Shape, metal abundance, chemistry, and origin of chondrules in the Renazzo (CR) chondrite
Shape, metal abundance, chemistry, and origin of chondrules in the Renazzo (CR) chondrite
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雷纳佐 (CR) 球粒陨石中球粒的形状、金属丰度、化学成分和起源
DOI：
10.1111/j.1945-5100.2008.tb00639.x
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发表时间：
2008
影响因子：
2.2
通讯作者：
A. Campbell
中科院分区：
文献类型：
--
作者：
D. Ebel;M. Weisberg;J. Hertz;A. Campbell
摘要-我们使用同步辐射X射线显微层析成像技术对一块˜1 cm的Renazzo(CR)球粒陨石中的8个完整球粒进行了3维(3D)成像，成像的边缘为˜17μm/体积元素(体素)。本文报道了球粒陨石中金属/硅酸盐比值的首次体积(3D)测量，并对球粒陨石的球度指数进行了量化。通过对8个球粒的测量和断层扫描数据的检验，整个球粒的体积金属丰度在1~37体积%之间。结果表明，单个随机2D切片不能可靠地获得单个球粒陨石中的金属丰度和金属颗粒位置。对样品进行物理切割，以多次与具有代表性的球粒相交，并验证3D数据。详细的2D化学分析与3D数据相结合，得到了具有超球粒陨石平均值的高度可变的整体球粒陨石镁/硅比值，但化学上不同的独立形成的球粒陨石在保留聚集的CR球粒陨石中的球粒陨石(太阳)Fe/Si比值方面是相辅相成的。这些结果与球粒陨石的局部形成和快速堆积形成的球粒+基质聚集体(陨石母体)相一致，它们保留了源区的整体球粒组成。
Abstract— We used synchrotron X‐ray microtomography to image in 3‐dimensions (3D) eight whole chondrules in a ˜1 cm3piece of the Renazzo (CR) chondrite at ˜17 μm per volume element (voxel) edge. We report the first volumetric (3D) measurement of metal/silicate ratios in chondrules and quantify indices of chondrule sphericity. Volumetric metal abundances in whole chondrules range from 1 to 37 volume % in 8 measured chondrules and by inspection in tomography data. We show that metal abundances and metal grain locations in individual chondrules cannot be reliably obtained from single random 2D sections. Samples were physically cut to intersect representative chondrules multiple times and to verify 3D data. Detailed 2D chemical analysis combined with 3D data yield highly variable whole‐chondrule Mg/Si ratios with a supra‐chondritic mean value, yet the chemically diverse, independently formed chondrules are mutually complementary in preserving chondritic (solar) Fe/Si ratios in the aggregate CR chondrite. These results are consistent with localized chondrule formation and rapid accretion resulting in chondrule + matrix aggregates (meteorite parent bodies) that preserve the bulk chondritic composition of source regions.