Unraveling the role of liquids during chondrule formation processes
Unraveling the role of liquids during chondrule formation processes
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DOI：
10.1016/j.gca.2017.03.038
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发表时间：
2018-01-15
影响因子：
5
通讯作者：
Zinner, Ernst
中科院分区：
文献类型：
--
作者：
Eugenia Varela, Maria;Zinner, Ernst
球粒形成过程涉及一系列机制，其性质尚不清楚。我们的注意力主要集中在太阳星云过程上，主要是解开最初形成球粒的液滴的来源。为此，我们开始破译从非平衡普通球粒陨石(UOC)铁粒陨石L/H3.6中形成富玻璃、PO和POP球粒的球粒组成的过程。一种成分是最初的耐火液体。这种冷却的液体以橄榄石中的原生玻璃包裹体或玻璃介稳状态出现，具有未分馏模式的微量元素丰度，缺乏地球化学(液晶)分馏所应具有的化学特征。在富玻璃球粒、PO球粒和POP球粒中观察到的未分馏的晶液分配系数表明，这些物体的形成不是由火成过程控制的。此外，分布在原始比值附近的具有不同地球化学性质和宇宙化学性质的元素(如Yb和La-Ce)的良好相关性表明，这种难熔液体的成因可能涉及宇宙化学(凝聚)而不是地球化学过程。我们最后讨论了第二个过程：在亚固相线温度下，可能发生在冷却星云内的碱-钙交换反应。这些固体/气体交换反应发生的程度将决定球粒的最终组成。(C)2017爱思唯尔有限公司。保留所有权利。
The process/es involved in chondrule formation cover a wide range of mechanisms whose nature is still unknown. Our attention is focused on solar nebula processes mainly in untangling the origin of the initial liquid droplets that turn into chondrules. To do this, we start deciphering the processes under which the chondritic constituents of glass-rich, PO and POP chondrules from the Unequilibrated Ordinary Chondrite (UOC) Tieschitz L/H3.6 could have been formed. One constituent is the initial refractory liquid. This chilled liquid, presented as primary glass inclusions in olivine or as glass mesostasis, has trace element abundances with unfractionated patterns and lacks the chemical signature that is expected from a geochemical (liquid-crystal) fractionation. The unfractionated crystal-liquid distribution coefficients observed in the glass-rich, PO and POP chondrules indicate that formation of these objects was not dominated by an igneous process. In addition, the good correlation of elements with different geochemical and cosmochemical properties (e.g., Yb and La-Ce) that spread around the primordial ratio, indicate that a cosmochemical (condensation) instead of a geochemical process may have been involved in the origin of this refractory liquid. We end up discussing a secondary process: the alkali-Ca exchange reaction that could have taken place within a cooling nebula at sub-solidus temperatures. The extent to which these solid/gas exchange reactions took place will determine the final composition of the chondrules. (C) 2017 Elsevier Ltd. All rights reserved.