Main Subjects : Ductile deformation

Inferred Inversely Reactivated Listric Fault at Chia Gara Anticline, Northern Iraq

Ibrahim Aljumaily; Nazar Abdullah

Iraqi National Journal of Earth Science, 2019, Volume 19, Issue 2, Pages 11-25
DOI: 10.33899/earth.2019.170280

Chia Gara anticline is an E-W extending doubly plunged fold, parallel to the Taurus Mountains having about (80) km length and (12) km width. It is located within the high folded zone of northern Iraq. The exposed rocks range in age from Late Triassic to Late Miocene. Structural analysis of the anticline performed through three traverses transverse to the general fold trend from western plunge zone towards east. Geometrical analysis of fold elements shows that Chia Gara anticline is asymmetrical vergingtowards north in both first and third traverses, whereas it is more or less symmetrical in the second traverse. Meanwhile, results of Fourier analysis demonstrates that the fold form is more developed in the northern limb of the anticline than in its southern limb, in the first and third traverses. Nevertheless, in the second traverse, the fold form seems more developed in the southern limb compared with the northern limb. The northern vergence of the anticline and its advance development in northern limb in the first and third traverses may reflect the impact of a suture vergent reversely slipped listric fault beneath the anticline sectors in these traverses. However, the obscure of such listric fault in the second traverse may be due to the effect of a sinistral (BF1) and a dextral (BF2) subsurface strike-slip faults transverse to the trend of Chia Gara anticline on either side of the second traverse. The surface expressions of them, as well as others like Zewa and Deralok faults (dextral) are evident in satellite image of the area. The southward pushing of the wedge between (BF1) and (BF2) had opposed the northward reverse displacement of the proposed listric fault beneath thesecond traverse. The effects of these strike-slip faults (BF1) and (BF2) are evident also in anticlockwise deflection of both axial plane and fold axis attitudes from first to the second traverse, and vice versa from second to the third traverse.

The Structural Development of Folds Shapes in the Western Zagros Fold/Thrust Belt of Iraq Using Fourier Analysis

Nabeel Al-Azzawi; Nazar Numan

Iraqi National Journal of Earth Science, 2019, Volume 19, Issue 2, Pages 26-41
DOI: 10.33899/earth.2019.170283

Depending upon the geometrical shapes of the fold profiles, the Western Zagros Fold/ Thrust Belt of Iraq has been subdivided into different geometrically distinctive and genetically significant four sectors using Fourier ratios suggested by Hudleston classification. Furthermore, the same belt has been subdivided into eight sectors using Singh and Gairola's classification. The sector names of the former are chevronic–sinusoidal, sinusoidal–parabolic, parabolic–semi elliptical and semi elliptical–box fold styles. Whereas in the later division, the sectors are almost chevronic, chevronic–sinusoidal, almost sinusoidal, sinusoidal–parabolic, almost parabolic, parabolic–semi elliptical, almost semi elliptical and semi elliptical–box fold styles.
         The investigation involves harmonic analysis (Fourier analysis) of the fold profiles by solving Fourier equations using the Gauss elimination method, determination of Fourier coefficients and Fourier ratios for forty major anticline structures that cover fairly evenly the Western Zagros Fold/ Thrust region. The procedure of harmonic analysis is carried out with FOLDN, a GWBASIC program written for this purpose. Fourier ratios are utilized for distinguishing different types of fold shapes.
         In general, the map of these sectors shows that the folds become progressively more developed in shape towards the north and northeast. The arrangement of the obtained fold sectors in the studied area, matches the folds initiated first near the Alpine Suture and with time, they propagated south and southwestward across the axis of orogeny. In addition, probably the process is still going on.

Structural and Tectonic Study of Qara Sard Anticline and Choplagh Syncline, from Sulaimaniya Area, Kurdistan Region, Northeastern Iraq

Saddam Al-khatony; Nabeel Al-Azzawi; Fadhil Lawa

Iraqi National Journal of Earth Science, 2019, Volume 19, Issue 1, Pages 39-58
DOI: 10.33899/earth.2019.170270

The study of the structural geology and tectonics of Qara Sard anticline and Goblagh syncline is carried out within the northwestern part of Zagros Fold-Thrust Belt (ZFTB) in Sulaimaniya area, Kurdistan region, Iraq. Qamchuqa Formation (Early Cretaceous) builds up the core of the anticline and overlain by Kometan, Shiranish and Tanjero formations (Late Cretaceous). Moreover, Khalakan Formation overlies Kometan Formation on the northeastern limb of the anticline. Tanjero Formation appears at the core of Choplaghsyncline. The structural geometrical analyses of seven traverses (P) cutting across the anticline and the syncline, revealed that the two folds are double plunging, and asymmetrical in all traverses except in P5 and P6 in Qara Sard anticline. Both folds are verging toward northeast; however, the anticline verges toward southwest and being vertical in P4 and P5 respectively. The geometrical analysis using PI diagrams reveal that the fold axis of Qara Sard anticline is sinuous and changing its trend in three attitudes. The first is NW-SE in the traverses P1, P2 and P3 with gradual clockwise drifting. The second one is WNW-ESE in P4, P5 and P6 and then returning in the third to the first attitude NW-SE in the traverse P7. Consequently, the area was influenced by four strike-slip faults. They are either transverse or inclined to the fold axis. These faults are Dolma Reza dextral, Choplaghsinistral, Lower Zab dextral and Dokan sinistral. They divided the area into four blocks moved in opposite directions depending on the strike-slip faults displacements. On the other hand, the study folds are affected by three reverse listric faults. They are suture-verged and parallel with the fold axis. Two of them affected the northeastern limb of Qara Sard anticline, whereas the third disturbed its southwestern limb. By investigations of the vertical changes of fold style, the reactivation of the suture listric fault (2) is detected. It appears as a rotational type so as its larger effect is on traverse P7 and its displacement is gradually reduced toward P4. Moreover, the reactivation time of this suture rotational listric fault was Turonian, it is reflected throughout verging change of the fault between Qamchuqa and Kometan formations in traverse P6.