New textural evidence on the origin of carbonado diamond: An example of 3-D petrography using X-ray computed tomography
New textural evidence on the origin of carbonado diamond: An example of 3-D petrography using X-ray computed tomography
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关于黑金刚石起源的新纹理证据：使用 X 射线计算机断层扫描的 3-D 岩相学示例
DOI：
10.1130/ges00908.1
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发表时间：
2013
期刊：
影响因子：
2.5
通讯作者：
C. Koeberl
中科院分区：
文献类型：
--
作者：
R. Ketcham;C. Koeberl
使用高分辨率 X 射线计算机断层扫描对 23 克拉黑金刚石中的内含物和孔隙度模式进行三维结构观察，揭示了有关这种神秘材料的性质和起源的新信息。突出的古铜色表面在纹理上与下面的内含物和孔隙空间的带状和分级相关，延伸到样本中几毫米。原位观察表明，几乎所有包裹体都是多矿物的，并显示出替代纹理，证实了先前的工作，表明孔隙网络是完全三维 (3-D) 连接的，并且几乎所有宏观包裹体都是次生的。大的金属夹杂物仅在紧邻样品边缘处发现，因此也可能是次生甚至第三次的。然而，我们也报告了在形成原始自形菱形十二面体的阶段后的假晶，单独的和成簇的直径为0.3至1毫米；尽管我们找不到该阶段持续存在的证据，但它仍然代表了黑金刚石中报告的第一个“真正的”宏观夹杂物，几乎可以肯定它是与金刚石材料同生形成的。孔隙系统本质上是三峰的，由单个和簇状假晶、长度为 0.1-0.3 mm 且具有明确优先方向的扁圆孔和形成连接网络的 20 µm 至 <1 µm 孔组成。我们的观察结果支持最近的工作，表明黑金刚石从碳过饱和流体中结晶，并表明第二阶段可能与孔排列织物的形成相对应。我们进一步假设，尽管当今的宏观夹杂物肯定是次要的，但组成它们的大块材料可能不是，而可能是原始夹杂物相的分解残留物。虽然还需要进一步验证，但围绕这一假设建立的模型可能会为黑金刚石的许多不寻常特征提供最简单的解释。
Three-dimensional textural observations of inclusion and porosity patterns in a 23carat carbonado diamond using high-resolution X-ray computed tomography reveal new information bearing on the nature and origin of this enigmatic material. A prominent patinaed surface is texturally linked to a banding and grading of inclusions and pore space beneath, extending several millimeters into the specimen. In situ observation demonstrates that almost all inclusions are polymineralic and show replacement textures, corroborating previous work indicating that the pore network is fully three-dimensionally (3-D) connected, and that virtually all macroinclusions are secondary. Large metal inclusions are only found immediately adjacent to the margin of the specimen, and are thus also likely to be secondary or even tertiary. However, we also report pseudomorphs after a phase forming pristinely euhedral rhombic dodecahedra, individually and in clusters from 0.3 to 1 mm in diameter; although we could fi nd no evidence of this phase persisting, it nevertheless represents the fi rst “true” macro-inclusion reported in carbonado, which almost certainly formed syngenetically with the diamond material. The pore system is essentially trimodal, consisting of single and clustered pseudomorphs, oblate pores 0.1‐0.3 mm in length with a clear preferred orientation, and 20 µm to <1 µm pores that form the connected network. Our observations support recent work suggesting that carbonado crystallized from a carbon-supersaturated fl uid and suggest that the second stage may correspond with the creation of the pore alignment fabric. We further postulate that, although the present-day macroinclusions are certainly secondary, the bulk material that comprises them may not be, and may instead be broken-down remains of the original included phase(s). While further verifi cation is needed, a model built around this hypothesis may provide the simplest explanation to many of the unusual features of carbonado.