Torrano Zachary A, Schrader Devin L, Davidson Jemma, Greenwood Richard C, Dunlap Daniel R, Wadhwa Meenakshi
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA.
Center for Meteorite Studies, Arizona State University, Tempe, AZ 85287, USA.
Geochim Cosmochim Acta. 2021 May 15;301:70-90. doi: 10.1016/j.gca.2021.03.004. Epub 2021 Mar 10.
A close relationship between CM and CO chondrites has been suggested by previous petrologic and isotopic studies, leading to the suggestion that they may originate from similar precursor materials or even a common parent body. In this study, we evaluate the genetic relationship between CM and CO chondrites using Ti, Cr, and O isotopes. We first provide additional constraints on the ranges of εTi and εCr values of bulk CM and CO chondrites by reporting the isotopic compositions of CM2 chondrites Murchison, Murray, and Aguas Zarcas and the CO3.8 chondrite Isna. We then report the εTi and εCr values for several ungrouped and anomalous carbonaceous chondrites that have been previously reported to exhibit similarities to the CM and/or CO chondrite groups, including Elephant Moraine (EET) 83226, EET 83355, Grosvenor Mountains (GRO) 95566, MacAlpine Hills (MAC) 87300, MAC 87301, MAC 88107, and Northwest Africa (NWA) 5958, and the O-isotope compositions of a subset of these samples. We additionally report the Ti, Cr, and O isotopic compositions of additional ungrouped chondrites LaPaz Ice Field (LAP) 04757, LAP 04773, Lewis Cliff (LEW) 85332, and Coolidge to assess their potential relationships with known carbonaceous and ordinary chondrite groups. LAP 04757 and LAP 04773 exhibit isotopic compositions indicating they are low-FeO ordinary chondrites. The isotopic compositions of Murchison, Murray, Aguas Zarcas, and Isna extend the compositional ranges defined by the CM and CO chondrites in εTi versus εCr space. The majority of the ungrouped carbonaceous chondrites with documented similarities to the CM and/or CO chondrites plot outside the CM and CO group fields in plots of εTi versus εCr, ΔO versus εTi, and ΔO versus εCr. Therefore, based on differences in their Ti, Cr, and O isotopic compositions, we conclude that the CM, CO, and ungrouped carbonaceous chondrites likely represent samples of multiple distinct parent bodies. We also infer that these parent bodies formed from precursor materials that shared similar isotopic compositions, which may indicate formation in regions of the protoplanetary disk that were in close proximity to each other.
先前的岩石学和同位素研究表明CM球粒陨石和CO球粒陨石之间存在密切关系，这使得有人提出它们可能起源于相似的前驱物质，甚至是同一个母体。在本研究中，我们使用Ti、Cr和O同位素评估CM球粒陨石和CO球粒陨石之间的成因关系。我们首先通过报告CM2球粒陨石默奇森、默里和阿瓜斯卡萨斯以及CO3.8球粒陨石伊斯纳的同位素组成，对整体CM球粒陨石和CO球粒陨石的εTi和εCr值范围提供了额外的限制。然后我们报告了几种先前报道与CM和/或CO球粒陨石群表现出相似性 的未分类和异常碳质球粒陨石的εTi和εCr值，包括大象冰碛（EET）83226、EET 83355、格罗夫纳山（GRO）95566、麦卡尔平山（MAC）87300、MAC 87301、MAC 88107和西北非洲（NWA）5958，以及这些样品子集的O同位素组成。我们还报告了其他未分类球粒陨石拉巴斯冰原（LAP）04757、LAP 04773、刘易斯悬崖（LEW）85332和柯立芝的Ti、Cr和O同位素组成，以评估它们与已知碳质和普通球粒陨石群的潜在关系。LAP 04757和LAP 04773的同位素组成表明它们是低FeO普通球粒陨石。默奇森、默里、阿瓜斯卡萨斯和伊斯纳的同位素组成扩展了CM和CO球粒陨石在εTi与εCr空间中定义的组成范围。在εTi与εCr、ΔO与εTi以及ΔO与εCr的图中，大多数记录显示与CM和/或CO球粒陨石相似的未分类碳质球粒陨石落在CM和CO群域之外。因此，基于它们Ti、Cr和O同位素组成的差异，我们得出结论，CM、CO和未分类的碳质球粒陨石可能代表多个不同母体的样本。我们还推断这些母体由具有相似同位素组成的前驱物质形成，这可能表明它们形成于原行星盘中彼此靠近的区域。
