Extensional Tectonics, Rifting, Formation of Sedimentary Basins, Cretaceous Volcanism, Emplacement of Dyke Swarms and Development of Hydrocarbon Pools: Case Studies from Peninsular India and Indian Ocean Region

Prolonged extensional regime in peninsular India resulted in formation of rift and grabens,elongated basins and Gondwana sedimentation along them.Downward progression of rift related faults caused decompression

岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics):华北克拉通东部早白垩世岩石圈减薄与破坏机理

华北克拉通岩石圈减薄和破坏机理长期以来存在争议,基于岩石学、岩石地球的化学分析研究突出强调深部过程的重要性。前人提出了两种重要模式:包括以拆沉作用为代表的top-down tectonics模型和以热-机械侵蚀与化学侵蚀,或地幔置换、交代作用的bottom-up tectonics模型。然而,对于这两种模式而言尚存在许多无法合理解释的问题,比如在此深部过程中,区域性岩石圈伸展有多大的贡献?地壳伸展构造是作为深部过程的响应,还是同为岩石圈伸展的产物?本文基于早白垩世东亚地区(尤其是华北克拉通东部地区)伸展构造与岩浆活动的综合分析,揭示出华北克拉通东部不同地区伸展构造变形与岩浆活动之间的时、空和成因关系有一定的差异。但整体上看,岩石圈伸展起着主导作用,控制着岩浆上侵和就位,在拆离断层下盘侵入形成各种规模的花岗质为主的侵入体,或于上盘喷发形成火山-沉积岩盆地。在伸展构造发育的不同阶段,可以有伸展早期、伸展期及伸展期后的岩浆活动。岩浆活动的强度及岩浆源区特点有显著的时空变化。一方面,在同一地区不同演化阶段其源区有很大的差异。表现为主体上是早期以古老下地壳源为主,随着壳/幔伸展作用演化,逐渐向混合源或独立幔源的演化。同时,不同地区岩浆源区的变化规律也显著不同。以胶辽地区为例,胶东整体上是壳幔混合源区对于岩浆演化有重要贡献;而辽东地区具有显著的源区演化特点:从剪切早期古老下地壳源区为主,并伴有幔源物质加入,剪切期古老下地壳为主,到剪切晚期和剪切期后以新生下地壳为主。本文认为岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics),可以合理地解释华北克拉通及邻区早白垩世构造-岩浆活动性。在该模型中,遭受伸展的华北克拉通岩石圈发生壳-幔拆离作用。在岩石圈伸展作用期间,地壳层次的拆离作用与岩石圈地幔层次上的拆离作用可以是耦合的或者是解耦的,从而导致华北克拉通岩石圈减薄过程中在地壳尺度上的拆离作用与变质核杂岩的剥露有三种不同的类型:同岩浆活动型伸展(C型:Co-magmatism mode extension)、无岩浆活动型伸展(A型:Amagmatism mode extension)和多阶段混合型(M型:Multi-mode extension)。

Characteristics of crustal variation and extensional break-up in the Western Pacific back-arc region based on a wide-angle seismic profile

The marginal sea and back-arc basins in the Western Pacific Ocean have become the focus of tectonics due to their unique tectonic location.To understand the deep crustal structure in the back-arc region,we present a 545-kmlong active-source ocean bottom seismometer(OBS)wide-angle reflection/refraction profile in the East China Sea.The P wave velocity model shows that the Moho depth rises significantly,from approximately 30 km in the East China Sea shelf to approximately 16 km in the axis of the Okinawa Trough.The lower crustal high-velocity zone(HVZ)in the southern Okinawa Trough,with V_(p) of 6.8-7.3 km/s,is a remarkable manifestation of the mantle material upwelling and accretion to the lower crust.This confirms that the lower crustal high-velocity mantle accretion is developed in the southern Okinawa Trough.During the process of back-arc extension,the crustal structure of the southern Okinawa Trough is completely invaded and penetrated by the upper mantle material in the axis region.In some areas of the southern central graben,the crust may has broken up and entered the initial stage of seafloor spreading.The discontinuous HVZs in the lower crust in the back-arc region also indicate the migration of spreading centers in the back-arc region since the Cenozoic.The asthenosphere material upwelling in the continent-ocean transition zone is constantly driving the lithosphere eastward for episodic extension,and is causing evident tectonic migration in the Western Pacific back-arc region.

Extensional Tectonic Framework of Post High and Ultrahigh Pressure Metamorphism in Dabieshan,China

The most prominent feature of the extensional tectonic framework of post high pressure (HP) and ultrahigh pressure (UHP) metamorphism in Dabieshan is the development of the multi layered extension detachment zones surrounding the core of the Luotian dome, and the separation of the UHP, HP and epidote blueschist units by the detachment zones, which form the vertically stacking sheet like slices of the HP and UHP metamorphic rocks. From the core outwards, exist the HP and UHP rock barren Dabie complex, UHP unit, HP unit and epidote blueschist unit. The extension tectonics of post HP and UHP metamorphic event constrain the distribution and present configuration of the HP and UHP metamorphic rocks, and the extensional tectonic framework bears some similarities to the Cordillera metamorphic core complex. It is suggested that partial melting happened in the Dabie gneiss complex (DGC) and UHP unit contemporaneously with the extrusion of UHP metamorphic rocks into the lower-middle crust. The formation and emplacement of the migmatite and granites are the response to the change in thermal state, facilitating the transfer from the compressive regime to extensional regime in the crust. The large scale crustal extension and uplift and the accompanying anatexis in Dabieshan are probably related to the delamination and magmatic underplating in the mantle and the lower crust.

The 144–140 Ma Mafic Dykes in North China and Northeast China Indicating Regional Extensional Tectonic Setting

Objective Previous studies indicate that the North China Craton（NCC）had undergone the loss of thickened lithosphere and fundamental change of physical and chemical property of lithospheric mantle（the destruction of NCC）during the Mesozoic.The peak period of the destruction of NCC is estimated to be 130 Ma,accompanied by widespread metamorphic core complex,rift basins,A-type granites and mafic dykes. However, it remains greatly controversial on the tectonic setting of NCC in the pre- 130Ma.

Phanerozoic Tectonic Evolution,Metallogenesis and Formation of Mineral Systems in China

The continental Asia is mainly composed of three major tectonic regimes,the Tethys,Paleo Asian Ocean,and West Pacific.It underwent multi-stage plate convergences,ocean-continent transformations,and subductions,collisions and/or collages,and post collisional(orogenic)extensions in Phanerozoic.Tectonic evolution of the Asia brings up a unique fault system and tectonic geomorphological features in the China's Mainland.Also,it provides a geodynamic background for the formation and evolution of metallogeneses and mineral systems,resulting in nonuniform distribution of tectono-metallogenic systems and metallogenic belts.The spatiotemporal distribution of mineral deposits in China and adjacent areas exhibits periodic variation under controlling of the full life Wilson cycle and tectonic evolution,forming the plate convergence-related mineral system in East Asia.Porphyry Cu deposits are mainly related to compressional systems in Paleozoic and early Mesozoic,and more closely related to post-collision extensional settings in late Mesozoic and Cenozoic.Orogenic Au deposits mainly formed in post-orogeny extensional setting.Alkaline rock related rare earth element deposits formed mainly at margins of the North China and Yangtze cratons.Granite-pegmatite Li and other rare metal deposits formed mainly in early Mesozoic,related to Indosinian post-orogeny extension.Tectono-metallogenic systems provide important basis for the prospecting of mineral resources.

Origin of high heat flow in the back-arc basins of Sumatra:An opportunity for geothermal energy development

Volcanic arcs such as the Barisan Mountains have been identified as attractive areas for the utilization of geothermal energy,as exemplified by Ulubelu in Lampung and Sarulla in North Sumatra.However,environmental factors in the Barisan Mountains remain a primary obstacle to the exploration and exploitation of geothermal energy.The back-arc basins of Sumatra exhibit the highest heat flow worldwide;however,the heat source in this area remains a controversial issue.This study aims to investigate the origin of the high heat flow in the back-arc basins of Sumatra(North,Central,and South Sumatra basins)based on geothermal data from 384 oil wells and the current literature for geological evaluation.The findings of this study indicate that the back-arc basins of Sumatra experienced severe extensional deformation during the Tertiary Period through a large pull-apart and slab rollback mechanism.This deformation resulted in the thinning of the continental crust in this region(27-32 km)and the formation of multiple normal faults.Consequently,the presence of magma resulting from mantle upwelling implies a high heat flow in the back-arc basins of Sumatra.This condition ranks the back-arc basins of Sumatra among the highest heat flow regions of the world,with heat flows>100 mW/m^(2).These findings indicate that the back-arc basins of Sumatra have significant opportunities to exploit their geothermal energy potential.This study provides novel insights into the potential of geothermal energy,particularly in the back-arc basins of Sumatra.

A Novel Three-stage Tectonic Model for Mississippi Valleytype Zn-Pb Deposits in Orogenic Fold-and-Thrust Belts

Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood. This study, through a comprehensive review of MVT deposits across global fold-and-thrust belts, introduces a novel model elucidating the mineralization process in the context of tectonic belt evolution. It is demonstrated that during the stage Ⅰ, regional compression is introduced by early stages of plate convergence, causing the folding and thrusting and creating structural or lithological traps such as evaporite diapirs and unconformity-related carbonate dissolution-collapse structures. Thereafter, in stage Ⅱ, hydrocarbons begin to migrate and accumulate within these traps, where reduced sulfur is generated through thermochemical or bacterial sulfate reduction concurrent with or preceding Zn-Pb mineralization. In the subsequent stage Ⅲ, as plate convergence persists, the regional stress transitions from compression to transpression or extension. Under these conditions, steeply-dipping extensional faults are generated, facilitating the ascent of metalliferous brines into early-formed structural or lithological traps. Precipitation of Zn and Pb sulfides occurs through the mixing of Zn-Pb-transporting fluids with pre-existing reduced sulfur or by interaction with hydrocarbons.

Extensional Tectonic System of Erlian Fault Basin Groupand Its Deep Background

The Erlian fault basin group, a typical Basin and Range type fault basin group, was formed during Late Jurassic to Early Cretaceous, in which there are rich coal, oil and gas resources. In the present paper the abundant geological and petroleum information accumulated in process of industry oil and gas exploration and development of the Erlian basin group is comprehensively analyzed, the structures related to formation of basin are systematically studied, and the complete extensional tectonic system of this basin under conditions of wide rift setting and low extensional ratio is revealed by contrasting study with Basin and Range Province of the western America. Based on the above studies and achievements of the former workers, the deep background of the basin development is treated.

Miocene Tectonic Evolution from Dextral-Slip Thrusting to Extension in the Nyainqentanglha Region of the Tibetan Plateau

Dextral-slip in the Nyainqentanglha region of Tibet resulted in oblique underthrusting and granite generation in the Early to Middle Miocene, but by the end of the epoch uplift and extensional faulting dominated. The east-west dextral-slip Gangdise fault system merges eastward into the northeast-trending, southeast-dipping Nyainqentanglha thrust system that swings eastward farther north into the dextral-slip North Damxung shear zone and Jiali faults. These faults were took shape by the Early Miocene, and the large Nyainqentanglha granitic batholith formed along the thrust system in 18.3-11.0 Ma as the western block drove under the eastern one. The dextral-slip movement ended at -11 Ma and the batholith rose, as marked by gravitational shearing at 8.6-8.3 Ma, and a new fault system developed. Northwest-trending dextral-slip faults formed to the northwest of the raisen batholith, whereas the northeast-trending South Damxung thrust faults with some sinistral-slip formed to the southeast. The latter are replaced farther to the east by the west-northwest-trending Lhtinzhub thrust faults with dextral-slip. This relatively local uplift that left adjacent Eocene and Miocene deposits preserved was followed by a regional uplift and the initiation of a system of generally north-south grabens in the Late Miocene at -6.5 Ma. The regional uplift of the southern Tibetan Plateau thus appears to have occurred between 8.3 Ma and 6.5 Ma. The Gulu, DamxungYangbajain and Angan graben systems that pass east of the Nyainqentanglha Mountains are locally controlled by the earlier northeast-trending faults. These grabens dominate the subsequent tectonic movement and are still very active as northwest-trending dextral-slip faults northwest of the mountains. The Miocene is a time of great tectonic change that ushered in the modern tectonic regime.

Evolution of Sedimentation and Tectonics of the Youjiang Composite Basin, South China

Located at the southern margin of the South China plate, the Youjiang basin is a closely related to the NW- and NE-trending syndepositional faults in respect to the configuration and structure of the basin. The evolution of the Youjiang basin progressed through two stages. In the Hercynian period, the opening of the Ailaoshan-Honghe ocean basin gave rise to a number of NW-trending rift belts in the Youjiang area. During this period, deep-water sediments were dominant and the basin was possesed of the characteristics of the rift system of passive continental margins. In the early Indosinian after the Dongwu movement, the circum - Pacific tectonism led to a major change in the configuration and structure of the basin. In the meantime, the Ailaoshan ocean basin began to be subducted towards the northeast, thus causing the basin to be split and expand again, and then the basin developed into the stage of the back -arc basin. At the end of the Indosinian period, the basin gradually closed from east to west, thus ending up the history of development of the Youjiang basin. In the various developmental stages, sediments in the basin, also limited by the Dongwu movement, were formed by superposition of sedimentation systems with different features, and a typical two-layered structure, which consisted of starved and compensated sediments, also occurred in the early stage. Likewise, volcanic activity in the basin involved two stages. Basin volcanic rocks of alkali and alkali-calcic series, which were controlled by NW-trending faults, occurred in the early stage, and basic and intermediate-acid volcanic rocks of calc-alkali and calcic series, which were controlled by NW- and NE-trending faults. From the above it follows that the Youjiang basin was formed by the combined action of the Palaeotethys and circum -Pacific tectonism.

Inversion of two-phase extensional basin systems during subduction of the Paleo-Pacific Plate in the SW Korean Peninsula:Implication for the Mesozoic “Laramide-style” orogeny along East Asian continental margin

During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where the Early-Middle Jurassic intra-arc volcano-sedimentary Oseosan Volcanic Complex was developed on top of the Late Triassic-Early Jurassic post-collisional sequences, namely the Chungnam Basin. The basin shortening was accommodated mostly by contractional faults and related folds. In the basement, regional high-angle reverse faults as well as low-angle thrusts accommodate the overall shortening, and are compatible with those preserved in the cover. This suggests that their spatial and temporal development is strongly dependent on the initial basin geometry and inherited structures.Changes in transport direction observed along the basement-sedimentary cover interface is a characteristic structural feature, reflecting sequential kinematic evolution during basin inversion. Propagation of basement faults also enhanced shortening of the overlying sedimentary cover sequences. We constrain timing of the Late Jurassic-Early Cretaceous(ca. 158-110 Ma) inversion from altered K-feldspar 40 Ar/39 Ar ages in stacked thrust sheets and K-Ar illite ages of fault gouges, along with previously reported geochronological data from the area. This "non-magmatic phase" of the Daebo Orogeny is contemporaneous with the timing of magmatic quiescence across the Korean Peninsula. We propose the role of flat/low-angle subduction of the Paleo-Pacific Plate for the development of the "Laramide-style" basement-involved orogenic event along East Asian continental margin.

Tectonics-palaeogeomorphology in rift basins: controlling effect on the sequence architecture

The relationship between deposition and tectonics of sedimentary basins has been a significant subject in recent years.Using typical rift basins such as the Nanpu Sag as an example,combined with the analysis of the tectonics-palaeogeomorphology of basins,we undertook a detailed study of the differences of the third-order sequences in different basins,the combination of depositional systems within the sequence framework and the distribution of depocenters and subsidence centers.Our results revealed a significant relationship between the tectonics-palaeogeomorphology of rift basins and the filling styles of sedimentary sequences.The basin structure plays a primary role in controlling the development of the third-order sequences and the boundary of these sequences is easily formed in basins with gentle slopes,shallow water and a small area.The characteristics of the tectonics-palaeogeomorphology of rift basins are dominated by half-grabens of extensional faults,which affect the temporal and spatial combination of sedimentary systems within the sequences as well as the distribution of depocenters and subsidence centers.Based on the development rules of the faults dominating the half-grabens of extensional faults,rift basins are classified into two types： the single fault segmented-linkage type and the multi-fault combination type.The main controlling factors of the temporal and spatial combination of sedimentary systems and the distribution of depocenters and subsidence centers in different basins are different.The characteristics of early segmentation and later linkage of the faults play a critical role in controlling the sedimentary system combination within the sequence framework and the temporal and spatial differences of depocenters and subsidence centers of the single fault segmented-linkage rift basins,while the differences in fault activities are the dominating factors of the multi-fault combination rift basins.

NUMERICAL MODELLING OF LITHOSPHERE EVOLUTION IN THE NORTH CHINA CRATON: THERMAL THINNING VERSUS TECTONIC EXTENSION THINNING

The boundary between lithosphere and asthenosphere essentially represents a thermal boundary (the solidus). Temperature variation across this boundary can lead to the change of lithosphere thickness. In the case of elevated temperatures in a lithospheric layer above 1 200℃, partial melting will begin and the result of that is a thinned lithosphere. The other mechanism that can also thin lithosphere is extension. Stretching during an extension event can result in a thinner and longer lithosphere. The two mechanisms above are the reason why we can alserve large variations in lithosphere thickness spatially across various continents and temporally throughout the geological history.

北山东南部早白垩世伸展构造变形:二维反射地震剖面解释与磷灰石裂变径迹测年的制约

为深入认识中亚造山带南缘晚中生代陆内变形过程及其动力学机制,通过野外地质观察、二维反射地震剖面解释及磷灰石裂变径迹测年,对北山东南部早白垩世伸展构造及早期挤压构造进行了详细解析。结果表明,一系列逆冲断层与褶皱构造造成下—中侏罗统发生强烈的挤压变形。地震剖面揭示出2条早白垩世伸展正断层,其中梭梭井断层为南东倾向的低角度铲式正断层,五道明断层为北西倾向的高角度正断层,二者共同切割了早期形成的褶皱-冲断系统,指示挤压-伸展构造的转换;梭梭井断层与五道明断层分别限定了早白垩世总口子盆地的北西和南东边界,使得其具有“地堑”样式,盆地内沉积的下白垩统生长地层发育,表明伸展正断层的活动时间为早白垩世晚期。磷灰石裂变径迹热史模拟结果显示,梭梭井断层下盘于132~110 Ma经历了快速冷却和剥露事件,该事件与其持续的正断层活动密切相关,进一步证实北山东南部晚中生代挤压-伸展构造的转换很可能发生在早白垩世晚期(133~129 Ma)。增厚地壳的重力垮塌与局部地幔上涌共同导致了中亚造山带南缘早白垩世的区域伸展作用。

北康盆地基底构造特征及其对南海南部构造演化的启示

南海南部是研究东南亚地区构造演化的关键场所,以构造相对简单的北康盆地为基础探讨其构造演化过程。为了确定研究区的构造特征,进行了地震综合解释、主控断层的定性、定量分析和盆地之下的岩石圈伸展因子分析。通过构造分析,发现北康盆地15.5 Ma界面(MMU)之下发育了多条大规模、低角度的拆离断层,界面之下的原型盆地为裂陷盆地,并且局部可表现为拆离盆地,符合被动大陆边缘细颈化带内的构造特征。对北康盆地构造演化过程进行分析并将其与曾母盆地进行对比,发现2个盆地的构造演化特征迥然不同,据此重新将南海南部挤出-逃逸构造区和古南海俯冲-拖曳构造区之间的分界线确定为西巴拉姆线。结合南海南、北部的陆缘盆地基底卷入构造的发育特征发现,南海陆缘岩石圈在发生破裂后,应变的集中主要体现在靠近洋壳的细颈化带和远端带部位,远离洋壳地区的应变受海底扩张的影响较小,这一特征可能与被动陆缘岩石圈的近端和远端在拉伸过程中的解耦相关。

Mesozoic doming extensional tectonics of Wugongshan, South China

Wugongshan in Jiangxi Province, China was a Mesozoic granitic dome-type extensional tectonics that is composed of metamorphic core complexes, ductile and brittle shear-deformed zones distributed around Mesozoic granites. Within it, the foliation defines an E-W elliptical shape and bears S-N stretching lineations. The axial part is located in Hongjiang-Wanlongshan area and occupied by oriented granites with coaxial symmetric shear fabrics. The southem and northern flanks, including rocks in the Anfu Basin to the south and the Pingxiang Basin to the north, display top-to-south and top-to-north motions, respectively. The ductile and brittle structures indicate a geometric and kinematic consistency. The extensional tectonics is developed on a Caledonian metamorphic basement and is unconformably covered by Late Cretaceous red beds. Isotopic ages on muscovite, biotite and whole rock by40Ar-39Ar, K-Ar and Rb-Sr suggest that the Wugongshan extensional doming began from the Triassic and ended in the Late Cretaceous. A geodynamic model is discussed.

Identification of Five Stages of Dike Swarms in the Shanxi-Hebei-Inner Mongolia Border Area and Its Tectonic Implications

Dike swarms are generally ascribed to intrusion of mantle-source magma result from extension. Basic dike swarms around the Shanxi-Hebei-Inner Mogolia borders in the northern peripheral area of the North China Craton can be divided into five age groups according to isotopic dating: 1800-1700 Ma, 800-700 Ma, 230 Ma, 140-120 Ma, and 50-40 Ma. Geological, petrological and isotope geochemical features of the five groups is investigated in order to explore the variation of the mantle material composition in the concerned area with time. And the various extensional activities reflected by the five groups of dike swarms are compared with some important tectonic events within the North China Craton as well as around the world during the same period.

Triassic Collisional Structures and Post-CollisionalDeformation of Bixiling UHP Rock Stack: Insightsfor Tectonic Evolution of UHP MetamorphicBelt in Dabie Massif, Central China

Detailed three-dimensional structural studies indicate that the Bixiling area, Dabie massif, central China shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze -Sino-Korean continental collision. New 1 : 10 000 scale structural mapping, combined with detailed petrological analysis in this area, has enabled us to accurately distinguish structures related to the Triassic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit. The collisional or compressional structures include the massive eclogite with a weak foliation, foliated eclogite or UHP ductile shear zones, as well as upper amphibolite facies shear zones, whereas the post-collisional deformation is characterized by a regionally, flat-lying foliation containing stretching lineations and common reclined folds. The former is present exclusively in the eclogite lenses and their margins, representing orogenic thickening or syn-collisional events, while the latter was best occurred on variable scales under amphibolite facies conditions, showing sub-vertical, extreme shortening and ductile thinning of the metamorphic rock stack. The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common. It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was, at least partly, responsible for exhumation of the UHP metamorphic rocks in the Dabie massif. A new tectonic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif. The Bixiling area thus provides a window, from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed. Regional studies in the Dabie Mountains have confirmed this interpretation.

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin(North China)and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates （the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west） towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.