Detachment Surface Morphology and Shortening Distribution in the Foreland Folds of Iraq

Determinations of detachment surface depth and amount of local shortening were carried out in the more specific location foreland folds of Iraq. Twenty one traverses of anticlinal structures which are normally distributed on the study area were used for this application. Two types of deformation styles were found in the study area. They are thinskinned and thick-skinned tectonics. Depth of the detachment surface generally increases towards east with as abnormal case appeared in Aqra Anticline. Westerlythe depth becomes shallower depth from the south towards Dohuk Anticline and it returns to increase toward the north. In Ain Zala, Butma West, Dohuk and Dahqan Anticlines and some parts of Bekhair Anticline, thin-skinned style was indicated. The shortening generally increases towards the north and northeast, with specific anomaly at Permam Dagh. It increases in the area after Permam Dagh to the north and northeast. However southeast of this area has low amount of shortening and the lowest appears in Qara chauq Anticline. keywords:Detachment surface, Shortening, Thick-skinned, Thin-skinned, folds. ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــــــــــــــــ وف تايطل ريصقتلا بسن عيزوتو لاصفنلاا حطس ةيجولوفروم قارعلا دنلار يعديمصلا قحلا دبع دومحم ينوتاخلا ىسيع مادص يوا زعلا رداق ليبن ضرلاا مومع مسق ضرلاا مومع مسق ضرلاا مومع مسق مومعلا ةيمك مومعلا ةيمك لا ةيمك مومع لصوملا ةعماج لصوملا ةعماح لصوملا ةعماج Nabeel K. Al-Azzawi et al. 04 صخمملا ثحبلا نمضت ةسا رد 12 ـل عطقم 21 ةعزوم قا رعلا يف يدنلاروفلا ما زحلا تايط نم ةبدحم ةيط باسحل مظنم لكشب حطس قمع . يعضوملا ريصقتلا رادقمو لاصفنلاا عون كانى نأ ريظ نا نم امىو ةقطنملا ىمع نا رطيسي ويوشتلا و كيمسلا ءاطغلا ةينوتكت ةينوتكت ءاطغلا . قيقرلا نيبت لاصفنلاا حطس نا ماع لكشب عم قرشلا هاجتاب دادزي يف ذوذش ةيط ةقطنم ةرقع , لحضتيو ىلا اًبرغ كوىد ةيط و دوعي مث . لامشلا هاجتاب اقمع دادزي يعضوملا ريصقتلا ةبسن دادزتو ب مشلا هاجتا لا قطنم يف ذوذش عم يقرشلا لامشلاو ة غاد مامريب , ةدايزلاب رمتست مث دعب هاجتاب ةقطنملا هذى لامشلاو لامشلا يقرشلا اضيا نيح يف ت لق هاجتاب لا بونج نم ,اي ةميق لقا ناو يعضوملا ريصقتلا ةبسنل ةيط يف ريظت هرق . خوج ةلادلا تاممكلا سلا ءاطغلا ,ريصقتلا ةبسن ,لاصفنلاا حطس : تايطلا ,قيقرلا ءاطغلا ,كيم . ـــــــــــــــــــــــــ ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــــــــــــــــــ INTRODUCTION The foreland belt of Iraq is situated at the northeastern margin of Arabian plate. It is restricted by the latitude (35 ° , 45 ' , 23 '' 37 ° ,05 ' ,11 '' ) north and longitude ( 42 ° ,28 ' ,22 '' 44 ° ,08 ' ,53 '' ) east (Fig. 1). This belt comprises several folds and faults and called a "fold/fault belt". Folds in this belt have two trends, Zagros and Taurus. The first is oriented in a northwest-southeast direction whereas the second has eastwest direction. Moreover these folds have two types of vergence directions, some folds verging towards north or northeast, while other toward south or southwest. Many methods have been used to calculate the amount of shortening in different deformed area, such as balancing cross section. Also many authors applied this method, such as (Bally et al. 1966); (Dahlstrom, 1969 and 1970) and (Elliot and Boyer, 1982) in Ramsay and (Huber, 1987) and (Suppe, 1985). (Billings, 1972) and (Ragan, 1985) suggested a method to measure shortening and depth of folding According to the definition that a detachment is a surface separating folded and unfolded strata in a vertical section (Depth of fold), the present study has used a mathematical method suggested by Al-Azzawi (2008) to calculate the local shortening percentage of the foreland folds.This technique is capable of determining the depth of detachment surface by adding new factor (additional tectonic uplift). To calculate the local shortening for any fold, the total amount of mass uplifted (in Anticline) and subsiding mass (in syncline) are used (Fig. 2). Twenty one traverses distributed in the foreland belt, were taken as samples for this analysis; these traverses taken across each of these foreland folds. Geological concepts using a series of appropriate mathematical equations are used by (Al-Azzawi, 2008). These equations which gave encouraging results for the detachment surface depth and shortening ratio are used in this work. Detachment Surface Morphology and Shortening Distribution. 04