荣成基底片麻岩原岩岩石成因及其构造意义

Extensive high to ultrahigh pressure metamorphic rocks are outcropped in the the Dabie-Sulu UHP orogenic belt. Disputes still exist about for protolith nature of metamorphic rocks, petrogenesis, tectonic setting, and influence on upper mantle during the Triassic deep subduction. In this study, a combined study of petrology, geochemistry, isotope geochemistry and zircon chronology was accomplished for high-grade gneisses in the basement of the ultrahigh-pressure metamorphic Rongcheng terrane to reveal protolith nature and petrogenesis of the gneisses and to disucss the magmatic succession along the northern margin of the Yangtze block in Neoproterozoic. Gneisses in the Rongcheng terrane are characterized by negative Nb, Ta, P and Ti anomalies, relatively low Sr/Y ratios and relatively high Ba/La, Ba/Nb and Ba/Zr ratios, mostly displaying geochemical affinity to Phanerozoic volcanic arc. Neoproterozoic protolith ages (0.7 ~ 0.8 Ga) and Paleoproterozoic average crustal residence time (1.92 ~ 2.21 Ga) favour a Yangtze affinity. The gneisses mostly display characteristics of enrichment of LREE, flat heavy rare earth elements (REE) patterns, moderately fractionation between LREE and HREE and slight negative or positive Eu anomalies, probably reflecting that melting took place in the middle to low crust (26 ~ 33 km), where amphibole fractionated from the melts and/or inherited from source material as major mineral phases in the source area. Sr-Nd isotopic composition of the gneisses supports this conclusion. According to εNd(t) and εHf(t) values, the gneisses can be divided into three groups. Gneisses of group I have the highest εNd(t) and εHf(t) values, corresponding to the range of -6 ~ -3 and -2.9 ~ 13.4, respectively. This suggests obvious influx of depleted mantle or juvenile crust in the formation of protoliths. Gneisses of group II have medium εNd(t) (-9 ~ -7) and εHf(t) values (-15.8 ~ -1.4), corresponding to relatively high TDM2(Nd) (1.99 ~ 2.31 Ga) and TDM2(Hf) (1.76 ~ 2.67 Ga) , respectively. This suggests these gneisses were formed by partial melting of Paleoproterozoic crust. Gneisses of group III have the lowest εNd(t) (-15 ~ -10) and εHf(t) values (-15.8 ~ -1.4), corresponding to the largest TDM2(Nd) (1.99 ~ 2.31 Ga) and TDM2(Hf) ( 1.76 ~ 2.67 Ga), respectively. This indicates that gneisses of group III were formed by remelting of Archean crustal material and further demonstrates existence of an Archean basement probably of the Yangtze affinity beneath the Rongcheng terrane. Gneisses of three groups have also certain different geochemical characteristics. Contents of REEs and trace elements reduce gradually from group I to group III. Zirconium saturation temperatures also show similar tendency. Compared to gneisses of group II and group III, gneisses of group I display geochemical feature similar to extensional tectonic setting, having relatively little influence by the source area. Therefore, geochemical characteristics for gneisses of group I can indictate that the protoliths of the Rongcheng gneisses formed in an extensional rifting tectonic setting. This conclusion is supported by the results of eclogites and gabbros previously reported in the Dabie-Sulu orogenic belt. Statistical results of the protolith ages of the Rongcheng gneisses show two age peaks around ~728 Ma and ~783 Ma with an about 50 Ma gap. Extensive magatism in abou 750 Ma along the northern margin of the Yangtze block can hardly be observed in the Rongcheng terrane. This phenomenon likely suggests discontinuous Neoproterozoic magmatism along the northern margin of the Yangtze block.

碎屑锆石年龄和Nd-Hf同位素组成对扬子基底演化的制约

The South China craton was formed by the collision of the Yangtze and Cathaysia blocks during the Neoproterozoic Jiangnan orogeny (also termed as the Jingnin or Sibao orogeny in Chinese literature). Basement rocks within the Yangtze block consist mainly of Proterozoic sediments of the Lengjiaxi and Banxi Groups. U-Pb ages of detrital zircons obtained by the LA-ICP-MS dating technique imply that the deposition of the Lengjiaxi Group continued until the Neoproterozoic. The youngest detrital zircons suggest a maximum deposition age of ~830 Ma for the Lengjiaxi Group, consistent with the initiation time of the deposition of the overlying Banxi Group, likely indicating continuous deposition of these two groups and a short temporal hiatus (~10 Ma) between the Neoproterozoic sedimentary rocks distributed in the South China craton. Detrital zircons from both the Lengjiaxi and Banxi Groups have a wide range of εHf(t) values from -12 to 14.2 and a continuous Nd and Hf model age spectrum from ~820 Ma to 2200 Ma. Some grains have model ages ranging up to ca. 2.9-3.5 Ga, indicating that both juvenile mantle material and ancient crust provided sedimentary detritus. This is also consistent with the Nd isotopic signature of sedimentary rocks recorded in the Lengjiaxi Group, suggesting a back-arc tectonic setting. The Banxi Group has slightly enriched Nd isotopic signatures relative to the Lengjiaxi Group, implying a higher percentage of old continental material in the sedimentary source. Combined with previously published data, new results can help us to reconstruct the Neoproterozoic tectonic evolution of the South China craton. The age spectrum of detrital zircons and Nd-Hf isotopic composition suggests a two-stage collision: Between 1000 Ma to 870 Ma, a continental magmatic arc was build up along the eastern margin of the Yangtze block. Convergence led to continent-based back-arc extension, subsidence and formation of a back-arc basin. Detritus originating from arc-related magmatic and old basement rocks was transported into this back-arc basin resulting in formation of the Lengjiaxi Group and its equivalents. At around 870 Ma, a second (oceanic) arc was formed by extension of an inter-arc basin, subduction subsequently led to the first collision and the emplacement of the blueschist mélange. Accretion of the magmatic arc lasted until the closure of an oceanic basin between the Yangtze and Cathaysia blocks at about 830 Ma. Shortly after the collision, subsequent uplift, further extension of the former back-arc basin and post-collisional granitoid magmatism caused a tilting of the Lengjiaxi sediments. Between 830 Ma and 820 Ma, subsequent closure of the oceanic back-arc basin and formation of the Jiangnan orogen took place, leaving a regional unconformity above the Lengjiaxi Group. Above this unconformity the Banxi Group was immediately deposited during the post-tectonic stage.

大别山碰撞造山带逆冲推覆构造运动学和动力学研究

Since the discovery of coesite-bearing eclogites in Dabie and Sulu region over ten years ago, the Dabie collisional orogen has been the "hot-spot" across the world. While many great progresses have been made for the last decade in the researches on the Dabie and Sulu UHP metamorphic rocks in the following fields, such as, petrology, mineralogy, isotope chronology, and geochemistry, the study of the structural geology on the Dabie orogen is still in great need. Thrust and nappe tectonics commonly developed in any collisional orogenic belt during the syncollisional process of the orogen. It is the same as the Dabic collisional orogen is concerned. The paper put much stress on the thrust and nappe tectonics in the Dabic orogenic belt, which have been seldom systematically studied before. The geometric features including the division and the spatial distribution of various thrust and nappe tectonics in the Dabie orogen have been first studied, which is followed by the detailed studies on their kinematic characteristics in different scales varying from regional tectonics to microtectonics. In the thesis, new deformation ages have been obtained by the isotopic methods of ~(40)Ar-~(39)Ar, Sm-Nd and Rb-Sr minerals-whole rock isochrons on the mylonites formed in three ductile shear zones which bounded three different major nappes in the Dabie collisional orogenic belt. And the petrological, geochemical characteristics of some metamorphic rocks as well as the geotectonics of their protoliths, which have also deformed in the ductile shear zone, are analyzed and discussed. In the paper, twelve nappes in the Dabie orogen are first divided, which are bounded by various important NWW or NW-strike faults and three NNE-strike faults. They are Shangcheng Nappe, Huoshan Nappe, Yuexi Nappe, Yingshanjian-Hengzhong Nappe, Huangzhen Nappe, Xishui-Huangmei Nappe, Zhoudang Nappe, Suhe-Huwan Nappe, Xinxian Nappe, Hong'an Nappe, Mulan Nappe and Hhuangpi-Susong Nappe. In the Dabie orogen, three types of thrust and nappe tectonics belonging to two stages have been confirmed. They are: (1) early stage ductile thrust -nappe tectonics which movement direction was top-to-the-south; (2) late stage brittle to ductile-brittle thrust-nappe tectonics which are characterized by double-vergence movement, including top-to-the-north and top-to-the-south; (3) the third type also belongs to the late stage which also characterized by double-vergence movement, including top-to-the-east and top-to-the-west, and related to the strike-slip movement. The deformation ages of both Wuhe-Shuihou ductile shear zone and Taihu-Mamiao ductile shear zone have been dated by ~(40)Ar-~(39)Ar method. ~(40)Ar/~(39)Ar plateau ages of biotite and mica from the mylonites in these two shear zones are 219.57Ma and 229.12Ma. The plateau ages record the time of ductile deformation of the ductile shear zones, which made the concerned minerals of the mylonites exhume from amphibolite facies to the middle-upper crustal conditions by the early stage ductile thrust-nappe tectonics. The mineral isochons of Sm-Nd and Rb-Sr dating on the same mylonite sample of the metamafic rocks are 156.5Ma and 124.56Ma respectively. The two isochron ages suggest that the mylonitic rock strongly deformed in the amphilbolite facies at 156Ma and then exhumed to the upper crustal green schist condition at 124Ma with the activities of the Quiliping-Changlinggang ductile shear zone which bounded to the southen edge of Xinxian Nappe. Studies of the petrological and geochemical characteristics of some meta-mafic rocks and discussion on the geotectonics of their protoliths indicate that their protoliths were developped in an island arc or back-arc basin or active continental margin in which calc-alkline basalts formed. This means that arc-accretion orogeny had evolved in the margins of North china plate and/or Yangtze plate before these two plates directly collided with each other during the evolution process of Dabie orogen. Three-stage evolution of the thrust-nappe tectonics in Dabie collisional orogen has been induced based on the above-mentioned studies and previous work of others. And a possible 3-stage exhumation model (Thrust-Positive Flower Structure Model) has also been proposed.

晚中生代松辽盆地形成的大地构造环境及成因机制

Directed by the theory of "Collision Tectonic Facies", the tectonic setting and dynamic mechanism of the formation of Songliao basin in late Mesozoic (J_3-K_1) are studied in the present thesis with the methods of petrology, petrochemistry, geochemistry and isotopic geochronology. The research contents in this paper include as followings. Firstly, the general tectonic frame is made up of different tectonic facies formed from Mid-late Proterozoic to Mesozoic, which are Huabei plate, the Chengde-Siziwangqi melange (Pz_1), the Wenduermiao magmatic arc (Pz_1), the Hegenshan-Chaogenshan melange (Pz_2), the accretion arec (Pz_1-P), the Raohe-Hulin melange (Mz), the magmatic arc (Mz) and the pull-apart basin on the magmatic arc (Mz). Secondly, the volcanic rock assemblages of Songliao basin and its adjacent area in late Mesozoic is the typical calc-alkaline of the magmatic arc. The types of volcanic rocks in the study area include basalts, basaltic andesites, andesites, dacites and rhyolites, and basic-intermediate volcanic rocks have higher alkalinity. The volcanic rock series in this area is the high-K calc-alkaline series. Thirdly, the total REE of volcanic rocks in Songliao basin and its adjacent area is higher than that of the chondrite. The pattern of the REE normalized by the chondrite shows the characteristics similar to that of the typical island arcs or the active continental margins in the earth, that is enrichment of LREE and depletion of Eu. The spider-diagram of the trace element normalized by the primitive mantle also expresses the similar features to that of the typical island arcs or the active continental margins, it has distinctive valleies of Nb, Ta, Sr, P, and Ti, as well as the peaks of La, Ce, Th, U, and K. The incompatible elements show that the high field strength elements, such as Nb, Ta, Ti, and P, are depletion while the low field strength elements, such as K, U, Pb, and Ba, are enrichment. These features are similar to those of orogenic volcanic rocks and imply the formation of the volcanic rocks in this area is related to the subduction. The degrees of both the enrichment of the HFS elements and depletion of the LFS elements become more obvious from basic to acid volcanic rocks, which suggests crustal contamination enhances with the magmatic crystallization and fractionation. The concentration of the compatible elements is W-shape, and anomalies in Cr and Ni suggest there is the contamination during the magmatic crystallization and fractionation. Fourthly, the isotopic age data prove the volcanic activity in the Songliao basin and its adjacent area started in the early-middle Jurassic, and ended in the end of the early Cretaceous-the beginning of the Cretaceous. The volcanism summit was the late Jurassic-the early Cretaceous (100 - 150Ma). Finally, the tectonic setting of volcanism in the late Mesozoic was magmatic arc, which originated the subduction of Raohe-Hulin trench to the northwest Asian plate. The subduction began in the middle Jurassic, and the collision orogenesis between the Sikhote-Alin arc and Asian continent was completed in the end of the early Cretaceous-the beginning of the late Cretaceous. The results of above tectonic processes were finally to format Nadanhada orogenic belt symbolized by the Raohe-Hulin suture or melange belt. The violently oblique movement of the Izanagi plate toward Asian plate in the late Mesozoic was the dynamic mechanism of above tectonic processes. At the same tome, the left-lateral strike-slip shear caused by the oblique movement of the Izanagi plate produced a series of strike-slip faults in east Asian margin, and the large scale displacements of these strike-slip faults then produced the pull-apart basing or grabens on the magmatic arc. Conclusively, the tectonic setting during the formation of the grabens of Songliao basin in the late Mesozoic was magmatic arc, and its dynamic mechanism was the pull-apart. In a word, there was a good coupling relation among the oblique subduction of the oceanic plate, collisional orogene between island arc and continental plate, strike-slip shear of the faults and the formation of the grabens in Songliao basin and its adjacent area in late Mesozoic. These tectonic processes were completed in the unoin dynamic setting and mechanism as above description.

Nonlinear excitations in electron-positron-ion plasmas in accretion disks of active galactic nuclei

The propagation of acoustic nonlinear excitations in an electron-positron-ion (e-p-i) plasma composed of warm electrons and positrons, as well as hot ions, has been investigated by adopting a two-dimensional cylindrical geometry. The electrons and positrons are modeled by hydrodynamic fluid equations, while the ions are assumed to follow a temperature-parametrized Boltzmann distribution (the fixed ion model is recovered in the appropriate limit). This situation applies in the accretion disk near a black hole in active galactic nuclei, where the ion temperature may be as high as 3 to 300 times that of the electrons. Using a reductive perturbation technique, a cylindrical Kadomtsev-Petviashvili equation is derived and its exact soliton solutions are presented. Furthermore, real situations in which the strength of the nonlinearity may be weak are considered, so that higher-order nonlinearity plays an important role. Accordingly, an extended cylindrical Kadomtsev-Petviashvili equation is derived, which admits both soliton and double-layer solutions. The characteristics of the nonlinear excitations obtained are investigated in detail

Effects of Accretion Flow on the Chemical Structure in the Inner Regions of Protoplanetary Disks

Aims. We study the dependence of the profiles of molecular abundances and line emission on the accretion flow in the hot (100 K) inner region of protoplanetary disks.
Methods. The gas-phase reactions initiated by evaporation of the ice mantle on dust grains are calculated along the accretion flow. We focus on methanol, a molecule that is formed predominantly by the evaporation of warm ice mantles, to demonstrate how its abundance profile and line emission depend on the accretion flow.
Results. Our results indicate that some evaporated molecules retain high abundances only when the accretion velocity is sufficiently high, and that methanol could be useful as a diagnostic of the accretion flow by means of ALMA observations at the disk radius of 10 AU.

High density mangrove plantation enhances surface accretion, surface elevation change, and tree survival in coastal areas susceptible to sea-level rise

Survival, growth, above ground biomass accumulation, soil surface elevation dynamics and nitrogen accumulation in accreted sediments were studied in experimental treatments planted with four different densities (6.96, 3.26, 1.93 and 0.95 seedlings m-2) of the mangrove Rhizophora mucronata in Puttalam Lagoon, Sri Lanka. Measurements were taken over a period of 1171 days and were compared with those from unplanted controls. Trees at the lowest density showed significantly reduced survival, whilst measures of individual tree growth did not differ significantly among treatments. Rates of surface sediment accretion (means ± S.E.) were 13.0 (±1.3), 10.5 (±0.9), 8.4 (±0.3), 6.9 (±0.5) and 5.7 (±0.3) mm yr-1 at planting densities of 6.96, 3.26, 1.93, 0.95, and 0 (unplanted control) seedlings m-2, respectively, showing highly significant differences among treatments. Mean (± S.E.) rates of surface elevation change were much lower than rates of accretion at 2.8 (±0.2), 1.6 (±0.1), 1.1 (±0.2), 0.6 (±0.2) and -0.3 (±0.1) mm yr-1 for 6.96, 3.26, 1.93, 0.95, and 0 seedlings m-2, respectively. All planted treatments appeared to accumulate greater nitrogen concentrations in the sediment compared to the unplanted control, and suggests one potential causal mechanism for the facilitatory effects observed; high densities of plants potentially contribute to the accretion of greater amounts of nutrient rich sediment. While this potential process needs further study, this study demonstrated how higher densities of mangroves enhance rates of sediment accretion and surface elevation, processes that may be crucial in mangrove ecosystem adaptation to sea level rise. There was no evidence that increasing plant density evoked a trade-off with growth and survival of the planted trees. Rather facilitatory effects enhanced survival at high densities, suggesting that local land managers may be able to take advantage of plantation densities to help mitigate sea-level rise effects by encouraging positive soil surface elevation increment, and perhaps even greater nutrient retention to promote mangrove growth and ameliorate nearshore eutrophication in tropical island environments.

Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing, and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared local thermodynamic equilibrium line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find that the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line emission from the disk and subsequently improving agreement with observations. We find that NH3, CH3OH, C2H2, and sulfur-containing species are greatly enhanced by the inclusion of turbulent mixing. We demonstrate that disk winds potentially affect the disk chemistry and the resulting molecular line emission in a manner similar to that found when mixing is included.

Multidimensional modelling of X-ray spectra for AGN accretion disc outflows - III. Application to a hydrodynamical simulation

We perform multidimensional radiative transfer simulations to compute spectra for a hydrodynamical simulation of a line-driven accretion disc wind from an active galactic nucleus. The synthetic spectra confirm expectations from parametrized models that a disc wind can imprint a wide variety of spectroscopic signatures including narrow absorption lines, broad emission lines and a Compton hump. The formation of these features is complex with contributions originating from many of the different structures present in the hydrodynamical simulation. In particular, spectral features are shaped both by gas in a successfully launched outflow and in complex flows where material is lifted out of the disc plane but ultimately falls back. We also confirm that the strong Fe Ka line can develop a weak, red-skewed line wing as a result of Compton scattering in the outflow. In addition, we demonstrate that X-ray radiation scattered and reprocessed in the flow has a pivotal part in both the spectrum formation and determining the ionization conditions in the wind. We find that scattered radiation is rather effective in ionizing gas which is shielded from direct irradiation from the central source. This effect likely makes the successful launching of a massive disc wind somewhat more challenging and should be considered in future wind simulations. © 2010 The Authors. Journal compilation © 2010 RAS.