GEODYNAMICS OF THE PAMIRS—HIMALAYA REGION

GEODYNAMICS OF THE PAMIRS—HIMALAYA REGION

Geodynamics of the Pamirs-Himalaya Region

The Pamirs—Himalaya region possessing a complex tectonic structure and high seismic activity is located at the central part of the Alpine—Himalayan fold belt. During long|term geodynamical studies we revealed new features of its modern structural plan steadily traced at different deep levels. The reconstruction of paleostresses by analyzing fracture patterns of Mesozoic—Cenozoic sedimentary rocks has been carried out in order to establish geodynamic regularities of the region under study and to propose a model of its development. Unlike traditional approaches to the problem of paleostress reconstruction from orientation of systems of rock joints, approaches which are based usually on the local strength criteria, we consider the formation of joint sets as a rheological instability manifesting in localized form. The systems of layers of localized plastic deformation are formed during lithification of sedimentary rocks and evolve with time into joint sets. The corresponding method of reconstruction of paleostress axes was developed. It was tested for some tectonically active regions: Central Asia, the Caucasus, the Crimea, Cuba, Iran, and others. The method was found to be useful for reconstruction of both history and spatial distribution of paleostress axes in active crustal blocks and near large geological structures. In the Pamirs—Himalaya region the fracturing of rocks has been investigated in about 1000 outcrops. By analyzing the Mesozoic—Cenozoic paleostress history it was confirmed that the structural features of the region (including an arc|like shape of the Pamirs—Tian Shan junction zone) are caused by movement of the Hindustan mobile plate towards the rather stable Eurasian plate during the Alpine cycle of development.