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Chinese Science Bulletin, Volume 62, Issue 21: 2407-2415(2017) https://doi.org/10.1360/N972016-01450

A chondrite strewn field was found in east of Lop Nor, Xinjiang

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  • ReceivedJan 24, 2017
  • AcceptedMar 20, 2017
  • PublishedJun 7, 2017

Abstract

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.


Funded by

国家自然科学基金(41273080,41473067,41490630)


Acknowledgment

感谢陨石爱好者王长令、杨可欣、张建立、许建疆和王辉在陨石收集过程中给予的帮助. 感谢伯尔尼大学的Hans-Erich工程师和桂林理工大学的刘奕志工程师在实验过程的帮助. 同时感谢南京大学张爱铖教授对于本文写作给予的鼓励及两位审稿人的建设性修改意见.


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  • Figure 1

    The distribution of meteorites in the deserts in and around Xinjiang. The red areas are the meteorites collection areas. The background map was copied from Google earth

  • Figure 2

    Land surface features of Sanfengshan area where the meteorites were collected. (a) The northwest area; (b) the middle area; (c) the southeast area

  • Figure 3

    Mass distribution of meteorites in Sanfengshan strewn field plotted on a Google earth map. The sizes of the meteorites increase from SE to NW

  • Figure 4

    Pictures of the meteorite of Sanfengshan strewn field. (a) A meteorite with intact fusion crust; (b) the largest fragment (~20 kg) from the largest meteorite from the strewn field, with rhegmalypt on one surface; (c) a 16.2 kg meteorite from the strewn field, with rhegmalypt and fusion crust; (d) Tuya 002, without fusion crust

  • Figure 5

    Back-scattered electron images of polished sections (POP, porphyritic olivine-pyroxene; PO, porphyritic olivine; ol, olivine; pyx, low-Ca pyroxene). (a) Tuya 002; (b) Tuya 003; (c) Tuya 004; (d) Tuya 005

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