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Geological, geophysical and geochemical data show that both of the Dabie Orogen and Hefei Basin formed during a Mesozoic orogeny. A three-stage development of the Hefei Basin includes down-warping, half grabben, and positive inversion. Both the uplift in orogen and the depression in basin resulted from the “de-rooting” of orogen and up-welling of the mantle.

International audience; With a cratonic nucleus, the North China Craton (NCC) experienced a complex tectonic evolution with multiphase compressional and extensional events during Mesozoic times. Along the northern part of the NCC, the Yinshan-Yanshan fold and thrust belt was a typical intraplate orogen. Jurassic and Cretaceous continental sedimentation, magmatism, widespread intraplate characterize the Yinshan-Yanshan orogenic belt. The geodynamic significance of these tectonic events is still in dispute. In the western part of the Liaoning province, the Yiwulüshan massif crops out at the eastern end of the Yinshan-Yanshan orogenic belt. The Yiwulüshan massif presents an elliptical domal shape with a NE-SW striking long axis. The structural evolution of this massif brings new insights for the understanding of the Mesozoic plutonic-tectonic history of the NCC. A multidisciplinary study involving structural geology, geochronology, Anisotropy of Magnetic Susceptibility (AMS) and gravity modeling have been carried out. The presentation of the new results splits into two parts. Part I (this paper) deals with field and laboratory structural observations, and presents the main geochronological results. The AMS, gravity modeling data will be provided in a companion paper (Part II). The early compressional deformation (D1) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulüshan massif. A detailed structural analysis allows us to distinguish several deformation events (D2, D3, and D4). The Cretaceous extensional structures, such as syntectonic plutons bounded by ductile normal faults, metamorphic core complexes, and half-graben basins are recognized in many places in East Asia. These new data from the Yiwulüshan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW-SE extensional Mesozoic tectonics occurred throughout the entire region.

International audience; Granitoids play an important role in deciphering both crustal growth and tectonic evolution of Earth. In the eastern end of the Yinshan-Yanshan belt of North China Craton, the Yiwulüshan massif is a typical region that presents the tectonic evolution features of this belt. Our field work on the host rocks has demonstrated two phases of opposite tectonics: compressional and extensional, however, the deformation is almost invisible in the intrusive rocks. To improve the understanding of the tectonic evolution of the Yiwulüshan massif and the Late Mesozoic tectonics of East Asia, a multidisciplinary study has been carried out. In this study, anisotropy of magnetic susceptibility (AMS) and gravity modeling have been applied on these Jurassic plutons (Lüshan, Jishilazi and Guanyindong), which intrude into the Yiwulüshan massif. According to laboratory measurements and microscopic observations on thin sections, the AMS of the Yiwulüshan massif is characterized by secondary fabrics, indicating that the intensive post solidus deformation has reset the (primary) magmatic magnetic fabrics. A relatively gentle NW dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of N34°E and N335°E orientations, namely LM1 and LM2, relatively. Gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif. Integrating all results from structural observation, geochronological investigation, AMS measurement and gravity modeling, two tectonic phases have been identified in the Yiwulüshan massif, posterior to the Jurassic (180-160 Ma) magmatism in the Yinshan-Yanshan area. The early one concerns a Late Jurassic-Early Cretaceous (~ 141 Ma) compressional event with a top-to-the-south to southwest sense of shear. The second one shows an Early Cretaceous (~ 126 Ma) NW-SE ductile extensional shearing. At that time, sedimentary basins widened and Jurassic plutons started to be deformed under post solidus conditions. In fact, the NW-SE trend of the maximum stretching direction is a general feature of East Asian continent during Late Mesozoic.

The top boundary of the ultra-high pressure metamorphic (UHPM) rocks in the Dabie Mountains, central China, has been mapped. The results show that the top boundary of the UHPM rocks is occupied by flat-lying felsic gneiss, on which tonalitic gneiss rests. Petrological and mineralogical evidence indicates a wide P-T gap across the boundary with an estimated peak metamorphic P-T value of the UHPM rocks being >30 kbar and 800 ± 50°C, and that of the tonalitic gneiss around 11 kbar and 800°C. Their P-T-t paths are different. The former has a clockwise path and the latter is counterclockwise. This implies that the UHPM rocks at the bottom and the tonalitic gneiss on top have been structurally juxtaposed together. The top boundary, i.e. the contact between the UHPM rocks and tonalitic gneiss, shows characteristics of a ductile shear zone. Microscopically, feldspar and quartz in the shear zone are characterized by ductile deformation. In larger scale, the top boundary is undulating. Shear sense in the top boundary is a two-way direction. Only the latest shear sense measured with c -axes of quartz show a consistent direction of top-to-the-north. The study provides some constraints to the exhumation process of the Dabie UHPM rocks.

Four main faults outline the metamorphic terrain in the Dabie Mountains, central China. The difference of metamorphic grade in the northern, central and southern parts is well-established. This study suggests that these metamorphic rocks belong to three individual geological-tectonic units, which are the northern Andean-type magmatic arc, the central UHPM rock-bearing melange zone and the mobilized sedimentary cover and basement of Yangtze southern continental margin. An old ductile sheared zone through Wuhe and the south of Yuexi-Shuihou divides the Dabie metamorphic complex into northern and central units. The northern unit is predominantly occupied by tonalitic-trondhjemitic grey gneisses and amphibolites facies metasediments. Several approximately E-W-trending ductile-sheared mylonitic belts cut through the grey gneisses, and are especially developed in the northern and southern margins of the unit (high-strain zones). There is a series of lenses of basic granulites, serpentinites and Grt-pyroxenites in the high-strain zones. They do not have the petrological and geochemical characteristics of ophiolitic rocks. However, they may represent the root of an arc combined with grey gneisses. Our study also demonstrates that all rocks from the northern block did not undergo eclogite facies metamorphism. Mesozoic post-collisional granites occur extensively in the Dabie terrain, especially in the northern unit. Coesite and diamond-bearing eclogites in the central unit indicate a regional ultra-high-pressure metamorphism of pressures of > 30 kbar and temperature of 600–800°C. Except for eclogites, various ultra-high-pressure metamorphic (UHPM) rocks include ultramafic rocks, marbles and other metamorphosed sedimentary rocks. They, as large-scale blocks, are mixed with lower P-T encompassing host rock orthogneisses. The central block is a UHPM rock-bearing melange zone. The south block is a metasedimentary sequence of continental margin of the Yangtze plate. The boundary between the central and southern blocks is located in the north from Huangzhen, extending eastwards through the dam of Huangliangting reservoir. In addition, the Foziling Group, north of the Dabieshan terrain was possibly deposited in an extensional basin on an extensional shear zone, comparable to the basin in the Variscan of France and the Caledonides of S. Norway (Dewey, Ryan and Anderson, Geological Society Special Publication No. 76, pp. 325–343, 1993). The authors hope that this information will provide more valid evidence of regional tectonic evolution.

International audience; The Xuefengshan Belt, characterized by large-scale fold and thrust structures and widespread granites, is a key area to decipher the tectonic evolution of the South China block. In this belt, two magmatic episodes are recorded by Early Paleozoic and Early Mesozoic granites. In this paper, we carried out precise SIMS zircon Usingle bondPb dating and in situ Lusingle bondHf isotopes measurements on these granitic plutons. Our study indicates that the Early Paleozoic and the Early Mesozoic granites are late-orogenic products of the Early Paleozoic orogen and the Middle Triassic Xuefengshan orogen, respectively. In the Xuefengshan Belt, the Early Paleozoic event is poorly registered, since this area corresponds to the outer zone of the early Paleozoic orogen. The Silurian-Early Devonian granites are late-orogenic plutons emplaced after the main tectonic and metamorphic stage in the Wuyi-Baiyun-Yunkai belt, coeval with a widespread, subsequent extensional event in eastern and southern South China. On the other hand, Triassic granites are formed in an intracontinental environment with weakly to strongly peraluminous signatures. Zircon Usingle bondPb ages presented here, associated with a summary of newly acquired data in the same region, suggest that the emplacement of anatectic granites occurred around 225-215 Ma, not in a rather wide range of ca. 245-200 Ma. In situ zircon εHf(t) values indicate a crust-derived source without a mantle-derived input for the two generations of granites. Combining our data with recent studies, we infer that the central area of the South China block has experienced two tectonothermal events: the Early Paleozoic magmatism developed as a result of the collapse of the Early Paleozoic orogen, while these Early Mesozoic granites can be the late-orogenic products of the intracontinental Xuefengshan orogen, most likely manifesting the far field effect by the

The northern Dabieshan metamorphic terrain (NDT) is an analogue of an Andean-type magmatic arc. The predominant rock type is a trondhjemitic-tonalitic-granodioritic (TTG) gneiss with bodies of meta...

Based on petrological, structural, geological and geochronological research, the authors summarize the progress of ultra-high pressure (UHP) metamorphic rock study since 1989 by Chinese geoscientists and foreign geoscientists in the Dabie-Su-Lu region. The authors introduce and discuss a two-stage exhumation process for the UHP metamorphic rocks that have various lithologies; eclogite, ultramafics, jadeitic quartzite, gneiss, schist and marble. The metamorphic history of UHP metamorphic rocks is divided into three stages, that is, the pre-eclogite stage, coesite eclogite stage, and retrograde stage. Prior to UHP metamorphism, the ultramafics had a high temperature environment assemblage of mantle and others had blueschist facies assemblages. The granulite facies assemblages, which have recorded a temperature increase event with decompression, have developed locally in the Weihai basaltic rocks. Isotopic ages show a long range from > 700 Ma to 200 Ma. The diversity in protoliths of UHP metamorphic rocks may be related to the variation of isotopic ages older than 400 Ma. The Sm-Nd dating of ~ 220 Ma could reflect the initial exhumation stage after the peak UHP metamorphism in relation to the collision between the Sino-Korean and Yangtze blocks and subsequent events. Petrological and structural evidence imply a two-stage exhumation process. During the initial exhumation, the UHP metamorphic rocks were sheared and squeezed up in a high P/T regime. In the second exhumation stage the UHP metamorphic rocks were uplifted and eventually exposed with middle crustal rocks.

International audience; The Tian Shan range offers a natural laboratory to study orogenic processes. Most of the previous studies focused on either the Palaeozoic evolution of the range or its Cenozoic intracontinental evolution linked with the India-Asia collision. In this study, it is shown that detailed field investigations on the relationship between sedimentary cover and basement constrain the Mesozoic evolution of the northern Tian Shan. Sedimentological observations argue for a limited transport distance for Lower and Uppermost Jurassic deposits. Geological sections presented in this paper show that, in preserved locations, Triassic to Jurassic sedimentary series present a continuous onlap type sedimentary unconformity on the top of the basement. At different scales, observations clearly evidence the existence of major palaeorelief during the Mesozoic. According to the present study, the topography of the current Tian Shan range and the associated movements along its northern front structures cannot be considered as the consequence of Cenozoic reactivation alone.

Coesite in a granulite host-rock is reported from Weihai City, northeastern Shandong Province, China. Coesite occurs as inclusions in garnet, which is separated from the fine-grained matrix of quartz + clinopyroxene + homblende by a zoned corona of plagioclase + clinopyroxene + orthopyroxene + hornblende. Petrological evidence shows that the coesite-bearing granulite is retrograded from eclogite. Three stages in the metamorphic history of the granulite have been recognized. (i) Coesite-eclogite stage: The assemblage reconstructed from the inclusions in garnet is Mg-rich garnet + omphacite + coesite + rutile. (ii) During the granulite stage, these minerals reacted to form quartz + clinopyroxene + hornblende (in the matrix), clinopyroxene + albite (omphacite pseudomorphs) and plagioclase + clinopyroxene + orthopyroxene + hornblende (as corona around garnet). (iii) Amphibolite stage: Earlier minerals were replaced by biotite, epidote and hornblende. The P-T conditions estimated with various geothermobarometers show a T-increasing and P-decreasing path from the eclogite stage (T ∼ 720°C, P > 28 kbar) to the granulite stage (T ∼ 850°C, P ∼ 10 kbar). Thus the exhumation of the ultra-high-pressure rocks in Weihai proceeded under increasing temperature, and may not have been as fast as it was thought before

International audience; The modern Tianshan (central Asia), which extends east-west on about 2500 km long with an average of more than 2000 m in altitude, is considered as a direct consequence of the reactivation of a Paleozoic belt due to the India - Asia collision. At first order, the finite structure of this range obviously displays a significant uprising of Paleozoic "basement" rocks - as a crustal-scale 'pop-up' - surrounded by two Cenozoic foreland basins. In order to characterize the coupling history of this Cenozoic orogeny with its northern foreland basin (Junggar basin), a detailed structural field work has been carried out on the northern piedmont of Tianshan. From Wusu to Urumqi, on about 250 km long, the thrusting of the Paleozoic basement on the Mesozoic or Cenozoic sedimentary series of the basin is remarkably exposed along several river valleys. In contrast, in other sections, the Triassic to Jurassic sedimentary series can be followed from the basin to the range where they unconformably overlie on the Carboniferous basement. These series are only gently folded along the "range front". These features imply that, at regional-scale, the Cenozoic reactivation of the Tianshan has not produced important deformation along its contact with the juxtaposed Junggar basin. The shortening ascribed to the Cenozoic intra-continental collision would either be localized in the range, mostly accommodated by reactivated Paleozoic structures or faults in the basement units, or in the distal parts of the Junggar basin, by folds and faults within the Cenozoic sedimentary series. Alternative hypothesis would be that the Tianshan uplift and the movements associated with along its northern front structures, which are traditionally assigned to its Cenozoic reactivation, might be reduced. Such characteristic significantly differs from other well-known orogenic ranges, such as the Canadian Rocky Mountains, the Appalachians, the Pyrenees which display highly folded foreland basins and thrust belts with rather well developed range front structures. This suggests that the Tianshan intra-continental range is rather "young" and still at a primary stage of its orogenic evolution. In other words, its front may be considered as an immature thrust belt. If considering the available tomographic data across the Tianshan, its actual uplift may probably be produced by an asymmetric intracontinental deformation mechanism, i.e. a deeper subduction of the Tarim plate below the Tianshan (to the south), with respect to the one of Junggar plate to the north of the range. Consequently, the Tianshan range offers an excellent natural laboratory to study the processes of the on-going orogeny-foreland basin coupling, ancient structures reactivation as well as initiation and development of range front structures.

International audience; The modern Tianshan mountain belt, located in Central Asia, offers a natural laboratory to study orogenic processes linked with convergent geodynamical settings. Most of the previous studies either focused on the Paleozoic evolution of the range - subductions, arc accretions and continental collision - or on its Cenozoic intra-continental evolution linked with the India-Asia collision. At first order, the finite structure of this range obviously displays a remarkable uprising of Paleozoic "basement" rocks - as a crustal-scale 'pop-up' - surrounded by two Cenozoic foreland basins. The present-day topography of the Tianshan is traditionally related to the latest intra-continental reactivation of the range. In contrast, the present field study of the northern Tianshan brings new and clear evidences for the existence of a significant relief, in this area, during Mesozoic times. The investigation zone is about 250 km long, from Wusu to Urumqi, along the northern flank of the Tianshan where the rivers deeply incised the topography. In such valleys, lithologies and structural relationships between Paleozoic basement rocks, Mesozoic and Cenozoic sedimentary series are particularly well exposed along several sections. Jurassic series are mostly characterized by coal-bearing, coarse-grained continental deposits. Within intra-mountain basins, sedimentary breccias, with clasts of Carboniferous basement rocks, have been locally found at the base of the series. This argues for the presence of a rather proximal palaeo-relief of basement rocks along the range front and the occurrence of proximal intra-mountain basins, during the Jurassic. Moreover, while a major thrust is mostly evoked between Jurassic deposits and the Paleozoic units, some of the studied sections show that the Triassic to Jurassic sedimentary series can be followed from the basin to the range. In these cases, the unconformity of the Mesozoic series on top of the Carboniferous basement has been locally clearly identified quite high in the mountain range or even, surprisingly, directly along the northern Tianshan "front" itself. Combining available information from geological maps, field investigations and numerous drilling wells, regional-scale cross-sections have been built. Some of them show "onlap" type deposit of the Triassic to Jurassic clastic sediments on top of the Paleozoic basement that was thus significantly sloping down to the North at that time. Our study clearly evidences, at different scales, the existence of a major palaeo-relief along the northern Tianshan range during Mesozoic, and particularly during Jurassic times. Such results are compatible with previous fission tracks and sedimentology studies. From this, the Tianshan's uplift and the movements associated with along its northern front structures, which are traditionally assigned to its Cenozoic reactivation, must be reduced. These new results question on the mode and timing of reactivation of structures and on the link between topography and intra-continental collisional settings.

The distributive characteristics of turbulence, turbulent velocity, turbulent intensity and Reynolds stress, in horizontal and vertical direction on leeward side of windbreak were discussed in this paper. The results show that all the three kinds of parameters of turbulence have the similar distributive patterns in lee, their peaks were around 10H for horizontal andZ/ H = 1 for vertical. The windbreak is important barrier to affect the structure and distribution of wind speed and turbulence. Porosities of windbreaks could alter the patterns of turbulence, therefore, affect the abilities and functions of windbreaks.

In eastern China, the Feidong-Zhangbaling Massif is located between the Dabieshan and Sulu areas along the Tan-Lu fault. Five tectonic-metamorphic events are distinguished there. The earliest deformation (D1), corresponding to a southward compression occurred during the subduction of the South China Block below the North China Block. Top-to-the-south shearing is coeval with the Late Permian-Early Triassic blueschist facies metamorphism, and possibly with the development of south-verging recumbent folds in the Neoproterozoic-Paleozoic sedimentary cover of the South China foreland. The main ductile deformation (D2) is an extensional one, characterized by top-to-the-north shearing, coeval with the early stage of exhumation of the high-pressure rocks. A top-to-the-NW ductile shearing, and microfolds overturned to the northwest belong to a second deformation phase of exhumation (D3) which is distinct from the main event (D2). Previous 40Ar-39Ar mica dates ranging between 245 Ma and 212 Ma suggest Late Permian-Early Triassic ages for the D1 to D3 events. The D4 event produced NE-SW trending folds in the sedimentary cover interpreted as gravity collapse structures. A Late Cretaceous brittle extensional event (D5) controls the opening and infill of continental half-grabens. In the study area, the Tan-Lu fault is a Cretaceous brittle normal fault. The lack of ductile deformation along the Tan-Lu fault cannot account for the exhumation of high-pressure metamorphic rocks.