摘要
新疆罗布泊以东65 km处的三峰山区域发现了陨石(Tuya 002~007)散落区,呈3 km×11 km的椭圆状.散落区内收集到130余块普通球粒陨石,总重超过160 kg,最大的陨石重30 kg,最小的陨石重约15 g.散落区为一南东-北西向分布且陨石样品逐渐增大的椭圆形区域,这意味着陨石从南东向以较低的角度进入地球大气层.除Tuya002(760 g)外,散落区内的陨石可能来自同一次陨石雨,陨石类型为L5,冲击程度为S2,风化程度为W3.Tuya 003的宇宙射线暴露年龄为45.6±4.4 Ma,因此三峰山陨石雨的流星体可能形成于约40 Ma时普通球粒陨石L群母体的破裂事件中.Tuya 002具有和其他三峰山陨石显著不同的外表特征,表面熔壳全部脱落,球粒清晰可见,为L4型普通球粒陨石,样品中有大量的硫酸钙.其宇宙射线暴露年龄为17.0±4.1 Ma,也证明了其不是三峰山陨石雨的产物.三峰山区域陨石的研究表明三峰山区域不是陨石富集区,而是L5普通球粒陨石散落区.因此,需要对其他一些区域的陨石样品进行矿物岩石学、风化特征、宇宙射线暴露年龄和居地年龄的研究,从而确定出新疆及其周边沙漠区域的陨石富集区.
The meteorites are the most important extraterrestrial samples for understanding the formation and the evolution history of the solar system, although ～382 kg lunar samples and ～1500 asteroid mineral grains have been returned by human space exploration activities. The Northwest region of China, especially the Xinjiang, has a vast area of sandy deserts and Gobi Deserts. The lower annual rainfall and the dry climate of this region provide a good condition for meteorite preservation. In recent years, the number of recovered meteorites from the Gobi Deserts in Xinjiang increased significantly. The Sanfengshan area, located about 65 km east of Lop Nor, is one of the research regions. We first collected three ordinary chondrites in Sanfengshan area on October 9, 2013. Then, we carried out 11 meteorite search campaigns in this area. More than 130 meteorite fragments with a total mass over 160 kg have been recovered. The map of all collected Sanfengshan meteorites depicts a clearly 3 km×11 km elliptic strewn field. The sizes are sorted in the SE-NW-oriented ellipsoid of the strewn field, therefore indicating that the meteor entered the atmosphere from SE at a low angle relative to the ground. In this study, six meteorites（Tuya 002–007） from the Sanfengshan field have been measured using a Scios-FIB field emission scanning electron microscope（SEM）, a JXA 8230 electron microprobe analysis（EMA）, and a self-made noble gas mass spectrometer. Among all of the collected meteorites, Tuya 002 is the only one unusual sample, which doesn＇t show any fusion crust on its surface. We inferred that Tuya 002 is not paired with the other collected meteorites. The well-defined chondrule boundaries and heavy weathering grade, i.e. W3（the occurrence of large amounts of calcium sulfate in Tuya 002 indicates that it suffered a heavy terrestrial weathering） also support the conclusion that Tuya 002 is obviously different from the other meteorites collected in the Sanfengshan area. In addition to Tuya 002, all the meteorites collected in this region most likely originate from one single meteoric shower. These meteorites all belong to the L5 ordinary chondrite group, with a moderate shock stage of S2 and a heavy weathering grade of W3. The cosmic ray exposure age of Tuya 003（the representative meteorite of the Sanfenghshan meteoric shower） is 45.6±4.4 Ma. This indicates that the meteoroid that produced the Sanfengshan meteoric shower could be produced in the 45 Ma break-up event on L chondrite parent body. On the other hand, petrographic observations and noble gas measurements shown that Tuya 002 belongs to the L4 ordinary chondrite group. A rather lower CRE age relative to the Sanfengshan L5 chondrites of 17.0±4.1 Ma has been calculated. This also indicates that Tuya 002 is not paired with other L5 meteorites collected in the same strewn field. Our studies shown that the meteorites collected in Sanfengshan area consist of more than one meteorite fall. It includes the main L5 meteorite fall（produced the Sanfengshan L5 strewn field） and the L4 meteorite fall（represented by Tuya 002）. This indicates that the Sanfengshan area is not a meteorite dense area. In recent years, several meteorite dense areas（e.g., Loulan Yizhi, Lop Nur, Argan, and Xingdi） have been gradually reported. The limited meteorite types found in such reported meteorite dense areas indicates that these regions are maybe not the real meteorite dense areas, but probably represents the meteorites strewn field. Therefore, it is necessary, in the future, to carry out detailed petrology, mineralogy, cosmic ray exposure age as well as terrestrial age measurements to identify the meteorite dense area in/around the Xinjiang.
作者
李世杰
王世杰
LEYA Ingo
SMITH Thomas
唐俊林
王鹏
曾小家
李阳
LI Shi Jie WANG ShiJie LEYA Ingo SMITH Thomas TANG JunLin WANG Peng ZENG XiaoJia LI Yang(Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China Physical Institute, University of Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland Sixth Geological Brigade, Division of Mines and Geology, Hami 839000, China University of Chinese Academy of Sciences, Beijing 100049, China)
出处
《科学通报》
EI
CAS
CSCD
北大核心
2017年第21期2407-2415,共9页
Chinese Science Bulletin
基金
国家自然科学基金(41273080
41473067和41490630)资助
关键词
陨石散落区
沙漠陨石
三峰山
宇宙射线暴露年龄
meteorite strewn field
desert meteorite
Sanfengshan
cosmic ray exposure age
