Spray J G, Thompson L M
Department of Geology, University of New Brunswick, Fredericton, Canada.
Nature. 1995 Jan 12;373(6510):130-2. doi: 10.1038/373130a0.
It is generally accepted that multi-ring basins are the consequence of very large impacts, but the mechanism by which they form is still a matter of contention. Most of what is currently known about multi-ring basins is based on remote studies of the Moon and, to a lesser extent, Mars and Mercury. But at least two multi-ring impact basins have been recognized on Earth--the Sudbury (Canada) and Vredefort (South Africa) impact structures--providing an opportunity to study their properties directly. Here we describe the distribution of friction melt (pseudotachylyte) in the floor of the Sudbury impact basin. Although the veins and dykes of pseudotachylyte decrease in both thickness and frequency of occurrence towards the basin periphery, the greatest volumes of friction melt appear to define four rings around the central impact melt sheet. Field evidence indicates that the rings originated as zones of large displacement, which facilitated localized frictional melting of the basin floor during the modification (collapse) stage of the cratering process. By analogy, we argue that the rings of other multi-ring impact basins are also likely to be the remnants of such large-displacement fault zones.
人们普遍认为，多环盆地是由非常大的撞击造成的，但其形成机制仍然存在争议。目前关于多环盆地的大部分认识是基于对月球的遥感研究，在较小程度上也基于对火星和水星的研究。但在地球上至少已经确认了两个多环撞击盆地——加拿大的萨德伯里和南非的弗里德堡撞击构造——这为直接研究它们的特性提供了机会。在这里，我们描述了萨德伯里撞击盆地底部摩擦熔体（假玄武玻璃）的分布情况。尽管假玄武玻璃的脉体和岩脉朝着盆地边缘在厚度和出现频率上都有所减小，但最大量的摩擦熔体似乎在中央撞击熔体片周围形成了四个环。实地证据表明，这些环起源于大位移区域，在撞击坑形成过程的改造（坍塌）阶段，这些区域促进了盆地底部的局部摩擦熔融。通过类比，我们认为其他多环撞击盆地的环也很可能是这种大位移断层带的遗迹。
