Abstract

According to data of dendrochronological investigations of larch trees that had grown on the Patom crater (Irkutsk oblast, Bodaibinskii district) and near its base, the initial period of the formation of the crater can be dated back to the late ¹⁵th‒early ¹⁶th centuries. In 1841‒1842, the trees under investigation recorded in annual rings a catastrophic event which caused a disturbance to their root systems, damage to tree stems, and the formation of compression wood. It is obvious that the event is associated with the time of formation of the late stage ring swell on which sparse larch trees are 93‒101 years of age, and on the central mound emerging upon completion of the formation of the Patom crater the age of the oldest tree is 7 years. Thus dendrochronological investigations confirm a long-lasting and multievent formation of the Patoma crater. In some periods, the deposition cone was evolving with a different intensity, sometime showing an explosive character. X-ray fluorescent analysis revealed a double Sr enrichment of larch wood at the time of significant activity of crater formation (1852‒1859) when plutonic fluids from the igneous source were able to enter the upper horizons of the Earth’s crust at the time of magma intrusion into water-containing rocks. The fluids were enriched with CO₂ and transported significant amounts of Sr, as a result of which the ⁸⁷Sr/⁸⁶Sr ratios in carbonate and terrigenous rocks assumed higher values in sandstone and schists on the early stage ring swell of the Patoma crater. The findings, coupled with geological data, suggest that the Patom crater emerged as a result of a phreatic explosion that occurred either at the time of magma intrusion into water-containing rocks or as a consequence of the fault and decompression of heated water-containing rocks.

中文翻译：

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原子弹陨石坑的时代：树木年代学和生物地球化学研究

摘要

根据在Patom火山口（Bodaibinskii区伊尔库茨克州）及其附近生长的落叶松树木的树轮年代学调查数据，火山口形成的最初时期可以追溯到¹⁵年代末至¹⁶年代初几个世纪。在1841-1842年间，被调查的树木在年轮中记录了一场灾难性事件，该事件导致其根系受到干扰，树茎受到破坏以及压缩木材的形成。很明显，该事件与晚期环形隆起的形成时间有关，稀疏的落叶松树年龄在93‒101岁，而在中央丘形成时，Patom火山口的形成已经结束。最老的树是7年。因此，树轮年代学研究证实了Patoma火山口的长期形成和多事件形成。在某些时期，沉积锥以不同的强度演化，有时表现出爆炸性。X射线荧光分析显示，火山岩形成的大量活动（1852‒1859）时，火成岩来源的深熔流体能够进入岩浆形成的地壳上层，从而使落叶松木材具有双重Sr富集作用。侵入含水岩石。流体富含一氧化碳₂和运移了大量的Sr，其结果是碳酸盐岩和陆源岩中⁸⁷ Sr / ⁸⁶ Sr的比值在Patoma火山口的早期环形隆升中的砂岩和片岩中具有较高的值。这些发现以及地质数据表明，Patom火山口的出现是由于岩浆侵入含水岩时发生的潜水爆炸或加热的含水岩的断层和减压造成的。 。