Impactite Generation in the El'gygytgyn Depression,Northeast Russia, as a Volcanic Phenomenon.1. The Geology and Age of Impactites

摘要

The El'gygytgyn depression structure consists of two elements, an older, larger depression (El'gygytgyn- 1) and a younger depression (Elgygytgyn-2) that is embedded eccentrically within it and contains the present-day Lake Ergygytgyn. The section of lake bottom sediments revealed by seismoacoustic surveys [18] is summarized. The upper stratified complex of bottom deposits, hence that of the lake depression, seems to have originated 2.6 million years ago, while the impactites are found to date back to the time interval between the end of the Late Miocene to Early Pliocene (about 2 million years). The impactites can be separated into a dacite-rhyolite (dominant) and basalt-andesitic (<= 1%) group. Those in the dacite—rhyolite group formed in the following order: impact ignimbrite to pumice to cinder to massive glass. It is shown that each impactite occurrence has its own rock associations, chemical composition, and age. The sculpture of fragments of massive impact glasses found at different distances from the geometric center of the El'gygytgyn depression (the hypothetical location of a meteorite fall [9]) rule out the possibility of their propagation from a single center, but is in agreement with the concept of individual local centers of impactite generation. It thus appears that all the features as described above are entirely in disagreement with the meteorite hypothesis for the origin of the Ergygytgyn depression and related impactites..