Abstract We report on the occurrence of a new high-pressure Ca-Al-silicate in localized shock melt pockets found in the feldspatic lunar meteorite Oued Awlitis 001 and discuss the implications of our discovery. The new mineral crystallized as tiny, micrometer-sized, acicular grains in shock melt pockets of roughly anorthitic bulk composition. Transmission electron microscopy based three-dimensional electron diffraction (3D ED) reveals that the CaAl4Si2O11 crystals are identical to the calcium aluminum silicate (CAS) phase first reported from static pressure experiments. The new mineral has a hexagonal structure, with a space group of P63/mmc and lattice parameters of a = 5.42(1) Å; c = 12.70(3) Å; V = 323(4) Å3; Z = 2. This is the first time 3D ED was applied to structure determination of an extraterrestrial mineral. The International Mineralogical Association (IMA) has approved this naturally formed CAS phase as the new mineral “donwilhelmsite” [CaAl4Si2O11], honoring the U. S. lunar geologist Don E. Wilhelms. On the Moon, donwilhelmsite can form from the primordial feldspathic crust during impact cratering events. In the feldspatic lunar meteorite Oued Awlitis 001, needles of donwilhelmsite crystallized in ~200 mm sized shock melt pockets of anorthositic-like chemical composition. These melt pockets quenched within milliseconds during declining shock pressures. Shock melt pockets in meteorites serve as natural crucibles mimicking the conditions expected in the Earth’s mantle. Donwilhelmsite forms in the Earth’s mantle during deep recycling of aluminous crustal materials, and is a key host for Al and Ca of subducted sediments in most of the transition zone and the uppermost lower mantle (460–700 km). Donwilhelmsite bridges the gap between kyanite and the Ca-component of clinopyroxene at low pressures and the Al-rich Ca-ferrite phase and Ca-perovskite at high-pressures. In ascending buoyant mantle plumes, at about 460 km depth, donwilhelmsite is expected to break down into minerals such as garnet, kyanite, and clinopyroxene. This process may trigger minor partial melting, releasing a range of incompatible minor and trace elements and contributing to the enriched mantle (EM1 and EM2) components associated with subducted sedimentary lithologies.

中文翻译：

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Donwilhelmsite，[CaAl4Si2O11]，一种新的月球高压钙铝硅酸盐，与俯冲陆地沉积物相关

摘要 我们报告了在长石月球陨石 Oued Awlitis 001 中发现的局部冲击熔池中出现了一种新的高压钙铝硅酸盐，并讨论了我们发现的意义。这种新矿物结晶为微小的、微米大小的针状颗粒，在大致呈斜长石块状组成的冲击熔池中结晶。基于三维电子衍射 (3D ED) 的透射电子显微镜显示 CaAl4Si2O11 晶体与静压实验中首次报道的硅酸铝钙 (CAS) 相相同。新矿物为六方结构，空间群为P63/mmc，晶格参数a = 5.42(1) Å；c = 12.70(3) 埃；V = 323(4) Å3；Z = 2。这是首次将 3D ED 应用于外星矿物的结构测定。国际矿物学协会 (IMA) 已批准这种自然形成的 CAS 相作为新矿物“donwilhelmsite”[CaAl4Si2O11]，以纪念美国月球地质学家 Don E. Wilhelms。在月球上，唐威海姆石可以在撞击坑事件期间从原始长石地壳中形成。在长石月球陨石 Oued Awlitis 001 中，针状柱状陨石在约 200 毫米大小的类似斜长岩化学成分的冲击熔体中结晶。在冲击压力下降期间，这些熔体在几毫秒内淬火。陨石中的冲击熔池充当模拟地球地幔中预期条件的天然坩埚。在铝质地壳材料的深度循环过程中，在地幔中形成唐威海姆石，并且是大部分过渡带和最上层下地幔（460-700 km）俯冲沉积物中铝和钙的主要宿主。Donwilhelmsite 弥合了低压下蓝晶石和单斜辉石的 Ca 组分与高压下的富铝钙铁氧体相和钙钛矿之间的差距。在上升的浮力地幔柱中，在大约 460 公里的深度，东威海姆石预计会分解成石榴石、蓝晶石和斜辉石等矿物。这一过程可能会引发轻微的部分熔融，释放出一系列不相容的微量元素和微量元素，并有助于与俯冲沉积岩性相关的富集地幔（EM1 和 EM2）成分。Donwilhelmsite 弥合了低压下蓝晶石和单斜辉石的 Ca 组分与高压下的富铝钙铁氧体相和钙钛矿之间的差距。在上升的浮力地幔柱中，在大约 460 公里的深度，东威海姆石预计会分解成石榴石、蓝晶石和斜辉石等矿物。这一过程可能会引发轻微的部分熔融，释放出一系列不相容的微量元素和微量元素，并有助于与俯冲沉积岩性相关的富集地幔（EM1 和 EM2）成分。Donwilhelmsite 弥合了低压下蓝晶石和单斜辉石的 Ca 组分与高压下的富铝钙铁氧体相和钙钛矿之间的差距。在上升的浮力地幔柱中，在大约 460 公里的深度，东威海姆石预计会分解成石榴石、蓝晶石和斜辉石等矿物。这一过程可能会引发轻微的部分熔融，释放出一系列不相容的微量元素和微量元素，并有助于与俯冲沉积岩性相关的富集地幔（EM1 和 EM2）成分。