Deformation structural style of the rioni foreland fold-and-thrust belt, western greater caucasus: Insight from the balanced cross-section
Victor AlaniaGeorge MelikadzePaolo PaceIstván FórizsTamar BeridzeOnise EnukidzeAnzor GiorgadzeAlexander Razmadze
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Abstract:
The Rioni foreland fold-and-thrust belt is part of the Greater Caucasus pro-wedge and is one of the most important examples of the collision-driven far-field deformation of the Arabia-Eurasia convergence zone. Here we show the deformation structural style of the Rioni foreland fold-and-thrust belt based on seismic reflection profiles and regional balanced cross-section. The main style of deformation within the Rioni foreland fold-and-thrust belt is represented by a set of fault-propagation folds, duplexes, and triangle zone. The regional balanced cross-section shows that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. Formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. A balanced section restoration of compressional structures across the Rioni foreland fold-and-thrust belt provides a minimum estimate of shortening of −40%, equivalent −42.78 km. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Using end-member modes of thrust sequences, the thrust-top basins are divided into: 1) Type I-piggyback basin, 2) Type II-break-back basin, and 3) Type III—formation of thrust-top basin characterized by bi-vergent geometry and related to combined, piggyback and piggyback back thrust sequences.Keywords:
Thrust fault
Syncline
Anticline
The study area is located in Dohuk Governorate; Northern Iraq. The aim of this study is to concentrates on the structural analysis in the plunge areas of Bekhair, Dohuk, Brifca and Zawita anticlines by using seismic sections. The four anticlines have NW – SE trend, which coincide with the main trend of the Zagros folds. Three seismic sections (DK-16, DK-20, and DK-22) were used to emphasize the structural analysis and recognize the faults caused by folds development and affected on the plunge areas of the four anticlines. The results showed that the main axis of Bekhair anticline exhibits two small plunges (northern and southern domes) with a syncline in between. The northern dome near Zawita village, is developed as a fault bend fold over northeast-wards dipping forethrust. The dome extends eastwards in form of structure A, which is also developed as a fault bend fold, and is named Deralosh anticline in this study. The southern dome near Besire village, is developed over a planner northeast-wards dipping forethrust (Bekhair Thrust) as a fault propagation fold with reverse displacement of about 225 m. The syncline between the two domes also plunges eastwards to connect with the axis of the major syncline and continues plunging eastward. This study shows that Zawita anticline is composed of two structures; (A) and (B) and is separated by a saddle area. Structure B, which is named Benarinke anticline, is developed over a northeast-wards dipping forethrust; as a fault propagation fold along reverse displacement of about 150 m. Banye small anticline (Baby structure) may exist in the northeast part of the study area. Brifca anticline is developed as a fault propagation fold over a main planner northeastern dipping forethrust that caused in over thrusting of the Pila Spi Formation over the Injana Formation of the adjacent syncline with horizontal displacement of about 750 m, whereas the northern limb is influenced by southwest dipping backthrust resulted in ~ 150 m reverse displacement. Based on the swing of the major syncline, a left lateral movement is detected on the western lateral ramp separated between Bekhair and Brifca anticlines, whereas a right lateral movement is represented by the other two extends in the eastern part of the study area. A structural geological map was drawn for the study area. This study also revealed that the anticline, which was believed as Zawita anticline by GEOSURV (1961), is composed of structure A (Deralosh anticline) and structure B (Benarinke anticline) separated by the saddle area.
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Anticline
Dome (geology)
Normal fault
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Three distinct stages of folding have been recognized in the area investigated. The earliest folds (F1), on approximately ENE.–WSW. axes, are (from south to north) the asymmetrical Creag na h-Iolaire anticline closing to the south, the Sròn Mhòr syncline, and the asymmetrical Loch Tummel anticline which closes to the north. The Creag na h-Iolaire anticline is correlated with the Aberfoyle anticline (Shackleton 1958). To the north of the River Tummel the general structure consists of a series of overturned folds, whose axial planes dip to the south (cf. Bailey 1925 ); according to A. L. Harris considerable northward movement has taken place here on a series of south-dipping slides. The Sròn Mhòr syncline occupies a central position between the two sets of oppositely directed overfolds, and represents the highest structural level exposed in the area. This fold is comparable in structural position with the Loch Awe syncline. The primary folds have been refolded during two subsequent phases of folding. The second-phase folds (F2) produced considerable deflexions of strike and the general trend of their axes is NNW–SSE. These folds display a considerable variety of styles. The third phase of folding (F3) is associated everywhere with diaphthoresis Few major structures were formed in the area during the F3 folding, but abundant minor structures were produced.
Anticline
Syncline
Folding (DSP implementation)
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Folds in accretionary complexes, especially those in the Mino-Tanba Belt, are often called not “syncline” or “anticline” but “synform” or “antiform” evenly. However, this usage is not correct, since it cannot distinguish an inverted fold from a normal one. They are structurally quite different and distinguished from each other as a syformal anticline and a syncline or as an antiformal syncline and an anticline in normal sedimentary strata. “Synform” and “antiform” are terms for the folds that are out of this distinction; they should be used when the stratigraphic relationship or the facing is unknown. This terminology should be followed also in accretionary complexes, and “syncline” and “anticline” should be defined not with a chronological relationship between the strata in the core and the limbs, as in many glossaries and encyclopedias, but with a facing direction of the both limbs, namely, as a fold whose limbs are facing syn-axisward or anti-axisward, respectively.
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The salt deposits in Vientiane Plain occurrence in Palaeocene Tagong Formation.The main Kalium-bearing minerals are carnallite and a little of sylvinite.During mineralization period,the Tagong Formation and salt deposits were controlled by NW-trending boundary faults and Tagong syncline.After mineralization period,the salt deposits were controlled by fold(salt syncline and salt anticline).The salt deposits formed broad and gentle fold under the horizontal stress.Inside syncline,deposition rate is relatively quickly and the thickness of clastic rocks upper salt seam is relatively large.On anticline,the thickness of clastic rocks upper salt seam is relatively thin.There are large density differences between salt deposits and clastic rocks,and the thickness of clastic rocks in the anticline is different from the one in syncline,so the salt deposits form differential loading.The salt deposits in syncline happened plastic flow towards anticline by larger loading.Thus the salt deposits in anticline become thicker,salt anticline form.The thickness of salt deposits in syncline becomes smaller.Thickness of the salt deposits in anticline is often great;its burial depth is shallow.The strata over anticline are often incomplete.With the salt anticline far development,the potash deposits pierce upper mudstone and expose oneself to relatively freshwater surroundings to suffer corrosion.
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The structural form in the Yan-Liao area consists of Yanliao clinorium,Yanliao synclinorium and Qinhuangdao antiform with their sub-grade folds and faults in Yanshan-western Liaoning Province.They formed a very complicated structural system.Yanliao clinorium forms during Indosinian movement,and Yanliao synclinorium during J1-J2 period and the Qinhuangdao antiform during J3-Kperiod.The inner Mongolian axial is the northern limb of the Yanliao clinorium.The southern faults of the inner Mongolian axial is the axial longitudinal faults of Yanliao synclinorium.The sediment in the J3 period is the fracture filling.Qinhuangdao fault may cut off the Yanliao synclinorium that resulted in the different patterns of the folds and faults in Yanshan and the western Liaoning.
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Anticline
Normal fault
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