Home – Home – Jornals – Geography and Natural Resources 2020 number 4

According to data of dendrochronological investigations of larch trees that had grown on the Patoma 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 15 ^th - early 16 ^th 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 a late circular wall on which sparse larch trees are 93-101 years of age, and on the middle mound emerging upon completion of the formation of the Patoma crater the age of the oldest tree is 71 years. Thus den drochronological investigations confirm a long-lasting and multievent formation of the Patoma crater. In some periods, the de position 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 ⁸⁷ Sr/ ⁸⁶ Sr ratios in carbonate and terrigenous rocks assumed higher values in sandstone and slatestone on the early circular wall of the Patoma crater. The findings, coupled with geological data, suggest that the Patoma crater emerged as a result of a phreatic explosion that occurred either at the time of magma intrusion into water-containing rocks or s a consequence of the fault and decompression of heater water-containing rocks.