南极格罗夫山陨石磁性分类研究

GYIG OpenIR > 研究生 > 学位论文

	南极格罗夫山陨石磁性分类研究
其他题名	Magnetic Classification of Meteorites from Grove Mountains, Antarctica
	罗红波
	2007-06-08
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	南极陨石格罗夫山陨石分类磁化率普通球粒陨石沙漠陨石风化作用
摘要	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。
其他摘要	Classification of Meteorites is a fundamental task required for further research. Measurements of magnetic susceptibility (χ) provides with us a fast, nondestructive and systematic method of meteorites classification. Recently, a few of papers have been published, with discussion on magnetic classification of meteorites. With fast increase of meteorite collection from the Grove Mountains area, Antarctica, study of magnetic susceptibility of these meteorites becomes an urgent demand. This paper presents the first measurements of magnetic susceptibility of 600 Grove Mountains (GRV) meteorites, 44 desert meteorites and 9 falls of meteorites in China. Classification of these meteorites based on magnetic susceptibility is discussed, in comparison with the results based on petrography and mineral chemistry. The main results are below: 1. Simulation measurements of magnetic susceptibility: The influence of size and shape of the meteorites on magnetic susceptibility measurements was evaluated by systematic measurement of simulation samples that were prepared by mixing powder of iron with plasticine. In addition, calibration on data determined by the MS2D probe and the MS2B sensor of MS2 magnetic susceptibility system was made using the same simulation samples. These analyses demonstrate that the reproducibility of the simulation samples with the same iron content is better than ±2% regardless of their different sizes and shapes. The measurements by MS2D can be well calibrated to the values by MS2B. 2. 600 meteorites collected from Grove Mountain, Antarctic, were measured for magnetic susceptibility using the MS2D probe.. In addition, another 375 fragments from the 600 whole meteorites, were also measured by the MS2B sensor. Most of the data measured by the MS2D probe and MS2B sensor show good agreement, with a regression coefficient (R2) of 0.97, Magnetic susceptibility distribution of the 600 Grove Mountain meteorites shows a three peak pattern, corresponding to H、L and LL groups, respectively. This pattern is nearly identical to that of other Antarctic finds reported earlier. 3. 44 desert finds and 9 falls of Chinese meteorites were measured for magnetic susceptibility. Magnetic susceptibility distribution of the desert meteorites also shows a three peak pattern, but with the peak positions shifted to lower values in comparison with the GRV meteorites. The falls of Chinese meteorites have highest mean susceptibility (㏒χ) of the same chemical groups of ordinary chondrites. These differences are mainly due to distinct weathering of meteorites, with the weathering degree increasing from falls to Antarctic meteorites to desert meteorites. 4. The magnetic susceptibility of the 172 equilibrated ordinary meteorites classified based on petrology and mineral chemistry shows slightly narrower ranges of ㏒χ values of individual groups in comparison with those of other antarctic meteorites. This difference may reflect distinct weathering condition in Grove Mountains area than in the trans-antarctic regions. 5. The validity of magnetic susceptibility-based classification of meteorites is discussed. Except for ~5% overlap between the neighboring chemical groups, the magnetic classification of the Grove Mountains meteorites shows good agreement with the result based on the petrological and mineralogical data, demonstrating effectivity of magnetic susceptibility as a key criterion of meteorite classification. It is also noticed that magnetic susceptibility of heavily weathered meteorites may be significantly reduced, hence further analyses of petrography and mineral chemistry are required for classification. Effect of fusion crust on magnetic susceptibility could be as large as >10% for small meteorites (< 3 g).
页数	60
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3328
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	罗红波. 南极格罗夫山陨石磁性分类研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2007.