南极瑞穗高原1987—1988年度表面物质平衡及其变化          下载免费PDF全文

张文敬  山内恭 《极地研究》1990,2(3):1-10

根据1987/1988年度表面物质积累资料,对Mizuho(瑞穗)高原该年度物质平衡的分布规律及其变化进行了讨论,同时还对年内短期天气过程及地形变化对物质平衡的影响进行了分析。研究发现1987/1988年度物质平衡的空间分布与多年平均状况存在较大区别:海拔550m以下的沿海地带表现为负物质平衡状态。从S_16点向内陆80km范围内为高值物质平衡区。年平均净物质平衡量达0.84m雪层深;80km到瑞穗高原内陆的瑞穗站之间为低值物质平衡区,年平均物质平衡量仅0.14m雪层深。在瑞穗高原,表面物质平衡水平表现为低积累,低支出的特征。此外,年内短期气候和地形变化对物质平衡的影响均大于多年平均状态,在高值物质平衡区,气候变化对物质平衡的影响大于地形变化的影响;而在低值物质平衡区,地形变化对物质平衡的影响则大于气候变化对物质平衡的影响。  相似文献   

Pan-African eclogite facies metamorphism of ultramafic rocks in the Shackleton Range, Antarctica     

T. ROMER  K. MEZGER  E. SCHMÄDICKE 《Journal of Metamorphic Geology》2009,27(5):335-347

In the Shackleton Range of East Antarctica, garnet-bearing ultramafic rocks occur as lenses in supracrustal high-grade gneisses. In the presence of olivine, garnet is an unmistakable indicator of eclogite facies metamorphic conditions. The eclogite facies assemblages are only present in ultramafic rocks, particularly in pyroxenites, whereas other lithologies – including metabasites – lack such assemblages. We conclude that under high-temperature conditions, pyroxenites preserve high-pressure assemblages better than isofacial metabasites, provided the pressure is high enough to stabilize garnet–olivine assemblages (i.e. ≥18–20 kbar). The Shackleton Range ultramafic rocks experienced a clockwise P–T path and peak conditions of 800–850 °C and 23–25 kbar. These conditions correspond to ∼70 km depth of burial and a metamorphic gradient of 11–12 °C km⁻¹ that is typical of a convergent plate-margin setting. The age of metamorphism is defined by two garnet–whole-rock Sm–Nd isochrons that give ages of 525 ± 5 and 520 ± 14 Ma corresponding to the time of the Pan-African orogeny. These results are evidence of a Pan-African suture zone within the northern Shackleton Range. This suture marks the site of a palaeo-subduction zone that likely continues to the Herbert Mountains, where ophiolitic rocks of Neoproterozoic age testify to an ocean basin that was closed during Pan-African collision. The garnet-bearing ultramafic rocks in the Shackleton Range are the first known example of eclogite facies metamorphism in Antarctica that is related to the collision of East and West Gondwana and the first example of Pan-African eclogite facies ultramafic rocks worldwide. Eclogites in the Lanterman Range of the Transantarctic Mountains formed during subduction of the palaeo-Pacific beneath the East Antarctic craton.  相似文献   

Summer fast ice evolution off Zhongshan Station,Antarctica     

雷瑞波  李志军  张占海  程言峰  窦银科 《极地研究(英文版)》2008,19(1):54-62

Based on the field data acquired in the program of fast ice observation off Zhongshan Station, Prydz Bay, East Antarctica during the austral summer 2005/ 2006, physical properties evolution of fast ice during the ice ablation season is analyzed in detail. Results show that the annual maximum ice thickness in 2005 occurred in later November, and then ice started to reek, and the ablation duration was 62 days; sea water under the ice became warmer synchronously; corresponding to the warming sea ice temperature, a ＂relative cold mid-layer＂ appeared in sea ice; the fast ice marginal line recoiled back to the shore observably, and the recoil distance was 20.9 km from 18 December 2005 through 14 January 2006. In addition, based on the data of sea ice thickness survey along the investigation course of MV Xuelong on December 18 of 2005, the ice thickness distribution paten in the marginal ice zone have been described ： sea ice thickness increased, but the diversity of floe ice thick-ness decreased from open water to fast ice zone distinctly.  相似文献   

Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core     

Luciano MARQUETTO  Susan KASPARI  Jefferson Cardia SIMOES  Emil BABIK 《大气科学进展》2020,37(5):545-554

This work presents the refractory black carbon(rBC)results of a snow and firn core drilled in West Antarctica(79°55'34.6"S,94°21'13.3"W)during the 2014?15 austral summer,collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse.The core was drilled to a depth of 20 m,and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling.The core was analyzed at the Department of Geological Sciences,Central Washington University(CWU),WA,USA,using a single particle soot photometer(SP2)coupled to a CETAC Marin-5 nebulizer.The continuous melting system was recently assembled at CWU and these are its first results.We also present experimental results regarding SP2 reproducibility,indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations,like those found in the Antarctic core.Dating was carried out using mainly the rBC variation and sulfur,sodium and strontium as secondary parameters,giving the core 17 years(1998?2014).The data show a well-defined seasonality of rBC concentrations for these first meters,with geometric mean summer/fall concentrations of 0.016μg L^?1 and geometric mean winter/spring concentrations of 0.063μg L^?1.The annual rBC concentration geometric mean was 0.029μg L^?1(the lowest of all rBC cores in Antarctica referenced in this work),while the annual rBC flux was 6.1μg m^?2 yr^?1(the lowest flux in West Antarctica records so far).  相似文献   

南极采用飞艇进行航空摄影测量的可行性探讨   总被引：3，自引：2，他引：1  

崔洪禹  孙微  牛彦彬  刘侃 《测绘与空间地理信息》2005,28(2):6-9

随着我国对南极科考工作的加强,迫切需要新的高精度的地形图资料。而由于南极特殊地域的限制,要求作业时间要尽可能地短,基于这种情况,在南极两站地区采用飞艇航摄手段获取高精度的两站地形图将成为最佳的可行手段。  相似文献   

南极海冰与气候   总被引：1，自引：0，他引：1  

康建成  唐述林  刘雷保 《地球科学进展》2005,20(7):786-793

在极区,海冰的形成在海洋上部和大气下部之间构成了新的交界面,改变了大洋表面的辐射平衡和能量平衡,隔离了海洋与大气之间的热交换和水汽交换;海冰冻融过程影响着大洋温、盐流的形成和强度;海冰对南大洋和南极大陆气象、气候有重要的影响,在气候环境系统中起着重要的作用。南极海冰作用区约占南半球雪冰作用区面积的58%,约占地球表面积的3.58%。其中,一年生海冰约占南极海冰区分布面积的83%;其分布面积从夏末2月份最小时的3×106 km2左右,到9月份冬末最大时的18×106 km2左右,一年中季节变化幅度可达15×106 km2,季节变化率>500%。海冰分布区域的年际变化较大。南极海冰区是影响季节和年际全球气候环境变化的重要区域。当前,国际南极海冰与气候研究的核心问题是海冰物理过程和在海冰区的海洋—大气相互作用。结合目前承担的研究课题,对国际南极海冰与气候研究的前沿动态和相关的国际计划进行了综述。  相似文献   

东南极拉斯曼丘陵镁铁质麻粒岩的变质作用演化   总被引：5，自引：4，他引：1  

周信  仝来喜  刘小汉  王彦斌  陈义兵 《岩石学报》2014,30(6):1731-1747

拉斯曼丘陵（Larsemann Hills）位于东南极普里兹构造带的中部,研究该区麻粒岩的变质作用演化对于理解普里兹带的构造属性至关重要。通过对该区含石榴石镁铁质麻粒岩转石详细的岩相学观察表明,峰期前进变质阶段矿物组合（M1）由角闪石+斜方辉石+单斜辉石+斜长石+黑云母+钛铁矿±石英±磁铁矿组成,其峰期矿物组合（M2）为石榴石+斜方辉石+单斜辉石+角闪石+钛铁矿±磁铁矿±石英,而代表后期与降压有关的叠加变质组合（M3）为斜方辉石+斜长石+单斜辉石+黑云母+钛铁矿±磁铁矿。矿物化学分析,结果显示其中石榴子石和斜方辉石具有弱的成分环带特征。利用THERMOCALC软件在NCFMASHTO体系下对该麻粒岩进行了详细的热力学模拟,结合传统温压计和平均温压计算结果,得出不同阶段温压条件分别为650~750℃/5.5~6.5kb （M1）,850~950℃/8~8.5kb （M2）,800~900℃/5.5~7.5kb （M3）。其变质作用演化为典型的峰期后近等温减压的（ITD）顺时针P-T轨迹。通过区域上镁铁质麻粒岩的对比分析,我们认为该镁铁质麻粒岩可能来源拉斯曼丘陵基岩露头。结合已有的年代学资料,表明该镁铁质麻粒岩的峰期变质事件可能对应于晚元古代格林威尔期构造事件,而后期退变质作用与早古生代的泛非期构造事件有关,意味着泛非期普里兹带可能是陆内造山带。  相似文献   

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events     

Nathan D. Sheldon  Ramananda Chakrabarti  Gregory J. Retallack  Roger M. H. Smith 《Sedimentology》2014,61(6):1812-1829

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.  相似文献   

Early Neoproterozoic granulite facies metamorphism of mafic dykes from the Vestfold Block,east Antarctica   总被引：2，自引：0，他引：2  

X. C. Liu  W.‐ Wang  Y. Zhao  J. Liu  B. Song 《Journal of Metamorphic Geology》2014,32(9):1041-1062

Proterozoic mafic dykes from the southwestern Vestfold Block experienced heterogeneous granulite facies metamorphism, characterized by spotted or fractured garnet‐bearing aggregates in garnet‐absent groundmass. The garnet‐absent groundmass typically preserves an ophitic texture composed of lathy plagioclase, intergranular clinopyroxene and Fe–Ti oxides. Garnet‐bearing domains consist mainly of a metamorphic assemblage of garnet, clinopyroxene, orthopyroxene, hornblende, biotite, plagioclase, K‐feldspar, quartz and Fe–Ti oxides. Chemical compositions and textural relationships suggest that these metamorphic minerals reached local equilibrium in the centre of the garnet‐bearing domains. Pseudosection calculations in the model system NCFMASHTO (Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃) yield P–T estimates of 820–870 °C and 8.4–9.7 kbar. Ion microprobe U–Pb zircon dating reveals that the NW‐ and N‐trending mafic dykes were emplaced at 1764 ± 25 and 1232 ± 12 Ma, respectively, whereas their metamorphic ages cluster between 957 ± 7 and 938 ± 9 Ma. The identification of granulite facies mineral inclusions in metamorphic zircon domains is also consistent with early Neoproterozoic metamorphism. Therefore, the southwestern margin of the Vestfold Block is inferred to have been buried to depths of ~30–35 km beneath the Rayner orogen during the late stage of the late Mesoproterozoic/early Neoproterozoic collision between the Indian craton and east Antarctica (i.e. the Lambert Terrane or the Ruker craton including the Lambert Terrane). The lack of penetrative deformation and intensive fluid–rock interaction in the rigid Vestfold Block prevented the nucleation and growth of garnet and resulted in the heterogeneous granulite facies metamorphism of the mafic dykes.  相似文献   

Volcanic eruption frequency over the last 45 ky as recorded in Epica-Dome C ice core (East Antarctica) and its relationship with climatic changes     

E. Castellano  S. Becagli  J. Jouzel  A. Migliori  M. Severi  J. P. Steffensen  R. Traversi  R. Udisti   《Global and Planetary Change》2004,42(1-4):195

The sulphate glacio-chemical profiles constitute a reliable proxy marker for reconstruction of past volcanic history, assuming a reliable method to distinguish sulphate spikes and to evaluate the flux of individual events is set up. The resulting volcanic event profile is used to reconstruct past event frequencies, and to investigate possible links between volcanism and climatic changes. Volcanic event signatures are useful also in comparing time scales from ice cores drilled at different locations. In this paper, a new method to pick out volcanic signals is proposed. It improves on methods based on the calculation of a threshold using a general mean value plus a multiple of the standard deviation by adding: (1) quantification of nonvolcanic sulphate contributions; (2) sulphate fluxes, instead of concentrations, accounting for accumulation rate changes; (3) data treatment using a log-normal statistic, instead of a Gaussian-type distribution, to take into account the real sulphate distribution; (4) a smoothed curve (weighted fitting) to better understand the residual variability of the sulphate background.This method is used to detect volcanic events throughout the 45 ky time span of the EDC96 ice core, drilled at Dome C on the East Antarctic plateau. A total of 283 volcanic signatures are recovered, with a mean of 6.3 events per millennium. The temporal event frequencies indicate that the last 2000 years were probably characterized by the highest volcanic activity in the period covered by the core and that there is no clear link between number of events recorded and climatic changes.  相似文献