Abstract
Joints are among the most widespread geologic structures as they are found in most each exposure of rock. They differ greatly in appearance, dimensions, and arrangement, besides they occur in quite different tectonic environments. This study is important because joints provide evidence on what kind of stress produced them (history of deformation) and also because they change the characteristics of the rocks in which they occur. The Measured data of joints from the studied area which are located in the high folded zone – Northeast of Iraq, were classified according to their relationship with the tectonic axes by projecting them stereographically using Schmidt net in GEOrient ver.9.5.0 software. The joint systems revealed the orientation of the major stress field that caused the area deformation. Two dominant joint systems were found in most stations of the studied area, which are hko>a (first place) and hko>b (second place). The main stress field direction from the joint’s classification is North East – South West which coincides with the opening of the red sea and the collision between Arabian and Iranian tectonic plates. The North West direction (which comes in the second place) it might be due to the rotational movement (counterclockwise) of the Arabian plate in addition to the effect of local stress in the area.
Highlights
The most common geological structures that are created in the upper crust are joints (Weinberger, et al; 2010)
The main jointing mechanisms are reactions of the host rock to a regional or local stress field, influence of pore pressure and hydro-fracturing, stress relaxation due to rock uplift, and/or jointing due to material shrinking (Engelder, 1985 and Bahat et al, 2005). They can be classified according to the basis of origin into: 1- Shear Joints: Joints caused by shear stresses. 2- Tension Joints: Joints that resulted from extensional stresses. 3- Columnar Joints
These joints are formed in igneous rocks that are formed during the cooling of lava when it derives out of the earth in a melted state
Summary
The most common geological structures that are created in the upper crust are joints (Weinberger, et al; 2010). Any thin natural planar crack that is not a fault, bedding, or cleavage and is larger than the grain size of the rock is a joint in the broadest sense of the word; Most Joints show no observable displacement parallel to their walls and are not developing faults, as can be seen by correlating details of the rock across the fracture (Suppe, 1985) They profoundly control the shape of many spectacular landforms, and play an important role in the sub-surface transport of fluids such as water and hydrocarbons (Pollard and Aydin, 1988; Gross and Eyal, 2007). The study aims to analyze the fracture yield with the folding and to determine the direction of forces that caused it
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