Continental collision slowing due to viscous mantle lithosphere rather than topography

Because the inertia of tectonic plates is negligible, plate velocities result from the balance of forces acting at plate margins and along their base. Observations of past plate motion derived from marine magnetic anomalies provide evidence of how continental deformation may contribute to plate driving forces. A decrease in convergence rate at the inception of continental collision is expected because of the greater buoyancy of continental than oceanic lithosphere, but post-collisional rates are less well understood. Slowing of convergence has generally been attributed to the development of high topography that further resists convergent motion; however, the role of deforming continental mantle lithosphere on plate motions has not previously been considered. Here I show that the rate of India's penetration into Eurasia has decreased exponentially since their collision. The exponential decrease in convergence rate suggests that contractional strain across Tibet has been constant throughout the collision at a rate of 7.03?×?10(-16)?s(-1), which matches the current rate. A constant bulk strain rate of the orogen suggests that convergent motion is resisted by constant average stress (constant force) applied to a relatively uniform layer or interface at depth. This finding follows new evidence that the mantle lithosphere beneath Tibet is intact, which supports the interpretation that the long-term strain history of Tibet reflects deformation of the mantle lithosphere. Under conditions of constant stress and strength, the deforming continental lithosphere creates a type of viscous resistance that affects plate motion irrespective of how topography evolved.     

Origin of a 'Southern Hemisphere' geochemical signature in the Arctic upper mantle

The Gakkel ridge, which extends under the Arctic ice cap for approximately 1,800 km, is the slowest spreading ocean ridge on Earth. Its spreading created the Eurasian basin, which is isolated from the rest of the oceanic mantle by North America, Eurasia and the Lomonosov ridge. The Gakkel ridge thus provides unique opportunities to investigate the composition of the sub-Arctic mantle and mantle heterogeneity and melting at the lower limits of seafloor spreading. The first results of the 2001 Arctic Mid-Ocean Ridge Expedition (ref. 1) divided the Gakkel ridge into three tectonic segments, composed of robust western and eastern volcanic zones separated by a 'sparsely magmatic zone'. On the basis of Sr-Nd-Pb isotope ratios and trace elements in basalts from the spreading axis, we show that the sparsely magmatic zone contains an abrupt mantle compositional boundary. Basalts to the west of the boundary display affinities to the Southern Hemisphere 'Dupal' isotopic province, whereas those to the east-closest to the Eurasian continent and where the spreading rate is slowest-display affinities to 'Northern Hemisphere' ridges. The western zone is the only known spreading ridge outside the Southern Hemisphere that samples a significant upper-mantle region with Dupal-like characteristics. Although the cause of Dupal mantle has been long debated, we show that the source of this signature beneath the western Gakkel ridge was subcontinental lithospheric mantle that delaminated and became integrated into the convecting Arctic asthenosphere. This occurred as North Atlantic mantle propagated north into the Arctic during the separation of Svalbard and Greenland.     

不可追踪的盲签名和多重盲签名方案

盲签名是指签名者不知道任何有关签名的信息,可以保护接收者的隐私,因此在电子支票支付等实际应用中有一定应用价值.于是设计了一种新的不可追踪的盲签名和多重盲签名方案,该方案不需要利用hash函数,只需要引入一个随机数,计算量较小,具有一定的实用价值.     

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes.In this paper,in-situ SIMS(Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton.It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton;the former has a range of 6.0‰ to 2.0‰(relative to VPDB) with an average value of 3.0‰ in their core areas,which is consistent with global peridotitic diamonds;the diamonds from the Yangtze Craton,however,have a carbon isotopic range from 8.6‰ to 3.0‰ with an average value of 7.4‰ in their core areas,being more consistent with global eclogitic diamonds.The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied.There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth,while no correlation was observed between δ13C and internal inclusions.The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization,and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds.In addition,the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances,implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other,not yet understood factors.The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton.     

强盲签名与惟一盲签名的等价性

以基于RSA体制的盲签名方案为讨论对象,将数字签名方案中的强不可伪造性引进到一般的盲签名中,给出了强盲签名方案的定义,并采用游戏归约调用证明方法将强盲签名方案的强不可伪造性攻击游戏与具有惟一性的盲签名方案的惟一性证明进行比较进而归约调用,得出结论:强盲签名方案与具有惟一性的盲签名方案是等价的,从而给出了具有惟一性的盲签名方案的更一般化的定义和判定方法,解决了判定一个盲签名方案是否具有惟一性的公开问题.     

一个基于椭圆曲线的代理签名和代理盲签名方案

代理签名和盲签名是比较新的两种签名类型。文中给出了基于椭圆曲线的一个椭圆曲线代理签名和代理盲签名方案，并对其安全性作了分析。     

单晶金刚石热稳定性灰色关联分析

通过对6种Ib型人造单晶金刚石在空气中DTA和TG曲线的分析，确定以DTA曲线的外推起始温度作为热稳定性的表征温度；继而基于灰色系统理论，提出采用灰色关联分析的量化评定方法对影响其热稳定性的4种因素进行分析，得出灰关联序，即各因素对热稳定性影响大小的排列顺序．结果表明：单晶金刚石的氮含量、晶形规则度是影响其热稳定性的主要因素，而粒度、抗压强度是次要因素；氮含量的影响最大，抗压强度的影响最小。     

无完全可信PKG身份签名的分层CES方案

针对管理型SaaS应用整体签批分层处理业务中隐私保护的需求,提出了一种无完全可信私钥生成中心（private key generator,PKG）身份签名的分层内容摘录签名（content extraction signature,CES）方案。采用分层摘录策略控制分片和签名摘录,基于身份签名克服了公钥基础设施证书管理复杂的问题,由租户和服务提供商的PKG独立生成用户私钥分量,在一定程度上克服了无完全可信PKG问题。分析表明,该方案具有用户私钥的私密性、CES的隐私性和不可伪造性,可推广应用于在线办公、在线图书销售等方面。     

中国大陆构造三分论

介绍了中国大陆构造分为三大部分,根据在板块构造理论的基础上考虑大陆构造问题,提出了大陆构造的研究方法.     

The oxidation state of Hadean magmas and implications for early Earth's atmosphere

Magmatic outgassing of volatiles from Earth's interior probably played a critical part in determining the composition of the earliest atmosphere, more than 4,000 million years (Myr) ago. Given an elemental inventory of hydrogen, carbon, nitrogen, oxygen and sulphur, the identity of molecular species in gaseous volcanic emanations depends critically on the pressure (fugacity) of oxygen. Reduced melts having oxygen fugacities close to that defined by the iron-wüstite buffer would yield volatile species such as CH(4), H(2), H(2)S, NH(3) and CO, whereas melts close to the fayalite-magnetite-quartz buffer would be similar to present-day conditions and would be dominated by H(2)O, CO(2), SO(2) and N(2) (refs 1-4). Direct constraints on the oxidation state of terrestrial magmas before 3,850?Myr before present (that is, the Hadean eon) are tenuous because the rock record is sparse or absent. Samples from this earliest period of Earth's history are limited to igneous detrital zircons that pre-date the known rock record, with ages approaching ～4,400?Myr (refs 5-8). Here we report a redox-sensitive calibration to determine the oxidation state of Hadean magmatic melts that is based on the incorporation of cerium into zircon crystals. We find that the melts have average oxygen fugacities that are consistent with an oxidation state defined by the fayalite-magnetite-quartz buffer, similar to present-day conditions. Moreover, selected Hadean zircons (having chemical characteristics consistent with crystallization specifically from mantle-derived melts) suggest oxygen fugacities similar to those of Archaean and present-day mantle-derived lavas as early as ～4,350?Myr before present. These results suggest that outgassing of Earth's interior later than ～200?Myr into the history of Solar System formation would not have resulted in a reducing atmosphere.     

大陆岩石圈的层状结构与地球双边界层

为建立全球构造运动的准地转体系,根据全球岩石圈计划最近揭示的客观事实和粘性流体动力学等理论,研究了全球岩石圈的层状结构及其流动性 ,据此建立了一个地球双边层模式.     

土被结构系统分类及其应用

提出土被结构是由土壤群体组成且具有整体性、结构性和功能性的耗散系统的观点;以土被结构空间有序为特征,充分考虑土被各种空间基础,即地貌类型,建立土被结构分类系统.并应用这个系统划分了渭南地区土被结构类型系统.     

The crust and mantle of Mars.

Clues to the history of Mars are recorded in the chemistry and structure of the planet's crust and mantle. The mantle is the rocky, interior region of the planet that transports heat generated during accretion and subsequent core formation. The crust formed by melting of the upper mantle, and has been shaped and re-distributed by impact, volcanism, mantle flow and erosion. Observations point to a dynamically active interior in the early phases of martian history, followed by a rapid fall-off in heat transport that significantly influenced the geological, geophysical and geochemical evolution of the planet, including the history of water and climate.     

CL and FTIR analysis on the diamonds in Wafangdian, Liaoning Province

The CL images show that the internal structures of the diamonds in Wafangdian, Liaoning Province is classified as three types: simple growth girdle zone, multi-stage growth complex girdle zone, and rare agate-like structure. These internal features reflect the complexity of growth processes of the diamonds. The FTIR analyses in micro area on diamond plates reveal the heterogeneity of the impurities of nitrogen and hydrogen. The variety of nitrogen contents and nitrogen aggregation states have been revealed not only in different diamonds from one kimberlite pipe but also in different zones of one diamond. The extent of conversion A defects to the aggregated B form is a function of the nitrogen aggregation temperature (TNA), mantle residence time (tMR), and nitrogen concentration of diamond. The interval of 0.6-0.7Ga from core to rim of diamond growth is obtained by using the FTIR curves and some geological data. The long period of diamond growth is identical with the feature in CL image.     

Dependence of nitrogen concentration in type Ib diamonds on synthesis temperature

Type Ib diamonds were grown by the temperature gradient method (TGM) at 5.5 GPa and 1500－1560 K in a china-type cubic anvil high pressure apparatus using Ni₇₀Mn₂₅Co₅ alloy as solvent/catalyst. The concentration of nitrogen (C_N) in type Ib diamonds synthesized at different synthesis temperatures was measured by a Fourier transform infrared (FTIR) spectrometer. The dependence of C_N in diamond on synthesis temperature was studied. For the type Ib diamonds synthesized using Ni₇₀Mn₂₅Co₅ as catalyst, its C_N decreases along with the increase of synthesis temperature.     

History of trace gases in presolar diamonds inferred from ion-implantation experiments

Diamond grains are the most abundant presolar grains found in primitive meteorites. They formed before the Solar System, and therefore provide a record of nuclear and chemical processes in stars and in the interstellar medium. Their origins are inferred from the unusual isotopic compositions of trace elements-mainly xenon-which suggest that they came from supernovae. But the exact nature of the sources has been enigmatic, as has the method by which noble gases were incorporated into the grains. One observation is that different isotopic components are released at different temperatures when the grains are heated, and it has been suggested that these components have different origins. Here we report results of a laboratory study that shows that ion implantation (previously suggested on other grounds) is a viable mechanism for trapping noble gases. Moreover, we find that ion implantation of a single isotopic composition can produce both low- and high-temperature release peaks from the same grains. We conclude that both isotopically normal and anomalous gases may have been implanted by multiple events separated in space and/or time, with thermal processing producing an apparent enrichment of the anomalous component in the high-temperature release peak. The previous assumption that the low- and high-temperature components were not correlated may therefore have led to an overestimate of the abundance of anomalous argon and krypton, while obscuring an enhancement of the light-in addition to the heavy-krypton isotopes.