Alexander Strom

Title : Geomorphic evidence of the tectonic delamination of the upper crust in central Tien Shan

Abstract:

Concept of the tectonic delamination of the lithosphere according to which its upper and lower “layers” can deform in different ways being divided by the detachment or zone of plastic deformations is based, mainly, on the regional geological, geophysical and seismological data. Additional geomorphic evidence supporting this neotectonic concept were found in Central Tien Shan, in Kyrgyzstan, on top of the ridges passing north from the so-called Minkush-Kokomeren neotectonic depression. The latter is a narrow basin about 120 km long and 1-8 km wide stretching in the East-West direction and composed of the deformed Neogene sediments. It is bounded by reverse faults both from North and South that divide Neogene red beds from the Proterozoic and Paleozoic rocks. Practically any ridge composed of these basement rocks represent neotectonic anticline. The most impressive landform is located on the crest of the Santash anticlinal ridge. It is a subrounded caldera-like cavity 3×2 km in size and up to 700 m deep with steep walls cross-cutting minor erosional landforms. According to the geological observations it originated as closed depression, which southern wall was dissected subsequently due to back erosion of the Kyzylkiol creek. Amount of rocks that “disappeared” in the ridge interior during its formation is ca. 3 km³. One more, much smaller (about 100 million m³), and less impressive landform – the Djuzumdy cavity, likely of similar origin, was identified about 35 km west from the Kyzylkiol cavity, at the axial part of the ridge composed of Paleozoic granites. Formation of such cavities can be explained neither by volcanic processes, nor by karst, not by pull-apart tectonic depression. It was hypothesized that they were formed at the final stage of tectonic warping of the uppermost “layer” of the delaminated upper crust separated from the rigid lower “layer” by nearly horizontal detachment towards which listric reverse faults widely developed in this part of the Tien Shan flatted out. Neotectonic folding produced by laterally directed stress caused upward warping of the upper crustal “layer” and creation of voluminous “tectonic cavern” in the anticline cores. Parts of the anticline crests above these caverns collapse forming caldera-like cavities. The proposed model, despite its exoticism, explained the whole set of the observable geomorphic and geological evidence of the study sites.
Audience Takeaway:

• Presentation links detailed geomorphic observations with regional neotectonic processes.
• It highlights the necessity to analyze the observable landforms and geological outcrops in theine entire complexity that is important for better understanding of various natural phenomena.

Biography:

Graduated from the Geological department of Moscow State University in 1975. Got PhD in 1999 in the Institute of Physics of Earth and Dr. habil. in Moscow State University in 2022.

Chief expert of the Geodynamics Research Center – branch of JSC "Hydroproject Institute", Moscow, Russia; Deputy head of seismic hazard assessment department, Russian Geotechnical Institute LLC, Visiting professor in SKLGP, Chengdu, China.

Member of Russian group of the IAEG and of the JTC1; Associate Editor of "Landslides"; Member of the Editorial board of the “Geoenvironmental Disasters” and “Georisk” Journals.

Studied large rockslides and performed field paleoseismological and seismotectonic investigations in the Tien Shan, Pamirs, Garhwal Himalayas, Great Caucasus, Western and Eastern Sayan mountains, Far East of Russia, Sakhalin, Mongolia and Northern Sudan. Translated in Russian the second edition of "Paleoseismology" and organized its publication in Russia. Worked as a deputy Chief editor of Seismic zoning map of Russia.

Collected the world-wide data base on seismic surface ruptures and studied hazards associated with active fault that cross trunk pipelines in Sakhalin and in Eastern Siberia.

Performed detail studies of morphological and structural features typical of rock slides and rock avalanches in the Central Asia region, Caucasus and other mountainous regions. Since 2006 have organized annual field training course on Rockslides and related phenomena in Kyrgyzstan. Compiled the database of large-scale rockslides in the Central Asia region and wrote a book “Rockslides and rock avalanches of Central Asia” published by Elsevier in 2018. Published more than 150 papers and book chapters in Russian and International journals and books. Participated in compilation od several standards and construction codes in Russia.