Recent volcanism in relation to plate interaction and deep-level geodynamics

The spatial distribution of recent (under 2 Ma) volcanism has been studied in relation to mantle hotspots and the evolution of the present-day supercontinent which we named Northern Pangea. Recent volcanism is observed in Eurasia, North and South America, Africa, Greenland, the Arctic, and the Atlantic, Indian, and Pacific Oceans. Several types of volcanism are distinguished: mid-ocean ridge (MOR) volcanism; subduction volcanism of island arcs and active continental margins (IA + ACM); continental collision (CC) volcanism; intraplate (IP) volcanism related to mantle hotspots, continental rifts, and transcontinental belts. Continental volcanism is obviously related to the evolution of Northern Pangea, which comprises Eurasia, North and South America, India, Australia, and Africa. The supercontinent is large, with predominant continental crust. The geodynamic setting and recent volcanism of Northern Pangea are determined by two opposite processes. On one hand, subduction from the Pacific Ocean, India, the Arabian Peninsula, and Africa consolidates the supercontinent. On the other hand, the spreading of oceanic plates from the Atlantic splits Northern Pangea, changes its shape as compared with Wegener’s Pangea, and causes the Atlantic geodynamics to spread to the Arctic. The long-lasting steady subduction beneath Eurasia and North America favored intense IA + ACM volcanism. Also, it caused cold lithosphere to accumulate in the deep mantle in northern Northern Pangea and replace the hot deep mantle, which was pressed to the supercontinental margins. Later on, this mantle rose as plumes (IP mafic magma sources), which were the ascending currents of global mantle convection and minor convection systems at convergent plate boundaries. Wegener’s Pangea broke up because of the African superplume, which occupied consecutively the Central Atlantic, the South Atlantic, and the Indian Ocean and expanded toward the Arctic. Intraplate plume magmatism in Eurasia and North America was accompanied by surface collisional or subduction magmatism. In the Atlantic, Arctic, Indian, and Pacific Oceans, deep-level plume magmatism (high-alkali mafic rocks) was accompanied by surface spreading magmatism (tholeiitic basalts).     

Generations of spreading basins and stages of breakdown of Wegener’s Pangea in the geodynamic evolution of the Arctic Ocean

Chronological succession in the formation of spreading basins is considered in the context of reconstruction of breakdown of Wegener’s Pangea and the development of the geodynamic system of the Arctic Ocean. This study made it possible to indentify three temporally and spatially isolated generations of spreading basins: Late Jurassic-Early Cretaceous, Late Cretaceous-Early Cenozoic, and Cenozoic. The first generation is determined by the formation, evolution, and extinction of the spreading center in the Canada Basin as a tectonic element of the Amerasia Basin. The second generation is connected to the development of the Labrador-Baffin-Makarov spreading branch that ceased to function in the Eocene. The third generation pertains to the formation of the spreading system of interrelated ultraslow Mohna, Knipovich, and Gakkel mid-ocean ridges that has functioned until now in the Norwegian-Greenland and Eurasia basins. The interpretation of the available geological and geophysical data shows that after the formation of the Canada Basin, the Arctic region escaped the geodynamic influence of the Paleopacific, characterized by spreading, subduction, formation of backarc basins, collision-related processes, etc. The origination of the Makarov Basin marks the onset of the oceanic regime characteristic of the North Atlantic (intercontinental rifting, slow and ultraslow spreading, separation of continental blocks (microcontinents), extinction of spreading centers of primary basins, spreading jumps, formation of young spreading ridges and centers, etc., are typical) along with retention of northward propagation of spreading systems both from the Pacific and Atlantic sides. The aforesaid indicates that the Arctic Ocean is in fact a hybrid basin or, in other words, a composite heterogeneous ocean in respect to its architectonics. The Arctic Ocean was formed as a result of spatial juxtaposition of two geodynamic systems different in age and geodynamic style: the Paleopacific system of the Canada Basin that finished its evolution in the Late Cretaceous and the North Atlantic system of the Makarov and Eurasia basins that came to take the place of the Paleopacific system. In contrast to traditional views, it has been suggested that asymmetry of the northern Norwegian-Greenland Basin is explained by two-stage development of this Atlantic segment with formation of primary and secondary spreading centers. The secondary spreading center of the Knipovich Ridge started to evolve approximately at the Oligocene-Miocene transition. This process resulted in the breaking off of the Hovgard continental block from the Barents Sea margin. Thus, the breakdown of Wegener’s Pangea and its Laurasian fragments with the formation of young spreading basins was a staged process that developed nearly from opposite sides. Before the Late Cretaceous (the first stage), the Pangea broke down from the side of Paleopacific to form the Canada Basin, an element of the Amerasia Basin (first phase of ocean formation). Since the Late Cretaceous, destructive pulses came from the side of the North Atlantic and resulted in the separation of Greenland from North America and the development of the Labrador-Baffin-Makarov spreading system (second phase of ocean formation). The Cenozoic was marked by the development of the second spreading branch and the formation of the Norwegian-Greenland and Eurasia oceanic basins (third phase of ocean formation). Spreading centers of this branch are functioning currently but at an extremely low rate.     

Plate reconstructions in the Arctic region based on joint analysis of gravity,magnetic, and seismic anomalies

Based on the analysis of various geophysical data, namely, free-air gravity anomalies, magnetic anomalies, upper mantle seismic tomography images, and topography/bathymetry maps, we single out the major structural elements in the Circum Arctic and present the reconstruction of their locations during the past 200 million years. The configuration of the magnetic field patterns allows revealing an isometric block, which covers the Alpha–Mendeleev Ridges and surrounding areas. This block of presumably continental origin is the remnant part of the Arctida Plate, which was the major tectonic element in the Arctic region in Mesozoic time. We believe that the subduction along the Anyui suture in the time period from 200 to 120 Ma caused rotation of the Arctida Plate, which, in turn, led to the simultaneous closure of the South Anyui Ocean and opening of the Canadian Basin. The rotation of this plate is responsible for extension processes in West Siberia and the northward displacement of Novaya Zemlya relative to the Urals–Taimyr orogenic belt. The cratonic-type North American, Greenland, and European Plates were united before 130 Ma. At the later stages, first Greenland was detached from North America, which resulted in the Baffin Sea, and then Greenland was separated from the European Plate, which led to the opening of the northern segment of the Atlantic Ocean. The Cenozoic stage of opening of the Eurasian Basin and North Atlantic Ocean is unambiguously reconstructed based on linear magnetic anomalies. The counter-clockwise rotation of North America by an angle of ~ 15° with respect to Eurasia and the right lateral displacement to 200–250 km ensure an almost perfect fit of the contours of the deep water basin in the North Atlantic and Arctic Oceans.     

Formation of the Eurasia Basin in the Arctic Ocean as inferred from geohistorical analysis of the anomalous magnetic field

A new combined magnetic database and a magnetic-profile map are developed for the Eurasia Basin as a result of adjusting all available historical and recent Russian and American magnetic data sets. The geohistorical analysis of magnetic data includes several steps: identification of linear magnetic anomalies along each trackline, calculation of the Euler rotation pole positions for the relative motion of the North American and Eurasian plates, analysis of temporal and spatial variations in the spreading rate, and plate reconstructions. The pattern of key Cenozoic magnetic isochrons (24, 20, 18, 13, 6, 5, 2a) is constructed for the entire Eurasia Basin. In the western half of the basin, this pattern is consistent with a recently published scheme [16]. In its eastern half, magnetic isochrons are determined in detail for the first time and traced up to the Laptev Sea shelf. The main stages in the seafloor spreading are established for the Eurasia Basin. Each stage is characterized by a specific spreading rate and the degree of asymmetry of the basin opening. The revealed differences are traced along the Gakkel Ridge. Systematic patterns in wandering of the Eurasia Basin opening pole are established for particular stages. The continent-ocean transition zone corresponding to the primary rupture between plates is outlined in the region under consideration on the basis of gravimetric data. The nature of different potential fields and bottom topography on opposite sides of the Gakkel Ridge is discussed. The characteristic features of the basin-bottom formation at main stages of its evolution are specified on the basis of new and recently published data. The results obtained are in good agreement with plate geodynamics of the North Atlantic and the adjacent Arctic basins.     

The atlantic margin of Iberia and Morocco, a reinterpretation

Morphology, magnetic and seismic properties, and the geology of the sea-floor and adjacent continent indicate that the area west of Iberia and Morocco is a deformed passive continental margin. Formation of this margin is envisaged as having proceeded through a doming and rifting phase, whereby thinned continental fragments became detached from the continent and each other to form a wide zone with geophysical characteristics intermediate between those of the continent and those of the ocean. A wedge-shaped basin opened between Iberia and some of the larger detached continental fragments, the Madeira—Tore Rise and Galicia Bank. The opening of this basin and of the Bay of Biscay in Late Jurassic—Early Cretaceous time is a direct consequence of the counter-clockwise rotation of Iberia between relatively stable Europe and eastward-moving Africa. During the Tertiary the continental margin became compressed in the north—south direction and pieces of the sea-floor were thrust up and over each other to form the predominantly northeast oriented Horseshoe Seamounts. At the same time left-lateral shears developed in the margin between then northward-moving Africa and Iberia and the eastward-spreading Atlantic. Massive outpourings of Late Tertiary to Recent lavas along some of these shears are responsible for the ultimate shape of the Atlantic margins of northwest Africa and Iberia.     

The contemporary North Pangea supercontinent and the geodynamic causes of its formation

The supercontinental status of the contemporary aggregation of continents called North Pangea is substantiated. This supercontinent comprises all continents with the probable exception of Antarctica. In addition to the spatial contiguity of continents, the supercontinent is characterized by the prevalence of the continental crust that combines North America and Eurasia, Eurasia and Africa, and Eurasia and Australia. Over the course of the 300–250-Ma evolution from Wegener’s Pangea to contemporary North Pangea, the aggregation of continents has not lost its supercontinental status, despite modification of the supercontinent shape and opening and closure of the newly formed Paleotethys, Tethys, Atlantic, and Indian oceans. Over the last 250–300 Ma, all movements of the lithospheric plates have most likely occurred within the Indo-Atlantic segment of the Earth, whereas the Pacific segment has remained oceanic. In short, the formation of the North Pangea supercontinent can be outlined in the following terms. The long and deep subduction of the lithospheric plates beneath Eurasia and North America gave rise to the stabilization of the continents and accumulation of huge bodies of the cold lithosphere commensurable in volume with the upper mantle at the deeper mantle levels. This brought about compensation ascent of hot mantle (mantle plumes) near the convergent plate boundaries and far from them. A special geodynamic setting develops beneath the supercontinent. Due to encircling subduction of the lithospheric plates and related squeezing of the hot mantle, an ascending flow, or plume (superplume) formed beneath the central part of the supercontinent. In our view, the African superplume broke up Wegener’s Pangea in the Atlantic region, caused the opening of the Atlantic and Indian oceans, and migrated to the Arctic Region 53 Ma ago.     

大陆真的能漂移吗?

魏根纳的大陆漂移设想起源于“对大西洋两岸吻合的直觉印象”.这种“吻合”是指大西洋两侧南美洲和非洲海岸线的吻合.然而,近数十年的海底地球物理和地质调查确已发现,大西洋及其两岸大陆的磁异常、地震层析图像、地震探测剖面以及洋中脊岩石中锆石年龄的测定都说明大西洋是大陆裂谷作用裂陷形成的海洋,两侧大陆并没有发生显著的水平位移,而世界各大陆块深达300~400 km大陆根的存在,似乎已基本否定了大陆发生大规模移动的可能.      

Tecto-sedimentary cycles and depositional sequences of the Mesozoic and Tertiary from the Pyrenees

Tectonic deformation in the Pyrenees is the result of an essentially continuous process which has a discontinuous effect in the style of deformation and consequently, in the sedimentary record. Tecto-sedimentary discontinuities can be correlated on a regional scale, allowing the differentiation of tecto-sedimentary cycles and depositional sequences. The relations between tectonics and sedimentation in the Pyrenees are expressed in the Mesozoic and Tertiary cyclicity.Ten tecto-sedimentary cycles have been distinguished. They are controlled by basin-forming and basin-modifying tectonics (rifting, wrenching, convergence) and are related to different successive basin-types.A first group of cycles corresponds to the episodic rifting: post-Hercynian interior fracture basin (cycle 1), spreading of the Ligurian Ocean (cycle 2), spreading of the central North Atlantic Ocean (cycle 3) and rifting of the Bay of Biscay in the context of the rotation of Iberia (cycle 4). A second group corresponds to the opening of the North Atlantic Ocean and to the change in the trajectory of Iberia along a W-E direction (cycle 5). The third group corresponds to prevailing wrench conditions grading from strike-slip plate displacement (cycle 6) to progressive oblique convergence (cycle 7). The fourth group of cycles (8, 9 and 10) corresponds to the generalization of convergence conditions; cycle 8 is the transition from wrench to foreland basin; cycle 9 corresponds to the development of migrating foreland basins in relation to thrust sheet emplacement; cycle 10 includes the unconformable clastic wedge ahead of the last thrust.These tecto-sedimentary cycles include one or several depositional sequences in which sedimentation is controlled by the interrelations between local tectonics, subsidence, eustacy and sediment supply. The analysis and definition of these sequences is given for the Cretaceous and Tertiary cycles. The depositional sequences from the Cretaceous wrench basin are essentially related to eustacy (sea level rise) together with subsidence during cycle 6, and wrench structuring during cycle 7. The depositional sequences from the foreland basins (cycles 8, 9 and 10) are related to changes in the type of basin.     

Geodynamic setting of recent volcanism in North Eurasia

A GIS layout of the map of recent volcanism in North Eurasia is used to estimate the geodynamic setting of this volcanism. The fields of recent volcanic activity surround the Russian and Siberian platforms—the largest ancient tectonic blocks of Eurasia—from the arctic part of North Eurasia to the Russian Northeast and Far East and then via Central Asia to the Caucasus and West Europe. Asymmetry in the spatial distribution of recent volcanics of North Eurasia is emphasized by compositional variations and corresponding geodynamic settings. Recent volcanic rocks in the arctic part of North Eurasia comprise the within-plate alkaline and subalkaline basic rocks on the islands of the Arctic Ocean and tholeiitic basalts of the mid-ocean Gakkel Ridge. The southern, eastern, and western volcanic fields are characterized by a combination of within-plate alkaline and subalkaline basic rocks, including carbonatites in Afghanistan, and island-arc or collision basalt-andesite-rhyolite associations. The spatial distribution of recent volcanism is controlled by the thermal state of the mantle beneath North Eurasia. The enormous mass of the oceanic lithosphere was subducted during the formation of the Pangea supercontinent primarily beneath Eurasia (cold superplume) and cooled its mantle, having retained the North Pangea supercontinent almost unchanged for 200 Ma. Volcanic activity was related to the development of various shallow-seated geodynamic settings and deep-seated within-plate processes. Within-plate volcanism in eastern and southern North Eurasia is controlled, as a rule, by upper mantle plumes, which appeared in zones of convergence of lithospheric plates in connection with ascending hot flows compensating submergence of cold lithospheric slabs. After the breakdown of Pangea, which affected the northern hemisphere of the Earth insignificantly, marine basins with oceanic crust started to form in the Cretaceous and Cenozoic in response to the subsequent breakdown of the supercontinent in the northern hemisphere. In our opinion, the young Arctic Ocean that arose before the growth of the Gakkel Ridge and, probably, the oceanic portion of the Amerasia Basin should be regarded as a typical intracontinental basin within the supercontinent [48]. Most likely, this basin was formed under the effect of mantle plumes in the course of their propagation (expansion, after Yu.M. Pushcharovsky) to the north of the Central Atlantic, including an inferred plume of the North Pole (HALIP).     

Avalonia,get bent!–Paleomagnetism from SW Iberia confirms the Greater Cantabrian Orocline

The amalgamation of Pangea formed the contorted Variscan-Alleghanian orogen,suturing Gondwana and Laurussia during the Carboniferous.From all swirls of this orogen,a double curve in Iberia stands out,the coupled Cantabrian Orocline and Central Iberian curve.The Cantabrian Orocline formed at ca.315–290 Ma subsequent to the Variscan orogeny.The formation mechanism of the Cantabrian Orocline is disputed,the most commonly proposed mechanisms include either(1)that south-westernmost Iberia would be an Avalonian(Laurussian)indenter or(2)that the stress field changed,buckling the orogen.In contrast,the geometry and kinematics of the Central Iberian curve are largely unknown.Whereas some authors defend both curvatures are genetically linked,others support they are distinct and formed at different times.Such uncertainty adds an extra layer of complexity to our understanding of the final stages of Pangea’s amalgamation.To solve these issues,we study the late Carboniferous–early Permian vertical-axis rotations of SW Iberia with paleomagnetism.Our results show up to 70
counterclockwise vertical-axis rotations during late Carboniferous times,concurring with the anticipated kinematics if SW Iberia was part of the southern limb of the Cantabrian Orocline.Our results do not allow the necessary penecontemporaneous clockwise rotations in Central Iberia to support a concomitant formation of both Cantabrian and Central Iberian curvature.The coherent rotation of both Gondwanan and Avalonian pieces of SW Iberia discards the Laurussian indenter hypothesis as a formation mechanism of the Cantabrian Orocline and confirms the Greater Cantabrian Orocline hypothesis.The Greater Cantabrian Orocline likely formed as a consequence of a change in the stress field during the late Carboniferous and extended beyond the Rheic Ocean suture affecting the margins of both Laurussia and Gondwana.     

特提斯地球动力学

特提斯是地球显生宙期间位于北方劳亚大陆和南方冈瓦纳大陆之间的巨型海洋,它在新生代期间的闭合形成现今东西向展布的欧洲阿尔卑斯山、土耳其-伊朗高原、喜马拉雅山和青藏高原。根据演化历史,特提斯可划分为原特提斯、古特提斯和新特提斯三个阶段,分别代表早古生代、晚古生代和中生代期间的大洋。大约在500Ma左右,冈瓦纳大陆北缘发生张裂,裂解的块体向北漂移,并使其与塔里木-华北之间的原特提斯洋在420～440Ma左右关闭,产生原特提斯造山作用,与北美-西欧地区Avalonia地体与劳伦大陆之间的阿巴拉契亚-加里东造山作用基本相当。原特提斯造山带之南、早古生代即已存在的龙木错-双湖-昌宁-孟连古特提斯洋在380Ma向北俯冲,使早期闭合的康西瓦-阿尼玛卿洋重新张开,并由于弧后扩张形成金沙江-哀牢山洋。330～360Ma左右,特提斯西部大洋由于南侧非洲板块和北侧欧洲板块的碰撞而关闭,形成欧洲华力西造山带。而特提斯东段的上述三条古特提斯洋在250Ma左右基本同时关闭,华北、华南、印支等块体聚合形成华夏大陆。该大陆与冈瓦纳大陆、劳亚大陆和华力西造山带一起围限形成封闭的古特提斯残留洋,并一直到晚三叠世-早侏罗世海水才全部退出。此后,南侧冈瓦纳大陆在三叠纪晚期重新裂解形成新特提斯洋,该洋盆在新生代初期由于印度和亚洲的碰撞而关闭。原、古、新特提斯三次造山作用基本代表了中国大陆显生宙期间的地质演化历史,并在此过程中形成了特色的特提斯域金属成矿作用。广布的被动陆缘和赤道附近的古地理位置,以及后期的造山作用同时也成就了特提斯域内巨量油气资源的形成;塑就的地貌与海陆分布格局,也对当时的古气候与古环境产生了重要影响。特别是,与原、古、新特提斯洋消亡相关的三次弧岩浆活动与显生宙地球历史上三次温室地球向冰室地球的转变,在时间上高度吻合。上述演化历史同时还表明,特提斯地质演化以南侧冈瓦纳大陆不断裂解、块体向北漂移并与劳亚大陆持续聚合为特征,其动力机制主要来自俯冲板片的拖拽力,而地幔柱是否对大陆的裂解与漂移有所贡献,则有待进一步评价。     

Thermal impact of the break-up of Pangea on the Iberian Peninsula, assessed by thermochronological dating and numerical modelling

Thermochronological studies of Variscan basement in Iberia yield cooling ages typically younger than ~ 200 Ma. In this paper, we explore the regional implications of this recurrent age maximum by examination of low and high temperature thermochronological datasets from all over Iberia. Based on these results, we show that in general the lack of cooling ages older than 200 Ma is the result of several important regional periods of thermal resetting. Resetting took place in areas of extension and burial during the Mesozoic break-up of Pangea. Evidence for large scale magmatism and mineralisation is found in Iberia during the Mesozoic, since at that time Iberia formed part of the Central Atlantic Magmatic Province and a large mineralization province extending from North Africa to Western Europe. Numerical modelling allows us to assess the conditions under which rocks in the upper crust may have been thermally reset and the mechanisms likely involved. Results show that active rifting combined with shallow magmatism, and to a lesser extent deep sedimentary burial, could have led to an increase of the geothermal gradient up to ~ 73 °C/km and the reset of thermochronometers with closure temperatures up to 200 °C. Yet, we suggest that also hydrothermal activity, associated to extensional basins, played an important role to the increase of temperatures of some basement rocks above 300 °C.     

Paleomagnetic implications on the evolution of the tethys belt from the atlantic ocean to the pamirs since the triassic

We first re-examined the apparent polar wander curves for stable Eurasia and Africa since the Triassic. These curves were then combined together with curves of North and South America according to the kinematics of the Atlantic ocean and a synthetic polar wander curve was given. Then, most of the paleomagnetic results from the Tethys mobile belt, from the Atlantic to the Pamirs, were analysed.Several groups of plates, microplates and blocks can be seen. First, relatively stable regions like Maghreb and Sicily, which have not moved much. Then we have a group formed by Iberia, Sardinia, Italy and, to a lesser extent, Corsica and the Western and Central Alps. For these blocks, movements are anticlockwise rotations chiefly driven by the anticlockwise rotation of Africa, but they are sometimes stronger.To the east, a major change takes place. The north of the Aegean Sea and the Ionian zone are clockwise rotated and these rotations are recent: Oligocene-Miocene for the first part, Pliocene to the present for the second part.A major problem arises in Turkey, Caucasus and Iran. Paleomagnetic results indicate a position far to the south of Eurasia, and, at the same time, geological evidence is in favour of a position close to Eurasia. We discuss these discrepancies.     

Passive margins of the North and Central Atlantic: A comparative study

The main features of the volcanic and nonvolcanic passive margins of the North and Central Atlantic are considered. The margins are compared using rather well-studied reference tectonotypes as examples. The conjugate margins of the Norwegian-Greenland region and the margins of West Iberia and Newfoundland are chosen as tectonotypes of volcanic and nonvolcanic margins, respectively. The structural and magmatic features of the margins and their preceding history are discussed. A complex of interrelated attributes is shown for each tectonotype. The Norwegian-Greenland region close to the Iceland plume is distinguished by narrow zones of stretched continental crust, rapid localization of stretching with breakup of the continent, a high rate of subsequent spreading, and intense magmatism with the formation of a thick new crust at the margin and the adjacent oceanic zone. The Iberia-Newfoundland region, remote from the plumes, is characterized by wide zones of stretched continental crust, long-term and diachronous prebreakup extension propagating northward, extremely restricted mantle melting during rifting and initial spreading, and frequent occurrence of ancient crustal complexes and serpentinized mantle rocks at the margin. Crustal faults and a thin tectonized oceanic crust appear along the margin under conditions of slow spreading. A model of hot and fast spreading with a high degree of melting in the mantle is applicable to the Norwegian-Greenland region, whereas a model of cold and slow amagmatic rifting with a long pre-breakup stretching and thinning of the lithosphere is appropriate to the Iberia-Newfoundland margins. The differences in the development of the margins is determined by the interaction of many factors: deep temperature, rheology of the underlying lithosphere, heterogeneities in the previously formed crust, and the duration and rate of stretching. All of these factors can be related to the effect of deep plumes and propagation of the extension zone toward the segments of the cold Atlantic lithosphere. Both types of margins also reveal similar features, in particular asymmetry. It is suggested that the rotation forces superimposed on the general tectonomagmatic pattern controlled by plumes could have been the cause of structural asymmetry.     

Plate tectonic evolution of the southern margin of Eurasia in the Mesozoic and Cenozoic

Thirteen time interval maps were constructed, which depict the Triassic to Neogene plate tectonic configuration, paleogeography and general lithofacies of the southern margin of Eurasia. The aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework. The Hercynian Orogeny was completed by the collision of Gondwana and Laurussia, whereas the Tethys Ocean formed the embayment between the Eurasian and Gondwanian branches of Pangea. During Late Triassic–Early Jurassic times, several microplates were sutured to the Eurasian margin, closing the Paleotethys Ocean. A Jurassic–Cretaceous north-dipping subduction boundary was developed along this new continental margin south of the Pontides, Transcaucasus and Iranian plates. The subduction zone trench-pulling effect caused rifting, creating the back-arc basin of the Greater Caucasus–proto South Caspian Sea, which achieved its maximum width during the Late Cretaceous. In the western Tethys, separation of Eurasia from Gondwana resulted in the formation of the Ligurian–Penninic–Pieniny–Magura Ocean (Alpine Tethys) as an extension of Middle Atlantic system and a part of the Pangean breakup tectonic system. During Late Jurassic–Early Cretaceous times, the Outer Carpathian rift developed. The opening of the western Black Sea occurred by rifting and drifting of the western–central Pontides away from the Moesian and Scythian platforms of Eurasia during the Early Cretaceous–Cenomanian. The latest Cretaceous–Paleogene was the time of the closure of the Ligurian–Pieniny Ocean. Adria–Alcapa terranes continued their northward movement during Eocene–Early Miocene times. Their oblique collision with the North European plate led to the development of the accretionary wedge of the Outer Carpathians and its foreland basin. The formation of the West Carpathian thrusts was completed by the Miocene. The thrust front was still propagating eastwards in the eastern Carpathians.During the Late Cretaceous, the Lesser Caucasus, Sanandaj–Sirjan and Makran plates were sutured to the Iranian–Afghanistan plates in the Caucasus–Caspian Sea area. A north-dipping subduction zone jumped during Paleogene to the Scythian–Turan Platform. The Shatski terrane moved northward, closing the Greater Caucasus Basin and opening the eastern Black Sea. The South Caspian underwent reorganization during Oligocene–Neogene times. The southwestern part of the South Caspian Basin was reopened, while the northwestern part was gradually reduced in size. The collision of India and the Lut plate with Eurasia caused the deformation of Central Asia and created a system of NW–SE wrench faults. The remnants of Jurassic–Cretaceous back-arc systems, oceanic and attenuated crust, as well as Tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems.     

Seismic models of inner parts of the Euro-Asian continent and its margins

Analogies are drawn between continental and continental margin structures on the basis of seismic data on the crustal structure of Eurasia and its Atlantic margins. Crustal thinning from the inner parts of the continent to its margins is observed to be a general feature common to the formation of deep midland depressions and sedimentary basins of shelf zones. The latter are characterized by crustal thinning and its assimilation. These phenomena cannot be explained solely be sea-floor spreading effects in the process of active rifting and formation of oceanic crust. It appears that the main role in the formation of the margins in played by processes of mantle erosion in connection with heating at continental margins and with the migration of mantle material to the lower part of the crust.     

南海南部礼乐盆地结构演化及其对区域地质背景的响应

运用丰富的二维地震资料,通过构造结构与地层结构的分析,对礼乐盆地的盆地结构演化与转型过程及其对南海地区复杂动力学背景的响应特征进行研究。结果表明:受控于NNE、NEE、NW和近EW向的断裂体系,礼乐盆地现今构造格局表现为"两坳一隆"的结构特征;两个关键的区域角度不整合T70和T50将礼乐盆地新生界自下而上划分为三层结构:陆缘裂陷层、漂移裂陷层和前陆-拗陷层;响应于太平洋板块俯冲、印度-欧亚板块碰撞、新南海扩张、古南海消亡和菲律宾海板块楔入等一系列周缘板块重组事件,礼乐盆地的盆地结构演化及转型经历了三个阶段:陆缘多幕裂陷阶段,盆地结构受控于NNE和NEE向断裂体系,南北坳陷连通;漂移裂陷阶段,NNE和NW向共轭断裂体系控制盆地格局,中部隆起形成,分隔南、北坳陷;前陆-拗陷阶段,前陆盆地结构形成,随后盆地因热沉降进入拗陷沉积阶段。     

Mesozoic tectonic evolution of the southwest continental Iberian Margin

An extensional event affected the southwest Margin of Iberia during Late Triassic to Early Cretaceous times, giving place to the Algarve basin. This basin was subjected to tectonic instability and it became infilled with siliciclastic and carbonate sequences with abundant interspersed volcanic rocks. Normal and strike-slip faults accommodated the deformation in the Algarve basin. The presence of a single flat or listric detachment surface is inferred from the study of hanging-wall structures. The dynamic and kinematic analyses of fault systems in the Spanish exposure of the Algarve basin allow us to establish three extensional phases. 1) A Late Triassic to Hettangian NE-SW directed extension associated with the initial breaking of Pangea and the opening of the Tethys in the eastern Mediterranean. 2) NW-SE extension from the Sinemurian to the Callovian, interpreted as a result of the activity as a sinistral fault of the Azores-Gibraltar transform boundary. 3) Finally, E-W extension during the Late Jurassic and Cretaceous, related to the North Atlantic rifting process.