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

顽火辉石球粒陨石储存了化学和同位素特征，反映了低氧逸度的形成条件。然而，关于它们的出生地、历史和形成地点，目前还没有达成一致意见：(1)虽然大多数学者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是通过碰撞熔化在先前存在的小行星中演化而形成的。同样存在争议的是，这两个亚群：EH(高铁)和EL(低铁)是否来自同一母体小行星。另一个不确定的问题是，单独的EH和El球粒陨石是来自不同的小行星还是来自同一母体。EH和EL球粒陨石的整体矿物学和矿物化学不同，可以清楚地识别EH和EL。该凝析方案认为，在碳氧比为0.83&0.95的范围内，奥德汉姆特(CaS)是最早的凝析油之一。在冷凝过程中，CaS以硫化物的形式结合了大部分的稀土元素和鳗系元素。相反，冲击熔化模型认为CaS是由冲击熔化形成的。对EH球粒陨石和EL球粒陨石中的奥德芒特及其伴生矿物的矿物学、稀土配分模式、146Sm/142同位素体系(t1/2=103Myr)以及奥德芒特和其他硫化物世代的铅-铅年龄进行了研究。这项多任务研究的目的是揭示：(1)EH-3和EL-3球粒陨石中的旧陨石的REE特征和146Sm/142同位素系统学，以及它们是否不同；(2)太阳星云最早时期凝聚和/或吸积事件与母体事件的年代学细节；(3)Almahata Sitta CT3小行星EL-3中不同类型石墨和硅铝石(Si2N2O)中N的碳、氮和氢同位素研究。对新发现的可能是从水星喷出的分化陨石NWA7325的矿物学、岩石学和同位素研究。

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.