Abstract
The article presents a systematic review of the available tectonophysical data on the state of crustal uplifts and basins in intracontinental orogens. Based on results of the tectonophysical analysis of data on earthquake focal mechanisms for the Altai-Sayan and Northern Tien Shan regions, it is established that in many cases the crust in the basins and uplifts has antipodal structures, considering various types of the state of stresses. In the crust of the uplifts, maximum compression axes are usually sub-horizontal; in the crust of the basins, only the axis of the principal stress of minimum compression (i.e. maximum deviatoric extension) is sub-horizontal. These observations correlate well with estimations of deformations on the surface of the crust on the basis of the GPS-geodesy data, as well as with stress measurements taken directly on mining sites. The antipodal structures and physical fields in the crust of the uplifts and basins are not a random phenomenon. This suggests a common mechanism of deformation at the stage of active formation of the uplifts and basins. However, results of a similar tectonophysical analysis performed for the crust of the Pamir plateau and Tibet show that minimum compression stresses are subhorizontal in these regions, and the geodynamic type of the state of stresses is determined as horizontal extension or horizontal shearing. This pattern contrasts sharply with the type of the state of stresses of horizontal compression in the crust of the mountain ranges around the plateau (the Himalayas, Kunlun, Tsilian Shan, Hindu Kush), as well as with the state of stresses of active orogenic structures of the Tien Shan and Altai-Sayan regions. Based on the stress values estimated for a range of geodynamic types of the state of stresses, it is estimated that additional compression stresses of the order of 5.4 kbar are required for the transition from horizontal extension to horizontal compression. If the regional strain rates currently recorded by the GPS-geodesy are taken into account, such additional stresses need to be applied for about 10 million years to fulfill the transition.
Highlights
Results of a similar tectonophysical analysis performed for the crust of the Pamir plateau and Tibet show that minimum compression stresses are sub-horizontal in these regions, and the geodynamic type of the state of stresses is determined as horizontal extension or horizontal shearing
This pattern contrasts sharply with the type of the state of stresses of horizontal compression in the crust of the mountain ranges around the plateau, as well as with the state of stresses of active orogenic structures of the Tien Shan and Altai-Sayan folded region before the Chuya (Altai)-Sayan regions
Based on the stress values estimated for a range of geodynamic types of the state of stresses, it is estimated that additional compression stresses of the order of 5.4 kbar are required for the transition from horizontal extension to horizontal compression
Summary
Целью настоящей работы является изучение механизмов генерации напряжений, действующих в континентальной коре в областях орогенов. Гзовского [Gzovsky, 1975], выяснение параметров напряженного состояния и механизмов их генерации в коре является основной обратной задачей тектонофизики. Установление условий нагружения и деформирования литосферы внутриконтинентальных орогенов, определяющих особенности морфологического строения и физических свойств пород коры горно-складчатых областей, является обратной задачей геодинамики [Leonov, 1995, 2009], тектонофизика при этом рассматривается как важнейший инструмент исследований. Увеличивая спектр сопоставляемых параметров, можно уменьшить число модельных вариантов условий нагружения и свойств геологического объекта, дающих результаты, близкие к природному объекту. Что подобные данные невозможно получить для всего исследуемого трехмерного участка коры, а также на то, что эти напряжения всегда являются средними для некоторых частей его объема, именно данные о напряженном состоянии коры следует рассматривать как критически необходимые при решении подобных задач. Продолжением этих работ также являлись исследования современного напряженного состояния коры Тибета, Памира и Гималаев – Высокая Азия (ВА) [Rebetsky, Alekseev, 2014]. Будем также различать горные поднятия, имеющие форму хребтов (резко выраженный градиент поверхности), и поднятия в виде нагорья и плато (плоская форма)
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