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.

顽火辉石储存反映低氧逸度下形成条件的化学和同位素特征。然而，关于它们的诞生地、历史和形成地点，却没有达成一致意见：（1）虽然大多数学者都同意它们是在太阳星云的最早期形成的，（2）美国的一些学者主张它们是通过撞击熔化先前存在的小行星而演化的。这两个亚群：EH（高铁）和EL（低铁）是否来自同一个母体小行星也存在争议。另一个不确定性是，单个的EH和单个的EL陨石是否来自不同的小行星或来自同一个母体。EH和EL矿物的体相矿物学和矿物化学是不同的，并允许从EL中明确识别EH。该冷凝方案认为，在C/O比> 0.83 < 0.95时，奥硅钙石（CaS）是最早的冷凝物之一。CaS在冷凝过程中以硫化物的形式掺入了大部分稀土元素和锕系元素。相反，冲击熔化模型认为CaS是由冲击熔化形成的。本文研究了高钾和低钾闪长岩中的老闪长岩及其伴生矿物、稀土配分模式、146 Sm/142 Nd同位素体系（T1/2 = 103 Myr）和老闪长岩及其他硫化物世代的Pb-Pb年龄。这种多任务审查的目的是发现：（1）EH-3和EL-3中的辉长花岗岩的REE特征和~（146）Sm/~（142）Nd同位素组成，如果它们不同，（2）太阳星云最早期的凝聚和/或增生事件和母体事件的年代学细节，（3）C-，对Almahata Sitta CT 3小行星EL-3中不同石墨类型和EL-3中硅华石（Si 2N 2 O）中N的N和H同位素研究。矿物学、岩石学和同位素研究新发现的分化陨石NWA 7325，推测是从水星喷出的。