Orogenic Evolution of the Pamir Mountains

Abstract

This dissertation consists of two parts, the first focused on the Pamir orogenic system and the second focused on the use of petrology to understand tectonic processes more generally. The Pamir Mountains are located at the western end of the Tibetan Plateau and are part of the Alpine-Himalayan orogenic belt. The Pamir has evolved from a Cordilleran-style orogen during the Mesozoic into a continent-continent collisional orogen during the Cenozoic. The examination of the Pamir Mountains takes an orogenic systems approach and investigates the foreland basin system, the retro- fold and thrust belt, the orogenic plateau hinterland, and the magmatic arc in the Pamir. Methods of analysis include structural geology, geochronology, thermochronology, petrology, geochemistry, sedimentology, stratigraphy, and numerical modeling, Tectonic processes and phenomena investigated include; intracontinental subduction, lithospheric delamination, crustal shortening, low-angle subduction, thrust belt evolution, subduction rollback, crustal anatexis, mantle drips, hinterland extension, high-flux events, crustal assimilation, syntectonic sedimentation, decoupled upper-lower crustal deformation, foreland basin sedimentation, subsidence dynamics, and sediment routing. The second part of the dissertation is focused on convergent orogenic systems more broadly and the development of petrologic and geochemical methods for interpreting tectonic processes. Igneous rocks and accessory minerals are studied, focusing on major and trace elements, radiogenic isotopic systems, and stable isotopic systems. Specific methods investigated include; geochemical proxies for crustal thickness, relating zircon element concentrations to whole rock compositions, interpreting the origin of spatial and temporal trends in radiogenic isotopic data, estimating mantle melt source regions, and the role of crustal assimilation in continental arcs.