Mineralogy and petrography of the Almahata Sitta ureilite
Mineralogy and petrography of the Almahata Sitta ureilite
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DOI：
10.1111/j.1945-5100.2010.01128.x
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发表时间：
2010-10
影响因子：
2.2
通讯作者：
M. Zolensky;J. Herrin;T. Mikouchi;K. Ohsumi;J. Friedrich;A. Steele;D. Rumble;M. Fries;S. Sandford;S. Milam;K. Hagiya;H. Takeda;W. Satake;T. Kurihara;M. Colbert;R. Hanna;J. Maisano;R. Ketcham;C. Goodrich;L. Le;G. Robinson;James Martinez;K. Ross;P. Jenniskens;M. Shaddad
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文献类型：
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作者：
M. Zolensky;J. Herrin;T. Mikouchi;K. Ohsumi;J. Friedrich;A. Steele;D. Rumble;M. Fries;S. Sandford;S. Milam;K. Hagiya;H. Takeda;W. Satake;T. Kurihara;M. Colbert;R. Hanna;J. Maisano;R. Ketcham;C. Goodrich;L. Le;G. Robinson;James Martinez;K. Ross;P. Jenniskens;M. Shaddad
翻译后摘要-我们进行了电池的17个样本的Almahata Sitta陨石的分析，确定三个主要的岩性和几个小的碎屑。主要岩性为（1）辉石为主、多孔性强、高度还原的岩性，（2）辉石为主的致密岩性，以及（3）橄榄石为主的致密岩性。虽然在kg尺度下，所有三种岩性似乎都可以平滑地相互过渡，但在g尺度下，这并不明显。该陨石是一种复混合的钠长石，具有一些有趣的特征，包括异常多变的孔隙度和辉石成分。虽然普通辉石是局部存在于Almahata Sitta，它是一个次要的阶段，在大多数（但不是所有）样品，我们已经观察到。低钙辉石（<5摩尔%的硅灰石）比成分定义的钙铝榴石更丰富;然而，我们发现即使是Almahata Sitta中的低钙辉石也具有单斜钙铝榴石晶体结构，因此被正确地称为钙铝榴石。由于Almahata Sitta陨石中的辉石主要是鸽子石，而鸽子石的丰度通常大于橄榄石，因此这颗陨石可能被称为鸽子石-橄榄石尿伊利石，而不是传统的橄榄石-鸽子石尿伊利石群。Almahata Sitta的岩性变化很大，揭示了一个复杂的历史，包括小行星火成岩结晶，撞击破坏，再加热和部分蒸发，高温还原和碳燃烧，以及再凝聚。
Abstract– We performed a battery of analyses on 17 samples of the Almahata Sitta meteorite, identifying three main lithologies and several minor ones present as clasts. The main lithologies are (1) a pyroxene‐dominated, very porous, highly reduced lithology, (2) a pyroxene‐dominated compact lithology, and (3) an olivine‐dominated compact lithology. Although it seems possible that all three lithologies grade smoothly into each other at the kg‐scale, at the g‐scale this is not apparent. The meteorite is a polymict ureilite, with some intriguing features including exceptionally variable porosity and pyroxene composition. Although augite is locally present in Almahata Sitta, it is a minor phase in most (but not all) samples we have observed. Low‐calcium pyroxene (<5 mole% wollastonite) is more abundant than compositionally defined pigeonite; however, we found that even the low‐Ca pyroxene in Almahata Sitta has the monoclinic pigeonite crystal structure, and thus is properly termed pigeonite. As the major pyroxene in Almahata Sitta is pigeonite, and the abundance of pigeonite is generally greater than that of olivine, this meteorite might be called a pigeonite‐olivine ureilite, rather than the conventional olivine‐pigeonite ureilite group. The wide variability of lithologies in Almahata Sitta reveals a complex history, including asteroidal igneous crystallization, impact disruption, reheating and partial vaporization, high‐temperature reduction and carbon burning, and re‐agglomeration.