东南极格罗夫山地区的陨石回收与研究

Chinese National Antarctic Research Expedition (CHTNARE) has collected 4480 meteorite specimens in the Grove Mountains, East Antarctica, from 1998 to 2003. According to the location characteristics and the diversity of the classification, the paper concludes that the Grove Mountains is another important meteorite concentration area in the Antarctica. The Concentration mechanisms at the site could be related to the last glacier activity and katabatic wind. An empirical model was proposed: 1) Probably during the Last Glacial Maximum, ice flow overrided the Gale Escarpment range in the area. Formerly concentrated meteorites were carried by the new glacier and stayed in the terminal moraine when the glacier retreated. 2) Blown by strong katabatic wind, Newly exposed meteorites on the ablation zone were scattered on the blue ice at the lee side of the Gale escarpment. Some of them would be buried when they were moved further onto the firn snow zone. Many floating meteorites stopped and mustered at the fringe of the moraine. The chemical-petrographic of 31 meteorites were assigned based on electron probe microanalyses, petrography and mineralogy, including 1 martian lherzolitic shergottite, 1 eucrite, 1 extreme fine grain octahedron iron meteorite, and 28 ordinary chondrites (the chemical groups: 7 H-group, 13 L-group, 6 LL-group, 2 L/LL group; the petrographic types: 6 unequilibrated type 3 and 22 equilibrated type 4-6). GRV99028 meteorite has the komatiite-like spinifex texture consisting of acicular olivine crystals and some hornblende-family minerals in the interstitial region. Possibly it has crystallized from a supercooled, impact-generated, ultramafic melt of the host chondrite, then experienced the retrogressive metamorphism. Four typical chondrule textures were studied: porphyritic texture, radiative texture, barred texture and glass texture. The minerals are characteristically enriched in MgO content.

东南极内陆格罗夫山和外缘拉斯曼丘陵地区基岩暴露年龄及其古气候含义

This paper is concerned of the I0Be and 26A1 exposure ages of bedrocks in the Grove Mountains (GMs), inland of East Antarctica, and in the Larsemann Hills, peripheral alongshore of East Antarctica, respectively. The results of our study indicate that the higher bedrock samples in two profiles in the GMs have minimum exposure ages of-2 Ma, and their 26Al/10Be can be projected into the erosion island, which means they only have simple exposure history. The actual exposure ages may be mid-late Pliocene because the bedrocks should have erosion. The relationship between the altitudes and cosmogenic nuclide concentrations of those higher samples suggests that they have not reached secular equilibrium, means that a higher than -2300m East Antarctic Ice Sheet (EAIS) existed in the GMs before mid-Pliocene, and decreased monotonously for a period since mid-Pliocene. Lower samples of the two profiles have much younger exposure ages, and had been covered at least once obviously implicated by that their 26Al/10Be are projected down to the erosion island. Using a 10Be-26Al project figure to determine the history of the GMs samples shows that the lower samples have minimum total initial exposure and cover time of 1.7-2.8Ma, suggesting that those samples were exposed initially since about late Pliocene too, and the interior EAIS fluctuated after late Plicoene obviously. The altitudes and exposure ages of all the GMs samples indicate that the ice surface level of the interior EAIS in the GMs was >2300m during or before mid Pliocene (more than 200m higher than present ice surface level), and only rose to -2200m during the fluctuation occurred after late Pliocene, thus the elevation of the interior EAIS in the GMs after mid-Pliocene was never higher than during or before mid Pliocene even during the Quaternary Glacial Maximum. According to data from the GMs and other parts of East Antarctica, a larger East Antarctic Ice Sheet existed before mid-Pliocene, thus the elevation decrease of interior EAIS in the GMs after mid Pliocene may be a director of volume decrease of the EAIS. Since the Antarctic climate has a cooling trend since ~3Ma, similar to the global climate change, the volume decrease of the EAIS since mid-Pliocene may beause of moisture supply decrease directly rather than atmosphere temperature change. As for the Larsemann Hills, samples farther to the glacier have exposure age of 40~50ka, means they exposed in the early time of Last Glacier Cycle, obviously earlier than the Last Glacial Maximum (LGM). Samples nearer to the glacier have exposure ages younger than LGM. Thus, different to the GMs, exposure ages of the Larsemann Hills samples have more obvious relationship to their distance from the glacier margin rather than to the altitudes of the samples.

东南极格罗夫山土壤研究与古环境分析

Three soil spots were found in Grove Mountains, east Antarctica during 1999-2000, when the Chinare 16th Antarctic expedition teams entered the inland Antarctica. The characteristics of soils in Grove Mountains are desert pavement coating the surface, abundant water soluble salt, negligible organ matter, and severe rubification and salinization, scarces of liquid water, partly with dry permafrost, corresponding with the soils of McMurdo, Transantarctic. The soils age of Grove Mountains is 0.5-3.5Ma. Podzolization and redoximorphism are the main features in coastal Wilks region, in addition, there is strong enrichment of organic matter in many soils of this region. The main soil processes of Fildes Peninsula of King George Island include the intense physical weathering, decalcification and weakly biochemical processes. Peat accumulation is the main processes in Arctic because of humid and cold environment.Based on synthesis of heavy minerals, particle size, quartz grain surface textures, as well as pollen in soils, the soils parent materials of Grove Mountains derived from alluvial sediment of the weathering bedrocks around soils, and formed during the warm period of Pliocene. The detailed information is followed .l)The results of heavy minerals particle size showed the parent minerals derived form the weathering bedrocks around soils. 2)The quartz sand surface textures include glacial crushing and abrasion such as abrasive conchoidal fractures and grain edges, abrasive subparallel linear fractures and angularity, subaqueous environments produce V-shaped and irregular impact pits, polished surface, and chemical textures, such as beehive solution pits, which showed the water is the main force during the sediment of the soil parent minerals. 3)The pollen consist of 40 plant species, of which at least 5 species including Ranunculaceae, Chenopodiaceae, Artemisia, Gramineae, Podocarpus belong to the Neogene vegetation except the species from the old continent. Compared with Neogene vegetation of Transantarctic Mountains, Antarctic, we concluded that they grow in warm Pliocene.

南极格罗夫山陨石磁性分类研究

陨石分类是一项基础性的工作，是开展深入研究的前提。磁化率(χ)的测量提供了一种快速简单、无损的陨石分类方法，国外已有一些学者开始对陨石的磁性分类开展了研究，但国内尚无这方面研究的报导。本文主要对从南极格罗夫山回收的陨石开展了磁性分类的初步研究，论文主要工作包括以下几个方面： 1) 进行了磁化率测量模拟实验：由于陨石样品具有不规则和大小不等的形状，通过对模拟样品测量，了解上述几何因素对磁化率测量精度和准确性的影响，并作出MS2磁化率测量系统MS2D探头与MS2B传感器测量值之间的校正曲线。对模拟样品测量结果的分析表明，不同形状和大小的样品(所含磁性矿物分布均一)在进行MS2D测量时，测量相对偏差可控制在2%以内，表明上述测量系统可以用于陨石的磁化率测量。 2) 对所选600块南极格罗夫山陨石用MS2D探头进行了磁化率测量，得出这600块陨石的磁化率㏒χ(10-9m3/kg)数据，并用MS2B探头测量其中375块用来作岩石矿物学分类用的小块劈分样品的磁化率㏒χ(10-9m3/kg)。这600块格罗夫山陨石磁化率分布模式与南极其他区域收集的陨石较吻合，对应H、L、LL群呈3个明显的峰分布。相同的陨石用MS2D与MS2B两种探头测量，将它们的磁化率数据进行对比，显示它们的结果相当一致(相关系数R2=0.97)，也同时证明MS2D用于磁化率测量是行之有效的。 3)测量了44块沙漠陨石和9块降落型陨石的磁化率，在此基础上对南极格罗夫山陨石、沙漠陨石及降落型陨石数据做了对比讨论。格罗夫山陨石、沙漠陨石及降落型陨石磁化率值分布出现不同程度的偏移，总体来说磁化率㏒χ平均值为降落型陨石>南极陨石>沙漠陨石，这主要是由于陨石所受风化程度的差异造成的。风化作用使陨石部分金属发生氧化，因而降低了磁化率。 4)基于陨石的岩石矿物学分类，172块平衡型普通球粒陨石的磁化率分布，与文献上南极陨石磁化率分布基本一致，不过格罗夫山H、L、LL型普通球粒陨石磁化率分布范围更为狭窄，反映了南极不同地区陨石风化程度的差异。 5)讨论了陨石磁化率分类的有效性，分析了部分异常值出现的原因。磁化率分类结果与部分格罗夫山陨石的岩石矿物学分类(申请者作为陨石分类小组成员完成了其中的部分工作)结果相当吻合，仅在群之间约有5%的重叠，表明磁化率可作为化学群分类的重要参考数据。由于各陨石所受风化程度的差异，风化程度较强的少量陨石在磁性分类的基础上，还需其他工作加以证实。部分小质量(小于3g)且有部分或完整熔壳的陨石，磁化率受熔壳的影响达10%以上，偏离了其初始矿物的磁化率值，不能反映其真实的化学群类型，这部分磁化率数据仅供参考。