Fine‐grained precursors dominate the micrometeorite flux
Fine‐grained precursors dominate the micrometeorite flux
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细粒前体在微陨石通量中占主导地位
DOI：
10.1111/j.1945-5100.2011.01292.x
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发表时间：
2012
影响因子：
2.2
通讯作者：
Y. Guan
中科院分区：
文献类型：
--
作者：
S. Taylor;G. Matrajt;Y. Guan
摘要/ Abstract摘要：对2000年南极采集的5682颗微陨石进行了光学分类，对其中2458颗微陨石进行了扫描电镜成像，并对具有异常结构或残余相的微陨石进行了200次元素测量和8次同位素测量。由于纹理提供了mm的加热程度和组成的信息，我们开发了纹理序列来说明细粒、粗粒和单一矿物mm如何随着加热的增加而变化。我们利用这些信息来确定产生mm的基质为主和矿物为主的前驱体材料（前驱体）的百分比。我们发现，收集中至少75%的mm来自细粒前体，其成分与CI和CM陨石相似，并且与动力学模型一致，该模型表明85%的小颗粒流入地球来自木星家族彗星。普通球粒陨石的下限估计为2-8%，基于含有含钠斜长石遗迹的mm。不到1%的mm具有球粒成分、CAI成分或可识别的球粒。单矿物mm通常在其外围有磁铁矿带。我们测量了它们的同位素组成，以确定磁铁矿带是否划定了在进入加热过程中受大气交换影响的体积。因为我们在橄榄石的同位素组成中看到很少的梯度，我们得出结论，磁铁矿是一个视觉标记，使我们能够选择和分析不受大气交换影响的区域。类似的磁铁矿带见于mm中含有的一些橄榄石和辉石残余颗粒中。
Abstract– 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.