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I-Xe and Ar-Ar chronology of enstatite chondrite and enstatite achondrite parent bodies in the Early Solar System

早期太阳系顽辉石球粒陨石和顽辉石无球粒陨石母体的 I-Xe 和 Ar-Ar 年代学

基本信息

批准号：
146310209
负责人：
Privatdozent Dr. Jens Hopp
金额：
--
依托单位：
Max-Planck-Institut für Chemie (Otto-Hahn-Institut)
依托单位国家：
德国
项目类别：
Priority Programmes
财政年份：
2010
资助国家：
德国
起止时间：
2009-12-31 至 2014-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/146310209?language=en
关键词：
Xe Ar chronology enstatite chondrite

项目摘要

Short-lived decay systems with half-lives of few million years allow a more precise detection of relative age differences between meteorites, their constitutents (i.e., chondrules, mineral phases) and meteorite groups as a whole than absolute chronometers like U-Pb or K-(Ar)-Ar. Common to all dating methods, the respective ages ideally represent the onset of temperature-dependent retention of a certain element system within the meteorite in question. As such, it is possible to establish a relative time-scale of formation and evolution of small bodies in the early Solar System. Within the proposed project application of the 129I-129Xe- with a half-life = 15.7 Ma and 53Mn-53Cr-chronometers with a half-life = 3.7 Ma should enhance our understanding of the thermal evolution of the enstatite chondrite parent bodies. Enstatite chondrites are subdivided in EH and EL subgroups which differ chemically, mineralogically and in their petrologic evolution. For example, new I-Xe-ages obtained within current project confirm the already known age sequence between EH and EL chondrites (EH are about 2-6 Ma older). However, this dichotomy is diffuse and observed variability in ages possibly a consequence of impact-induced partial resetting of the I-Xe system. This hypothesis is supported by multiple isochrones of differing ages in the I-Xe and K-(Ar)-Ar systems and significantly lowered 39Ar-40Ar ages in EH chondrites, i.e., in an isotope system more easily affected by thermal disturbances. This is likely similarly valid for EL chondrites, but disturbance appears coeval with still ongoing metamorphism on the EL parent body. In order to better understand the time-scales involved in parent body processes (i.e., metamorphism, impact events) additional I-Xe analyses of petrologic types which have been not or only poorly investigated (EL3-5, EH6) are planned within the proposed project. Furthermore, the Mn-Cr chronometer as an additional chronometer will be applied for dating of enstatite chondrites. Because respective carrier phases differ in their retentivity (both, within one element system and in comparison to other element systems) thermal evolution of the (at least) two enstatite chondrite parent bodies might be reconstructed, provided retention temperatures are known sufficiently well.

半衰期为几百万年的短寿命衰变系统允许更精确地检测陨石之间的相对年龄差异，它们的成分（即，陨石球粒，矿物相）和陨石群作为一个整体比绝对计时器，如U-Pb或K-（Ar）-Ar。所有测年方法的共同点是，各自的年龄理想地代表了所讨论的陨石中某种元素系统的温度依赖性保留的开始。因此，有可能建立早期太阳系小天体形成和演化的相对时间尺度。在拟议的项目中，129 I-129 Xe-半衰期= 15.7 Ma和53 Mn-53 Cr-半衰期= 3.7 Ma的计时器的应用应增强我们对顽火辉石球粒陨石母体热演化的理解。顽火辉石又分为EH和EL两个亚类，这两个亚类在化学、矿物学和岩石学演化上都有区别。例如，在本项目中获得的新的I-同位素年龄证实了EH和EL-同位素之间已知的年龄序列（EH年龄约为2-6 Ma）。然而，这种二分法是弥漫性的，观察到的年龄变化可能是影响引起的I-CRYSTAL系统部分重置的后果。I-Ar和K-（Ar）-Ar系统中不同年龄的多个等时线和EH型榴辉岩中显著降低的~（39）Ar-~（40）Ar年龄支持了这一假说，更容易受到热扰动的影响。这可能同样适用于EL陨石，但扰动似乎与EL母体上仍在进行的变质作用是同时代的。为了更好地理解母体过程中涉及的时间尺度（即，变质作用、撞击事件），在拟定项目中计划对尚未调查或调查不足的岩石类型（EL 3 -5、EH 6）进行额外的I-XRD分析。此外，锰铬精密计时器作为补充计时器将用于顽火辉石的定年。由于各自的载体相不同，在他们的保留（无论是在一个元素系统内，并在与其他元素系统相比）的热演化的（至少）两个顽火辉石球粒陨石母体可能被重建，提供保留温度是已知的足够好。