Late Mesozoic Research Articles

Coupling mechanism of basin and orogen in the Tianshan Orogenic Belt since Late Mesozoic: Influence on the source–sink process of sandstone‐type uranium mineralization

The coupling mechanism of the Tianshan Orogenic Belt (TOB) and the basins on its sides (Junggar, Turpan–Hami, Tarim, Yili, etc.) since the Late Mesozoic was complex and multi‐levelled. Based on gravity, magnetism, Moho discontinuity, and lithospheric velocity structure of the TOB, together with the structural and sedimentary data of the basins, a model is proposed to reflect the influence of the basin–orogen coupling on the regional source–sink processes of sandstone‐type uranium mineralization since the Late Mesozoic. Generally, there are four main stages of tectonic movements that have changed the coupling mechanism of basin and orogeny: including the Early Yanshanian Movement, the Late Yanshanian Movement, the Middle Himalayan Movement, and the Late Himalayan Movement. These four movements together controlled the mineralization of the sandstone‐type uranium deposits in the TOB together. The mineralization of sandstone‐type uranium deposits in the TOB can be divided into three metallogenic stages: the ore‐bearing formation stage (T‐J2), the tectonic reversal‐related metallogenic stage (J3‐N1), and the epigenetic regenerating ore‐preserving stage (N2‐Q). The tectonic reversal‐related metallogenic stage can be subsequently divided into three sub‐stages: the pre‐metallogenic stage (J3), the sub‐metallogenic stage (K), and the main metallogenic stage (E‐N1). The associated uplift led to the deformation of the mineralized strata in the basins, while the reducing agent migration along faults enhanced the reduction environment within the strata, which affected the enrichment and distribution of the uranium mineralization in the strata. Meanwhile, the recharge and the change of flow state of groundwater also contributed to the later transformation and mineralization. The intra‐continental subduction caused deep lithospheric buckling and depression in the TOB, accompanied by local‐scale mantle convection, which accounts for both tectonic and geodynamic settings for the regional basin–orogen coupling mechanism. In addition, the far‐field effect of the India–Eurasian collision also provided the driving force for the sandstone‐type uranium mineralization in the TOB.

Geological characteristics, geodynamic setting of magmatism and metallogeny of Early Cretaceous Sn (W) deposits in southeastern coastal belt of China, and their implication for exploration

我国华南是世界上最重要的锡矿资源省之一，其锡矿成矿时代从新元古代、古生代、早中生代至晚中生代均有发育，其中以晚中生代锡矿成矿作用最为重要，成矿集中在中晚侏罗世（160~150Ma）和晚白垩世（100~80Ma）。然而，最近在东南沿海成矿带新识别出一期早白垩世锡（钨）（145~130Ma）成矿事件，改变了以往华南锡（钨）矿床时空分布格局。本文在详细介绍东南沿海早白垩世锡（钨）矿床地质特征基础上，系统总结了其成岩成矿时空分布，并与南岭板内锡（钨）成矿作用进行对比，浅析了早白垩世锡（钨）矿的成岩成矿背景和找矿潜力。研究显示，早白垩世锡（钨）成矿主要发生在东南沿海成矿带的粤东和赣州会昌地区，矿床类型以斑岩型和锡石硫化物型为主。与成矿有关的岩石为黑云母花岗岩和花岗斑岩，成因上属于高分异I型或A型，与南岭板内锡（钨）矿相比，具有较高的锆石ε_Hf（t）值和较低δ¹⁸O值，以及较高成岩温度，表明成岩过程中有较多新生地壳或地幔物质加入。结合区内发育同时期基性岩脉，认为华南这期早白垩世锡（钨）矿形成于岩石圈伸展背景，与古太平洋板块俯冲后撤有关。最后指出覆盖大面积晚白垩世火山岩的东南沿海地区，火山岩盖层下部具有寻找该期锡（钨）矿床的找矿潜力。;South China is one of the most important tin provinces in the world, and the tin mineralization formed from Neoproterozoic, Early Paleozoic, to Early and Late Mesozoic are well developed in this area. In particular, the Late Mesozoic tin mineralization is the most important one, happened at two age peaks of the Middle-Late Jurassic (160~150Ma) and Late Cretaceous (100~80Ma), respectively. However, an Early-Cretaceous (145~130Ma) tin (tungsten) metallogenic event has also been newly recognized in southeastern coastal belt of China. This makes a change in temporal-spatial framework of tin (tungsten) deposits. In this paper, based on detailed observations of geological characteristics of the Early Cretaceous tin (tungsten) deposits in southeastern coastal belt, we summarize the temporal-spatial distribution of these deposits and their associated magmatisms, and compared them with those in the Nanling Range, in order to identify their metallogenic geodynamic setting and implications for metallogenic potential. The Early Cretaceous tin (tungsten) deposits are mainly developed in the coastal eastern Guangdong Province and Huichang district of the southern Jiangxi Province. Genetically, the tin mineralization mainly comprises porphyry and cassiterite-sulfide-vein types, and associated granitoids include biotite granite and granitic porphyry characterized by high-fractionated I- and A-type affinities. Compared with those in the Nanling Range, these granites display higher zircon ε_Hf(t) and δ¹⁸O values, as well as higher magma temperatures, indicating a contribution of more mantle or juvenile crustal components. Given the coeval mafic dikes in the region, we suggest that the Early Cretaceous tin (tungsten) deposits were formed in the setting of lithospheric extension, triggered by the retreat of the subducting paleo-Pacific plate. Finally, we suggest that there is potential for tin (tungsten) exploration under the large-scale cover of Late Cretaceous volcanic rocks in southeastern coastal belt of China.

Interactions between thin- and thick-skinned tectonics at the western Sichuan Basin, China

This study investigates the geometry, kinematics, and interaction of thin- and thick-skinned tectonics at the western Sichuan Basin adjacent to the eastern margin of the Tibetan Plateau. A two-level detachment system, comprising a shallow Triassic and basal Precambrian detachment, was identified. Three-dimensional (3-D) structural modeling was applied to demonstrate the geometry of the shallow detachment that developed in the Sichuan foreland basin. The shallow detachment forming material is an evaporite sequence deposited in the Middle Triassic, which was subsequently buried beneath the foreland basin and later subsided rapidly during the flexural loading process during the Late Triassic. In the Cenozoic, this set of evaporite rocks developed into an effective shallow detachment, transferring geologic slip from the Longmen Shan range front to the Sichuan Basin. The structure of this shallow detachment exhibits an asymmetrical characteristic, with its deepest location consistent with the Mesozoic foreland depression. This relationship indicates that foreland subsidence in the Late Mesozoic is the main factor controlling the geometry of the detachment. In the southern Cenozoic foreland basin, the development of thrust faults above the Precambrian basal detachment resulted in a local deformation and uplift of the shallow detachment, resulting in a lower basal slope (0.5°–1°) of the sedimentary basin taper and a high internal distribution. In contrast, the sedimentary basin taper in the north has a high basal slope that mainly translates along the shallow detachment, lacking thrusting-related structures. This study reveals that the pre-existing stratigraphic architecture of the sedimentary basin can influence the subsequent structural deformation of the foreland basin. This has important implications for other foreland basins with multistage crustal shortening processes.

Geochronology and geochemistry of late Jurassic–Early Cretaceous volcanic rocks in the southern Great Xing’an range, NE China: constraints for late Mesozoic tectono-magmatic evolution

ABSTRACT Late Mesozoic volcanic rocks are widespread in the Great Xing’an Range (GXR), Northeast (NE) China. However, details of the tectono-magmatic evolution during the Late Mesozoic are poorly understood. In this paper, new zircon U–Pb, Lu–Hf, and whole-rock geochemical data from Late Mesozoic volcanics in the southern GXR, are used to further constrain the tectono-magmatic evolution of the region. Late Mesozoic magmatism in the GXR, eastern Mongolia and southern Transbaikalia occurred during the Early Cretaceous (120–140 Ma) and Late Jurassic (150–163 Ma) periods. Late Jurassic trachyandesites-trachytes show a low rare earth element and moderate light rare earth element (LREE) enrichment with no Eu anomalies. Early Cretaceous trachytes are characterized by an LREE enrichment and negative Eu anomalies. Contemporaneous rhyolites exhibit a significant LREE enrichment, A–type granitoid affinity, and pronounced negative Eu anomalies. Different negative Nb, Ta, and Ti anomalies, and positive zircon εHf(t) values, indicate that the ~160 Ma trachyandesites-trachytes are derived from partial melting of the lithospheric mantle that was metasomatized by subduction-related fluids. The ~125 Ma trachytes and rhyolites were possibly generated by partial melting of the accreted Meso-Neoproterozoic lower crust. New and previously published geochemical, isotopic and geochronological data from the southern GXR, eastern Mongolia and East-Transbaikalia, suggest that Late Jurassic–Early Cretaceous volcanism in the southern GXR occurred during the post-collisional extension after the closure of the Mongol–Okhotsk Ocean.

Early Cretaceous trachybasalt-trachyte-trachyrhyolitic volcanism in the Nyalga basin (Central Mongolia): sources and evolution of continental rift magmas

As shown by geological, mineralogical, and isotope geochemical data, trachybasaltic-trachytic-trachyrhyolitic (TTT) rocks from the Nyalga basin in Central Mongolia result from several eruptions of fractionated magmas within a short time span at about 120 Ma. Their parental basaltic melts formed by partial melting of mantle peridotite which was metasomatized and hydrated during previous subduction events. Basaltic trachyandesites have high TiO2 and K2O, relatively high P2O5, and low MgO contents, medium 87Sr/86Sr(0) ratios (0.70526-0.70567), and almost zero or slightly negative εNd(T) values. The isotope geochemical signatures of TTT rocks are typical of Late Mesozoic basaltic rocks from rift zones of Mongolia and Transbaikalia. The sources of basaltic magma at volcanic centers of Northern and Central Asia apparently moved from a shallower and more hydrous region to deeper and less hydrated lithospheric mantle (from spinel to garnet-bearing peridotite) between the Late Paleozoic and the latest Mesozoic. The geochemistry and mineralogy of TTT rocks fit the best models implying fractional crystallization of basaltic trachyandesitic, trachytic, and trachyrhyodacitic magmas. Mass balance calculations indicate that trachytic and trachydacitic magmas formed after crystallization of labradorite-andesine, Ti-augite, Sr-apatite, Ti-magnetite, and ilmenite from basaltic trachyandesitic melts. The melts evolved from trachytic to trachyrhyodacitic and trachyrhyolitic compositions as a result of prevalent crystallization of K-Na feldspar, with zircon, chevkinite-Ce, and LREE-enriched apatite involved in fractionation. Trachytic, trachyrhyodacitic, and trachyrhyolitic residual melts were produced by the evolution of compositionally different parental melts (basaltic trachyandesitic, trachytic, and trachyrhyodacitic, respectively), which moved to shallower continental crust and accumulated in isolated chambers. Judging by their isotopic signatures, the melts assimilated some crustal material, according to the assimilation and fractional crystallization (AFC) model.

Fracture prediction in the tight-oil reservoirs of the Triassic Yanchang Formation in the Ordos Basin, northern China

It is important to predict the fracture distribution in the tight reservoirs of the Ordos Basin because fracturing is very crucial for the reconstruction of the low-permeability reservoirs. Three-dimensional finite element models are used to predict the fracture orientation and distribution of the Triassic Yanchang Formation in the Longdong area, southern Ordos Basin. The numerical modeling is based on the distribution of sand bodies in the Chang 71 and 72 members, and the different forces that have been exerted along each boundary of the basin in the Late Mesozoic and the Cenozoic. The calculated results demonstrate that the fracture orientations in the Late Mesozoic and the Cenozoic are NW–EW and NNE–ENE, respectively. In this paper, the two-factor method is applied to analyze the distribution of fracture density. The distribution maps of predicted fracture density in the Chang 71 and 72 members are obtained, indicating that the tectonic movement in the Late Mesozoic has a greater influence on the fracture development than that in the Cenozoic. The average fracture densities in the Chang 71 and 72 members are similar, but there are differences in their distributions. Compared with other geological elements, the lithology and the layer thickness are the primary factors that control the stress distribution in the study area, which further determine the fracture distribution in the stable Ordos Basin. The predicted fracture density and the two-factor method can be utilized to guide future exploration in the tight-sand reservoirs.

Exhumation history of the West Kunlun Mountains, northwestern Tibet: Evidence for a long-lived, rejuvenated orogen

How and when the northwestern Tibetan Plateau originated and developed upon pre-existing crustal and topographic features is not well understood. To address this question, we present an integrated analysis of detrital zircon U–Pb and fission-track double dating of Cenozoic synorogenic sediments from the Kekeya and Sanju sections in the southwestern Tarim Basin. These data help establishing a new chronostratigraphic framework for the Sanju section and confirm a recent revision of the chronostratigraphy at Kekeya. Detrital zircon fission-track ages present prominent Triassic–Early Jurassic (∼250–170 Ma) and Early Cretaceous (∼130–100 Ma) static age peaks, and Paleocene–Early Miocene (∼60–21 Ma) to Eocene–Late Miocene (∼39–7 Ma) moving age peaks, representing source exhumation. Triassic–Early Jurassic static peak ages document unroofing of the Kunlun terrane, probably related to the subduction of Paleotethys oceanic lithosphere. In combination with the occurrence of synorogenic sediments on both flanks of the Kunlun terrane, these data suggest that an ancient West Kunlun range had emerged above sea level by Triassic–Early Jurassic times. Early Cretaceous fission-track peak ages are interpreted to document exhumation related to thrusting along the Tam Karaul fault, kinematically correlated to the Main Pamir thrust further west. Widespread Middle–Late Mesozoic crustal shortening and thickening likely enhanced the Early Mesozoic topography. Paleocene–Early Eocene fission-track peak ages are presumably partially reset. Limited regional exhumation indicates that the Early Cenozoic topographic and crustal pattern of the West Kunlun may be largely preserved from the Middle–Late Mesozoic. The Main Pamir–Tam Karaul thrust belt could be a first-order tectonic feature bounding the northwestern margin of the Middle–Late Mesozoic to Early Cenozoic Tibetan Plateau. Toward the Tarim basin, Late Oligocene–Early Miocene steady exhumation at a rate of ∼0.9 km/Myr is likely related to initial thrusting of the Tiklik fault and reactivation of the Tam Karaul thrust. Thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the West Kunlun orogen at this time. This episode of exhumation and uplift, associated with magmatism across western Tibet, is compatible with a double-sided lithospheric wedge model, primarily driven by breakoff of the Indian crustal slab. Accelerated exhumation of the mountain front at a rate of ∼1.1 km/Myr since ∼15 Ma supports active compressional deformation at the margins of the northwestern Tibetan Plateau. We thus propose that the West Kunlun Mountains are a long-lived topographic unit, dating back to Triassic–Early Jurassic times, and have experienced Middle–Late Mesozoic to Early Cenozoic rejuvenation and Late Oligocene–Miocene expansion.

한반도에서 산출된 화석목재의 다양성

In order to understand the broad outline and palaeobotanical significances, the fossil woods from the Korean Peninsula were integrated through the literature surveys. Types and diversity of them are gradually increasing from Mesozoic to Cenozoic, especially increased sharply in Cenozoic. During the Early Mesozoic, six conifer taxa belonging to four genera were described, which corresponds to about 6% of the Daedong flora. Those of the Late Mesozoic are all conifers, consisting of fifteen taxa belonging to seven genera, which corresponds to about 29% of the Nakdong flora. During the Neogene, thirty four taxa belong to sixteen families were described. Those woods mostly consist of dicotyledon and have the greatest diversity compared to other geologic eras, which corresponds to about 83% of the Janggi flora. It is inferred that such a rapid increase of the silicified wood fossils in Neogene are due to the abundant presence of dicotyledon in floral composition and of pyroclastic rocks in strata, which are appropriate for preserving wood as fossils.

Geochemistry of granitoids from the basement of the Kuril island arc system

This paper reports the characteristics of granitoids from the Pacific slope of the Kuril island arc system, which were discovered by the authors during geological and geophysical operations in three cruises of the R/V Akademik M. Lavrent’ev. The major and trace element compositions of these rocks were determined, their role in the formation of the submarine Vityaz Ridge was evaluated, and they were compared with granitoids from the Brouton group of submarine volcanoes and xenoliths from Simushir Island and the Sea of Okhotsk. Granitoids from various structures of the basement of the Kuril island arc system are hypabyssal rocks derived from andesite magmas. Their common features are related to the formation on the continental crust under convergent geodynamic conditions involving compression due to the movement and subduction of the Pacific plate beneath the Asian continent. The problem of the basement of the Kuril island arc system was discussed, the composition and age of its rocks were determined, and the history of the geologic development of the Pacific slope of the arc starting from the Late Mesozoic was briefly described.

Evidence that low‐temperature oceanic hydrothermal systems play an important role in the silicate‐carbonate weathering cycle and long‐term climate regulation

The feedbacks between changes in atmospheric CO2 levels, climate, and CO2 drawdown into rocks are incompletely understood. In particular, the role of the upper oceanic crust in this long‐term carbon cycling is debated. Here, a simple model for the precipitation of calcite in the upper oceanic crust is developed with the aim of understanding why Late Mesozoic upper oceanic crust contains several times higher CO2 concentrations (~2.5 wt%) than Cenozoic upper oceanic crust (~0.5 wt%). The modeling shows that neither heating of seawater, nor leaching of Ca from the rock with charge balance maintained by Mg uptake by the rock, can lead to >0.2 wt% CO2 uptake by the oceanic crust. Alkalinity production during fluid‐rock reaction in the crust allows substantially more CO2 to be taken up by the crust in calcite, and is consistent with changes in the major element composition of Late Mesozoic upper oceanic crust due to hydrothermal alteration. The higher CO2 content of Late Mesozoic than Cenozoic upper oceanic crust thus requires greater alkalinity production by fluid‐rock reactions in the Late Mesozoic. This may have been due to higher bottom water temperature and/or seawater having a different composition leading to different secondary minerals forming in the Late Mesozoic. Irrespective of the mechanism, the negative feedback on atmospheric CO2 levels provided by enhanced hydrothermal CO2 consumption in the Late Mesozoic was of similar magnitude to that from continental weathering.

Late paleozoic age of deformations in the Tseel metamorphic belt (Mongolian Altai)

The large suture zones of Central Asia formed dur� ing Paleozoic accretional events were reactivated in the Late Paleozoic-Early Mesozoic in the course of thrust and strikeslip deformations (1). Among such structures is the Erkis-Bulgan fault formed in the Cambrian-Middle Ordovician (2). The fault occurs for more than 2000 km in West Mongolia, North China, and East Kazakhstan, where it is observed in the Irtysh shear zone. Metamorphic complexes of var� ious nature and ages expose in the environs of this shear zone. The chronology of stages of metamor� phism and deformations plays a key role in reconstruc� tions of the history of the formation of accretional structures in Central Asia and in the tectonothermal models of the evolution of the collisional zones. We have made an attempt to determine age relationships between brittle-plastic deformations and metamor� phism within the Tseel metamorphic belt located in

Contrasted Perceptions of Uluru

Uluru is an inselberg shaped in arkosic sandstone located in the arid plains of central Australia. The indigenous people believed it rose out of a sand hill and has since remained unchanged. The various minor landforms represented mythological animals, people, and events of the Dreamtime. Later investigators interpreted the residual as remaining after long-distance scarp retreat, or as due to scouring by the wind or by the waters of a huge lake. The inselberg and its decorations have been construed in terms of climatic variations. Uluru also has been interpreted as a compressed and resistant compartment that was exposed as a low rise in the latest Mesozoic. The initial rise shed runoff. The steep flanks were shaped in the Eocene by deep subsurface weathering followed by stripping of the regolith and exposure of bedrock forms. Large tafoni and breaks of slope were formed on the southern side where permeable sediments abutted the residual. Following their exposure, basal flares and footcaves were shaped during a later period of subsurface weathering. The inselberg has grown as a relief feature not by uplift, but by the lowering of the surrounding plains. The morphology of Uluru is an expression of episodic exposure.

New Pelecinid Wasps (Hymenoptera: Proctotrupoidea: Pelecinidae) from the Yixian Formation of Western Liaoning, China

Abstract:Three well‐preserved fossil Pelecinids from the Late Mesozoic Yixian Formation, Liaoning Province, China are described and assigned to two new species, Eopelecinus huangi sp. nov. and Eopelecinus tumidus sp. nov. in Eopelecinus Zhang, Rasnitsyn and Zhang, 2002. As of now, 17 species have been included in this genus, which is the most diverse in the Pelecinidae family. With new information and characters obtained from these new specimens, the diagnosis of Eopelecinus Zhang, Rasnitsyn and Zhang, 2002 is emended.

New Genus and Species of Fossil Dragonflies (Insecta: Odonata) from the Yixian Formation of Northeastern China

Two well-preserved fossil dragonflies from the Late Mesozoic Yixian Formation, Liaoning Province, China are described and assigned to a new genus, Sopholibellula gen. nov. in Araripelibellulidae Bechly, 1996, closely related to the type genus Araripelibellula. This new genus differs from Araripelibellula in the following characters: origins of RP and MA distinctly separated at arculus in both pairs of wings; anal loop wider and shorter, with Y-shaped veins inside; MA and IR2 not zigzag; several small intercalary veins present in the postdiscoidal area of hindwing; cells smaller and much more dense, especially in the apex and hind margin; bigger in size. Structures, including head, abdomen and parts of legs, were first described in details of this family.

Seismic structure, crustal architecture and tectonic evolution of the Anatolian-African Plate Boundary and the Cenozoic Orogenic Belts in the Eastern Mediterranean Region

Abstract The modern Anatolian–African plate boundary is represented by a north-dipping subduction zone that has been part of a broad domain of regional convergence between Eurasia and Afro–Arabia since the latest Mesozoic. A series of collisions between Gondwana-derived ribbon continents and trench-roll-back systems in the Tethyan realm produced nearly East–West-trending, subparallel mountain belts with high elevation and thick orogenic crust in this region. Ophiolite emplacement, terrane stacking, high‐P and Barrovian metamorphism, and crustal thickening occurred during the accretion of these microcontinents into the upper plates of Tethyan subduction roll-back systems during the Late Cretaceous–Early Eocene. Continued convergence and oceanic lithospheric subduction within the Tethyan realm were punctuated by slab breakoff events following the microcontinental accretion episodes. Slab breakoff resulted in asthenospheric upwelling and partial melting, which facilitated post-collisional magmatism along and across the suture zones. Resumed subduction and slab roll-back-induced upper plate extension triggered a tectonic collapse of the thermally weakened orogenic crust in Anatolia in the late Oligocene–Miocene. This extensional phase resulted in exhumation of high‐P rocks and medium- to lower-crustal material leading to the formation of metamorphic core complexes in the hinterland of the young collision zones. The geochemical character of the attendant magmatism has progressed from initial shoshonitic and high‐K calc‐alkaline to calc‐alkaline and alkaline affinities through time, as more asthenosphere-derived melts found their way to the surface with insignificant degrees of crustal contamination. The occurrence of discrete high-velocity bodies in the mantle beneath Anatolia, as deduced from lithospheric seismic velocity data, supports our Tethyan slab breakoff interpretations. Pn velocity and Sn attenuation tomography models indicate that the uppermost mantle is anomalously hot and thin, consistent with the existence of a shallow asthenosphere beneath the collapsing Anatolian orogenic belts and widespread volcanism in this region. The sharp, north-pointing cusp (Isparta Angle) between the Hellenic and Cyprus trenches along the modern Anatolian–African plate boundary corresponds to a subduction-transform edge propagator (STEP) fault, which is an artifact of a slab tear within the downgoing African lithosphere.

Crustal Detachment and Destruction of the Keel of North China Craton: Constraints from Late Mesozoic Extensional Structures

Extensional crustal detachment is one of the most important tectonic responses of lithosphere thinning. Late Mesozoic extensional structures, i.e., detachment faults, metamorphic core complexes (mcc's) and fault depression basins, are commonly found in North, South and Northeast China, eastern Mongolia and the Baikal region. The detachment faults associated with these extensional structures may root into either the upper crust (detachment faults of fault depression basins), upper to middle crust (detachment faults), or middle crust (detachment faults in mcc's). Crustal detachments in North China have features, such as kinematic polarity, geometrically regional symmetry and local asymmetry, and are widely and inhomogeneously distributed. These usually take place during the period between 140 and 60 Ma, and lead to thinning of both the crust and the lithosphere. This study reveals that there is no definite correlation between variation of thickness of the present lithosphere and the development and distribution of Late Mesozoic extensional structures in the North China Craton (NCC). The general tendency is that thickness of lithosphere increases from Northeast China to the Baikal region, which means that the present lithosphere is wedge-shaped and the abrupt changes in lithosphere thickness in East Asia are closely related to Cenozoic rifting. It is also found that there is extensive lithosphere thinning in Late Mesozoic detachment (or coeval mantle detachment), and the lithosphere in a vast area from Baikal to Northeast China is thinned in a unified regional extensional stress field. All of the above indicates that destruction of the NCC's keel in the Late Mesozoic was a response of regional crustal detachment and lithospheric thinning in East Asia.

Role of transverse strike-slip faults in the structure of the Karpinsky Ridge and their kinematics

The segmented structure of the Karpinsky Ridge is determined by NE-trending transverse strikeslip faults with offsets of approximately 30–40 km. The newly recognized Pribrezhny Fault and the well-known Agrakhan Fault are the largest. A new correlation scheme for structural elements of the ridge’s eastern segment and its underwater continuation is proposed with account of offset along the Pribrezhny Fault. According to this scheme, the Semenovsky Trough rather than the Dzhanai Trough is an onshore continuation of the underwater Zyudevsky Trough. The uplift located south of the Zyudevsky Trough is correlated with the Promyslovy-Tsubuk Swell offset along the Pribrezhny Fault. In turn, this uplift is displaced along the right-lateral strike-slip fault that coincides with the Agrakhan Fault. The transverse faults were formed during the Early Permian collision related to the closure of the basin, which was presumably underlain by the oceanic crust. The faults were active during the Early Triassic rifting and Late Triassic inversion. Judging from the map of the surface of the Maikop sediments, the Agrakhan Fault does not cross the Terek-Caspian Trough. Bending arcwise, the fault joins a system of right-lateral strike-slip faults that border the Daghestan Wedge in the east. A system of rightlateral strike-slip faults may also be traced along the western coast of the Caspian Sea. The Agrakhan Fault as a northern element of this system functioned mostly in the Late Paleozoic-Early Mesozoic in connection with the formation of the fold-thrust structure of the Karpinsky Ridge. In the east the faults of the southern segment bound the Caucasus syntaxis of the Alpine Belt; they have retained their activity to the present day.

Isophlebiid dragonflies from the Late Mesozoic of eastern Transbaikalia (Odonata: Isophlebiidae)

Based on the study of more than 300 isophlebiid specimens from several Late Mesozoic sites in eastern Transbaikalia (Ukurei, Tergen’, Glushkovo, and Byankino formations), new genera and species are described: Xeta olovica, Dahurium draco, and Sinitsia sophiae. The insect-bearing deposits are dated Late Jurassic according to analysis of their odonatofauna.

A Possible Long‐tailed Bird with a Pygostyle from the Late Mesozoic Yixian Formation, Western Liaoning, China

Abstract An incomplete caudal vertebral series (IVPP V11309) from the Yixian Formation of late Mesozoic, Jianshangou area of Beipiao, western Liaoning Province, may represent a new bird. The tail is composed of at least 12 free caudal vertebrae and the most distal 5 caudal vertebrae co‐ossified into a pygostyle. The pygostyle is plate‐like and slightly curved dorsally. The anterior free caudals are amphiplatyan. The anterior caudal surfaces of the last three free caudals are concave, but their posterior articular surfaces are convex. The pygostyle is regarded as the first appeared flight apparatus during the evolutionary process from Archaeopteryx to neornithes. The pygostyle appeared in most early fossil birds and almost all the modern birds. Although their morphologies are different, they are basically formed by at least four last caudal vertebrae. The specimen V11309 is regarded as a bird rather than a non‐avian theropod dinosaur based on the following characters: short caudal vertebrae, numerous pits present on the surfaces of the centra and, a foramen present between the basal part of the fused neural spines, which is similar to that of Struthio camelus. The discoveries of pygostyles from the therizinosauroids and oviraptorosaurs may provide strong evidence for supporting the origin of birds from small theropod dinosaurs. The structure of the pygostyle in specimen V11309 is different from those of Beipiaosaurus (Therizinosauroid) and Nomingia (oviraptorosaur). The most parsimonious interpretation is that these pygostyle‐like structures are independently acquired by Beipiaosaurus and Nomingia during their evolutionary process.

Geochemistry of the ophiolite and island-Arc volcanic rocks in the Mianxian-Lueyang suture zone, southern Qinling and their tectonic significance

Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The diabase dike swarm shows LREE enrichment but slightly negative Eu anomaly. Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace element ratios of Ti/V, Th/Ta, Th/Yb and Ta/Yb. One is the MORB-type basalt with LREE depletion, representing the fragments of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between theQinling and Yangtze plates during the Middle Paleozoic-Early Mesozoic era. The other comprises the island-arc volcanic rocks including tholeiitic basalt and a large amount of calc-alkaline intermediate-acid volcanic rock, which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin. This indicates that the Mianxian-Lueyang limited ocean basin had undergone a whole process of development, evolution and vanishing from Devonian-Cretaceous to Permian. And the Qinling area had become an independent lithospheric microplate, on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic-Early Mesozoic. That is to say, the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.