Mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions
Mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions
复制标题
DOI：
10.1038/nature02882
复制
发表时间：
2004-09-16
期刊：
影响因子：
64.8
通讯作者：
Haack, H
中科院分区：
文献类型：
--
作者：
Bizzarro, M;Baker, JA;Haack, H
原始或未分化的陨石（球粒陨石）可以追溯到太阳系的起源(1)，因此保存了围绕年轻太阳的吸积盘最早演化过程中发生的物理和化学过程的记录。这些陨石中存在的最古老的太阳系材料是毫米到厘米大小的富含钙铝的包裹体 (CAI) 和铁镁硅酸盐球粒（球粒），它们可能起源于先前存在的星云固体的热处理(2-4)。目前认为球粒的形成时间与 CAI 之后 2-3 百万年（Myr）类似（参考文献 5-10），这一时间尺度与早期太阳系中小粒子的动态寿命不一致（11）。在这里，我们报告了阿连德陨石 CAI 和球粒中短命 Al-26 核素的原位衰变导致过量 Mg-26 的存在。六个 CAI 定义了对应于初始 Al-26/Al-27 比率 (5.25 +/- 0.10) x 10(-5) 的等时线，以及不确定性低至 +/-30,000 年的各个模型年龄，表明这些物体可能在短至 50,000 年的时间内形成。相比之下，球粒记录的初始 Al-26/Al-27 比率范围从 (5.66 +/- 0.80) 到 (1.36 +/- 0.52) x 10(-5)，表明阿连德球粒形成与 CAI 形成同时开始，并持续了至少 1.4 Myr。阿连德和其他球粒陨石记录的球粒形成过程可能在年轻的太阳系中持续了至少 2-3 密尔。
Primitive or undifferentiated meteorites (chondrites) date back to the origin of the Solar System(1), and thus preserve a record of the physical and chemical processes that occurred during the earliest evolution of the accretion disk surrounding the young Sun. The oldest Solar System materials present within these meteorites are millimetre- to centimetre-sized calcium-aluminium-rich inclusions (CAIs) and ferromagnesian silicate spherules (chondrules), which probably originated by thermal processing of pre-existing nebula solids(2-4). Chondrules are currently believed to have formed similar to2-3 million years (Myr) after CAIs (refs 5-10)-a timescale inconsistent with the dynamical lifespan of small particles in the early Solar System(11). Here, we report the presence of excess Mg-26 resulting from in situ decay of the short-lived Al-26 nuclide in CAIs and chondrules from the Allende meteorite. Six CAIs define an isochron corresponding to an initial Al-26/Al-27 ratio of (5.25 +/- 0.10) x 10(-5), and individual model ages with uncertainties as low as +/-30,000 years, suggesting that these objects possibly formed over a period as short as 50,000 years. In contrast, the chondrules record a range of initial Al-26/Al-27 ratios from (5.66 +/- 0.80) to (1.36 +/- 0.52) x 10(-5), indicating that Allende chondrule formation began contemporaneously with the formation of CAIs, and continued for at least 1.4 Myr. Chondrule formation processes recorded by Allende and other chondrites may have persisted for at least 2-3 Myr in the young Solar System.