GeoArabia, 2012, v. 17, no. 4, p. 109-156 Gulf PetroLink, Bahrain Tectonostratigraphic overview of the Zagros Suture Zone, Kurdistan Region, Northeast Iraq Basim Al-Qayim, Azad Omer and Hemin Koyi ABSTRACT The northwestern segment of the Zagros Orogenic Belt of the Kurdistan Region of Iraq includes the Zagros Suture Zone which is consisting of allochthonous Tethyan Triassic–Eocene thrust sheets. The zone is bounded by the Zagros Main Reverse Fault in the northeast, and the Zagros Thrust Front in the southwest. Parts of this zone’s rocks are represented by stacks of thrust mega- sheets obducted over the autochthonous Cretaceous–Cenozoic sequence of the Arabian Plate margin. Each sheet represents a specific Tethyan tectono- stratigraphic facies, and includes (from older to younger): isolated Triassic carbonate platforms (Avroman Limestone), Jurassic carbonate imbricates (Chia Gara, Sargelu and other formations), radiolarites (Qulqula Group), sedimentary mélange (sedimentary-volcanic units of the Qulqula Group), ophiolites (Mawat and Penjwin ultramafics complexes), and Cenozoic fore-arc volcano- sedimentary sequences (Walash Group). Petrography, facies interpretation and lithostratigraphic correlation of these allochthons along four traverses across the Zagros Suture Zone of the examined area indicate that they evolved during the closure of the Neo-Tethys Ocean. Their stacking pattern and tectonic association resulted from two important events: the Late Cretaceous obduction processes, and the Late Miocene–Pliocene collision, uplift, folding and suturing between the Arabian Plate and the Sanandaj-Sirjan Block of Iran. Based on these field observations and by using the model of the Iranian Zagros evolution, a tectonic scenario is proposed to explain the history and evolution of the Zagros Suture Zone in this area. INTRODUCTION The NW-trending Zagros Orogenic Belt extends about 2,000 km from the Anatolian Fault of southeastern Turkey to the Makran Zone in southern Iran, and is part of the Alpine-Himalayan Mountain Chain (Figure 1). The belt resulted from the Late Cretaceous and Cenozoic convergence of the Iranian terranes and the Arabian Plate, when the intervening Neo-Tethys Ocean went through a succession of subduction, obduction and collision stages (Alavi, 1994; Sharland et al., 2001; Agard et al., 2005). An integral part of the belt is preserved in the mountainous region of northeast Iraq (Figures 2 and 3). However, this part of the belt remains less studied and under- explored as that of the southeastern Iranian and Omani parts. The present study offers a general review of the tectono-stratigraphic architecture of the area as an integral contribution to the understanding of the geological history of the Zagros Orogenic Belt. We present the results of detailed field examinations, petrographic studies, and litho-stratigraphic correlation of the exposed tectono-stratigraphic units of this zone. Future studies aimed at obtaining biostratigraphic control and petroleum geological and geophysical data are planned. The study area is located in the Sulaimani Governorate of the Kurdistan Region of northern Iraq. It extends from the Mawat area to the east of Sulaimani City down to the surroundings of Halabja (Figures 4 and 5). Four traverses were selected perpendicular to the tectonic strike of the Zagros Orogenic Belt to cover the regional tectono-stratigraphic domain of the area. Each traverse represents an elongated block, a few kilometers wide and tens of kilometers long and covers a particular portion of the suture zone. (1) Traverse 1 is oriented N20°E and located northeast of Sulaimani City. It extends from the axis of Azmur Mountain to the Iraqi-Iran border (Figure 6). 109 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/4/109/4570449/al-qayim.pdf by guest on 25 September 2021 Al-Qayim et al. 30ºE 40º 50º60º TURKMENISTAN Anatolian Fault TURKEY Caspian 40ºN Sea 40º Zagros Main Reverse Fault Tigris River CYPRUS LEBANON Euphrates IRAN SYRIA River Study Zagros Orogenic Bel Mediterranean Area Sea IRAQ JORDAN t KUWAIT 30º ARABIAN PLATE 30º BAHRAIN Makran Zone QATAR EGYPT Gulf of Oman UNITED ARAB EMIRATES SAUDI OMAN ARABIA Red Sea 20º 20º Arabian SUDAN YEMEN Sea ERITREA Owen Fracture Zone Aden 0 500 ETHIOPIA Gulf Of 30º 40º 50º Km Banog Figure 1: The Kurdistan region lies in the northeastern part of Iraq, where the Arabian Plate and Iranian terranes collide along the Zagros Orogenc Belt. (modified from Sharland et al., 2001). (2) Traverse 2 is oriented N35°E and covers the Penjwin-Said Sadiq area (Figure 7). (3) EW-oriented Traverse 3 extends from the Iraqi-Iran border to the town of Khurmal (Figure 8). (4) EW-oriented Traverse 4 is located to the east of Halabja City, and connects Byara to Tawela (Figure 9). Within each of these traverses several side traverses and sections were measured to document lithological character and associations. Major structural features such as shear zones, boudinage, major and minor folds and faults are reported. Lithostratigraphic correlation was conducted to construct the local and regional stratigraphic architecture within the postulated tectonic framework (Figure 10). Samples were collected from each unit to investigate various lithologic features. Each sample was thin-sectioned for petrographic studies to define lithology, sedimentary components, and to differentiate between mineralogical and textural criteria of each lithologic association. 110 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/4/109/4570449/al-qayim.pdf by guest on 25 September 2021 Tectonostratigraphy of Zagros Suture Zone, Iraq 43°E 44° 45° 46° 47° TURKEY Zagros Imbricate Zone Britlis Imbricate zone 37°N N 37° 0 50 Zagros Suture Zone km Qulqula zone Cenozoic units Basic massive Zagros Imbricate Cretaceous units Zone Chwarta subzone Zagros High Folded Zone Halabja subzone Mosul 36° Zagros Suture 36° Erbil Zone Shalair Zone A' IRAN Zagros Low Folded Zone Zagros Main Reverse Fault Sulaimani 3 Kirkuk Figure IRAQ 35° 35° A Zagros Thrust Front High Zagros Zagros Foredeep Fault Reverse Fault Tikrit Zagros Mountai Front Fault Mesopotamian 34° Zone 34° n 43° 44° 45° 46° 47° Banog Figure 2: Regional tectonic map of northeast Iraq showing major tectonic subdivisions (after Al-Kadhumi et al., 1996). Tectonic zones and boundaries follow this study nomenclature. Southwest Northeast Zagros Zagros Zagros Folded Zone Shalair Imbricate Suture Low Folded Zone High Folded Zone Zone Zone Zone Upper Lower Zagros Mountain Lower Fars High Zagros 4 A Igneous Complexes A' Bakhtiari Fm Bakhtiari Fm Front Fault Fm Reverse Fault U pp 0 er Fars Fm 5 Km 4 L. and M. Jurassic Fms Permo-Triassic Fms Arabian Plate Margin Sediments Zagros Thrust Front Depth (Km) Cambrian Fms 8 Infra-Cambrian Fms 0 Zagros Main Decollement Reverse Fault Basement 10 Km 12 Figure 3: Regional geologic cross-section across northeast Iraq showing major tectonic divisions and major tectonic boundaries. (Slightly modified after Ibrahim, 2009). 111 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/4/109/4570449/al-qayim.pdf by guest on 25 September 2021 Al-Qayim et al. 45°10'E 45°20' 45°30' 45°40' 45°50' 46° 46°10' 46°20' 36°N 36° Mawat 35°50' 35°50' Shalair Zone Figure Zagros Suture 6 Zone 35°40' Chwarta 35°40' Penjwin Sulaimani Zagros Imbricate ReverseHigh Fault Zagros Zone 35°30' 35°30' Figure Thrust Front 7 Zagros Zagros Folded Zone Said Sadiq 35°20' Figure 8 Zagros Main35°20' Reverse Fault N 0 15 Figure 9 km Halabja 45°10' 45°20' 45°30' Derbandikhan 45°50' 46° 46°10' 46°20' Banog Figure 4: Landsat image of northeast Iraq showing major tectonic divisions and the location of the detailed studied blocks (image from Google Earth Resources). PREVIOUS STUDIES Bolton’s contribution to the geology of the Zagros Suture Zone remains the foundation of all succeeding studies and geological mapping campaigns of the area (Bolton, 1955, 1956, 1958a, b, c). His 1:100,000-scale geological maps of the Kurdistan region in Iraq were the first, and are still considered the basic background for all recently published geologic maps of the area. Bolton’s stratigraphic nomenclature of the area remains unchanged, though revision is needed in the light of later geological concepts such as plate tectonics and sequence stratigraphy, and newly accomplished work on the area. The most recent geologic map of the area was compiled by Ma’ala (2008) at a scale of 1:250,000 for the Geological Survey and Mineral Investigation State Organization of Iraq (GEOSURV). It is considered the most reliable mapping resource of the Zagros Suture Zone (Figure 5). The ages of the stratigraphic units of the zone that are discussed in our study are mainly taken from the chart that accompanies the geologic map (Figure 10). The tectonic review by Jassim and Buday (2006) applied new vision to the area’s evolution. Ibrahim (2009) presented a regional review of the tectonic style and evolution of the Zagros Orogenic Belt of the Kurdistan Region of Iraq using a scaled analogue sand model. Other works include local 112 Downloaded from http://pubs.geoscienceworld.org/geoarabia/article-pdf/17/4/109/4570449/al-qayim.pdf by guest on 25 September 2021 Tectonostratigraphy of Zagros Suture Zone, Iraq 45°20'E 45°30'45°40' 45°50' 46° 46°10'46°20' IRAN Mawat 36°50'N Shalair Zone Figure 6 Zagros Suture 36°40' Chwarta Zone Penjwin 7 Sulaimani N 36°30' Figure 0 15 km Said Sadiq 36°20' Derbandikhan Figure 8 Cretaceous– Lake Cenozoic Foreland Sequence Figure 9 Halabja 36°10' Derbandikhan Zagros Imbricate Zone Banog Zagros Imbricate Zone Zagros Suture Zone Upper Red Beds unit Naopurdan–Walash Group Quaternary Lower Red Beds unit Ophiolite Complex Geological contact Tanjero and Aqra–Bekhma fms Qulqula Conglomerate Formation Axis of anticline Shiranish Formation Qulqula Radiolarian Formation Axis of syncline Balambo–Kometan formations Jurassic Imbricates Thrust fault Undifferentiated Jurassic Avroman Limestone Formation Normal fault Sequence Figure 5: General geologic map of the study area showing location of the investigated traverses (Geologic map after Ma’ala, 2008, tectonic divisions and boundaries following nomenclature of this study).