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Fine-grained precursors dominate the micrometeorite flux

Taylor, Susan and Matrajt, Graciela and Guan, Yunbin (2012) Fine-grained precursors dominate the micrometeorite flux. Meteoritics and Planetary Science, 47 (4). pp. 550-564. ISSN 1086-9379. doi:10.1111/j.1945-5100.2011.01292.x.

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We optically classified 5682 micrometeorites (MMs) from the 2000 South Pole collection into textural classes, imaged 2458 of these MMs with a scanning electron microscope, and made 200 elemental and eight isotopic measurements on those with unusual textures or relict phases. As textures provide information on both degree of heating and composition of MMs, we developed textural sequences that illustrate how fine-grained, coarse-grained, and single mineral MMs change with increased heating. We used this information to determine the percentage of matrix dominated to mineral dominated precursor materials (precursors) that produced the MMs. We find that at least 75% of the MMs in the collection derived from fine-grained precursors with compositions similar to CI and CM meteorites and consistent with dynamical models that indicate 85% of the mass influx of small particles to Earth comes from Jupiter family comets. A lower limit for ordinary chondrites is estimated at 2–8% based on MMs that contain Na-bearing plagioclase relicts. Less than 1% of the MMs have achondritic compositions, CAI components, or recognizable chondrules. Single mineral MMs often have magnetite zones around their peripheries. We measured their isotopic compositions to determine if the magnetite zones demarcate the volume affected by atmospheric exchange during entry heating. Because we see little gradient in isotopic composition in the olivines, we conclude that the magnetites are a visual marker that allows us to select and analyze areas not affected by atmospheric exchange. Similar magnetite zones are seen in some olivine and pyroxene relict grains contained within MMs.

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Guan, Yunbin0000-0002-7636-3735
Additional Information:© 2011 The Meteoritical Society. Issue published online: 26 April 2012; Article first published online: 2 November 2011; Received 15 May 2011; revision accepted 22 September 2011. The authors thank Dave Joswiak and Dr. Hope Ishii for reviewing this article and providing many helpful suggestions. Dr. Gregory Herzog is thanked for the many helpful discussions on this work. We thank NSF (Dr. Julie Palais, program manager) for funding the collection of micrometeorites from the SPWW and NASA (Dr. David Lindstrom, program manager) for funding the analysis of the 2000 collection. The authors also thank Sarah E. Wengert and other Women in Science Project students at Dartmouth College for imaging hundreds of these micrometeorites and Dr. Charles Daghlian for comentoring these students. Editorial Handling––Dr. Donald Brownlee
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Issue or Number:4
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Official Citation:Taylor, S., Matrajt, G. and Guan, Y. (2012), Fine-grained precursors dominate the micrometeorite flux. Meteoritics & Planetary Science, 47: 550–564. doi: 10.1111/j.1945-5100.2011.01292.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31620
Deposited On:23 May 2012 23:09
Last Modified:09 Nov 2021 19:56

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