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Potassium isotope systematics of the LL4 chondrite Hamlet: Implications for chondrule formation and alteration
Meteoritics and Planetary Science ( IF 2.2 ) Pub Date : 2020-07-27 , DOI: 10.1111/maps.13545
Piers Koefoed 1, 2 , Olga Pravdivtseva 1, 3 , Heng Chen 1, 2 , Carina Gerritzen 4 , Maxwell M. Thiemens 5 , Kun Wang 1, 2
Affiliation  

Here, we apply recently developed high‐precision K isotope analyses to individual components of the LL4 chondrite Hamlet in order to investigate key processes which occurred during chondrite formation. The K isotopic compositions of all Hamlet chondrules range from −1.36‰ to −0.24‰ δ41K while the matrix and bulk samples show ranges of −0.89‰ to −0.80‰ and −0.86‰ to −1.08‰ δ41K, respectively. This range of δ41K values is significantly less than what was seen by in situ K isotopic analysis of Semarkona and Bishunpur chondrules, a likely effect of the different chondrite petrologic types, analytical artifacts in the SIMS analyses, and chondrule rim effects. Strong evidence for secondary parent‐body alteration effects within Hamlet suggests its K fractionation and distribution are dominantly controlled by these processes. Interestingly, the strong correlation between δ41K and chondrule mass suggests that chondrule size played a significant role in the K isotopic distribution within Hamlet. This trend is likely a result of either inherited initial differences in the chondrule K isotopic ratios which were not completely overprinted or mechanisms involved in the metamorphism processes creating variations. This K isotope correlation with chondrule mass could also be suggestive of chondrule‐forming nebular processes; nevertheless, it is currently unable to definitively favor any specific model. The K isotopic similarities between Hamlet and bulk ordinary chondrites suggest that all LL chondrites, if not all ordinary chondrites, may have formed via the same processes. Nevertheless, analysis of more pristine chondrules from chondrites of lower metamorphic grade is required to further assess any nebular processes of chondrule formation.

中文翻译:

LL4球粒陨石哈姆雷特族的钾同位素体系:对球粒形成和改变的影响

在这里,我们将最近开发的高精度K同位素分析应用于LL4球粒陨石哈姆雷特的各个组成部分,以研究在球粒陨石形成过程中发生的关键过程。所有哈姆雷特球粒的K个同位素组成范围从-1.36‰至-0.24‰δ 41 ķ而基质和散装样品显示的范围-0.89‰至-0.80‰和-0.86‰至-1.08‰δ 41 K,分别。该范围内的δ 41K值显着小于Semarkona和Bishunpur软骨的原位K同位素分析所观察到的值,这是不同的球粒岩岩石学类型,SIMS分析中的分析伪像和软骨边缘效应的可能影响。有证据表明哈姆雷特体内次生母体发生了变化,表明其K的分离和分布受这些过程的控制。有趣的是,δ之间的强相关性41钾和软骨质量表明,软骨大小在哈姆雷特的钾同位素分布中起着重要作用。这种趋势可能是由于软骨素K同位素比率的继承性初始差异(未完全套印)或涉及变质过程的机制所致。这种钾同位素与软骨质量的相关性也可能暗示了形成软骨的神经突。但是,它目前无法明确支持任何特定模型。哈姆雷特和块状普通球粒陨石之间的K同位素相似性表明,如果不是所有普通球粒陨石,所有LL球粒陨石可能都是通过相同的过程形成的。不过,
更新日期:2020-10-05
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