Beck P, Gillet Ph, El Goresy A, Mostefaoui S
Laboratoire de Sciences de la Terre, CNRS UMR 5570, Ecole Normale Supérieure de Lyon et Université Lyon I, 46 allée d'Italie, 69364 Lyon Cedex 7, France.
Nature. 2005 Jun 23;435(7045):1071-4. doi: 10.1038/nature03616.
The accretion of the terrestrial planets from asteroid collisions and the delivery to the Earth of martian and lunar meteorites has been modelled extensively. Meteorites that have experienced shock waves from such collisions can potentially be used to reveal the accretion process at different stages of evolution within the Solar System. Here we have determined the peak pressure experienced and the duration of impact in a chondrite and a martian meteorite, and have combined the data with impact scaling laws to infer the sizes of the impactors and the associated craters on the meteorite parent bodies. The duration of shock events is inferred from trace element distributions between coexisting high-pressure minerals in the shear melt veins of the meteorites. The shock duration and the associated sizes of the impactor are found to be much greater in the chondrite (approximately 1 s and 5 km, respectively) than in the martian meteorite (approximately 10 ms and 100 m). The latter result compares well with numerical modelling studies of cratering on Mars, and we suggest that martian meteorites with similar, recent ejection ages (10(5) to 10(7) years ago) may have originated from the same few square kilometres on Mars.
小行星碰撞形成类地行星以及火星和月球陨石被送至地球的过程已得到广泛建模。经历过此类碰撞产生的冲击波的陨石，有可能被用于揭示太阳系演化不同阶段的吸积过程。在此，我们已确定了一颗球粒陨石和一颗火星陨石所经历的峰值压力及撞击持续时间，并将这些数据与撞击标度律相结合，以推断撞击体的大小以及陨石母体上相关撞击坑的大小。冲击事件的持续时间是根据陨石剪切熔体脉中共存高压矿物之间的微量元素分布推断出来的。结果发现，球粒陨石中的冲击持续时间和相关撞击体大小（分别约为1秒和5千米）比火星陨石中的（分别约为10毫秒和100米）大得多。后一结果与火星上撞击坑形成的数值模拟研究结果吻合良好，并且我们认为，具有相似近期喷出年龄（10^5至10^7年前）的火星陨石可能源自火星上相同的几平方千米区域。
