Tectonic Evolution of the Zagros Suture-and Imbricate Zones in Iraq

Sammanfattning: Orogenic belts are expressions of tectonic activity, often host various natural resources (e.g. petroleum and minerals reserves), and influence the society and environment through hazards (e.g. landslides, earthquakes), climate and cultural divides. The Alpine-Himalayan system is one of the most important orogenic belts in the world with regards to all these aspects. The Zagros Fold-and-Thrust Belt is a part of the central Alpine-Himalayan system, where a wealth of natural resources have been found, including one of the largest petroleum reserves in the world, and many mineral deposits.This thesis focuses on the Imbricate- and Suture zones of the Zagros Fold- and Thrust Belt in Iraq. Research activities here have been limited, mainly due to the apparent relative depletion in natural resources and because of geopolitical security issues.The study area consists of rock masses that have formed as the result of convergence between the Arabian and Eurasian plates from the Late Cretaceous to the present day. Bedrock comprise alternating sequences of Mesozoic siliciclastic and carbonaceous rocks. It is a key area to study ongoing continental collision.The objective of this thesis is to improve the knowledge of the crustal architecture of this relatively unknown part of the Zagros Fold- and Thrust Belt. The results form a basis for future natural resources exploration.The thesis work consists of a local desk study of alluvial fans using remote sensing data (Landsat 8, Operation Land Imager satellite data and Digital Elevation Model), and two seasons of structural geological field work along regional traverses. The study area of field work is 1800 km2 large. The results were subsequently incorporated into a 3D structural framework model in the software Move of Petroleum Experts, Edinburgh, UK (version 2019.1).Remote sensing and GIS techniques were used to analyze neotectonic activity of alluvial fans.  Their formation and morphology are influenced by subsurface faulting. Results indicate the location of active faults, and allowed their extrapolation along strike.The aim of field work is to constrain the tectonic history of the area. Structural data were collected from six traverses, varying in length from 4.4 to 25.0 km, using a combination of digital and traditional methods. Based on the style and geometry of the mesoscale folds, buckling is suggested as the dominant mechanism for folding, where flexural slip folding has been followed by shear folding. I have estimated the amount of internal crustal shortening using Ramsey’s equation: Most intense shortening observed close to the Suture zone (~60%). The amount of shortening is about 10% less in the Imbricate zone (~50%).Based on the results above, 3D geological models have constructed. They reveal the structural styles and role of pre-existing faults, and their influence on the crustal architecture of the area. These models act as a base for potential natural resource explorations activities. The structural evolution of thrust sheets within the study area occur as a piggyback sequence. The structural style of the Suture zone is characterized by three main thrust sheets, that are subparallel with the NW-SE striking and NE dipping Main Zagros Fault.The structural framework of the 3D geological models presented in this thesis are derived purely from surface data (field work, remote sensing), and represents the state of art. At this stage, there are no clear candidates for future natural resources exploration. In order to advance the 3D geological models, subsurface data are required, such as seismic and borehole data. These type of data will provide better constraints at depth, which may be key for finding prospects for exploration within the Imbricate and Suture zones.

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