Keywords : Joints

Structural and Tectonic Study of Brifka Anticline, Northern Iraq

Mahmood A. H. Al-Sumaidaie; Nabeel K. Al-Azzawi

Iraqi National Journal of Earth Science, 2018, Volume 18, Issue 1, Pages 29-58
DOI: 10.33899/earth.2018.159278

A structural and tectonic study was carried out in the area between Baikher and Shaikhan anticlines. It is revealed that the main distinct structural feature is an anticline extending 16 Km northwest – southeasterly obeying the Zagros Range trend. This anticline with 6 km width and 16 km length called Brifka Anticline.
Several geologic formations are exposed in the studied area, ranging in time span from the Paleocene to Miocene periods. These formations are Kolosh, Khurmala, Gercus, Avanah and Pila Spi where Kolosh represented the core and Pila Spi makes the carapace of the anticline.
The geometrical analysis of this fold along four selected traverses revealed that the anticline is asymmetrical, mostly overturned and verged towards southwest, except in the fourth traverse it is appeared verging towards south. The anticline axis is oriented northwest -southeasterly in the first three traverses whereas it trended towards east- west in the fourth one.
The study included the vertical investigation of fold style of folded formations. It appeared that the anticline axis in Pila Spi Fn. is slightly changed from that of Kolosh Fn. in the first and forth traverses, whereas it changed anti clockwise 11-16° from Kolosh to Pila Spi formations in the second and third traverses.
The present study showed that the systems okl>c and hol>c are the most dominant joints in the first three traverses whereas hko>a system and ac set are abundant in the fourth traverse. It also revealed that the system hko>a are more abundance than hko>b system which indicate that the compression phase was tensive than the alternative tension.
Faults were investigated by field work and satellite image interpretation. It revealed three strike-slip faults inclined to the fold axis. They are BF1, BF2 and Besary faults. Another fault was concluded from the geometric properties and vergency of Brifka anticline. It is a foreland listric fault. This was followed by the determination of the formation thicknesses in order to conclude the sense of displacement of this fault. The determination appeared that the thicker sediments are in the area of the southwestern limb reflecting that the fault is reactivated as reverse foreland listric fault.(.