Tektites are reduced (Fe2+) glasses formed by the quenching of molten material ejected from Earth’s surface as a result of a hypervelocity impact. The vast majority of tektites are usually homogeneous glasses, but rare samples containing mineral inclusions can provide insights about the source material, sample thermal history, and tektite formation process. Tektites from two distinct strewn fields presenting Ca-phosphate inclusions detected from anomalous magnetic susceptibility were studied: one sample from the Ivory Coast tektite (ICT) field ejected at 1.07 Ma from the Bosumtwi crater (10.5 km in size) in Ghana and two Muong Nong type samples from the Australasian tektite field (MN-AAT) ejected at 0.79 Ma from a crater possibly situated in southeast Asia. In ICT, Ca-phosphate inclusions are systematically embedded in lechatelierite (SiO2 glass). In MN-AAT Ca-phosphate are either embedded in lechatelierite or in Fe-rich glass forming schlieren. Multiscale petrographic characterization using correlative microscopy associating scanning electron microscopy, microprobe and, transmission electron microscopy reveals that rounded inclusions in ivoirite are composed of acicular Ca-phosphates (merrillite) embedded in an amorphous P-rich glass. In MN-AAT, inclusions consist mostly of single droplets of Fe-Mg rich Ca-phosphate (structurally related to apatite), but few droplets often forming an emulsion texture show a complex assemblage of apatite, magnetite, pyroxene, and spinel growing from a Pt-rich nucleus. Diffusion profile around lechatelierite domains reveals maximum temperatures greater than 2200–2400 °C in the impact plume of the Australasian tektite and the Ivory coast tektite. Heating time is of the order of seconds-tens of seconds rather than minutes as previously suggested (20 s for MN-AAT and 5 s for ICT). The number, the density, and the fact that inclusions are entirely crystallized in MN-AAT support relatively slow cooling rates (<200 °C/h), in comparison with the faster cooling rates (>2000 °C/h) indicated by the precipitation of amorphous P-rich glass in ICT. In both impact events, ejecta that had been heated to high temperatures did not remain in the vapor plume for an extended period of time and landed rapidly (within tens of seconds) at a relatively high temperature (>1000 °C) on the Earth’s surface.

中文翻译：

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科特迪瓦和澳大拉西亚 Muong-Nong 型 tektites 中磷酸钙内含物的来源


Tektites 是由超高速撞击从地球表面喷出的熔融物质淬火而形成的还原 （Fe2+） 玻璃。绝大多数 tektite 通常是均质玻璃，但含有矿物夹杂物的稀有样品可以提供有关源材料、样品热历史和 tektite 形成过程的见解。研究了来自两个不同散布的田的 Tektites，这些田呈现从异常磁化率中检测到的钙磷酸盐包裹体：一个来自象牙海岸 tektite （ICT） 场的样品以 1.07 马 的速度从加纳的 Bosumtwi 陨石坑（大小 10.5 公里）喷出，以及来自澳大拉西亚 tektite 田 （MN-AAT） 的两个 Muong Nong 型样品，以 0.79 马 从可能位于东南亚的陨石坑喷出。在 ICT 中，磷酸钙内含物系统地嵌入 lechatelierite（SiO2 玻璃）中。在 MN-AAT 中，磷酸钙要么嵌入 lechatelierite 中，要么嵌入富铁玻璃中，形成纹影。使用相关显微镜结合扫描电子显微镜、微探针和透射电子显微镜进行的多尺度岩相学表征表明，象牙石中的圆形包裹体由嵌入非晶态富 P 玻璃中的针状磷酸钙（梅里利石）组成。在 MN-AAT 中，包裹体主要由单滴富含 Fe-Mg 的磷酸钙（在结构上与磷灰石相关）组成，但少数液滴通常形成乳液质地，显示出磷灰石、磁铁矿、辉石和尖晶石的复杂组合，这些物质从富含 Pt 的原子核中生长出来。lechatelierite 域周围的扩散剖面显示，澳大利亚 tektite 和象牙海岸 tektite 的撞击羽流的最高温度大于 2200-2400 °C。 加热时间大约为几秒到几十秒，而不是以前建议的几分钟（MN-AAT 为 20 秒，ICT 为 5 秒）。与 ICT 中非晶态富磷玻璃沉淀所表明的较快冷却速率（>2000 °C/h）相比，MN-AAT 中夹杂物的数量、密度和夹杂物完全结晶的事实支持相对较慢的冷却速率 （<200 °C/h）。在两次撞击事件中，被加热到高温的喷射物并没有在蒸汽羽流中停留很长时间，而是在相对较高的温度（>1000 °C）下迅速（在几十秒内）降落在地球表面。