Mineralogical, REE and 146Sm-142Nd isotopic systematics of the earliest solar condensates in unequilibrated Enstatite chondrites

不平衡顽火辉石球粒陨石中最早太阳凝聚物的矿物学、稀土元素和 146Sm-142Nd 同位素系统学

• 批准号: 211141497
• 负责人: Professor Dr. Ahmed El Goresy (†)
• 金额: --
• 依托单位: Bayerisches Forschungsinstitut für Experimentelle Geochemie und Geophysik (BGI)
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/211141497?language=en
• 关键词: Mineralogical; REE; 146Sm; 142Nd; isotopic

Enstatite chondrites store chemical and isotopic signatures reflecting formational conditions at low oxygen fugacity. There is however no agreement on their birth place, history and locality of formation: (1) While the majority of scholars agree on their formation in the earliest episodes of the solar nebula, (2) Several scholars in the USA advocate for their evolution by impact melting in pre-existing asteroids. It is also disputed if the two subgroups: EH (high iron) and EL (low iron) emerged from the same parental asteroids. A further uncertainty is if individual EH, on the one hand and individual EL chondrites on the other came from different asteroids or from the same parent body. Bulk mineralogy and mineral chemistry in EH and EL chondrites are different and allow a clearcut recognition of EH from EL. The condensation scheme considers oldhamite (CaS) to be one of the earliest condensates at C/O ratios from > 0.83 < 0.95. CaS incorporated the majority of the REE and Actinides during condensation as sulfides. In contrast, the impact melting model considers CaS to have formed by impact melting. A mineralogical study of oldhamite and associated minerals, their REE patterns, their 146Sm/142Nd isotopic system (T1/2 = 103 Myr) and Pb-Pb ages of oldhamite and other sulfide generations in individual EH- and EL-chondrites is being conducted. Aims of this multitask scrutiny are to uncover: (1) REE signatures and 146Sm/142Nd isotopic systematics of oldhamites in EH-3 and in EL-3 chondrites, and if they are different (2) chronological details of condensation and/or accretionary and parent body events in earliest episode of the solar nebula, (3) C-, N- and H-isotopic investigations of different graphite types in EL-3 and of N in sinoite (Si2N2O) in the EL-3 in Almahata Sitta CT3 asteroid. Mineralogical, petrological and isotopic investigations of the newly recovered differentiated meteorite NWA7325 that was presumably ejected from the planet Mercury.

顽火辉石球粒陨石存储反映低氧逸度形成条件的化学和同位素特征。然而，对于它们的诞生地、历史和形成地点尚未达成一致：（1）虽然大多数学者都同意它们是在太阳星云的最早时期形成的，（2）美国的一些学者主张它们的演化现有小行星的撞击融化。这两个亚群：EH（高铁）和 EL（低铁）是否来自同一个母系小行星也存在争议。进一步的不确定性是，一方面是单个 EH，另一方面是单个 EL 球粒陨石是否来自不同的小行星或来自同一母体。 EH 和 EL 球粒陨石的块体矿物学和矿物化学不同，可以清楚地识别 EH 和 EL。该缩合方案认为绿铜矿 (CaS) 是 C/O 比 > 0.83 < 0.95 的最早的缩合物之一。 CaS 在缩合过程中以硫化物形式吸收了大部分 REE 和锕系元素。相反，冲击熔化模型认为 CaS 是通过冲击熔化形成的。目前正在对绿铜矿和伴生矿物、它们的 REE 模式、它们的 146Sm/142Nd 同位素系统 (T1/2 = 103 Myr) 以及绿铜矿和单个 EH 和 EL 球粒陨石中其他硫化物代的 Pb-Pb 年龄进行矿物学研究。这项多任务审查的目的是揭示：(1) EH-3 和 EL-3 球粒陨石中的稀土元素特征和 146Sm/142Nd 同位素系统学，以及它们是否不同 (2) 凝结和/或增生和沉积的年代细节。太阳星云最早发生时的母体事件，(3) 不同石墨类型的 C、N 和 H 同位素研究EL-3 中的 N 和 Almahata Sitta CT3 小行星 EL-3 中的 sinoite (Si2N2O) 中的 N。对新发现的差异化陨石 NWA7325 进行矿物学、岩石学和同位素研究，该陨石可能是从水星喷射出来的。