆的同事们,德国的Zentrum für Luft und Raumfahrt Berlin在科学期刊《美国矿物学家》上发表了他们的发现。

Besides the about 382 kilograms of rocks and soils collected by the Apollo and Luna missions, lunar meteorites allow valuable insights into the formation of the Moon. They are ejected by impacts onto the lunar surface and subsequently delivered to Earth.

Some of these meteorites experienced particularly high temperatures and pressures. The extreme physical conditions often led to shock melting of microscopic areas within these meteorites. These shocked areas are of great relevance as they mirror pressure and temperature regimes similar to those prevailing in the Earth's mantle. Therefore, the microscopic shock melt areas are natural crucibles hosting minerals that are otherwise naturally inaccessible at the Earth's surface. Minerals like wadsleyite, ringwoodite, and bridgmanite, constitute large parts of the Earth's mantle. Theses crystals were synthesized in high-pressure laboratory experiments. As natural minerals they were first described and named based on their occurrences in meteorites.

The new mineral donwilhelmsite is the first high-pressure mineral found in meteorites with application for subducted terrestrial sediments. It is mainly composed of calcium, aluminum, silicon, and oxygen atoms. Donwilhelmsite was discovered within shock melt zones of the lunar meteorite Oued Awlitis 001 found in 2014 in the Western Sahara. This meteorite is compositionally similar to rocks comprising the Earth's continents. Eroded sediments from these continents are transported by wind and rivers to the oceans, and subducted into the Earth's mantle as part of the dense oceanic crust. While being dragged deeper into the Earth mantle the pressure and temperature increases, and the minerals transform into denser mineral phases. The newly discovered mineral donwilhelmsite forms in 460 to 700 kilometre depth. In the terrestrial rock cycle, donwilhelmsite is therefore an important agent for transporting crustal sediments through the transition zone separating the upper and lower Earth's mantle.

This pan-European collaboration was essential to obtain the lunar meteorite, recognize the new mineral, understand its scientific relevance, and to determine the crystal structure of the tiny, the thousands part of a millimeter thick, mineral crystal with high accuracy. "At the GFZ, we used transmission electron microscopy to investigate microstructural aspects of the samples," says Richard Wirth from the section "Interface Geochemistry." "Our investigations and the crystal structure analyses of the colleagues from the Czech Republic once again underline the importance of transmission electron microscopy in the geosciences."

The new mineral was named in honor of the lunar geologist Don E. Wilhelms, an American scientist involved in landing site selection and data analyses of the Apollo space missions that brought to Earth the first rock samples from the Moon. Part of the meteorite Oued Awlitis 001, acquired by crowdfunding initiative "Help us to get the Moon!," is on display at the Natural History Museum Vienna.

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