TECTONIC EVOLUTION OF THE HIMALAYAN OROGEN AND THE AFGHANISTAN-PAKISTAN SYNTAXIS

The US Geological Survey has been working with the Afghanistan Geological Survey on several geologic issues such as: earthquake hazards, mineral resource assessments, oil and gas exploration, and hydrology. The geologic history and tectonic evolution of the region is relevant to all of these topics. The India-Eurasia collision and the closing of the Tethys Ocean have created an immense, active orogen that includes much of Afghanistan. This collisional orogen has resulted in the formation of the complex Afghanistan-Pakistan syntaxis on the western flank of the main Himalayan mountain belt. We summarize the regional tectonics of the area, from 300 Ma to the present, including: the formation of the Tethys Ocean, the closing of the Tethys, the initial collision between India and Eurasia about 40 to 50 Ma, and present-day subduction and mountain building processes. We present cross-sections illustrating the timing of the several distinct terrane collisions and the migration of the thrust fronts along the main Himalayan arc. In addition, the more complex tectonic evolution of the Afghanistan-Pakistan syntaxis region is analyzed, emphasizing plate rotation and oblique convergence along the Chaman fault, generating transpressional tectonics. The metamorphism associated with the collision is also examined with a particular interest in the contrasts between metamorphic grades present in the syntaxis region versus the main Himalayan belt. This information will prove beneficial in the education of Afghan scientists for a better understanding of the origin and significance of the more pertinent economic and hazard geology topics.