Finite Strain Estimation in Baba Dome Using Fry Method (NE Iraq)

Literatures survey indicates that no such study carried out concerning strain measurement and analysis in the concerned area. The well-known field and laboratory work carried out. An accurate ellipse was determined for each ab, bc and ac planes for each formation exposed in Baba dome using Matlab program with a relatively new toolbox (Polylx). Then for each sample the mentioned ellipses was mathematically compiled to generate strain ellipsoid with long, intermediate and short axes with their orientations using Mathcad software. Then the long and short axes of strain ellipsoids projected on ab plane and delineated. Because Baba dome took the present form during last phase of Alpine Orogeny (Miocene -Pliocene) with contemporaneous deposition of MioPliocene formations, the present study deduced that the strain is directly proportional to the stress i.e. elastic deformation. Therefore, the orientation of short axes of strain ellipsoids should coincide with orientation of maximum stress axes giving rise the orientation of maximum stress direction in sampled station. Keyword: Finite strain, Fry method, Strain, Stress Kirkuk University Journal /Scientific Studies (KUJSS) Volume 10, Issue 3, September 2015 , p.p(192-204) ISSN 1992 – 0849 Web Site: www.kujss.com Email: kirkukjoursci@yahoo.com, kirkukjoursci@gmail.com 193 يلكلا لاعفولاا هيمخت ب يف يارف ةقيرط لامعتسا اباب ةبق قارعلا قرش لامش ناركيد تجهب ذيرد 1 فلخ ذمحم ذعو ، 2 يجولويجلا نسق / مولعلا ةيلك / كوكرك ةعهاج 1 duraid337@gmail.com , 2 waadmohammed89@gmail.com :ثحبلا ملاتسا خيرات 25 / 1 / 2015 :ثحبلا لىبق خيرات 8 / 3 / 2015 صخلملا سلا تاسا ردلا لدت ةسا رد ذيفنت مدع ىلا ةقبا ليمحتو باسح صخت ةقطنم يف لاعفنلاا ةسا ردلا فن . يربتخملاو يمقحلا لمعلا ذ ةعبتملا تاقايسلا بسحو . تددح ( تايوتسملا نم لكل داعبلاا ةيئانث جيلاىا ab,bc,ac ) اباب ةبق يف فشكتم نيوكت لكل بلاتاملا جمانرب مادختسا قيرط نع كلذو و لا جيلاىلاا فيلوت آيضاير آفنا ةروكذملا نيواكتلا جذامن نم اييمع لوصحلا مت يت عم داعبلاا ةيثلاث جيلاىا ىمع لوصحمل كلذو رواحملا لاوطا : روحم لا ليوط لاو طسوتم لاو مت ثيح روحم لك هاجتاو ريصق ملا روطلا يف تنوكت اباب ةبق نا امب .داكثاملا جمانرب قيرط نع رواحملا هذى تاىاجتاو لاوطا باسح ةينابلا تاكرحمل رخأت نيسوياملا يف تثدح يتلاو لابجمل – ،ةسا ردلا ةقطنم نيواكت بيسرت عم نما زتي وىو نيسويلابلا ضا رتفلااو جاتنتسلاا مت : نا .دايجلاا عم ةرشابم ةقلاع ول لاعفنلاا نأف مدقتام ىلا آدانتساو قباطتي داعبلاا يثلاث لاعفنلاا جيمىلا ريصقلا روحملا هاجتا م عم يف مظعلاا دايجلاا هاجتا لثمي يذلاو مظعلاا دايجلاا روح ةجذمنلا تاطحم ةجذمنلا تاطحم . تاممكلا ةلادلا : يمكلا لاعفنلاا داهجلاا ،لاعفنلاا ،يا رف ةقيرط ،

proposed a bootstrap version of the mentioned normalized Fry method. The image-analysis method [10] uses Gaussian blur filter for distinction between the areas of largest and smallest pixel intensities in a Fry plot image. It then applies the optimal threshold value and an inversion filter for extraction of the sharp central vacancy.
The recent analytical methods, such as the point-count density method, or the continuous function method use a trial and error approach for searching the best-fit ellipse through the central vacancy in a normalized Fry plot [11].
The aim of the present study is to estimate finite strain for various formations cropped out in study area.

2.LOCATION AND GEOLOGIC SETTING
The study area coverd 250 km. 2 lies within Iraqi territory between longitude (E44°06' 09″ - Tectonically, the study area lies on the NE region of Arabian Plate. It lies within low folded zone of Unstable shelf area and contains many sinuous anticlines (some of them affected by reverse faults on the SW limb) separated by relatively wide syncline filled by fine clastic deposits of Quaternary age, [12]. Baba dome (study area) is one of largest oil trap in the world. Extensive geophysical & geologic works carried out during exploration of oil. This study is a surface contribution to mentioned studies. The present study is considered the first dealing with strain in the study area.
Structurally, the study area on geologic map appears as trace of reverse fault with inclined bed (23°-60°) toward NE, Figure (2). The fault plane is within sulfurous bed of Middle Miocene causing the SW limb obscure, while depth wise the study area is simple symmetrical fold, [13].

4.FINITE STRAIN ANALYSIS
All ellipses in three perpendicular plane lies in zone 2, Figure (4), A,B &C. This zone due to [16] shows dominant shortening in one sector and dominant stretching in another. Due to (op sit) competent layers involved in such strain field shows buckle fold. The change in area (ΔA) is very small and negligible.
Various shape of the determined strain ellipsoid according to Flinn diagram, [16] in the study area. 72% to 28% are the percent of flattening and constriction respectively. All ellipsoids that and constriction forms divide the study area in to two parts: SW and NE respectively with some exceptions see Figure 4D. The Late Alpine deformations i.e. fold and fault in the study area can be described by two stages: the first "plastic" that was responsible for fold formation, the second "elastic" that was responsible for reverse fault and joint development respectively. Both stages were continuous and the second stage is younger and caused by differential stress with aid of salts layer that prevent fault to continue more downward.
The witnesses that lead to say that finite strain is directly proportion to stress in the study area are: -The timing of Late Alpine Orogeny, Mio-Pliocene, is close to the age of studied formations.
This means that there was no time for strain accumulation pre orogeny.
-The aforementioned elastic stage means that the strain is directly proportion to stress, [17].
Consequently, the orientation of the short axes of the calculated strain ellipsoid axes (1+e 3 ) should coincide with the maximum stress orientation .Hence by drawing the orientation of strain ellipsoids axes on a map may represent the orientation of major principal stress orientation. -From above mentioned findings, the stress orientations for each station are estimated assuming that strain is directly proportion to stress due to the contemporaneous timing of last phase of Alpine Orogeny and the age of the exposed formations.
-The authors highly recommend another strain calculating method to carry out in the study area to compare the results and to be sure that the present calculation is near to truth.