Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA.
Nat Commun. 2013;4:1404. doi: 10.1038/ncomms2414.
High-pressure minerals in meteorites provide clues for the impact processes that excavated, launched and delivered these samples to Earth. Most Martian meteorites are suggested to have been excavated from 3 to 7 km diameter impact craters. Here we show that the Tissint meteorite, a 2011 meteorite fall, contains virtually all the high-pressure phases (seven minerals and two mineral glasses) that have been reported in isolated occurrences in other Martian meteorites. Particularly, one ringwoodite (75 × 140 μm(2)) represents the largest grain observed in all Martian samples. Collectively, the ubiquitous high-pressure minerals of unusually large sizes in Tissint indicate that shock metamorphism was widely dispersed in this sample (~25 GPa and ~2,000 °C). Using the size and growth kinetics of the ringwoodite grains, we infer an initial impact crater with ~90 km diameter, with a factor of 2 uncertainty. These energetic conditions imply alteration of any possible low-T minerals in Tissint.
陨石中的高压矿物为挖掘、发射和将这些样本运送到地球的冲击过程提供了线索。大多数火星陨石被认为是从直径 3 到 7 公里的撞击坑中挖掘出来的。在这里，我们表明，2011 年坠落的 Tissint 陨石包含了在其他火星陨石的孤立事件中报道的几乎所有高压相（七种矿物和两种矿物玻璃）。特别是，一个橄榄石（75×140μm²）代表了在所有火星样本中观察到的最大颗粒。总的来说，Tissint 中普遍存在的、尺寸异常大的高压矿物表明，冲击变质作用在这个样本中广泛分布（25GPa 和2000°C）。利用橄榄石颗粒的大小和生长动力学，我们推断初始撞击坑的直径约为 90 公里，不确定性为 2。这些能量条件意味着 Tissint 中任何可能的低 T 矿物都发生了变化。
