Pixel‐scale evaluation of SSM/I sea‐ice algorithms in the marginal ice zone during early fall freeze‐up

Observed reduction in recent sea ice areal extent and thickness has focused attention on the fact that the Arctic marine system appears to be responding to global‐scale climate variability and change. Passive microwave remote‐sensing data are the primary source underpinning these reports, yet problems remain in geophysical inversion of information on ice type and concentration. Uncertainty in sea‐ice concentration (SIC) retrievals is highest in the summer and fall, when water occurs in liquid phase within the snow–sea‐ice system. Of particular scientific interest is the timing and rate of new ice formation due to the control that this form of sea ice has on mass, energy and gas fluxes across the ocean–sea‐ice–atmosphere interface. In this paper we examine the critical fall freeze‐up period using in situ data from a ship‐based and aerial survey programme known as the Canadian Arctic Shelf Exchange study combined with microwave and optical Earth observations data. Results show that: (1) the overall physical conditions observed from aerial survey photography were well matched with coincident moderate‐resolution imaging spectroradiometer data and Radarsat ScanSAR imagery; (2) the shortwave albedo was linearly related to old ice concentration derived from survey photography; (3) the three SSM/I SIC algorithms (NASA Team (NT), NASA Team 2 (NT2), and Bootstrap (BT)) showed considerable discrepancies in pixel‐scale comparison with the Radarsat ScanSAR SICs well calibrated by the aerial survey data. The major causes of the discrepancies are attributed to (1) the inherent inability to detect the new thin ice in the NT and BT algorithms, (2) mismatches of the thin‐ice tie point of the NT2 algorithm, and (3) sub‐pixel ambiguity between the thin ice and the mixture of open water and sea ice. These results suggest the need for finer resolution of passive microwave sensors, such as AMSR‐E, to improve the precision of the SSM/I SIC algorithms in the marginal ice zone during early fall freeze‐up. Copyright © 2006 John Wiley & Sons, Ltd.     

南秦岭勉略蛇绿构造混杂带辉长辉绿岩类微量-稀土元素地球化学

应用元素地球化学方法．研究了勉略带中辉长辉绿岩的相关特征．结果表明．勉略蛇绿构造混杂带内的辉长岩属高铝强碱质辉长岩类，是地幔橄榄岩部分熔融的产物。辉绿岩墙群属强碱铝质基性岩类，过渡族元素蛛网图与辉长岩类几乎完全相同，其不相容元素与辉长岩类总体趋势相一致．反映了一种递进岩浆演化趋势。因此，本区辉长岩与辉绿岩墙群具同源岩浆分异演化的地球化学特征．其均为勉略蛇绿岩的重要组成端元。     

TEMPORAL SPATIAL VARIATION CHARACTERISTICS OF CRUST DEFORMATION OF ACTIVE TECTONIC BLOCKS IN NORTH CHINA

1　IntroductionTomonitorthecurrentcrustalmotionandearthquakehazardsinNorthChinaarea,theFirstCrustalMonitoringandApplicationCenter (FC MAC)oftheChinaEarthquakeAdministration(CEA)hasestablishedaGlobalPositioningSystem(GPS)monitoringnetworkinNorthChinaandtheCapital(Beijing)Circlearea .TheobservedstationsaremainlydistributedinthenorthernpartofNorthChinaandCapitalCirclearea (Fig .1 ) .Theregionisbetween 1 0 7°Eand 1 2 2°E (about 1 40 0km) ,andbetween 33°Nand 42°N (about 80 0km) .…     

河南省西峡北部金矿分布特征浅析

从剪切带及原岩建造分析入手，论述了工作区内金矿的分布特征和主要控矿因素。区内的金矿床（点）无论其物质来源和时代如何，就其空间位置而言绝大多数金矿直接产在剪切变形变质带─—脆性及脆－韧性剪切带中。Ｆｅ／（Ｆｅ＋Ｍｇ）高比值的容矿岩石有利于金的沉淀富集。     

横断山区地质构造分区

位于青藏高原东南部的横断山区,是我国东部环太平洋区与西部古地中海区间的交接过渡地带,也是我国地质结构最为复杂的一个区域。作者根据1981—1985年在当地考察资料,将本区分出5条具洋壳性质的强变形构造带,2块具陆壳性质的地块,它们相间并列。文章论述了各条块的发育特征及区域演化历史。     

Shallow earthquakes in a viscoelastic shear zone with depth-dependent friction and rheology

Summary. Most crustal earthquakes of the world are observed to occur within a seismogenic layer which extends from the Earth's surface to a depth of a few tens of kilometres at most. A model is proposed in which the shear zone along a transcurrent plate margin is represented as a viscoelastic medium with depth-dependent power-law rheology. A frictional resistance linearly increasing with depth is assumed on a vertical transcurrent fault within the shear zone. Such a model is able to reproduce a continuous transition from the brittle behaviour of the upper crust to the ductile behaviour at depth. Assuming that the shear zone is subjected to a constant strain rate from the opposite motions of the two adjacent plates, it is found that there exists a maximum depth H below which tectonic stress can never reach the frictional threshold: this may be identified as the maximum depth of earthquake nucleation. The value of H is consistent with observations for plausible values of the model parameters. The stress evolution in the shear zone is calculated in the linear approximation of the constitutive equation. A change in rigidity with depth, which is also introduced in the model, may reproduce the high vertical gradient of shear stress, which has been measured across the San Andreas fault, and the fact that most earthquakes are nucleated at some depth in the seismogenic layer. A crack which drops the ambient stress to the dynamic frictional level is then introduced in the model. To this aim, a crack solution is employed without a stress singularity at its edges, which is compatible with a frictional stress threshold criterion for fracture. A constraint on the vertical friction gradient is obtained if such cracks are assumed to be entirely confined within the seismogenic layer.     

青海石炭纪孢子花粉及其地层意义

青海石炭系分布广泛,沉积类型多样,产有丰富的动植物化石,并具重要特征。石炭系保存有属种众多而又丰富的孢子和花粉,其组合基本可与国内和西欧、苏联、北美同时期孢子花粉带比较。根据孢子花粉材料,讨论了关于时代、古地理及孢子花粉分布问题。     

Progressive metamorphism in a crustal-scale shear zone: an example from the Léon region, north-west Brittany, France

This paper describes the progressive metamorphism and deformation of a series of metasediments, Le Conquet Schists and their higher grade equivalents, which occur as tectonically emplaced screens within a sequence of foliated gneisses, the Gneiss de Brest and Gneiss de Lesneven. The sequence exhibits a steep south to north increase in metamorphic grade from garnet-staurolite schist to sillimanite gneiss and sillimanite-K-feldspar migmatite. The relationship of mineral growth to foliation development has been established for individual screens. At least five phases of deformation (D1-D5) are preserved. Analysis of porphyroblast inclusion trails is used to demonstrate sequential mineral growth during the successive development of orthogonal foliations S1-S4. Porphyroblasts continued to grow during the subsequent development of C-S mylonite fabrics and extensional crenulation cleavages which are genetically related to a series of high-strain zones (D5). Mineral assemblages, phase relations and mineral chemistry are consistent with porphyroblast growth being the result of continuous reactions. Microstructure-porphyroblast relations are used to show that although mineral growth proceeded during continuous reactions, these only operated episodically. Phase relations, mineral chemistry and P-T estimates are used to constrain P-T trajectories and these are linked to the deformation histories within individual screens. A comparison between the resulting pressure-temperature-deformation paths is used to demonstrate that the metamorphic peak occurred progressively later and at successively lower pressures with increasing metamorphic grade. It is suggested that the early evolution of the belt is the result of crustal thickening by overthrusting. The subsequent history is one of progressive heating and unroofing of the higher grade rocks in a dextral strike-slip transtensional shear zone.