Mineralogical anatomy and implications of a Ti–Sc-rich ultrarefractory inclusion from Sayh al Uhaymir 290 CH3 chondrite
Mineralogical anatomy and implications of a Ti–Sc-rich ultrarefractory inclusion from Sayh al Uhaymir 290 CH3 chondrite
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DOI：
10.1016/j.gca.2015.04.052
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发表时间：
2015-08
影响因子：
5
通讯作者：
A. Zhang;Chi Ma;N. Sakamoto;Rucheng Wang;W. Hsu;H. Yurimoto
中科院分区：
文献类型：
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作者：
A. Zhang;Chi Ma;N. Sakamoto;Rucheng Wang;W. Hsu;H. Yurimoto
富钛矿物普遍存在于原始辉长岩的富钙铝包裹体中。它们不仅对检验具有太阳成分的气体的凝结模型很重要，而且对限制早期太阳星云的氧化还原条件也很重要。在这项研究中，我们报告了详细的矿物学特征和氧同位素组成的富钛钪超难熔包体A0031从CH 3球粒陨石Sayh al Uhaymir 290。A0031包裹体结构致密，内部为红云母、富Sc黑云母、富Ti铁橄榄石和钙长石。一些六角铁、钙钛矿和尖晶石晶体作为包裹体存在于这些矿物中。富钛透辉石的外围是一层富铝钛透辉石和两粒顽火辉石。这种纹理强烈表明A0031具有凝结起源。潘圭特是其第三次出现在自然界和类似的成分类型潘圭特从阿连德陨石。A0031中的富Sc黑云母化学式为（Ti 4+，Ti 3+，Mg，Sc，Al）3 O 5，具有铁板钛矿结构。这是自然界中第二份关于Ti 3 O 5的报告，但却是第一次描述在太阳星云中作为超耐火相形成的黑云母。在A0031中发现的富Sc黑云母揭示了早期太阳星云中Ti_3O_5的稳定性，支持了以往平衡凝聚计算的预言。在A0031中的panguite、富Sc的黑云母和富Ti的davisite显示出较大的Ti 3 +/Titot变化。A0031的原始性意味着不同富钛矿物间的Ti 3 +/Titot变化是其主要特征。我们认为，Ti ~（3+）和Ti ~（4+）的分布主要受它们对这些富Ti、Sc、Al矿物的竞争能力控制。A0031中富钛硅铝镁矾的Ti ~（3+）/Ti ~（3+）比值与其它碳质硅铝镁矾中的Ti ~（3+）/Ti ~（3+）比值相似，表明大多数难熔包裹体可能形成于高还原性的星云环境。A0031的16 O亏损同位素组成证实了太阳星云中CH富Ca-Al包体的多种储氧层的存在。
Titanium-rich minerals are common in Ca–Al-rich inclusions from primitive chondrites. They are important not only for testing the condensation models for a gas with a solar composition, but also for constraining the redox conditions of the early solar nebula. In this study, we report the detailed mineralogical features and its oxygen isotope compositions of a Ti–Sc-rich ultrarefractory inclusion A0031 from a CH3 chondrite Sayh al Uhaymir 290. The A0031 inclusion has a compact and layered texture with the interior consisting of panguite, Sc-rich anosovite, Ti-rich davisite, and anorthite. A few hexaferrum, perovskite, and spinel crystals are present as inclusions in these minerals. Outside of Ti-rich davisite are a layer of Al–Ti-rich diopside and two grains of enstatite. This texture strongly suggests that A0031 has a condensation origin. Panguite is its third occurrence in nature and similar in composition to the type panguite from the Allende meteorite. Sc-rich anosovite in A0031 has a chemical formula of (Ti4+,Ti3+,Mg,Sc,Al)3O5with the pseudobrookite structure. This is the second report of Ti3O5in nature, but is the first description of anosovite formed in the solar nebula as an ultrarefractory phase. The discovery of Sc-rich anosovite in A0031 reveals the stability of Ti3O5in the early solar nebula and supports the prediction of previous equilibrium condensation calculations. The panguite, Sc-rich anosovite, and Ti-rich davisite in A0031 show a large variation in Ti3+/Titot. The primitive nature of A0031 implies that the variations in Ti3+/Titotamong different Ti-rich minerals are primary features. We propose that the distribution of Ti3+and Ti4+could be controlled mainly by their various competition abilities of incorporating into these Ti–Sc–Al-rich minerals. Similarity of Ti3+/Titotvalue between Ti-rich davisite from A0031 and those in other carbonaceous chondrites indicates that most refractory inclusions might have formed in highly reducing nebular settings. The16O-depleted isotope compositions of A0031 confirm the existence of diverse oxygen reservoirs for CH Ca–Al-rich inclusions in the solar nebula.