Structural Analysis and Tectonic Interpretation of Brittle Failure Structures at Perat Anticline – NE Iraq
Iraqi National Journal of Earth Sciences,
2012, Volume 12, Issue 2, Pages 17-42
AbstractPerat anticline is located about 100 km. northeast Mosul city. It extends
NW-SE for about 35 km through high folded zone of the foreland fold belt of the Zagros collision zone.
Joints were classified into sets and systems according to their relations with three mutually perpendicular tectonic axes. Tension sets are ac and bc, the first one formed by extension along fold axis accompanying direct compression perpendicular to fold trend, whereas the second is the product of relaxation that succeeded the primary compression. The shear systems are hko, hol and okl developed successively during direct compression and subsequent relaxation episodes of each tectonic pulse.
Planar calcite veins occupying ac, bc and hko joint sets and systems are also prevalent in the study area. Furthermore, singular and conjugate enechelon lenticular vein arrays are displayed within some carbonate units of study area. They enclose acute angles either with a or b tectonic axes indicating that they have been formed under two alternating stress regimes. The maximum horizontal compressive stress axis was perpendicular and parallel to the fold axis in the first and second regimes respectively.
The planar and lenticular vein arrays are associated with two orthogonal pressure solution sets (stylolite seams). The peaks of them refer also to the mentioned directions of the maximum horizontal compressive stress. The juxtaposition of these two brittle structure types reflects their kinematic interrelation and hence non-dilation deformation type.
Paleostress analysis of mesofaults falls into compressive, extensional and strike slip states. σ1 axis of compressive and strike slip states lies in normal and parallel orientations with respected fold axis. Whereas σ3 axis of extensional state lies normally to the same fold axis. This state seems compatible with the final uplift of the fold which supplemented also by development of bedding parallel stylolite seams with vertically pointing peaks.
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