The accretionary history of ureilites: A systematic re-evaluation.

铀陨石是一种岩石学复杂的陨石，作为地幔残留岩，除了从原始的未改变的陨石中已知的一些特征外，还显示出高温改造的证据。它们构成了太阳系物质的重要组成部分，是第二丰富的非原始地外岩石类型。然而，关于它们的起源模式和进化步骤，仍有几个悬而未决的问题。该项目将解决两个关键问题，即假设脉状物质的外源来源(占10vol%)和主要硅酸盐矿物(橄榄石和辉石)普遍表现出的还原轮缘的生成。解开这些榴辉石组分演化的约束，将同时揭示塑造早期太阳系的重要地质过程。榴辉石演化的工作假说是一种修正的影响情景：已经确定，榴辉石母体(UPB)在其历史很早就遭受了破坏性影响，即当部分熔融仍在进行中(Goodrich等人)。2015年和其中的参考文献)。冲击器很大，而且--就像这里假设的那样--仍然没有像UPB一样完全凝固。与以前的遭遇相比，城市规划局也已经在结构上受到了削弱(“预先破碎”：Michel等人。2004年)。在撞击时，富碳液态金属相被注入到UPB的孔隙空间中[类似于灰岩的形成：Yang等人。(2010)和Scheinberg等人。(2015)]。外源碳-金属成分随后引发橄榄石和辉石的还原。根据碎片大小和孔隙几何形状的不同，还原反应从内到外变化，并可能很快停止(即，根据初步结果，在几天内[Patzer等人]。2017]))。

Ureilites are petrographically complex meteorites that - as mantle restites - show evidence for high-temperature alteration in addition to a few features known from primitive, unaltered meteorites. They constitute a significant portion of Solar System material, being the second most abundant type of non-primitive extraterrestrial rocks. Yet, several open questions regarding their mode of origin and steps of evolution remain. This project will address two key topics concerning ureilite components, namely the assumed exogenous origin of vein material (constituting up to 10 vol%) and the generation of reduction rims ubiquitously exhibited by major silicate minerals (olivine and pyroxene). Unraveling constraints on the evolution of those ureilite components will concurrently reveal important geological processes shaping the early Solar System.The working hypothesis for the evolution of ureilites is a modified impact scenario: It has been established that the ureilite parent body (UPB) suffered a disruptive impact very early in its history, i.e. while partial melting was still underway (Goodrich et al. 2015 and references therein). The impactor was large and - so assumed here - still incompletely solidified like the UPB. The UPB was also already structurally weakened from previous encounters (“pre-shattered”: Michel et al. 2004). Upon impact, a carbon-rich liquid metal phase got injected into the pore space of the UPB [in analogue to the formation of pallasites: Yang et al. (2010) and Scheinberg et al. (2015)]. The exogenous carbon-metal component then sparked reduction of olivine and pyroxene. Depending on fragment size and pore space geometry, the reduction reaction varied from inside out and probably ceased quickly (i.e., within a matter of days as based on preliminary results [Patzer et al. 2017]).