珠江口盆地西部文昌A凹陷断裂特征与成因探讨

在前人勘探解释的基础上,通过三维高分辨率地震资料,应用相干属性分析等技术对区域断裂进行精细化解释。研究表明盆地内发育着典型的犁式、花状构造、旋转正断层等伸展构造样式,在珠三南断裂影响下,南部边界断裂以阶梯状排列形成断阶构造。始新世—中中新世,断裂走向在持续右旋张扭应力场下以NE→EW→NWW顺时针方向旋转,张裂强度逐渐减弱。晚始新世—早渐新世,盆地在太平洋板块俯冲后退、印亚板块碰撞、古南海向南俯冲下发育EW向断裂,晚渐新世在南海扩张事件影响下前期右旋应力场得到加强,形成大量近EW向断裂,中新世后演化为NWW向断裂。文昌A凹陷断裂构造的演化、成因机制与南海北部陆缘应力场变化一致。该研究有利于进一步了解南海北部陆缘含油气盆地的构造特征和演化规律,提高油气勘探开发的效率。     

珠江口盆地珠三坳陷断裂特征与油气成藏

珠江口盆地珠三坳陷为南海北部陆缘拉张型含油气盆地。受区域构造应力场变化控制,盆地在构造演化过程中主要经历了三期断裂活动,发育了3种类型断裂,古新世-早渐新世发育NE向伸展断裂,晚渐新世-早中新世发育近EW向走滑伸展断裂,中中新世至今发育NW向走滑伸展断裂。主干断裂和次级断裂的平面组合样式主要有平行式、羽状、雁列式、帚状,剖面组合样式主要有Y字形、阶梯状、负花状。断裂活动对珠三坳陷的油气生成、运移、聚集具有重要的控制作用。控凹的主干断裂活动控制了生烃凹陷的分布和烃源岩的热演化,断裂活动控制形成了多种类型圈闭,长期继承性活动断裂是浅层油气藏形成的主要运移通道。主干断裂带是珠三坳陷油气复式富集成藏的有利区带,文昌凹陷北坡断阶带和琼海凸起、阳江低凸起披覆背斜带也是珠三坳陷油气有利成藏区带。     

新生代区域伸展方向转变对珠三坳陷断裂体系发育演化的控制作用

沉积盆地内断裂体系的复杂性与多样性及其形成演化机制长期以来备受关注。以南海北部陆缘珠三坳陷为研究目标，在大量三维地震资料构造解析的基础上，分析了新生代区域伸展方向的转变规律，探讨了其对断裂体系发育演化的控制作用。研究结果表明：珠三坳陷断裂具有多走向、多级别、多性质的特点，依据断裂走向可以划分为NNE-NE、NWW-NW和近EW向3组，不同走向断裂发育特征、断裂性质及分布规律存在差异。新生代珠三坳陷区域伸展方向经历了顺时针旋转的演化，由古新-中始新世神狐-文昌组沉积期的NW-SE向，转变为晚始新-早中新世恩平-珠江组沉积期的近SN向，到中中新世韩江组沉积期至今的NNE-SSW向。新生代区域伸展方向的转变与先存断裂共同控制了珠三断裂体系的发育演化，整体上导致各演化阶段活动断裂特征存在差异。从具体断裂上看主要表现在：古新-始新世强烈活动的南断裂带南支西段在中晚期消亡；南断裂带北支不同分段的断裂性质存在一定差异；走向弯曲的琼海1号、南断裂带北支文昌B凹北段晚期发生局部构造反转。以上几方面现象共同反映了新生代区域伸展方向转变对珠三坳陷断裂体系发育演化的控制作用。     

琼东南盆地陵水凹陷构造演化及其对深水大气田形成的控制作用

琼东南盆地陵水凹陷构造演化及其对深水大气田形成的控制作用成为深水区研究的热点。利用钻井地质、地震勘探资料,运用层序地层学、构造解析方法,认识了陵水凹陷的构造动力学机制和构造变形;探讨了陵水凹陷构造演化及其对深水大气田形成的控制作用;提出了陵水凹陷经历了古新世—始新世断陷、渐新世坳—断、早中新世断—坳和中中新世—更新世坳陷(深水盆地)4期构造演化阶段的新认识,并认为构造演化控制了深水大气田的形成。(1)古新世—始新世断陷、渐新世坳—断作用分别控制了湖相、海陆过渡相—海相烃源岩分布,中中新世—第四纪坳陷作用拓宽了烃源岩生气时窗;(2)渐新世坳—断作用控制发育了扇三角洲储层,中中新世—更新世坳陷作用控制发育了深水限制型、非限制型碎屑岩储层和碳酸盐岩生物礁储层;(3)渐新世坳—断演化阶段以走滑—伸展构造变形为主,控制发育了断鼻、断背斜圈闭,中中新世—更新世坳陷作用控制发育了深水限制型重力流水道砂岩性圈闭群、非限制型盆底扇岩性圈闭和生物礁地层圈闭;(4)渐新统、中中新统地层超压产生断裂/裂隙,构成了良好的天然气输导体系。     

珠江口盆地开平凹陷断裂构造特征与动力学机制探讨

珠江口盆地作为南海北部陆缘勘探程度较高的含油气盆地,断裂特征分析对认识盆地演化模式和油气成藏机理至关重要。根据高分辨率地震数据和钻井资料对盆地西南部开平凹陷进行精细地震地质解释,依据断裂级别与规模将该区断裂构造类型划分为一级控盆断裂、二级控凹断裂、三级控带断裂以及四级控圈断裂;在地震剖面上识别出“Y”字型断层、阶梯状断层及卷心型断层等多种剖面组合样式;根据断裂平面分布图识别出平行式、雁列式、斜交式3种平面组合类型;定量统计断裂走向特征可知,在右旋应力场作用下,自始新世到早中新世断裂走向持续发生近NE→EW→近NW向的顺时针旋转,且断裂活动性逐渐减弱。并认为受印度?欧亚板块碰撞、太平洋板块俯冲后撤和古南海持续南移的影响,盆地形成典型的伸展拉张应力场环境,促成始新世?渐新世期间近NE向、EW向和中新世期间发育的近NW向3组断裂发育。对开平凹陷的地质构造特征加以解释补充,为南海北缘洋陆过渡带的发育特性和成因机制提供参考。     

莺歌海盆地的构造反转作用及其油气勘探意义

莺歌海盆地是北西走向红河断裂带末端在第三纪走滑运动形成的扭张性断陷盆地，控制盆地形成演化的构造动力在早-晚渐新世和中-晚中新世发生了改变，导致盆地内部发生了两期性质不同的构造反转作用。晚渐新世-中中新世期间的构造反转表现为轴向近南北的褶皱变形和沉降中心向东南方向的迁移，晚中新世至今的构造反转使盆地西北边缘的北东走向断裂发生反转逆冲。晚渐新世-中中新世构造反转作用导致盆地西北部和中南部的油气聚集特征存在明显差异。     

莱州湾地区郯庐断裂带的构造特征及其新生代演化

郯庐断裂带中段分东西两支从莱州湾进入渤海,在莱州湾地区的构造特征与演化历史一直鲜为人知。通过对横穿研究区的两条地震测线的解释和分析,揭示了该区郯庐断裂带中段在研究区的构造差异,研究表明郯庐断裂带东西两支在该研究区表现出不同的断裂性质,西支断裂表现为正断层,东支断裂表现为走滑断层。郯庐断裂是本研究区的主控断裂,通过对本地区地层形态及其组合、断层的剖面形态和空间展布规律的深入研究,揭示了郯庐断裂带在莱州湾地区新生代以来的构造演化历史:古新世—始新世的伸展阶段、渐新世—中新世早期的挤压和右行走滑阶段、中新世中晚期至今的稳定发展阶段,这几个不同时期的演化阶段主要受太平洋板块运动的方向和速度变化的控制。     

张扭性断陷盆地构造样式与油气成藏的关系——以珠江口盆地恩平凹陷新生界为例

从张扭性断陷盆地的断裂特征入手,结合构造动力学形成机制,总结了恩平凹陷的构造样式特征及有利圈闭类型,并探讨了构造样式对烃源岩的形成和油气富集区带的控制作用。结果表明:恩平凹陷为双向伸展的上下构造层变形系统的叠合,即古近系为NE—EW向伸展构造系统,新近系为NW—NWW向伸展—张性扭动构造系统;发育了4大类伸展型构造样式,构造样式演化控制了半地堑结构、烃源岩发育情况、油气的初始运移方向和断裂构造带与圈闭类型分布,为新生界油气藏的形成创造了有利条件。     

北部湾盆地雷东凹陷主控断层发育特征及其形成机制

北部湾盆地是我国海域较早开展油气勘探的地区之一,已经历50多年的油气勘探历程。目前的油气勘探区块主要集中于涠西南、福山凹陷等局部地区,盆地整体勘探程度较低,勘探突破少。因此,加强雷东凹陷等后备区的地质研究与资源评价十分必要。分析了北部湾盆地雷东凹陷主控断裂的发育特征、演化规律及其形成机制,并探讨了其对沉积充填与油气运聚成藏的控制作用。北部湾盆地雷东凹陷3条主干断裂的活动对沉积相带分布的控制作用十分明显,形成了东、西2个次洼,次洼内各有2个沉降中心。东次洼北断裂和西次洼南断裂是受NW—SE向拉张作用形成的NE向伸展断层,而西次洼北断裂是具平移剪切断层性质的转换断层。始新世早期,西次洼南断裂活动强烈,西次洼北断裂、东次洼北断裂开始发育;始新世晚期,西次洼南断裂活动减弱直至停止,西次洼北断裂、东次洼北断裂持续活动直至渐新世晚期停止;中新世断裂不发育,整体为拗陷阶段。雷东凹陷油气勘探应从有利疏导体系评价着手,在凹中隆、南部斜坡、北部陡坡等有利的油气优势运聚区寻找突破。     

渤海海域构造应力场演化及其在油气聚集中的作用

渤海海域位于渤海湾盆地东部,在盆地区域动力学背景下,形成了渤海海域特征的沉积和构造环境。渤海海域新生代具有早期断陷、后期拗陷的特点,断裂以NE—NNE走向为主,其次是EW走向,再次是NW走向。通过区域构造演化和沉积体系的深入研究,将海域新生代地质构造活动按构造应力的方向、大小和其他构造形变参数划分为4个期次:①古新世;②始新世—渐新世;③中新世—早更新世;④晚更新世至今。在一系列构造演化过程中,构造应力场的变化对海域内的3组主要断裂具有重要的影响。不同方向的断裂在不同阶段应力场的作用下,所表现的特征和对油气的控制作用是不同的,尤其是NNE—NE向断裂在构造演化过程中多次具有走滑活动,油气主要聚集在走滑作用所派生的局部圈闭或附近存在的构造弱化带中。     

尖峰北盆地地质构造及油气勘探潜力

尖峰北盆地位于南海北部大陆边缘南部,是一个新生代沉积盆地。盆地发育了A、B、C、D、E5套地震层序;盆地内地质构造复杂,断裂发育,平面上断裂展布方向主要有NE向、近EW向和NW向三组,断裂可分为正断层及平移断层,以正断层为主。古新世—始新世为盆地形成时期即断陷阶段,盆地内部充填了大量河湖相沉积。渐新世—中中新世为盆地发展期即坳陷阶段,盆地沉积类型由陆相逐步过渡到海陆过渡相和海相。中中新世末期,盆地相对隆升,部分地区遭受剥蚀。晚中新世—全新世为区域沉降阶段,盆地及其围区以稳定的浅海-半深海相沉积为主。盆地早期河湖相、三角洲相沉积分布范围较广,最大沉积厚度超过4500m,具有一定的生烃能力;盆地储盖条件良好,油气运移条件良好;尖峰北盆地具备较好的油气潜力。     

Structural development and tectonic evolution of Gunsan Basin (Cretaceous–Tertiary) in the central Yellow Sea

This study analyzes the structural development of the Gunsan Basin in the central Yellow Sea, based on multi-channel seismic reflection profiles and exploratory well data. The basin comprises three depressions (the western, central, and eastern subbasins) filled with a thick (ca. 6000 m) Cretaceous to Paleogene nonmarine succession. It was initiated in the early Cretaceous due to intracontinental extension caused by oblique subduction of the Izanagi plate under the Eurasian plate and sinistral movement of the Tan-Lu fault. The basin appears to have undergone transtension in the late Cretaceous–Eocene, caused by dextral movement of the Tan-Lu and its branching faults. The transtension was accommodated by oblique intra-basinal normal faults and strike-slip (or oblique-slip) movement of a NE-trending bounding fault in the northern margin of the central subbasin. The entire basin was deformed (NE–SW contraction) in the Oligocene when tectonic inversion occurred, possibly due to the changes in strike-slip motion, from right- to left-lateral, of the Tan-Lu fault. During the early Miocene, extension resumed by reactivation of the pre-existing normal and transpressional faults. A combination of extension, uplift, and erosion resulted in differential preservation of the early Miocene succession. At the end of the early Miocene, extension ceased with mild contraction and then the basin thermally subsided with ensued rise in sea level.     

Tracing the middle strand of the North Anatolian Fault Zone through the southern Sea of Marmara based on seismic reflection studies

We studied the active deformation zone of the middle strand of the North Anatolian Fault Zone through the southern part of the Sea of Marmara by means of high-resolution as well as deep seismic reflection data. Our main objective was to investigate the active deformation within the uppermost sedimentary layers at high resolution as well as deeper sedimentary layers, focusing on the tectonic and stratigraphic setting between Gemlik and Bandırma. The middle strand of the North Anatolian Fault reaching the Gulf of Gemlik is a main fault which has a lazy-S shape in the Gulf of Gemlik, and extends westwards to Bandırma as a main fault which is an E–W-trending single right-lateral fault controlling the zone along the Gemlik and Bandırma sub-basins. Small-scale faults, consistent with a dextral shear regime, are present in the vicinity of the main fault. Several oblique fault groups parallel to the main fault were detected. The deformation in the Gulf of Gemlik is characterized by a series of synthetic and antithetic faults emanating from the main fault. The boundary faults in the Gulf of Gemlik have a compressive component, which indicates the sill areas of the gulfs of Gemlik and Bandırma to be push-up structures. Four seismic stratigraphic units were identified in the sediments of the gulfs of Gemlik and Bandırma, providing evidence of tectonic influence. The present tectonic structure between Gemlik and Bandırma is not a pull-apart structure. The microseismic study in this area has shown that fault planes are either strike-slip or compressional, and that the stress tensor is compatible with pure strike-slip in the E–W fault system.     

南沙海区万安盆地构造演化与成因机制

本文基于地震、钻井和区域地质资料,运用回剥法和平衡剖面技术定量研究了万安盆地的构造沉降和伸展程度,重建盆地的构造演化史并探讨其成因机制。模拟结果表明,万安盆地构造沉降曲线为多段式,其南北部构造沉降差异明显,且沉降中心逐渐向南发展的趋势。晚始新世-渐新世（37.8~23.03 Ma BP）盆地中、北部快速沉降,存在两个沉降中心;早中新世（23.03~16.0 Ma BP）盆地南部也发生快速沉降,整个盆地存在3个沉降中心;中中新世（约16.0~11.63 Ma BP）沉降作用减弱,盆地进入裂后热沉降期。万安盆地的伸展和形成演化呈现北早南晚的特征,与南海海底扩张密切相关,同时受控于万安断裂带交替地右旋-左旋走滑作用,是伸展和走滑双重作用的结果。盆地的构造演化过程可细分为4个阶段:初始裂谷期、主要裂谷期、走滑改造期和裂后加速沉降期。     

Middle to Late Cenozoic tectonic events in south and central Palawan (Philippines) and their implications to the evolution of the south-eastern margin of South China Sea: Evidence from onshore structural and offshore seismic data

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan.     

Tectonics, basin subsidence mechanisms, and paleogeography of the Caribbean-South American plate boundary zone

Using a mega-regional dataset that includes over 20,000 km of on- and offshore 2D seismic lines and 12 wells, we illustrate three different stages of fault formation and basin evolution in the Caribbean arc-South American continent collisional zone. Transpressional deformation associated with oblique collision of the Caribbean arc migrates diachronously over a distance of ∼1500 km from western Venezuela in Paleogene time (∼57 Ma) to a zone of active deformation in the eastern offshore Trinidad area. Each diachronous stage of pre-, syn-, and post-collisional basin formation is accompanied by distinct patterns of fault families. We use subsidence histories from wells to link patterns of long-term basinal subsidence to periods of activity of the fault families.

Stage one of arc-continent collision

Initial collision is characterized by overthrusting of the south- and southeastward-facing Caribbean arc and forearc terranes onto the northward-subducting Mesozoic passive margin of northern South America. Northward flexure of the South American craton produces a foreland basin between the thrust front and the downward-flexed continental crust that is initially filled by clastic sediments shed both from the colliding arc and cratonic areas to the south. As the collision extends eastward towards Trinidad, this same process continues with progressively younger foreland basins formed to the east. On the overthrusting Caribbean arc and forearc terranes, north-south rifting adjacent to the collision zone initiates and is controlled by forward momentum of southward-thrusting arc terranes combined with slab pull of the underlying and subducting, north-dipping South American slab. Uplift of fold-thrust belts arc-continent suture induces rerouting of large continental drainages parallel to the collisional zone and to the axis of the foreland basins.

Stage two

This late stage of arc-continent collision is characterized by termination of deformation in one segment of the fold-thrust belt as convergent deformation shifts eastward. Rebound of the collisional belt is produced as the north-dipping subducted oceanic crust breaks off from the passive margin, inducing inversion of preexisting normal faults as arc-continent convergence reaches a maximum. Strain partitioning also begins to play an important role as oblique convergence continues, accommodating deformation by the formation of parallel, strike-slip fault zones and backthrusting (southward subduction of the Caribbean plate beneath the South Caribbean deformed belt). As subsidence slows in the foreland basins, sedimentation transitions from a marine underfilled basin to an overfilled continental basin. Offshore, sedimentation is mostly marine, sourced by the collided Caribbean terranes, localized islands and carbonate deposition.

Stage three

This final stage of arc-continent collision is characterized by: 1) complete slab breakoff of the northward-dipping South American slab; 2) east-west extension of the Caribbean arc as it elongates parallel to its strike forming oblique normal faults that produce deep rift and half-grabens; 3) continued strain partitioning (strike-slip faulting and folding). The subsidence pattern in the Caribbean basins is more complex than interpreted before, showing a succession of extensional and inversion events. The three tectonic stages closely control the structural styles and traps, source rock distribution, and stratigraphic traps for the abundant hydrocarbon resources of the on- and offshore areas of Venezuela and Trinidad.     

南黄海盆地东北凹构造特征及伸缩率研究

通过选取南黄海盆地东北凹典型地震剖面,开展精细的构造解释,系统梳理了东北凹构造样式特征。采用平衡剖面恢复技术和伸缩率计算方法,恢复了东北凹各时期的地质演化剖面,分析了东北凹不同构造演化阶段的伸缩率变化特征。研究表明,南黄海盆地东北凹主要发育伸展构造、走滑构造(负花状)和反转构造等多种构造组合样式,经历了晚侏罗世的仪征运动和渐新世末的三垛运动,相应地在中—上侏罗统和渐新统沉积时期,东北凹处于明显的收缩阶段,伴随发育TK40和T20不整合界面。同时,本文结合区域应力场特征,探讨了南黄海盆地东北凹的构造演化历程:以两次构造运动为界,划分为3个构造演化阶段(晚三叠世—侏罗纪的初始断陷阶段、白垩纪—渐新世的裂陷-反转阶段、新近纪—第四纪的区域沉降阶段)。南黄海盆地东北凹伸缩率的时空变化及构造演化过程,是对“晚中生代以来,古太平洋板块相对欧亚板块俯冲汇聚速率和方向的改变”的局部响应。     

珠江口盆地东沙隆起的沉降史及其动力机制

根据东沙隆起及其周围钻井资料的一维构造沉降对比分析,结合前人在基底、盖层及断裂等方面的研究,将东沙隆起地区的构造演化分为5个阶段:自垩纪挤压阶段、古新世-早渐新世伸展断陷阶段、早渐新世末期抬升剥蚀阶段、晚渐新世-中新世快速的裂后沉降阶段、晚中新世以来断块升降阶段.认为下地壳高速层是促使早渐新世末期抬升剥蚀的重要因素,而...     

南海西缘曾母西断裂构造特征及其对盆地沉积发育的控制作用

通过解释重新处理的曾母盆地多道地震数据,结合重、磁异常资料,对前人提出南海西缘最南部发育近S-N向“曾母西断裂”的分布区域进行了重新厘定,详细解释了曾母西断裂的构造特征,具体分析了其结构、组成和空间展布特征。确定曾母西断裂由①号断层和②号断层所构成,曾母西①号断层位于4°30′~7°N、109°30′~110°E,主断层面倾向ESE,走向NEN,其为康西坳陷的大型控边断层;曾母西②号断层分布于3°~5°N、109°30′~110°30′E,主断层面倾向NE,走向NNW,其为塔陶垒堑的大型控边断层,曾母西①号断裂往南的延伸终止于曾母西②号断裂。同时分析讨论了曾母西断裂的构造活动特征以及对曾母盆地沉积发育的控制作用。     

Structural evolution of the Kopeh Dagh fold-and-thrust belt (NE Iran) and interactions with the South Caspian Sea Basin and Amu Darya Basin

We present a detailed stratigraphic and structural study of the Kopeh Dagh fold-and-thrust belt in NE Iran, which is an investigation of the complex polyphased tectonic history of this belt and its links with the adjacent South Caspian Sea and Amu Darya basins. Based on numerous field surveys, a large amount of 2D and 3D seismic data, borehole data and more than 150 new biostratigaphic datings, a new detailed biostratigraphic chart and 4 main regional cross-sections illustrate the importance of lateral facies variations and structural inheritance in the present-day structure of the belt.After the Cimmerian orogeny corresponding to the closure of the Paleotethys Ocean in Late Triassic/Early Jurassic times, a Middle Jurassic post-collisional rifting event was associated with the deposition of one of the main source rocks of the Kopeh Dagh and the Amu Darya Basin (Kashafrud Formation). Following this rifting event, over 7 km of sediments were accumulated until the Tertiary above a regional post-Triassic unconformity. The occurrence of local uplifts during the Late Cretaceous-Early Paleocene is interpreted as a consequence of regional-scale modification of plate-slab coupling in the Neotethys subduction zone. The main inversion of the Kopeh Dagh occurred at Late Eocene times, when the far-field deformation developed in Eurasia as a consequence of the locking of the Neo-Tethys subduction. This folding phase is sealed in the western part of the belt by a major Eocene-Oligocene unconformity at the base of the thick sedimentary series belonging to the South Caspian Sea Basin. The bulk of sedimentary infill in the South Caspian Sea Basin is Oligocene and younger, and it is probably related to syn-compressional downward flexure of the resistant basement basin at the onset of the Alpine phase. In the eastern part of the Kopeh Dagh, this deformation is characterized by Middle Jurassic graben inversion with evidence of forced folding, short-cuts and as well by larger scale basement uplifts. In contrast, the northwestern part of the belt shows thrust faults involving basement and fault-propagation folds within the sedimentary sequence. The Kopeh Dagh presents tectonic structures that are parallel to the Paleotethys suture zone, which emphasizes the importance of the structural inheritance and inversion processes during the structural evolution of the belt. Finally, a change from a mostly dip-slip to a mostly strike-slip tectonics occurred during the Pliocene within the Kopeh Dagh as a consequence of a major tectonic reorganization in North-East Iran.