Orogenic evolution of the Zagros mountains




Barber, Douglas Edward

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This dissertation addresses the Phanerozoic tectonic and paleogeographic evolution of the Zagros orogenic belt. The Zagros formed due to multiple deformation events affiliated with the opening and closure of the Neotethys ocean, serving as the Middle Eastern link between the European and Asian segments of the Alpine-Himalayan belt. The first chapter of this dissertation introduces the main tectonic problems and motivational questions addressed by this research, and provides additional background information. The remaining chapters can be divided into two sections. The first topical section of this dissertation includes four chapters primarily focusing on the timing and controls of deformation patterns and stratigraphic evolution during the Arabia-Eurasia collision. These studies apply an orogenic-systems approach involving integrated assessment of the fold thrust belt, orogenic plateau hinterland, foreland basin system, and subduction-related metamorphic rocks in the Zagros. Multiple low-temperature thermochronometric and thermal modeling techniques are used to evaluate Cenozoic spatiotemporal exhumation history across its hinterland and fold-thrust belt regions. High-temperature apatite and rutile U-Pb thermochronometers are combined with Ti-in-Quartz thermometry to reveal the timing and nature of lower-crustal metamorphism and subduction exhumation affiliated with the onset of Arabia-Eurasia collision. The foreland basin stratigraphic and drainage response to Zagros orogenesis is evaluated by integrated sedimentologic analysis, tectonic subsidence modeling, and detrital multi-mineral geo-thermochronometry and geochemistry. Depositional ages of these units are constrained by Sr-isotope analysis combined with detrital multi-mineral geo-thermochronometry. In these chapters, we investigate key concepts during Zagros orogenic development including crustal shortening, continental underthrusting, structural inheritance, magmatic evolution, tectonic-climatic interactions, controls on foreland basin evolution, plateau growth, subduction exhumation, and far-field tectonic linkages. The second part of this dissertation includes two chapters pertaining to the pre-Zagros paleogeography and accretionary history of tectonic sub-units that now form central components of the Zagros orogen and Turkish-Iranian plateau. Previous models regarding the origin and paleogeographic evolution of the Sanandaj-Sirjan Zone (the igneous-metamorphic core of the Iranian Zagros) are evaluated using detrital zircon U-Pb and trace-elemental provenance analysis. We also examine the timing and nature of Late Cretaceous Proto-Zagros collisional event in N Arabia by novel multi-mineral isotopic and trace-elemental analyses of its foreland basin sedimentary record. Overall, this dissertation contributes to the tectonic understanding of Arabia-Eurasia collisional zone, and has potential broader implications for collisional orogenic systems and methodological approaches to detrital multi-mineral provenance and chronostratigraphy techniques.


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