The objective of this project is about a kinematic analysis of a shear zone, specifically a graben structure. The surface of the study area has also been investigated, this is to understand if a faulting reactivation has occurred due to glacial impact. The graben structure is exposed along a road cut, next to the E18 highway at Ekolsund, 14km east of Enköping. The results of the report are based on field studies of the geometrical relationship pattern of fracture planes, relative displacement along fracture and a kinematic analysis of movements along fractures. A high resolution terrain model was acquired in the analyzing of the graben structure formation and to create a geometrical 3D brittle deformation model. This model was applied to reconstruct the deformation process. The area contains a more than 1,1km long dextral NE-trending strike-slip fault feature in a polydeformed Precambrian bedrock. The fault is connected NE to one of the regional structure that delimits the bedrock blocks. The fault is visible both as a topographical feature from the ground and from aerial photos. While the project followed through it was clear that the area had been subjected to reactivation. The evidence for this claim stems from an observed semivertical fracture plane with conjugating subhorizontal striations markers that contain an alternating plunge and trend. Other evidence for a reactivation scenario is the fault gouges that contain horizontal striation as well as steep plunging striation, indicating a dip-slip faulting movement. The main zone of faulting displays lower altitude than the surrounding rock. This indicates an asymmetric graben structure that has been subjected to polydeformation. When analyzing the results, it is concluded that a pull-apart basin event has occurred. It’s highly possibly that it has been undergoing modifications during its geological history, resulting in a polydeformed reactivation of the minor faults outlining the graben structure. / Syftet med denna studie är att utföra en kinematisk analys av en förkastningszon, speciellt där en mindre graben struktur utbildats. Ytan för det studerade området är även det viktigt, det är för att förstå ifall en förkastningsreaktivering har skett i och med en glacial påverkan. Graben strukturen är blottad längs en vägskärning, utmed E18 vid Ekolsund, 14km österut om Enköping. Resultatet av rapporten är baserat på fältstudier med fokus på geometriska relationsmönster hos sprickplan, relativa förskjutningar längs sprickor och en kinematisk analys av rörelser längs sprickor. En högupplöst terrängmodell var erhållen vid analys av grabenstrukturens formation och för att skapa en 3D sprödtektonisk deformationsmodell. Modellen var tillämpad vid rekonstruering av deformationsprocessen. Området innefattar en mer än 1,1km lång dextral NO-orienterad strike-slip förkastning i en polydeformerad Prekambrisk berggrund. Förkastningen är ansluten NO till en av de regionala strukturerna som begränsar berggrundsblocken. Förkastningen är synlig både på marknivå och från flygfoton. Medan projektet fortlöpte blev det tydligare att området blivit utsatt för en reaktivering. Beläggen för detta påstående grundar sig i de observerade semi-vertikala sprickplanen med konjugerande subhorisontala striationer som har alternerande stupning och trend. Andra belägg för ett reaktiveringsscenario är de fault gouge strukturerna som innehåller horisontala striationer såväl som stupande striationer, vilket indikerar på en dip-slip förkastningsrörelse. Huvudzonen av förkastningen uppvisar lägre altitud än kringliggande bergyta. Det här indikerar en asymmetrisk graben struktur som har utsatts för polydeformation. Vid analys av resultatet, så kan det sammanfattas att en pull-apart basin förkastning har inträffat. Däremot är det mycket möjligt att zonen har undergått fler modifikationer under dess geologiska historia, vilket har resulterat i en polydeformerad reaktivering av mindre förkastningar som gett kontur dragen åt graben strukturen.

>Magister Scientiae - MSc / The thesis provides a study into the main structural features of the Namaqua Region and their relation to the intrusion of the Keimoes Suite. This was achieved by producing a digitized map of the Namaqua Region structural framework using a LandSAT image and MOVE software for remote sensing. The structural framework showed an array of shear zones and fault systems which trend in a NW-SE direction. The validation of the sense of movement, location and orientation of the shear zones was done by field mapping. The general orientation of all shear zones was NW-SE. The sense of movement along the Neusspruit, Boven Rugzeer and Trooilapspan shear zones was found to be dextral strike slip movement and the Cnydas shear zone had a sinistral strike slip movement. The location of the shear zones were determined by analyzing the deviation in general foliation trend which was visualized using Rose Diagrams. The field data and the remote sensing were found to agree with the transpressive environment of the Namaqua Region. The oblique collision of the Namaqua-Natal crustal block with the Kaapvaal Craton during the orogenic event at ~1.2 Ga created a compressionalgeotectonic setting which allowed for the intrusion of the early to late syn-tectonic Keimoes Suite granites. The lateral escape of the Namaqua-Natal crustal block took place along the western margin of the Kaapvaal Craton. This was brought on by prolonged compression which resulted in the formation of a releasing bend in the Namaqua Region. This releasing bend produced the negative flower structure with dextral shear zones which facilitated the intrusion of the post-tectonic Keimoes Suite granites.

This study presents numerical modeling of geologic processes based on Discrete Element Method (DEM), including modeling of pull-apart basin development based on Particle Flow Code (PFC) and simulation of deformation and earthquake potential of Ordos Block (China) under present tectonic stress regime based on Universal Distinct Element Code (UDEC). A scale-independent modeling approach based on PFC2D has been established to simulate the development of pull-apart basins. The micro-scale PFC models are used to investigate crack propagation and basin development in releasing sidestep systems with pure strike-slip, transtensional, and transpressional master faults, respectively. In each system, three typical models including 30° underlapping, 90° non-overlapping, and 150° overlapping releasing sidesteps are chosen. The modeling results are compared with pull-apart basins in nature. The geometric differences of pull-apart basins result from both the initial strike-slip fault geometries and its various evolution stages. Rhomboidal basins which have larger basin length than the amount of motion form in overlapping systems and do not progress through the spindle-shaped and lazy-Z-shaped stages such as the Dead Sea basin. Rhomboidal basins with cross-basin faults tend to form in underlapping systems. Finally, the origin of rhomboidal pull-apart basins, depocenters of pull-apart basins, cross-basin faults and their significances, models for pull-apart basin development, and minimum displacements and ages to form pull-apart basins are discussed. A two-dimensional UDEC model involving Ordos Block and adjacent areas is set up. Boundary conditions based on present tectonic regime are assumed. Block rotations, shear stress and displacement on faults, ratio of shear to normal force are simulated. Slip tendency which represents the assessment of the potential for causing slip on individual faults and earthquake-prone of the faults is predicted. Modeling results are compared with geologic evidences.