• 文章目录 •

### 宇宙尖晶石与地球尖晶石的比较

1. 南京大学地球科学系
• 收稿日期:1997-03-20 修回日期:1997-03-20 出版日期:1997-03-20 发布日期:1997-03-20

### A COMPARISON BETWEEN C0SMIC SPINEL AND TERRESTRIAL SPINEL

Wan Yu-qiu1, Wang Erkang1, Zhang Wen-lan2

1. 1. Department of Earth Sciences, Nanjing University, Nanjing, 210093; Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093; 2. State Key Laboratory of Mineral Deposit Research, Nanjing University, Nanjing 210093
• Received:1997-03-20 Revised:1997-03-20 Online:1997-03-20 Published:1997-03-20

Abstract: Magnetic spinels are reported in all extraterrestrial objects which have experienced melting in the earth atmosphere, such as in the fusion crusts of meteorites and micrometeorites, in the chondritic extraterrestrial particles extracted from deep-sea sediments, and in polar ice, and in glassy microspherules from a late Pliocene impact. Based on above-mentioned reports as well as our studies of cosmic dusts from Suzhou granite, an introduction to the physical and chemical characteristics of “cosmic” spinels, such as the section appearances, chemical compositions, occurrence features and their origins, as well as a comparison with terrestrial spinels, is given in this review. Cosmic spinels usually display dendritic, skeleton, cruciform and octahedral morphologies, which are characteristic of rapid crystallization from a high-temperature melt. They contain variable amounts of MgO, Al2O3, and Cr2O3, with high NiO and relatively low TiO2. The average bulk composition of cosmic spinels is expressed as a solid solution of spinel end members, showing that the two dominant components are magnetite and magnesioferrite. All cosmic spinels have a trevorite content. Cosmic spinels always display a relatively high iron oxidation state, usually being characterized by a Fe3+/Fetotal ratio greater than 70%, and even higher, nearly reaching 100 atom% in late Pliocene microspherules and Suzhou granite cosmic dusts. But for the terrestrial spinels, they contain no more than 1 mol% trevorite. Magnesioferrite is also rarely present. All terrestrial spinels generally have a Fe2+/Fetotal ratio less than 70%, and have not been reported to be with a dendritic, skeleton or octrahedral morphologies in their sections. Cosmic spinels are characterized by a high nickel concentration due to the relatively high abundance of this element in extraterrestrial and a high iron oxidation state resulting in crystallization under a high oxygen fugacities. So it is suggested that the cosmic spinels in the geologica1 record are of two implications: they are a marker of cosmic material and they contain informat[on about the mode of accretion of this materia1.